JP2007314012A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic radial tire suitable for a large size vehicle tire capable of enhancing belt durability and simultaneously obtaining sufficient track wandering property. <P>SOLUTION: In the pneumatic radial tire having a crossing belt layer of two layers or more comprising a steel cord, the steel cord 10 has 1+m+n structure, a twisting direction an inner sheath 13 and an outer sheath 15 is twisted in the same direction, clearances S1, S2 between respective mutual adjacent sheath filaments 14, 16 constituting an inner sheath 13 and an outer sheath 15 are 0.008 mm or more in average, and a crossing angle θ of a twisted angle θ1 of the inner sheath filament 14 relative to an axis of the steel cord and a twisted angle θ2 of the outer sheath filament relative to the axis of the steel cord is 10° or less. Bending hardness per one cord of the steel cord 10 is 8-11.5 N and the belt rigidity is 950-1,450 N/25 mm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a pneumatic radial tire, and more particularly, for large vehicles that improve fatigue resistance of a steel cord used for a belt ply to improve belt durability and at the same time obtain good wandering performance. The present invention relates to a pneumatic radial tire suitable for a tire.

  Conventionally, pneumatic radial tire belt plies for large vehicles such as trucks and buses are made of steel cords to ensure tire strength and tread rigidity, as well as high cornering power and good steering stability. Crossed belts with more than one layer are used.

  In recent years, flat tires with a reduced flatness ratio have become widespread in large vehicle tires due to the lower floor of the chassis, and the tread width has increased with respect to the tire height, increasing the tread rigidity and increasing the contact surface. As a result, the amount of deformation of the vehicle becomes small, and the wandering performance when climbing over a step on a road surface such as a kite is lowered, resulting in a problem that steering stability is impaired.

  轍 As a means to improve wandering performance, for example, the belt cord is thinned to give flexibility to the belt cord, the cord driving density is reduced to reduce the belt rigidity, the radius of curvature of the tread surface However, in the former, the tire strength also decreases as the belt rigidity decreases and the durability is impaired, and in the latter, the tread ground pressure becomes uneven or the load is biased to some grounding parts. There is a problem that the belt durability is lowered and uneven wear tends to occur at an early stage.

  On the other hand, the steel cord with the 3 + 9 + 15 × 0.23 + 1 structure shown in FIG. 8, which is conventionally used as a belt cord, combines the strength and flexibility of the cord and has a good wandering property. The problem is that the cross-sectional area of the filament decreases due to fretting wear caused by friction between the wrapping wire W and the outer sheath filament, and the strength of the cord gradually decreases. Due to moisture entering from the groove bottom crack, the corrosion resistance is inferior and the cord cost is high.

  Therefore, it is conceivable to use a two-layer structure steel cord such as 3 × 0.20 + 6 × 0.35 shown in FIG. 5 to increase the filament diameter to solve the problems of cord strength, rubber penetration, and cost. However, since the filament diameter is large, the cord rigidity is increased, and the cord flexibility necessary for wandering is impaired.

  In order to solve the problems of the three-layer steel cord, a two-layer sheath is arranged around one core filament, and the sheath layers are twisted in the same direction and at the same pitch so Steel cord (Patent Document 1) with a 1 + 18 compact twist structure (see Fig. 6) for line contact, and thinned and thinned sheath filaments to improve rubber permeability and remove wrapping wires Steel cords (Patent Documents 2 and 3) having a 1 + 6 + (10 to 11) structure (see FIG. 7) have been disclosed, and low-cost steel cords with reduced fretting wear and stranded wire man-hours have been proposed.

The compact twisted steel cords such as the 1 + 18 structure disclosed in the above document 1 are advantageous in terms of reducing fretting wear and improving fatigue resistance and cord cost by making the filament line contact. The cord has a non-circular polygonal shape because it is packed and arranged, and due to the lack of rubber penetration, the cord may be scattered due to impact or shear strain applied to the belt, or some filaments may be pre-ruptured In addition, there is a problem that durability is lowered due to corrosion fatigue due to moisture permeation from trauma and adhesion deterioration with rubber.
Japanese Utility Model Publication No. 3-29355 JP-A-8-232179 Special table 2003-519299 gazette

  In view of the above problems, the present invention reduces the steel cord used for the belt ply, improves its rubber penetration and fretting resistance, improves belt durability, and at the same time obtains good wandering performance. The present invention provides a pneumatic radial tire suitable for a large vehicle tire.

  As a result of intensive studies to solve the above-mentioned problems, the inventor of the present invention specifies the filament constituting the core and sheath of the 1 + m + n structure and the twist configuration of the inner sheath and the outer sheath in the steel cord used for the belt ply. By improving rubber penetration and fretting resistance of steel cords and improving belt durability, it is possible to optimize belt rigidity and to improve wandering performance by adding moderate flexibility to belt cords. Is found.

  That is, the invention according to claim 1 is a pneumatic radial tire having two or more cross belt layers made of steel cord, wherein the steel cord has a core made of a single filament disposed in the center. 1 + m + n structural steel cord (m is 5), comprising an inner sheath composed of m inner sheath filaments arranged around the core and an outer sheath comprising n outer sheath filaments arranged around the inner sheath Or 6 and n is 10 or 11), and the inner sheath and outer sheath are twisted in the same direction, and the gap between adjacent sheath filaments constituting the inner sheath and outer sheath is an average. 0.008 mm or more and the stiffening of the inner sheath filament The crossing angle θ between the twist angle θ1 with respect to the cord cord and the twist angle θ2 with respect to the steel cord shaft of the outer sheath filament is 10 ° or less, and the bending hardness per cord of the steel cord is 8 to 11 A pneumatic radial tire having a belt rigidity of 950 to 1450 N / 25 mm.

The invention according to claim 2 is the pneumatic radial tire according to claim 1, wherein the core filament diameter dc and the inner sheath filament diameter d1 of the steel cord satisfy the relationship of the following formula (1). It is.
0.055 ≧ (dc + d1) sin (π / m) −d1 ≧ 0.008 (mm) (1)

  According to a third aspect of the present invention, the core filament diameter dc is 0.23 mm or more, the filament diameter ds constituting the inner sheath and the outer sheath is 0.25 mm or less, and the ratio of the dc to ds is 0.00. 3. The pneumatic radial tire according to claim 1, wherein 80 ≦ dc / ds ≦ 1.2.

  The invention according to claim 4 is the pneumatic radial tire according to claim 3, wherein the inner sheath filament and the outer sheath filament all have the same diameter.

  The invention according to claim 5 is the pneumatic radial tire according to any one of claims 1 to 4, wherein the twist angle θ1 of the inner sheath filament is 12 to 20 °.

  The invention according to claim 6 is the pneumatic radial tire according to any one of claims 1 to 5, wherein a cutting load of the steel cord is 1800 N or more.

  The invention according to claim 7 is a pneumatic radial tire according to any one of claims 1 to 6, which is a tire for a large vehicle having a tire cross-sectional width of 300 mm or more and an aspect ratio of 80% or less.

  According to the pneumatic radial tire of the present invention, it is possible to improve the belt durability by balancing the rubber penetration and the fretting resistance of the 1 + m + n structure steel cord in a well-balanced manner, and to obtain a good wandering property. The price of steel cord can be reduced.

  Hereinafter, a pneumatic radial tire according to an embodiment of the present invention and a steel cord used for the belt ply will be described with reference to the drawings.

  FIG. 1 is a half sectional view of a radial tire T showing an example of a pneumatic radial tire for trucks and buses according to an embodiment of the present invention. Reference numeral 3 denotes a tread portion, 5 denotes a sidewall portion, and 4 denotes a bead. Part CL is a tire center.

  The tire T includes a tread portion 3, a pair of sidewall portions 5 connected at both shoulder portions of the tread portion 3, and a bead portion 4 following the sidewall portion 5. A carcass ply 2 folded and locked by a pair of left and right bead cores 6 and a four-layer belt ply 1 in which steel cords are inclined and arranged with respect to the tire circumferential direction are provided on the tread portion 3 on the outer side in the tire radial direction of the carcass ply 2. is doing. The belt plies 1 are arranged such that the belt cords cross between the second and third belt plies 1B.

  For the carcass ply 2, steel cords such as 3 + 9 + 15 × 0.175, 3 + 9 + 15 × 0.22, 3 + 9 × 0.22, 3 + 8 × 0.22 are used in one ply. Further, instead of the steel cord, an organic fiber tire cord such as polyester or aramid may be used.

  The belt ply 1 is made of a steel cord having a 3 × 0.20 + 6 × 0.35 structure arranged at an angle of about 60 ° with respect to the tire circumferential direction from the carcass ply 2 on the outer side in the tire radial direction. No. 1A, No. 2 and No. 3 belts 1B made of 1 + m + n structure steel cords according to the present invention, which are arranged crossing the belt cords at an angle of about 23 ° with respect to the tire circumferential direction, with respect to the tire circumferential direction It consists of No. 4 belt 1C made of 1 × 5 × 0.38 structure steel cord arranged at an angle of about 23 °, and No. 2 and No. 3 belts 1B form a working belt that mainly reinforces the tread portion 3. Yes.

  The steel cord used for the No. 2 and No. 3 belts 1B includes a core made of one filament arranged in the center, an inner sheath made of m inner sheath filaments arranged around the core, and the inner sheath Is a steel cord having a structure of 1 + m + n (m is 5 or 6, n is 10 or 11) composed of n outer sheath filaments arranged around the outer periphery of the wire.

  In the steel cord having the 1 + m + n structure, m is 5 or 6 filaments, and n is 10 or 11 filaments. That is, steel cords having a structure of 1 + 5 + 10, 1 + 5 + 11, 1 + 6 + 10, 1 + 6 + 11 can be mentioned.

  Here, it is difficult to twist the inner sheath and the outer sheath in the same direction while stabilizing the cross-sectional shape because the cord cross-sectional shape is flattened when two cores are twisted because the core is made of one filament. Yes, if three or more strands are twisted, a continuous void is formed in the core, resulting in a decrease in corrosion resistance, and by using a single core, the inner sheath can be twisted simultaneously, simplifying the stranded wire process It is because it can be made. Further, when the number of sheath layers becomes three or more, the twisted structure becomes complicated. In particular, when three or more layers are twisted in the same direction, the straightness of the cord and the residual torsion are difficult to adjust, which makes manufacturing difficult.

  When the number of filaments m of the inner sheath is 4 or less, the inner sheath filament easily moves around the core and is biased to deteriorate rubber penetration. To arrange 7 or more, the diameter difference between the core and the inner sheath filament is reduced. It is necessary to increase the strain, and the strain applied to the core increases and the fatigue resistance decreases. The reason why the number n of outer sheath filaments is 10 or 11 is the same reason.

  FIG. 2 is a cross-sectional view of a cord showing an example of a 1 + m + n structure steel cord according to the present invention. One core filament 12 having a filament diameter dc constituting a core 11 arranged at the center, and around the core 11 It consists of six inner sheath filaments 14 having a filament diameter d1 constituting the arranged inner sheath 13 and eleven outer sheath filaments 16 having a filament diameter d2 constituting the outer sheath 15 arranged around the inner sheath 13. A steel cord 10 having a 1 + 6 + 11 structure in which an inner sheath 13 and an outer sheath 15 are twisted in the same direction.

  FIG. 3 is a cord cross-sectional view showing another example of the 1 + m + n structure steel cord according to the present invention, and is arranged around one core filament 22 having a filament diameter dc ′ arranged at the center and around the core 21. The five inner sheath filaments 24 having the filament diameter d1 ′ constituting the inner sheath 23 and the ten outer sheath filaments 26 having the filament diameter d2 ′ constituting the outer sheath 25 arranged around the inner sheath 23. The steel cord 20 has a 1 + 5 + 10 structure in which the inner sheath 23 and the outer sheath 25 are twisted in the same direction.

  Hereinafter, a steel cord according to the present invention will be described mainly based on a steel cord 10 having a 1 + 6 + 11 structure shown in FIG.

  In the present invention, the filament diameter dc of the core filament 12 is preferably 0.23 mm or more, and the filament diameter ds of the inner sheath 13 and the outer sheath 15 is preferably 0.25 mm or less. Thereby, in order to secure the strength as a belt cord in the 1 + m + n structure, the balance between the inner sheath 13 and the filaments 14 of the outer sheath 15 arranged around the core 11 is improved, and the same sheath It becomes easy to form the gaps S1 and S2 into which the rubber enters between the adjacent sheath filaments.

  The upper limit of the core filament diameter dc is not particularly limited, but is less than 0.30 mm, more preferably 0.27 mm or less. If it is 0.30 mm or more, the bending hardness of the cord increases, the belt rigidity increases, and it becomes difficult to obtain good wrinkle wandering properties. In addition, it is known that the fatigue resistance of the filament is highly dependent on the filament diameter. If dc exceeds 0.35 mm, the filament surface distortion increases, which is disadvantageous for fatigue resistance, and the core has a thick filament. If is used, the straightness of the code is also deteriorated, and the processability such as the topping process is lowered.

  The lower limit of the sheath filament diameter ds is not particularly limited, but is preferably 0.18 to 0.24 mm, more preferably 0.20 to 0.23 mm. If it is less than 0.18 mm, it will be difficult to ensure the strength as a belt cord for a large tire in a 1 + m + n structure, and the filament wireability will be reduced, that is, the belt will be poor in productivity due to a decrease in wire drawing speed or an increase in wire breakage. As a business code, it is not worth the cost.

  The relationship between the core filament diameter dc and the filament diameter ds constituting the inner sheath filament 14 and the outer sheath filament 16 is preferably 1 <dc / ds ≦ 1.2.

  In the case of the 1 + 6 + 11 structure shown in FIG. 2, by making the core filament diameter dc slightly larger than the inner sheath and outer sheath filament diameter ds, the straightness of the cord is improved, and the inner sheath filament 14 is adjacent to each other and the outer sheath filament 16 Gaps S1 and S2 through which rubber enters the cord 10 can be formed between the adjacent ones. The gaps S1 and S2 both need to be 0.008 mm or more on average, preferably 0.01 mm or more, and more preferably 0.02 to 0.06 mm.

  In addition, by slightly increasing the core filament diameter dc, the contact pressure between the core filament 12 and the inner sheath filament 14 can be reduced to prevent a decrease in fatigue properties. However, if the difference between the core filament diameter dc and the inner sheath filament diameter d1 is larger than 1.2 times, the difference in fatigue between the two increases, and the inner sheath filament 14 becomes easy to move around the core filament 12, Since the filament 14 is biased and the rubber penetration is reduced and the fretting wear of the core filament 12 is increased, and the fatigue resistance is lowered.

  At this time, the diameter d1 of the inner sheath filament 12 and the diameter d2 of the outer sheath filament 16 may all be the same filament diameter ds, or d1 and d2 may be different. Also, different diameter filaments may be combined in the same sheaths 13 and 15, but the cord productivity is affected, for example, an increase in the number of filament members and the stranded wire process becomes complicated. It is preferable to use filaments having the same diameter in the sheath.

  In the case of the 1 + 5 + 10 structure shown in FIG. 3, the core filament diameter dc and the sheath filament diameter ds are within the range satisfying the relationship of 0.80 ≦ dc / ds ≦ 1.2, and the core filament diameter dc is greater than the sheath filament diameter ds. The filament diameter ds that can form gaps S3 and S4 into which the rubber penetrates into the cord 20 is formed between adjacent inner sheath filaments 24 and adjacent outer sheath filaments 26. Just choose. Also in this case, the gaps S3 and S4 both need to be 0.008 mm or more on average, preferably 0.01 mm or more, and more preferably 0.02 to 0.06 mm.

In the present invention, when the steel cord 10 is configured by combining the core filament 12 and the sheath filaments 14 and 16, it is preferable that the core filament diameter dc and the inner sheath filament diameter d1 satisfy the relationship of the following formula (1). .
0.055 ≧ (dc + d1) sin (π / m) −d1 ≧ 0.008 (mm) (1)

  The value obtained from the above equation (1) is the geometrically obtained average value T of the shortest distances between the inner sheath filaments 14 and 14, with the filament cross section in the cord cross section taken as a perfect circle.

  Actually, since the sheath filament 14 is wound around the core 11, the filament cross section has an elliptical shape, and the actual gap S1 between the inner sheath filaments 14 and 14 is slightly smaller than the value obtained by the above equation (1). Strictly speaking, the elliptical shape varies depending on the twist pitch of the sheath filament.

  The present inventor has conducted intensive research on unvulcanized characteristics of rubber for coating steel cords, that is, rubber flowability at the time of vulcanization, pressure between rubber and distance between filaments, and rubber penetration into the cord. As a result, it has been found that if dc and d1 have a value of 0.008 mm or more obtained from the formula (1), rubber penetration ability reaching the core is possible.

  That is, if the value of the formula (1) is 0.008 mm or more, the covered rubber can sufficiently penetrate into the core 11 inside the cord at the time of tire vulcanization, and if it is less than 0.008 mm, the rubber penetration into the cord is possible. It has become inadequate and the knowledge that the present invention cannot be achieved sufficiently has been obtained.

  Moreover, when the range of Formula (1) exceeds 0.055 mm, the deviation of the sheath filament is likely to occur in the cord manufacturing process and the topping process, and it becomes difficult to achieve the present invention.

  In the steel cord 10 according to the present invention, as shown in FIG. 2, all six outer sheath filaments 14 are not tightly twisted around the core filament 12, and actually some of the filaments 14 are in close contact. The other filaments 14 are slightly lifted from the core filament 12. Accordingly, the actual gaps S1 and S2 are formed larger than the value obtained by the above formula (1), and the actual gap is preferably 0.01 mm or more, and more preferably 0.015 mm or more.

  Further, in order to form the gaps S1 and S2 that can ensure sufficient rubber intrusion, the molding rate of the sheath filaments 14 and 16 is made slightly larger than usual, for example, 95 to 120%, and the sheath filament 14 is intentionally deposed from the core 11. 16 may be twisted together. Furthermore, the apparent filament diameter may be increased by applying a helical or wave-like kneading in the longitudinal direction of the core filament 12 with an amplitude of about 1.05 to 1.2 times the core filament diameter dc.

  In the steel cord 10 according to the present invention, the inner sheath 13 and the outer sheath 15 are twisted in the same direction. This alleviates the problem of fretting wear due to point contact of filaments based on different direction twists, which is the main cause of reduced cord strength of layer twist cords, and increases the contact area between filaments to increase the contact pressure per unit area. The fretting resistance can be improved by reducing the size.

  As shown in FIG. 4, in the steel cord 10, the intersection angle θ between the twist angle θ <b> 1 of the inner sheath filament 14 with respect to the cord axis O and the twist angle θ <b> 2 of the outer sheath filament 16 with respect to the cord axis O is 10 ° or less. It is.

  As a result, the outer sheath filament 16 is prevented from falling into the valley between the inner sheath filaments 14 and 14, and the formation of the gaps S1 and S2 is ensured by making the cross-sectional shape of the steel cord 10 close to a circle, and rubber penetration is achieved. And the problem of stress concentration on the specific filament of the cross-section polygonal cord can be solved.

  When the crossing angle θ between θ1 and θ2 exceeds 10 °, the inner sheath filament 14 and the outer sheath filament 16 are brought into point contact, the contact pressure between them increases, fretting wear increases, and the cord strength tends to decrease. . Further, the fretting portion has the filament surface plated and the filament is easily corroded, which adversely affects the corrosion fatigue property of the cord. In particular, in belt plies, moisture from external wounds may induce belt separation due to a decrease in adhesion that initiates corrosion at the plated portion, and rather, rather than a strong decrease phenomenon, it prevents corrosion due to plating and improves corrosion fatigue. Fretting resistance is important from the viewpoint.

  In general, θ1 and θ2 have a relationship of θ1 ≧ θ2, that is, the outer sheath 15 is twisted at a pitch P2> P1 longer than the inner sheath 13, and the fatigue resistance, the cord productivity decreases, and the cord unit mass I try to suppress the increase.

  In the present invention, the twist angle θ1 of the inner sheath filament 14 is preferably 12 to 20 °.

  If the twist angle θ1 of the inner sheath filament is less than 12 °, the filament axis approaches parallel to the cord axis O, that is, the twist pitch P1 becomes long and the fatigue resistance decreases, and exceeds 20 °. Since the twist pitch P1 becomes too short and the twist efficiency is lowered, it is not preferable.

  The 1 + m + n structure steel cord according to the present invention having the above configuration has a bending hardness of 8 to 11.5 N per cord, and a belt ply using the cord has a belt rigidity of 950 to 1450 N / 25 mm. .

  If the bending hardness per cord is less than 8N, the steel cord becomes flexible and the belt rigidity can be ensured. The cornering performance and steering stability are lowered, and the tire weight increases when the number of cords driven is increased to ensure the belt rigidity. And the problem of reduced adhesion occurs. Further, if it exceeds 11.5N, the cord becomes too stiff and it becomes difficult to improve the wandering property. For this reason, if the number of cords to be driven is reduced, the cord interval becomes large, and the tread portion is more resistant to external damage, particularly nails. The cut resistance due to sharp metal is reduced.

  In the present invention, the bending hardness per steel cord is in the above range, and the belt rigidity of the belt ply using the cord is designed to be in the range of 950 to 1450 N / 25 mm. The belt durability can be improved and good wandering performance can be obtained without impairing the tire characteristics.

  The bending hardness per cord is a value defined by the maximum load (N) when one steel cord is bent at a center portion with a distance between fulcrums of 25 mm.

  Further, the belt rigidity is defined as a value obtained by multiplying the bending hardness (N) per one cord by the number of belt ply cords (lines / 25 mm).

  The cutting load of the 1 + m + n structure steel cord having the above configuration is preferably 1800 N or more. This is because when the cord cutting load is less than 1800 N, the number of driving per unit width increases when the cord cutting load is used for a belt ply of a large tire, and separation tends to occur, resulting in a decrease in tire durability.

Each filament constituting the steel cord according to the present invention is made of high carbon steel having a carbon content of about 0.70 to 0.95% by weight (for example, a piano wire defined in JIS G3502), and has a carbon content of 2500 to 3500 N / has mm ² approximately tensile strength, further strength from the viewpoint of weight reduction is preferably 2700N / mm ² or more, and more preferably high tensile strength filament in further 2900N / mm ² or more. However, if the tensile strength exceeds 3500 N / mm ² , fatigue resistance decreases due to deterioration of wire drawing workability 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. Further, ternary alloy plating in which a brass contains a small amount of a third metal such as cobalt or nickel may be used.

  In the production of the steel cord, for example, in the steel cord 10, the six filaments 14 of the inner sheath 13 arranged around the core filament 12 are converged from the end plate to the collective voice, and a normal buncher type twisting machine or tubular 1 + 6 structure is formed by being introduced into a twisted wire machine and twisted at a predetermined pitch. Next, the 1 + 6 structure once wound on the bobbin is pulled out, 11 filaments 16 of the outer sheath 15 are arranged around it, and converged on the collective voice from the end plate, and a normal buncher type twisting machine or tubular type twisted wire The steel cord 10 having a 1 + 6 + 11 structure is manufactured by two stranded wire processes by being twisted at a predetermined pitch in the same direction as the 1 + 6 structure.

  In addition, using two buncher type twisting machines connected on the same line, the first out-in-out type buncher type twisting machine is used to twist the 1 + 6 inner sheath, Eleven outer sheath filaments 16 are arranged around the 1 + 6 structure, converged from the end plate to the collective voice, and introduced into the second out-in type buncher type twisted wire machine to produce the 1 + 6 + 11 structure steel cord 10 in one step. be able to.

  Moreover, it can replace with the said buncher type stranding machine, and can also manufacture the 1 + 6 + 11 structure steel cord 10 similarly by 1 process even if it uses the two tubular type stranding machines connected on the said same line. Here, the first twisting machine may be a buncher type twisting machine and the second twisting machine may be a tubular type twisting machine, or vice versa.

  According to the steel cord manufacturing method described above, the twist pitch P1 of the inner sheath 13 and the twist pitch P2 of the outer sheath 16 can be arbitrarily set, that is, the twist angles θ1 and θ2 can be freely controlled. And θ2 can be easily set.

  The pneumatic radial tire of the present invention uses the steel cord as a reinforcing material for the belt ply, thereby improving the rubber penetration and fretting resistance in a well-balanced manner, and achieving a long life with excellent belt durability. It can be a pneumatic radial tire, and is particularly suitable for tires having a tire cross-sectional width of 300 mm or more and a flatness ratio of 80% or less used for large vehicles such as trucks and buses. Moreover, the cord productivity can be increased over the conventional 3 + 9 + 15 structure steel cord, which can contribute to cost reduction.

  Next, the present invention will be specifically described with reference to examples.

  In accordance with the cord specifications described in Table 1 and Table 2, each steel cord of 1 + m + n structure (m is 4 to 6, n is 9 to 11) of Examples and Comparative Examples is used with a normal tubular twisted wire machine. It was manufactured by a single stranded wire process.

  The filaments used in these steel cords were dry-drawn from a 5.5 mm rod of piano wire material SWRS82A material defined in JIS G3502 to an intermediate wire of a predetermined diameter by repeating patenting and wire drawing. After the surface was subjected to brass plating (copper ratio 64%, plating adhesion amount 4.5 g / Kg), it was obtained by final wire drawing using a normal wet wire drawing machine.

  The steel cords of Conventional Examples 1, 2, and 3 are manufactured by using a tubular twisted wire machine by a conventional method using filaments obtained in the same manner as described above.

  These steel cords were evaluated by the following test methods for rubber penetration, fretting resistance by a belt fatigue test, durability of a tire using the steel cord as a working belt, and wrinkle resistance. The results are shown in Tables 1 and 2.

[Fretting resistance (belt fatigue test)]
The number of cords in Conventional Example 1 is 10.5 / 25 mm, and the number of cords corded in each steel cord is adjusted so that the belt strength is equivalent to this, and a belt strip-shaped vulcanized sample embedded in rubber (width) 3 × length 45 cm). After 50000 cycles of bending fatigue using a 1-inch pulley with a firestone belt fatigue tester, take out the cord from the sample after the belt fatigue test and measure the fretting wear level of the inner sheath and outer sheath using a microscope. The observation was magnified 20 times. “◎” indicates that fretting is hardly observed, “○” indicates that the filament diameter reduction rate reaches 1/8 of the maximum diameter, and “○” indicates that the filament diameter reduction rate reaches 1/6 of the maximum diameter. “△” indicates that the filament diameter reduction rate reaches a maximum of ¼ of the diameter, and “×” indicates that the filament diameter reduction rate reaches a maximum of ½ of the diameter. Table 1 shows.

[Rubber penetration]
The cord taken out from the vulcanized sample for the belt fatigue test was carefully removed over 25 cm of the outer sheath, and the rubber adhesion length of the inner sheath was measured. The case where the outer periphery of the inner sheath was adhered to rubber over the entire length of 25 cm was evaluated as 100 points. Table 1 shows the average value of five cords. The larger the index, the better the rubber penetration.

[Tire durability]
The number of cords in Conventional Example 1 is 10.5 / 25 mm, and the number of cords to be corded in each steel cord is adjusted so that the belt strength is equivalent to this, and each rubber-coated topping sheet is prepared, and a predetermined width and angle A radial tire having a size of 315 / 70R22.5 was manufactured by applying the material cut in step 2 to the No. 2 and No. 3 cross belt plies (working belts). Tire durability was evaluated by a drum test under the following conditions. Carcass is a 3 + 9 + 15 × 0.175 steel cord (15 driven / 25 mm) 1 ply, 1st belt is 3 × 0.20 + 6 × 0.35 steel cord (8 driven / 25 mm), 4th belt Is a 1 × 5 × 0.38 steel cord (11 driven / 25 mm), and all other parts are made of common members.

<Drum test conditions>
Using a drum testing machine having a 1700 mm diameter rotating drum made of steel with a smooth surface, the ambient temperature is 38 ± 3 ° C., the tire internal pressure is 900 KPa, the load load is 4500 Kg, and the speed is 56 Km / h, 8 Km / h every 12 hours. The speed was increased and the vehicle was run until a tire failure occurred. Table 1 shows the distance traveled until the failure occurred, using an index with the conventional example 1 as 100. The larger the index, the better the durability.

[轍 Wandering properties]
Each prototype tire has an internal pressure of 900 kPa, is mounted on the front wheel of a large trailer truck, runs on a test road surface with a kite (width 40 cm, depth 5 cm, kite slope angle 35 ° cross-section inverted trapezoidal shape) The ride-over performance when escaping from the vehicle was evaluated by a feeling test with three test drivers. Smoothly pass over the kite, “○” for those that do not feel wobbling the steering wheel after overriding, “△” for those that do not get over the kite a little and feel the wobbling feeling after steering over, difficult to get over the kite In the table, when the steering wheel operation after overriding was evaluated as “x”, the result was shown in the table.

  Conventional Example 1 has insufficient rubber penetration, and the twisting directions of the inner sheath and outer sheath are different and inferior in fretting resistance, but the cord bending hardness is moderate and the belt rigidity is flexible. Ring property is good. In Conventional Example 2, the cord bending hardness is maintained at the same level as in Conventional Example 1, and the wandering property is improved, but the rubber penetration is very poor due to the compact twist, and the durability is lowered due to the dispersion of the cord and corrosion fatigue. Is expected. Conventional Example 3 had a large filament diameter and increased cord bending hardness, and the wandering property deteriorated due to an increase in belt rigidity.

  In Examples 1 to 3, it is understood that the cord bending hardness is maintained at the same level as that of Conventional Example 1, the wandering property is improved, the rubber penetration property and the fretting resistance are compatible, and the tire durability is excellent.

  On the other hand, in Comparative Example 1, the core filament exceeds 1.2 times the sheath filament, and the strain tends to concentrate thickly, and the durability as in the example cannot be obtained, and Comparative Example 2 has four inner sheaths. Therefore, since the shape of the cord is not stable, the durability is lowered. In Comparative Example 3, the outer sheath filament is biased and the durability is insufficient. In Comparative Example 4, there are 12 outer sheath filaments. The penetration was inferior and the same result as in Conventional Example 2 was obtained. In Comparative Example 5, the crossing angle θ exceeds 10 ° and the inner sheath and outer sheath filaments are in point contact and inferior in fretting resistance. In Comparative Example 6, the cord strength is less than 1800 N, and it is necessary to increase the number of belt cords to be driven. A decrease in tire durability was observed due to the separation. In Comparative Example 7, the cord bending hardness was large and the wandering property was lowered, and in Comparative Example 8, the outer sheath filament was made more than 0.25, so the cord bending hardness was further increased. As a result, wandering performance deteriorated.

  As described above, the present invention can be applied to pneumatic radial tires for large vehicles such as trucks and buses, and can improve wandering performance and tire durability. It is suitable for a pneumatic radial tire having an aspect ratio of 80% or less.

1 is a half sectional view of a pneumatic radial tire according to an embodiment. It is sectional drawing of the 1 + 6 + 11 structure steel cord of embodiment. It is sectional drawing of the 1 + 5 + 10 structure steel cord of embodiment. It is a sheath side view explaining a filament twist angle. It is sectional drawing of a 3 + 6 structure steel cord. It is sectional drawing of a 1 + 18 structure steel cord. It is sectional drawing of a 1 + 6 + 11 structure steel cord. It is sectional drawing of a 3 + 9 + 15 structure steel cord.

Explanation of symbols

10 ... Steel cord 11 ... Core 12 ... Core filament 13 ... Inner sheath 14 ... Inner sheath filament 15 ... Outer sheath 16 ... Outer sheath filament S1, S2 ... Clearance between filaments

Claims (7)

A pneumatic radial tire having two or more cross belt layers made of steel cord,
The steel cord includes a core made of one filament arranged at the center, an inner sheath made of m inner sheath filaments arranged around the core, and n outer sheaths arranged around the inner sheath. A 1 + m + n structure steel cord (5 or 6 and n is 10 or 11) provided with an outer sheath made of a filament, and the twisting direction of the inner sheath and the outer sheath is twisted in the same direction,
While the gap between adjacent sheath filaments constituting the inner sheath and outer sheath is 0.008 mm or more on average,
The angle of intersection θ between the twist angle θ1 of the inner sheath filament with respect to the steel cord shaft and the twist angle θ2 of the outer sheath filament with respect to the steel cord shaft is 10 ° or less, and
A pneumatic radial tire characterized by a bending hardness per cord of the steel cord of 8 to 11.5 N and a belt rigidity of 950 to 1450 N / 25 mm. The pneumatic radial tire according to claim 1, wherein a core filament diameter dc and an inner sheath filament diameter d1 of the steel cord satisfy a relationship of the following formula (1).
0.055 ≧ (dc + d1) sin (π / m) −d1 ≧ 0.008 (mm) (1) The core filament diameter dc is 0.23 mm or more, the filament diameter ds constituting the inner sheath and outer sheath is 0.25 mm or less, and the ratio of dc to ds is 0.80 ≦ dc / ds ≦ 1.2. The pneumatic radial tire according to claim 1, wherein the pneumatic radial tire is a pneumatic radial tire. The pneumatic radial tire according to claim 3, wherein the inner sheath filament and the outer sheath filament all have the same diameter. The pneumatic radial tire according to any one of claims 1 to 4, wherein a twist angle θ1 of the inner sheath filament is 12 to 20 °. The pneumatic radial tire according to any one of claims 1 to 5, wherein a cutting load of the steel cord is 1800 N or more. The pneumatic radial tire according to any one of claims 1 to 6, wherein the tire has a tire cross-sectional width of 300 mm or more and a flatness ratio of 80% or less.

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