JP2011235683A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic radial tire capable of improving high-speed durability and uneven wear resistance.SOLUTION: At least one layer of carcass layer 4 divided in a tire width direction within a center region of a tread portion 1 is disposed between a pair of bead portions 3, 3. A plurality of layers of belt layers 7 are arranged on the outer periphery side of the carcass layer 4 in the tread portion 1. There is disposed at least one layer of a belt cover layer 8 in which reinforcing cord is arranged at an angle of not more than 5 degrees to the tire peripheral direction on the outer peripheral side of the belt layers 7. As the reinforcing cord of the belt cover layer 8, a polyolefin ketone fiber cord is used, the thermal shrinkage of which is not more than 2.0% at 150°C and which has a structure expressed in the following formula (1):-(CH-CH-CO)n-(R-CO)m-, wherein 1.05≥(n+m)/n≥1.00, and R is an alkylene group with the carbon atoms of not less than 3.

Description

  The present invention relates to a pneumatic radial tire including a carcass layer divided in the tire width direction in the center region of the tread portion and a belt cover layer including a reinforcing cord oriented in the tire circumferential direction in the tread portion. The present invention relates to a pneumatic radial tire that can improve high-speed durability and uneven wear resistance.

  In recent years, in a pneumatic radial tire, it has been proposed to divide at least one carcass layer in the tire width direction in the center region of the tread portion in order to reduce the weight for improving the fuel efficiency and further improve the riding comfort. (For example, see Patent Documents 1 to 3). In a pneumatic radial tire having such a divided carcass structure, the carcass layer and the belt layer are integrated to form a pressure vessel, and it is lightweight to eliminate a part of the carcass layer from the lower region of the belt layer. Contributes to the improvement of ride quality and ride comfort.

  However, in the pneumatic radial tire having the split carcass structure as described above, a belt cover layer including a reinforcing cord oriented in the tire circumferential direction is provided on the outer peripheral side of the belt layer in the tread portion in order to improve high-speed durability. When a nylon fiber cord is used as the reinforcing cord, the center region of the tread portion tends to be depressed due to heat shrinkage stress after vulcanization of the reinforcing cord constituting the belt cover layer. Is causing the problem of getting worse.

JP 2008-37265 A JP 2008-37266 A JP 2008-279820 A

  An object of the present invention is a pneumatic radial tire having a carcass layer divided in the tire width direction in the center region of the tread portion and a belt cover layer including a reinforcing cord oriented in the tire circumferential direction in the tread portion. An object of the present invention is to provide a pneumatic radial tire that can improve the performance and uneven wear resistance.

  In order to achieve the above object, a pneumatic radial tire according to the present invention includes at least one carcass layer divided in the tire width direction in a center region of a tread portion between a pair of bead portions, and the carcass in the tread portion. A plurality of belt layers are arranged on the outer peripheral side of the layers, and at least one belt cover layer formed by arranging reinforcing cords at an angle of 5 degrees or less with respect to the tire circumferential direction is arranged on the outer peripheral side of these belt layers. A pneumatic radial tire comprising a polyolefin ketone fiber cord having a structure represented by the following formula (1) having a heat shrinkage rate of 2.0% or less at 150 ° C. as a reinforcement cord of the belt cover layer: It is characterized by being used.

_{- (CH 2 -CH 2 -CO)} n- (R-CO) m- ··· (1)
Here, 1.05 ≧ (n + m) /n≧1.00,
R is an alkylene group having 3 or more carbon atoms.

  In the present invention, in a pneumatic radial tire including a carcass layer divided in the tire width direction in the center region of the tread portion and a belt cover layer including a reinforcing cord oriented in the tire circumferential direction in the tread portion, By using a polyolefin ketone fiber cord with a low thermal shrinkage at 150 ° C as the reinforcement cord, the shape of the tire during inflation is optimized, so that the improvement effect of high-speed durability based on the polyolefin ketone fiber cord can be enjoyed. However, uneven wear resistance can be improved. Further, the use of the polyolefin ketone fiber cord as the reinforcing cord for the belt cover layer contributes to reduction of rolling resistance and road noise. The heat shrinkage rate at 150 ° C. is the heat shrinkage rate of the dipped cord, and is measured in accordance with the measurement conditions of the dry heat shrinkage rate after heating specified in JIS L1017.

  In the present invention, the length Wa in the tire width direction of the divided portion of the carcass layer preferably satisfies the relationship of 0.10 ≦ Wa / W ≦ 0.95 with respect to the maximum width W of the belt layer. As a result, it is possible to sufficiently obtain the riding comfort improvement effect and the weight reduction effect based on the divided carcass structure without accompanying deterioration in rolling resistance.

  Moreover, in this invention, it is preferable that the radial direction growth rate Ic in the tire center position at the time of inflation exists in the range of 0.0%-1.0%. By setting the radial growth rate Ic at the tire center position during inflation in the above range, deterioration of rolling resistance can be avoided.

  Here, the radial growth rate Ic is the growth rate of the radial dimension during inflation relative to the radial dimension during non-inflation. The radial dimension during inflation is a tire radial dimension measured in accordance with the tire measurement method specified in the JATMA standard. In a passenger car tire, the tire is fitted to an applicable rim. This is the dimension in the tire radial direction when the internal pressure is 180 kPa. The non-inflated radial dimension is a dimension in the tire radial direction in a state where the tire is fitted to the applied rim and the internal pressure is 0 kPa. The tire center position is the center position in the tire width direction, that is, the position of the tire equator.

1 is a meridian cross-sectional view showing a pneumatic radial tire according to an embodiment of the present invention. It is meridian sectional drawing which shows the pneumatic radial tire which consists of other embodiment of this invention. It is meridian sectional drawing which shows the pneumatic radial tire which consists of further another embodiment of this invention.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. 1 to 3 each show a pneumatic radial tire according to an embodiment of the present invention. In FIG. 1, 1 is a tread portion, 2 is a sidewall portion, and 3 is a bead portion. Between the pair of left and right bead portions 3 and 3, at least one carcass layer 4 divided in the tire width direction in the center region of the tread portion 1 is disposed. The carcass layer 4 includes a plurality of carcass cords extending in the tire radial direction, and is folded back from the tire inner side to the outer side around the bead core 5 disposed in each bead portion 3. As the carcass cord, an organic fiber cord is preferably used, but a steel cord may be used. The inclination angle of the carcass cord with respect to the tire circumferential direction is set in a range of 80 ° to 90 °. A bead filler 6 is disposed on the outer periphery of the bead core 5, and the bead filler 6 is wrapped around the folded portion of the carcass layer 4.

  A plurality of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. These belt layers 7 include a plurality of belt cords inclined with respect to the tire circumferential direction, and are arranged so that the belt cords cross each other between the layers. As the belt cord, a steel cord is preferably used, but an organic fiber cord may be used. The inclination angle of the belt cord with respect to the tire circumferential direction is set in a range of 15 ° to 40 °.

  On the outer peripheral side of the belt layer 7, at least one belt cover layer 8 in which reinforcing cords are arranged at an angle of 5 ° or less with respect to the tire circumferential direction is disposed for the purpose of improving high-speed durability. . The belt cover layer 8 preferably has a jointless structure in which a strip material formed by aligning at least one reinforcing cord and covering with rubber is continuously wound in the tire circumferential direction.

  The belt cover layer 8 can select the arrangement | positioning area | region suitably according to the speed range of a tire. In FIG. 1, the belt cover layer 8 is composed of a belt cover layer 8A (full cover) that covers the entire belt layer 7 and a belt cover layer 8B (edge cover) that covers both ends of the belt layer 7 locally. ing. As another structure, a structure in which only the belt cover layer 8A (full cover) covering the entire belt layer 7 is provided on the tread portion 1 (FIG. 2), or both ends of the belt cover layer 7 are locally provided on the tread portion 1. It is also possible to adopt a structure (FIG. 3) in which only the belt cover layer 8B (edge cover) is provided.

  As the reinforcing cord of the belt cover layer 8, a polyolefin ketone fiber cord (POK) having a structure represented by the following formula (1) is used.

_{- (CH 2 -CH 2 -CO)} n- (R-CO) m- ··· (1)
Here, 1.05 ≧ (n + m) /n≧1.00,
R is an alkylene group having 3 or more carbon atoms.

  Polyolefin ketone fiber cords having such a structure are disclosed in JP-A-1-124617, JP-A-2-112413, US Pat. No. 5,194,210, JP-A-9-324377, and JP-A-2001-115007. , And can be obtained by melt spinning or wet spinning disclosed in JP-A-2001-131825.

  In the formula (1), when the fraction of m (an alkylene unit other than ethylene) increases, the tire traveling growth increases and the durability decreases. This is presumably because the crystal structure of the spun fiber changes with an increase in m units, and the secondary binding force between the molecular chains decreases. More preferably, an alternating copolymer consisting essentially of ethylene and carbon monoxide where m = 0 is used. It is preferable to use wet spinning to produce such fibers.

  The heat shrinkage rate at 150 ° C. of the polyolefin ketone fiber cord is 2.0% or less. If this heat shrinkage rate exceeds 2.0%, the tire surface is likely to be depressed due to heat shrinkage of the polyolefin ketone fiber cord after vulcanization. The polyolefin ketone fiber cord is preferably subjected to a dip treatment with a treatment liquid containing resorcin / formalin / latex (RFL). The polyolefin ketone fiber cord is preferably heat-treated for 60 to 180 seconds at a heat treatment zone and a normalization zone at a treatment temperature of 200 to 240 ° C., respectively.

  In the pneumatic radial tire including the carcass layer 4 divided in the tire width direction in the center region of the tread portion 1 and the belt cover layer 8 including the reinforcing cord oriented in the tire circumferential direction in the tread portion 1 as described above, As a reinforcing cord for the belt cover layer 8, a polyolefin ketone fiber cord having a thermal contraction rate at 150 ° C. smaller than that of a nylon fiber cord is used to optimize the tire shape during inflation. It is possible to improve uneven wear resistance while enjoying the effect of improving the high-speed durability based on the above. In addition, since the polyolefin ketone fiber cord has a higher elastic modulus than the nylon fiber cord, in addition to improving high-speed durability, rolling resistance and road noise can be reduced.

  In the pneumatic radial tire, the length Wa in the tire width direction of the divided portion of the carcass layer 4 is 0.10 ≦ Wa / W ≦ 0.95, more preferably, with respect to the maximum width W of the belt layer 7. The relationship is 0.20 ≦ Wa / W ≦ 0.70. As a result, it is possible to sufficiently obtain the riding comfort improvement effect and the weight reduction effect based on the divided carcass structure without accompanying deterioration in rolling resistance. If the value of Wa / W is too small, the flexibility of the tread portion 1 is lowered, so that the riding comfort is deteriorated and the effect of reducing the tire weight is also reduced. On the other hand, if the value of Wa / W is too large, the rigidity of the tread portion 1 is excessively lowered, so that the rolling resistance is deteriorated.

  In the pneumatic radial tire, the radial growth rate Ic at the tire center position Pc during inflation is preferably in the range of 0.0% to 1.0%. For example, when the tire outer diameter at the tire center position Pc at the time of non-inflation is Dcn and the tire outer diameter at the tire center position Pc at the time of inflation is Dci, the radial growth rate Ic is (Dci−Dcn). ) / Dcn × 100%.

  In the pneumatic radial tire including the carcass layer 4 divided in the tire width direction in the center region of the tread portion 1 and the belt cover layer 8 including the reinforcing cord oriented in the tire circumferential direction in the tread portion 1 as described above, By setting the radial growth rate Ic at the tire center position Pc at the time of inflation within a predetermined range, deterioration of rolling resistance can be avoided. When the radial growth rate Ic is larger than 1.0%, the contact length in the tire center region becomes long, so that the rolling resistance is deteriorated.

  In the pneumatic radial tire, the radial growth rate Ic at the tire center position during inflation can be adjusted by the internal pressure or pressurization time of the post-cure inflation process after vulcanization of the tire. For example, the radial growth rate Ic can be reduced by increasing the internal pressure in the post-cure inflation process and increasing the pressurization time. The internal pressure in the post-cure inflation process is preferably set in the range of 100 kPa to 500 kPa, and the pressurization time is preferably set in the range of 5 minutes to 20 minutes.

  In the above-described embodiment, the pneumatic radial tire including one carcass layer having a divided structure has been described. However, the present invention can also be applied to a pneumatic radial tire including two or more carcass layers. . In a pneumatic radial tire including two or more carcass layers, at least one carcass layer needs to have a divided structure, but all carcass layers may have a divided structure.

  In the tire size 235 / 40R17, one carcass layer divided in the tire width direction in the center region of the tread portion is arranged between a pair of bead portions, and two belt layers are provided on the outer peripheral side of the carcass layer in the tread portion In a pneumatic radial tire in which a belt cover layer in which reinforcing cords are arranged on the outer peripheral side of these belt layers at an angle of 5 degrees or less with respect to the tire circumferential direction is arranged, at the tire center position at the time of inflation Radial growth rate Ic, ratio Wa / W of tire width direction length Wa of carcass layer split portion and maximum width W of belt layer, structure of belt cover layer, cord material, cord structure, cord Tables of Comparative Examples 1 to 3 and Examples 1 to 5 in which the heat shrinkage rate at 150 ° C. and the number E of cords driven per cm width of the belt cover layer were set as shown in Table 1. It was manufactured ya.

  Regarding the structure of the belt cover layer in Table 1, “JE” indicates a belt cover layer (edge cover) that selectively covers both ends of the belt layer, and “JF” covers the entire belt layer. “JEF” indicates one belt cover layer (full cover), one belt cover layer (edge cover) that selectively covers both ends of the belt layer, and one layer that covers the entire belt layer. A thing provided with a belt cover layer (full cover) is shown. Each of these belt cover layers has a jointless structure in which a strip material having a width of 5 mm formed by arranging a plurality of reinforcing cords and covering them with rubber is continuously wound in the tire circumferential direction.

  These test tires were evaluated for rolling resistance, road noise, uneven wear resistance, and high-speed durability by the following evaluation methods, and the results are also shown in Table 1.

Rolling resistance:
Each test tire was assembled on a wheel having a rim size of 17 × 7.5 JJ, and rolling resistance was measured under the condition of an air pressure of 230 kPa. The evaluation results are shown as an index using Comparative Example 1 as 100, using the reciprocal of the measured value. It means that rolling resistance is so small that this index value is large.

Road noise:
Each test tire was assembled to a wheel with a rim size of 17 × 7.5 JJ and mounted on a test vehicle, and the sound inside the vehicle was measured when traveling on a test course having a rough road surface at a speed of 50 km / h with an air pressure of 230 kPa. The evaluation results are shown as an index using Comparative Example 1 as 100, using the reciprocal of the measured value. A larger index value means a smaller road noise.

Uneven wear resistance:
Each test tire was assembled on a wheel of rim size 17 × 7.5JJ and mounted on a test vehicle. After running on a paved general roadway for 50000 km at an air pressure of 230 kPa, the amount of uneven wear generated on the shoulder rib was measured. The evaluation results are shown as an index using Comparative Example 1 as 100, using the reciprocal of the measured value. A larger index value means less uneven wear resistance.

High speed durability:
Using a drum testing machine equipped with a steel drum with a smooth drum surface and a diameter of 1707 mm, the test was inflated at a peripheral temperature of 38 ± 3 ° C., a rim size of 17 × 7.5 JJ, and a test internal pressure of 180 kPa. The load is set to 120% of the maximum load capacity specified by JATMA, the running speed is set to 120 km / h for 2 hours, and then the running speed is set to 150 km / h for 30 minutes. Thereafter, the traveling speed was stepped up by 10 km / h every 30 minutes, and the traveling distance until the tire broke was measured. The evaluation results are shown as an index with Comparative Example 1 as 100. It means that high speed durability is excellent, so that this index value is large.

  As is clear from Table 1, the tires of Examples 1 to 5 were able to improve rolling resistance, road noise, uneven wear resistance and high-speed durability in comparison with Comparative Example 1. On the other hand, since the tires of Comparative Examples 2 and 3 use nylon fiber cords as the reinforcement cords for the belt cover layer, the uneven wear resistance deteriorates and the effect of improving high-speed durability is small.

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 8 Belt cover layer

Claims (3)

At least one carcass layer divided in the tire width direction in the center region of the tread portion is disposed between a pair of bead portions, and a plurality of belt layers are disposed on the outer peripheral side of the carcass layer in the tread portion. A pneumatic radial tire in which at least one belt cover layer in which reinforcing cords are arranged at an angle of 5 degrees or less with respect to the tire circumferential direction is arranged on the outer peripheral side of the layer, and as a reinforcing cord for the belt cover layer A pneumatic radial tire characterized by using a polyolefin ketone fiber cord having a heat shrinkage rate of 2.0% or less at 150 ° C. and having a structure represented by the following formula (1).
_{- (CH 2 -CH 2 -CO)} n- (R-CO) m- ··· (1)
Here, 1.05 ≧ (n + m) /n≧1.00,
R is an alkylene group having 3 or more carbon atoms.   The length Wa in the tire width direction of the divided portion of the carcass layer satisfies the relationship of 0.10 ≦ Wa / W ≦ 0.95 with respect to the maximum width W of the belt layer. The described pneumatic radial tire.   The radial radial tire according to claim 1 or 2, wherein a radial growth rate Ic at a tire center position during inflation is in a range of 0.0% to 1.0%.

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