JP2020093746A - Pneumatic tire - Google Patents

Abstract

To provide a pneumatic tire which allows reduction of a tire weight and can improve handling stability and durability.SOLUTION: A pneumatic tire has a carcass, a belt layer in which a cord is arranged on an outer periphery of a crown part of the carcass obliquely with respect to a tire circumferential direction, and a belt reinforcement layer in which an organic fiber cord is arranged on an outer periphery of the belt layer along the tire circumferential direction. The organic fiber cord is composed of aromatic polyamide fibers. A load in 2% extension of one organic fiber cord is 100 N or less. A product of the load (N) in 2% extension of one organic fiber cord and the number (pieces/25 mm) of implantation pieces is 1000-2000. The pneumatic tire has a rubber sheet between the belt layer and the belt reinforcement layer.SELECTED DRAWING: Figure 1

Description

The present invention relates to a pneumatic tire.

In a pneumatic tire, an organic fiber cord made of nylon 66 has been conventionally used for a belt reinforcing layer.

When an organic fiber cord made of nylon 66 is used for the belt reinforcing layer, it is necessary to increase the number of belt reinforcing layers and enhance the hoop effect in order to improve steering stability. However, there has been a problem that an increase in the number of belt reinforcing layers leads to an increase in tire weight.

JP, 2013-216249, A JP-A-4-166402

Against the above problems, the present inventor, as a result of diligent studies, by appropriately using, as the organic fiber cord, an aromatic polyamide fiber, it is possible to improve the steering stability while reducing the tire weight. I found it. However, since the organic fiber cords made of aromatic polyamide fibers are rigid and difficult to stretch, they cannot follow the expansion during tire vulcanization molding, bite into the belt, break the belt, and deteriorate the durability. was there.

In view of the above points, an object of the present invention is to provide a pneumatic tire capable of improving steering stability and durability while reducing tire weight.

It should be noted that Patent Documents 1 and 2 describe a pneumatic tire using an organic fiber cord made of aromatic polyamide fiber (aramid fiber) as the organic fiber cord used for the belt reinforcing layer. It does not describe properties such as load at 2% elongation of the fiber cord.

The pneumatic tire according to the present invention is a carcass, a belt layer in which cords are arranged in an inclined arrangement with respect to the tire circumferential direction on the outer circumference of the crown portion of the carcass, and an organic fiber cord is provided on the outer circumference of the belt layer along the tire circumferential direction. In a pneumatic tire having an arranged belt reinforcing layer, the organic fiber cord is made of an aromatic polyamide fiber, and a load at 2% elongation per one organic fiber cord is 100 N or less. The product of the load (N) at the time of 2% extension and the number of hammered in (25/mm) is 1000 to 2000, and a rubber sheet is provided between the belt layer and the belt reinforcing layer.

The rubber sheet may have a thickness of 0.5 to 0.9 mm.

The organic fiber cord may have a twisting coefficient of 1600 to 2300.

According to the pneumatic tire of the present invention, excellent steering stability and durability can be obtained while reducing the tire weight.

1 is a half sectional view of a pneumatic tire according to an embodiment of the present invention.

Hereinafter, matters related to the implementation of the present invention will be described in detail.

The pneumatic tire according to the embodiment shown in FIG. 1 is a pneumatic radial tire for passenger cars, in which a pair of left and right bead portions 1 and sidewall portions 2 and radial outer ends of the left and right sidewall portions 2 are joined together. The carcass 4 is provided with a tread portion 3 provided between both sidewall portions so as to be connected to each other, and a carcass 4 extending across a pair of bead portions is provided.

The carcass 4 is composed of at least one carcass ply whose both ends are locked by an annular bead core 5 embedded in the bead portion 1 from the tread portion 3 to the sidewall portion 2. The carcass ply is formed by arranging carcass cords made of organic fiber cords or the like substantially at right angles to the tire circumferential direction and covered with a coating rubber.

A belt layer 6 is disposed between the carcass 4 and the tread rubber portion 7 on the outer peripheral side of the carcass 4 in the tread portion 3 (that is, on the outer side in the tire radial direction). The belt layer 6 is provided so as to overlap the outer circumference of the crown portion of the carcass 4, and can be configured by one or a plurality of belt plies, usually at least two belt plies. In the present embodiment, the carcass The first belt ply 6A on the side and the second belt ply 6B on the side of the tread rubber portion are composed of two belt plies. The belt plies 6A and 6B are formed by inclining steel cords at a predetermined angle (for example, 15 to 35 degrees) with respect to the tire circumferential direction, and arranging the steel cords at predetermined intervals in the tire width direction. Each belt ply has a steel cord covered with a coating rubber. The steel cords are arranged so as to intersect with each other between the two belt plies 6A and 6B.

A belt reinforcing layer 8 is provided between the belt layer 6 and the tread rubber portion 7 on the outer peripheral side of the belt layer 6 (that is, on the outer side in the tire radial direction). The belt reinforcing layer 8 is a cap ply that covers the belt layer 6 with the belt reinforcing ply over its entire width. The belt reinforcing ply is formed by coating organic fiber cords arranged substantially parallel to the tire circumferential direction with a coating rubber. That is, the belt reinforcing layer 8 is formed by arranging organic fiber cords along the tire circumferential direction, and a ribbon-shaped rubber (also referred to as a rubber strip) having organic fiber cords is provided so as to cover the entire width direction of the belt layer 6. It can be formed by spirally winding at an angle of 0 to 5 degrees with respect to the tire circumferential direction.

A rubber sheet 9 is provided between the belt layer 6 and the belt reinforcing layer 8. By providing the rubber sheet 9, it is possible to suppress the contact between the steel cord of the belt layer 6 and the organic fiber cord of the belt reinforcing layer 8 due to expansion during tire molding. In the present embodiment, the rubber sheet 9 can be formed so as to cover the entire width direction of the belt layer 6.

The thickness of the rubber sheet 9 is not particularly limited, but is preferably 0.5 to 0.9 mm. When the thickness of the rubber sheet 9 is 0.5 mm or more, it is difficult for the steel cord of the belt layer 6 and the organic fiber cord of the belt reinforcing layer 8 to contact each other, and when it is 0.9 mm or less, the tire weight is reduced. Cheap.

The rubber composition used for the rubber sheet 9 is not particularly limited, but preferably has a Mooney viscosity of 55 to 75M. When the Mooney viscosity of the rubber composition used for the rubber sheet 9 is within the above range, it is easy to suppress contact between the steel cord of the belt layer 6 and the organic fiber cord of the belt reinforcing layer 8. Here, in the present specification, the “Moonie viscosity” is based on JIS K6300, the unvulcanized rubber is preheated at 100° C. for 1 minute, and the torque value after 4 minutes from the start of rotation is measured in Mooney units. Use the measured value.

The organic fiber cords forming the belt reinforcing layer 8 according to this embodiment are made of aromatic polyamide fibers. The aromatic polyamide fiber is a polyamide having an aromatic skeleton in the main chain, and may be a para aramid or a meta aramid. For example, a known aramid fiber used in the present technical field can be appropriately used.

As the organic fiber cord, a yarn obtained by bundling a large number of aromatic polyamide filaments is twisted in the Z direction to form a lower twisted yarn, and a plurality of the obtained lower twisted yarns are aligned to form an S direction which is opposite to the lower twisted direction. A double twist structure in which two lower twist yarns are twisted together may be used.

The load at the time of 2% extension per one organic fiber cord is not particularly limited as long as it is 100 N or less, but it is preferably 85 N or less, and more preferably 70 N or less. When it is 100 N or less, the organic fiber cord of the belt reinforcing layer 8 easily follows the expansion at the time of tire molding, and it is easy to suppress the biting into the steel cord of the belt layer 6. If the organic fiber cord of the belt reinforcing layer 8 bites into the steel cord of the belt layer 6, the cord of the belt layer 6 may be broken. The value of the load at the time of extension of 2% may be adjusted, for example, by adjusting the elastic modulus of the aromatic polyamide fiber forming the organic fiber cord, adjusting the cord structure or the number of twists, or RFL (resorcin-formalin-latex). This can be performed by adjusting the type and adhesion amount of a known adhesive treatment liquid such as a treatment liquid. For example, by increasing the number of twists, the load at 2% extension can be reduced.

Here, in the present specification, the load at the time of 2% extension per one organic fiber cord means a tensile test according to JIS L1017, a temperature of 20±2° C. and a relative humidity (65±4) specified in JIS L0105. )% standard values are measured in a laboratory.

The product of the load (N) at the time of 2% extension and the number of fibers (25 mm) driven per organic fiber cord is not particularly limited as long as it is 1000 to 2000, but 1100 to 1900 is more preferable. When it is 1000 or more, excellent steering stability due to the hoop effect is easily obtained, and when it is 2000 or less, the hoop effect does not become too large, and the excellent ground contact shape of the pneumatic tire is easily maintained.

The fineness of the organic fiber cord is not particularly limited, but is preferably 850 to 3500 dtex, more preferably 1700 to 2800 dtex, and further preferably 2000 to 2500 dtex. Here, the fineness is also called a nominal fineness or a display fineness.

The twist coefficient (K) of the organic fiber cord is not particularly limited, but is preferably 1600 to 2300, and more preferably 1600 to 2200. When the twisting coefficient is 1600 or more, the load at 2% elongation of the organic fiber cord tends to be 100 N or less, and when the twisting coefficient is 2300 or less, the effect of improving the steering stability is easily obtained.

Here, the twist coefficient (K) is represented by the following formula (I), T is the number of twists per 10 cm (times/10 cm), D is the nominal fineness (dtex), and P is the aromatic polyamide. The density (g/cm ³ ) of the fiber is shown.
K=T(D/P) ^1/2 ...(I)

The number of twists (twist/10 cm) of the above-mentioned twist per 10 cm of the organic fiber cord is not particularly limited, but may be 25-70 times/10 cm, and is preferably 40-60 times/10 cm. The number of lower twists can usually be set to a value similar to the number of upper twists.

The number of organic fiber cords to be driven (lines/25 mm) is not particularly limited, but may be 10 to 32 lines/25 mm, and is preferably 17 to 32 lines/25 mm.

The type of pneumatic tire according to the present embodiment is not particularly limited, and various tires such as tires for passenger cars and tires for heavy loads used for trucks, buses and the like can be mentioned.

In the above embodiment, the belt reinforcing layer 8 has been described as a cap ply that covers the belt layer 6 with the entire width thereof, but the present invention is not limited to this, and the end portion of the belt layer 6 on the outer side in the tire width direction and its periphery. May be an edge ply covering the above, and the edge ply may be a part in which both ends of the cap ply in the tire width direction are folded back.

Examples of the present invention will be shown below, but the present invention is not limited to these examples.

An organic fiber cord having the structure and the number of twists shown in Table 1 below was produced. The produced organic fiber cords were arranged in the number of driven fibers shown in Table 1, and a belt reinforcing ply was produced by using a calendering device as a topping cloth. In Comparative Example 1, a cord material was nylon 66 (Ny66), and in Examples 1 to 3 and Comparative Examples 2 to 5, a cord material was polyparaphenylene terephthalamide (aramid). ..

The measuring methods for the organic fiber cord and the belt reinforcing ply are as follows.

・Cord diameter: One organic fiber cord is bent into four so that the twist does not return, and four are arranged in parallel so that they do not sag. The diameter was 9.5±0.03 mm and the load was 1666±29.4 mN), and the leg was dropped from a height of about 6.5 mm for measurement.

・Load at 2% extension per one organic fiber cord: Tensile test according to JIS L1017 was conducted, and the standard for the organic fiber cord was temperature 20±2°C and relative humidity (65±4)% specified in JIS L0105. The test was performed in the test room, and the load at 2% elongation was measured.

-Thickness of belt reinforcing ply: Using a belt reinforcing layer member before vulcanization, the member is placed so as not to sag, and a predetermined dial gauge (leg diameter 9.5 ± 0.03 mm, load 1666 ± 29. 4 mN), the leg was dropped from a height of about 6.5 mm, and the member thickness was measured.

A radial tire having a tire size of 225/45R18 was vulcanized and molded using the obtained belt-reinforcing ply and the rubber sheet having a thickness shown in Table 1 (Moonie viscosity: 65M) according to a conventional method. In Comparative Examples 1 to 5, no rubber sheet was used.

All the tires had the same configuration except the belt reinforcing layer and the rubber sheet. As the cords in the belt ply, steel cords having a configuration of 2+2×0.25 were used, and the number of driven steel cords was 23 cords/25.4 mm, and the cord angle was +27°/−27° with respect to the tire circumferential direction. The belt reinforcing ply has organic fiber cords arranged on the outer periphery of the belt layer such that the major axis direction thereof is parallel to the belt surface.

As the carcass ply, an organic fiber cord made of rayon and having a cord structure of 1840 dtex/3 was formed into one ply with 21/25 mm of the driven fibers.

Each of the obtained pneumatic tires was evaluated for member weight, belt breakage, steering stability, and durability. The evaluation method of each evaluation item is as follows. In addition, in Comparative Example 5, since the belt was broken, steering stability and durability were not evaluated.

Member weight: The total weight of the belt reinforcing layer, which is shown as an index with the total weight of the belt reinforcing layer of Comparative Example 1 as 100. The smaller the number, the lighter it is.

-Belt breakage: The belt cord was taken out from the vulcanized tire and it was confirmed that the belt cord was not broken.

-Steering stability: Each tire was adjusted to the standard air pressure of the vehicle by using a standard rim specified by JIS, and mounted on a passenger car with a displacement of 2000 cc. Then, in a test course for evaluating steering stability, three trained test drivers conducted a comprehensive sensory evaluation of steering stability such as steering response, rigidity and grip. At this time, the comparative example 1 was set to 6 points and a relative comparison was performed with a maximum of 10 points, and the average score of 3 persons was shown as an index with the comparative example 1 being 100. The larger the value, the better the steering stability.

Durability: A durability test was conducted with a drum type tester in accordance with the conditions defined in the US automobile safety standard FMVSS139, and the running distance until failure of the tire was measured, and the value of Comparative Example 1 was set to 100. It was displayed by the index. The larger the index, the better the durability.

The results are as shown in Table 1, and in Examples 1 to 4, the member weight was reduced and the steering stability and durability were improved as compared with Comparative Example 1. Moreover, the belt was not broken.

Comparative Example 2 has the same configuration as that of Example 1 except that it does not have a rubber sheet, and is inferior in durability as compared with Example 1.

Comparative Example 3 is an example in which the product of the load at the time of 2% elongation of the organic fiber cord and the number of driving is less than the lower limit value. Compared with Comparative Example 1, the effect of improving the steering stability is not obtained and the durability is improved. Was inferior.

Comparative Example 4 is an example in which the product of the load at the time of 2% elongation of the organic fiber cord and the number of driving exceeds the upper limit value, and as compared with Comparative Example 1, the steering stability and durability were poor.

Comparative Example 5 is an example in which the load of the organic fiber cord at the time of 2% extension exceeds 100 N, and the belt is broken.

The pneumatic tire of the present invention can be used in various vehicles such as passenger cars, light trucks and buses.

1...bead part 2...sidewall part 3...tread part 4...carcass 5...bead core 6...belt layer 6A...first belt ply 6B...second belt ply 7...tread rubber part 8... Belt reinforcement layer 9: rubber sheet

Claims (3)

Air having a carcass, a belt layer in which cords are arranged obliquely with respect to the tire circumferential direction on the outer periphery of the crown portion of the carcass, and a belt reinforcing layer in which organic fiber cords are arranged on the outer periphery of the belt layer along the tire circumferential direction. In the tire containing
The organic fiber cord is made of aromatic polyamide fiber,
The load at the time of 2% extension per organic fiber cord is 100 N or less,
The product of the load (N) at the time of extension of 2% and the number of driven fibers (25 mm) per one organic fiber cord is 1000 to 2000,
A pneumatic tire comprising a rubber sheet between the belt layer and the belt reinforcing layer. The pneumatic tire according to claim 1, wherein the rubber sheet has a thickness of 0.5 to 0.9 mm. The pneumatic tire according to claim 1 or 2, wherein the twisting coefficient of the organic fiber cord is 1600 to 2300.

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