JP3387571B2 - Pneumatic radial tire - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire, and more particularly, to further improve the rolling resistance by further reducing the weight of the tire and improve the wear resistance. And a pneumatic radial tire with further improved steering stability. [0002] With the spread of automobiles and the enhancement of expressways,
The radialization of tires is progressing, and the radialization rate for passenger cars is about 90%, and the radialization rate for truck and bus tires is 5%.
It has reached just over 0%. Thus, the widespread use of radial tires is due to their unique radial structure, which is superior in wear resistance, high-speed resistance and steering stability as compared with conventional bias tires. As is well known, a radial tire has a tread portion and a pair of side portions formed on both layers of the tread portion and a pair of bead portions formed on the inner periphery of the side portion, respectively. And a belt layer surrounding the carcass layer. The carcass layer and the belt layer play an important role in maintaining the strength of the tire together with the bead portion.
Generally, the belt layer is composed of two or more plies in which cords are arranged at 10 ° to 30 ° with respect to the tire circumferential direction, and the carcass layer is substantially 90 ° with respect to the tire circumferential direction.
Is formed from one or two plies arranged in a single layer. [0004] The characteristic of the radial tire lies in the belt layer and the carcass layer. The carcass layer gives flexibility to the tire, and the belt layer restrains the carcass layer. I have. Since the tread surface portion is swollen by the belt layer, the movement of the tread surface portion is suppressed, and the good tire characteristics are obtained. [0005] In line with the trend of energy saving since the first oil shock, the fuel efficiency of automobiles has become a great vehicle characteristic, and radial tires having better tire characteristics than conventional tires have various angles. Therefore, improvement for low fuel consumption has been demanded. [0006] The fuel efficiency of an automobile depends on improving the thermal efficiency of the engine and how the running resistance can be reduced. Tires, which are one of the important components for automobiles, greatly affect running resistance and play a role in reducing fuel consumption. The running resistance of the vehicle generally includes (1) rolling resistance caused by mechanical loss such as friction of each bearing,
(2) air resistance, (3) gradient resistance, (4) acceleration resistance, and (5) tire rolling resistance. Among them, the ratio of the tire rolling resistance in the above (5) varies depending on the speed of the vehicle.
It is said to reach 50% or more in the speed range of km / h or less. When the rolling resistance of a tire is further analyzed from its mechanism, it can be divided into (a) hysteresis loss, (b) frictional resistance, and (c) air resistance, wherein the hysteresis loss is 90% of the tire rolling resistance. It is said to occupy more. It is needless to say that reducing the hysteresis loss is extremely effective in reducing the tire rolling resistance and, in turn, reducing fuel consumption of the automobile. It is generally known that the rolling resistance caused by the hysteresis loss is represented by the following equation. Rolling resistance = H / 2πr where, H = ΣUi · sinδ · Vir = tire radius Ui: strain energy sinδ of each part of tire: energy loss amount of each part of tire Vi: volume of each part of tire From this, a factor for reducing the hysteresis loss When the tire radius is fixed, the hysteresis loss is U
It can be seen that i, sin δ, and Vi are affected. [0010] Ui is easily affected by the tire shape and other external factors, and it is difficult to grasp it quantitatively. For this reason, as a means for reducing the hysteresis loss, a method generally used at present is to reduce sin δ and Vi. Until now, sin δ and Vi have been taken as methods for reducing sin δ by adopting a low heat generation tread and compound, and increasing the rigidity of the tire belt layer to reduce deformation of the tread and reduce energy loss. In addition, for Vi, the weight of each member is reduced. When the tread and the compound lower the heat generation, the wet road characteristics decrease, the safety on wet road surface decreases,
You can't easily take this method. Further, the method of increasing the rigidity of the belt layer of the tire has a limit because the riding comfort is deteriorated. Although the weight reduction of each member is effective, simply reducing the weight of each member not only reduces the durability but also lowers the basic performance of the tire. It is well known that it is difficult to reduce the weight of each member while maintaining the basic performance. Under such difficult conditions, in order to reduce the weight of the tire, a new material having properties comparable to those of the conventional material, and furthermore, a lightweight new material has been required. At present, generally used radial tire structures for passenger cars have a carcass layer in which cords are arranged at approximately 90 ° with respect to the tire circumferential direction, and cords are arranged at 15 ° to 30 ° with respect to the tire circumferential direction. It is composed of a belt layer. An organic fiber cord such as nylon or polyester is used as the carcass member. On the other hand, a steel cord is mainly used for the belt layer. The steel cord has an initial modulus greater than that of the organic fiber cord, so that the rigidity of the belt layer is increased and the radial ply for the passenger car is increased.
It is an important material for maintaining excellent properties of tires. However, since the steel cord has a very low tensile strength per weight, the weight of the tire, especially the weight of the belt layer, increases, so that the weight of the steel belt accounts for 15 to 17% of the weight of the entire tire. That is, how to reduce the weight of the belt layer is important in reducing the tire rolling resistance. From the viewpoint of weight reduction, the above-mentioned organic fiber cords are used as the belt material. However, since these cords have a lower tensile modulus than the steel cord, the rigidity of the belt layer is insufficient, and the steering stability and abrasion resistance are poor. And the modulus at high temperatures decreases the durability at high speeds.
Cannot be used as a substitute for steel cord. Therefore, development of a lightweight, high-strength, high-elasticity fiber material that can replace the steel cord has been desired. However, in recent years, the use of an aromatic polyamide fiber having a very high tensile modulus among organic fiber materials as a tire belt material has reduced the weight of a tire and has reduced rolling resistance. Attempts have been made to reduce the speed and to improve the speed, durability and steering stability.
Such an aromatic polyamide fiber has a tensile strength of 250.
kg / mm ² or more, a tensile modulus of 10000 kg / mm ² or more high-modulus aramid fibers, for example DuPont Kevlar mainly composed of poly -p- phenylene terephthalamide chain (KE
VLAR) ^R and Kevlar 149 ^R. Some proposals have been made to use these aromatic polyamide fibers for the belt layer (for example, JP-A-62-85702 and JP-A-1-239134), but these belt layers have low in-plane rigidity. However, steering stability was not always satisfactory. On the other hand, the uniformity of the pneumatic radial tire is improved, the high-speed durability is improved without deteriorating the uniformity of the tire, and a reduction in durability of the belt portion due to an external injury is prevented. It has been proposed to use flat monofilaments for the belt reinforcing layer provided outside the carcass layer of the tread for the purpose of improving rolling resistance (for example, JP-A-2-185805 and JP-A-3-7-85).
No. 9402). However, it is necessary for these pneumatic radial tires to further reduce the weight of the tire and further reduce the rolling resistance. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a pneumatic radial tire in which the rolling resistance is reduced by further reducing the weight of the tire, and the wear resistance and steering stability are further improved. [0018] According to the present invention SUMMARY OF], a pneumatic radial tire having a belt layer and the belt reinforcing layer in the carcass layer outer tread, Fang as a belt layer
1.5 to 2.8 times the diameter of the cord made of aromatic polyamide
A flat organic fiber monofilament having a cross-sectional shape having a ratio of a major axis a to a minor axis b (a / b) of 1.5 or more and a denier number of 2000 to 4000 is used as a belt reinforcing layer using at least one sheet-like material having a thickness of Provided is a pneumatic radial tire having a reinforced tread portion. Hereinafter, the configuration of the pneumatic radial tire according to the present invention and its operational effects will be described in detail. According to the present invention, as described above, the belt layer provided outside the carcass layer of the tread of the pneumatic radial tire is made of an aromatic polyamide. Belt layer consisting of aromatic polyamide used in the present invention are represented for example tensile modulus 10000 kg / mm ² or more, the tensile strength of 250 kg / mm ² or more high modulus aromatic polyamide (aramid) fibers, for example by the following formula Twist coefficient K is 1000-2200
The cord is given a twist and heat treated under a tension of at least 0.8 g / d and embedded in a rubber having a dynamic elastic modulus of 7.0 to 13.0 MPa. The sheet is formed into a sheet 1.5 to 2.8 times the diameter of the cord, and the sheet is formed as at least one belt layer. K = T√ΔDK: twist coefficient T: twist number (T / 10 cm) D: total denier number of cord The high elasticity aromatic polyamide fiber used in the present invention is basically p-type. A fiber made of phenylene terephthalamide with a tensile strength of 250 kg / mm ² or more,
Preferably it has a tensile modulus has a 10000 kg / mm ² or more properties, is currently marketed as high-modulus aramid fibers, DuPont Kevlar 49 ^R and Kevlar 149
^R can be used. Kevlar 49 ^R has a tensile strength of about 280 kg / mm ^2, a tensile modulus of about 13000kg / mm
² Kevlar 149 ^R has a tensile strength of about 270 kg
/ Mm ² and a tensile modulus of about 19000 kg / mm ² . These are conventional aramid fibers, for example, tensile strength of about 280 kg / mm ² of DuPont Kevlar ^R, tensile modulus compared to about 6000 kg / mm ^2, a tensile modulus of about 2 to 3 times higher. However, these high-elasticity aramid fibers have a lower elongation than conventional low-elasticity aramid fibers as described above, and have poor flex fatigue resistance due to their more rigid molecules, so that tire reinforcement is required. It is preferable that an appropriate twist be imparted to use. That is, it is preferable that the cord is formed by giving a twist having a twist coefficient K represented by the above formula in the range of 1000 to 2200. The cord thus obtained is subjected to, for example, a dry heat treatment after applying an appropriate adhesive, and then to 0.8 g / cord.
Heat treatment is performed with a tension of d or more. Here, the application of the adhesive may be performed before the twisted cord, but the heat treatment under a tension of 0.8 g / d or more is preferably performed after the cord is formed. The heat treatment temperature is preferably from 180 to 250C. The reason why the tension applied during the heat treatment is set to 0.8 g / d or more is that when the tension is less than 0.8 g / d, the structural elongation under the stress load due to the twist resulting from the twisting cannot be sufficiently suppressed. For this reason, even if a highly elastic aramid fiber is used, its elasticity cannot be used effectively. The tension here is more preferably in the range of 1.0 to 2.0 g / d from such a viewpoint. If the tension is too high, cord breakage during processing and damage to the fiber filaments may occur. [0024] The adhesive-treated cord thus obtained is embedded in rubber having a dynamic elastic modulus preferably in the range of 7.0 to 13.0 MPa. When the dynamic elastic modulus is less than 7.0 MPa, sufficient rigidity of the belt layer cannot be obtained even when the high elasticity aramid fiber is used, so that there is a possibility that steering stability and high-speed performance may not be improved. If it exceeds 13.0 MPa, the heat generated by the rubber increases, which may cause a decrease in the high-speed performance of the tire due to the heat generated. From such a viewpoint, the dynamic elastic modulus of the rubber is more preferably from 9.0 to 11.0 MPa. The rubber used here is not particularly limited, and an additive such as carbon black is blended with a rubber that has been conventionally used as a belt layer such as general natural rubber and styrene-butadiene copolymer rubber (SBR). Rubber composition. In manufacturing the belt layer, the cord is embedded in the rubber as described above, and the thickness of the cord is determined by the diameter of the cord.
The sheet is formed into a 1.5 to 2.8 times, preferably 1.8 to 2.4 times , sheet, and this sheet is used as at least one belt layer. Here, the cord diameter is 1.5
When the thickness is less than twice, the belt rigidity is increased, but the fatigue resistance of the belt cord is reduced, and the durability of the tire may be deteriorated. In particular, the high elasticity aramid fiber used in the present invention is inferior in fatigue resistance because the molecule is more rigid than the low elasticity aramid fiber.
It is particularly preferable to make it 5 times or more in order to secure tire durability. On the other hand, when the thickness is more than 2.8 times, the belt rigidity is greatly reduced, and there is a possibility that the advantage of the high elasticity aramid fiber cannot be enjoyed. The pneumatic radial tire according to the present invention comprises a belt reinforcing layer provided outside the belt layer, and the cross section of the belt reinforcing layer is a ratio of the major axis a to the minor axis b (a / b). ) Is 1.5 or more, preferably 2 to 4, and the denier number is 2000 to 4000, preferably 2200 to 380.
The tread portion is reinforced by using zero-twisted flat organic fiber monofilaments which are arranged in parallel with the major axis direction oriented in the tire width direction. As a result, the plane of the monofilament faces in the tire tread surface direction, so that the in-plane bending rigidity of the belt reinforcing layer is improved, and the steering stability can be improved. The belt reinforcing layer is formed by embedding a plurality of flat monofilaments in rubber to form a sheet. The rubber may be any rubber composition conventionally used as a rubber for a belt reinforcing layer. Can be. As a material of the flat organic fiber monofilament used for the belt reinforcing layer of the present invention, for example, nylon 6 having a fiber forming property is used.
6 (polyhexamethylene adipamide), nylon 6 (polycaprolactam), polyamide fiber such as nylon 46 (polytetramethylene adipamide), polyethylene terephthalate (PET) fiber, polyethylene naphthalate fiber (PEN), polyvinyl Alcohol (PV
A) and the like. The flat monofilament used for the belt reinforcing layer of the pneumatic radial tire according to the present invention has no twist and has a high modulus, so that it is not necessary to apply an excessive tension during the heat treatment for bonding, and therefore the heat shrinkage is low. . Here, the adhesive heat treatment means that the monofilament is heat-treated according to a conventional method in order to enhance the adhesiveness to rubber. In the present invention, a flat monofilament having a denier of 2000 to 4000 is used. However, if the denier is less than 2,000, the abrasion resistance and the steering stability decrease, which is not preferable. If the denier exceeds 4,000, the rolling resistance increases. At the same time, separation occurs particularly in the rubber gauge between the cords in the width direction, which causes a problem in durability. In the present invention, since the belt reinforcing layer is formed using a flat monofilament cord, the bending strain generated in the cord can be reduced, and the durability and fatigue resistance can be improved. EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but it goes without saying that the scope of the present invention is not limited to these Examples. Examples 1 to 3, Comparative Examples 1 to 6, and Comparative Examples A pneumatic radial tire (tire size: 185 /) was prepared by combining a belt layer and a belt reinforcing layer manufactured using cords having the materials shown in Table 1. 60R14),
The rolling resistance, abrasion resistance and steering stability of the obtained tire were evaluated, and the tire weight was measured. The belt layer is made of a cord (steel:
2 + 2 (0.25), aramid: Kevlar 4 manufactured by DuPont containing poly-p-phenyleneterephthalamide as a main component
9) was manufactured by embedding in a rubber composition having the following composition so as to have a thickness of 1.3 mm at a number of 50 per 5 cm. The belt structure has a cord angle of 2 with respect to the tire circumferential direction.
The belt layer was arranged on the carcass layer side so as to be 0 °.
Note that the carcass layer was provided with 1500d / 2 polyester cords at 50 cords / 5cm and the cord angle was 90 ° with respect to the tire circumferential direction. Components (parts by weight) Natural rubber (NR) 100 Carbon black (HAF) 60 Zinc oxide 10 Antioxidant 2 Cobalt naphthenate 1 Cobalt stearate 1 Melamine resin 4.5 Cresol resin 1 Vulcanization accelerator 0.5 Sulfur ¹⁾ 7.5 1) Insoluble sulfur treated with 20% oil On the other hand, the belt reinforcing layer is a cord shown in Table 1 (66N: nylon 66 having a ratio of major axis / minor axis of 2) and twisted as shown in Table 1. 42 × 42, 840 denier × 2 multifilaments and non-twisted monofilaments of various deniers) are prepared and treated with a resorcinol / formalin / rubber latex (RFL) adhesive, and then heat-treated for bonding. Code was made. The treated cords were buried in unvulcanized rubber having the following composition at a driving number of 32/5 cm to form a belt reinforcing layer, and vulcanized to produce tires shown in Table 1. To evaluate the uniformity (RFV) and high-speed durability of these tires, a uniformity measurement test and an indoor durability test (a drum diameter of a test machine of 1707 mm) were performed under the following test conditions. Ingredients (parts by weight) Natural rubber (NR) 65 Styrene-butadiene copolymer rubber (SBR) 20 Polybutadiene rubber (BR) 15 Carbon black (GPF) 60 Process oil 7 Stearic acid 1 Zinc oxide 5 Sulfur 3 Vulcanization Accelerator 1 FIG. 1 shows the tire structures shown in Examples and Comparative Examples. In FIG. 1, a pair of left and right bead wires 3, 3
A carcass part 4 is mounted between the two parts. In the tread 1, two belt layers 5 and a belt reinforcing layer 6 are arranged on the carcass part 4 in an annular shape in the tire circumferential direction. 2 is a side wall. The tire evaluation method is as follows. Rolling resistance: The tire, the air pressure of which has been adjusted by preliminary running, is rotated at a peripheral speed of 150 km / hr on a drum having an outer diameter of 1707 mm, and then the drum is coasted. Was calculated by subtracting the rotational resistance of the drum when no load was applied, and expressed as an index. Abrasion resistance: After running 40,000 km under the conditions of design normal load and air pressure specified by JATMA, the wear amount of each tire was measured and indicated as an index to the wear amount of the conventional tire. Driving stability: In the feeling test of the test driver, the tire of the conventional example was evaluated as an index with 100 points. The results are shown in Table 1. The above three characteristics indicate that the larger the numerical value, the better the result. Tire weight (indicated by an index): The weight of each tire was indicated by an index when the tire weight of the control example was set as a reference (100). A smaller value indicates that the tire is lighter. [Table 1] As described above, according to the present invention,
For example, as shown in Examples 1 to 3, the belt layer is made of aramid fiber, and the belt reinforcing layer has a denier of 200.
By comprising from 0 to 4000 monofilaments, rolling resistance, abrasion resistance and steering stability are improved, and further reduction in tire weight is achieved. On the other hand, when a steel cord was used for the belt layer and there was no belt reinforcing layer (Comparative Example 1), all of the characteristics were inferior to those of the control example. Code (Comparative Example 2)
Although the rolling resistance and steering stability are improved, the tire weight is equivalent to the control and is not improved. Aramid fiber was used for the belt layer, but when there was no belt reinforcing layer (Comparative Example 3), the abrasion resistance and steering stability were poor,
When the 840 denier multifilament is used for the belt reinforcing layer (Comparative Example 4), all three properties are inferior. Further, the denier of the monofilament of the belt reinforcing layer is 2
If it is less than 000 (Comparative Example 5), the abrasion resistance and steering stability are poor, and if it exceeds 4000 denier, the rolling resistance is not improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view showing the structure of an example of a pneumatic radial tire according to the present invention. [Description of Signs] 1 ... Tread 2 ... Sidewall 3 ... Bead wire 4 ... Carcass part 5 ... Belt layer 6 ... Belt reinforcement layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B60C 9/00 B60C 9/18-9/22

Claims (1)

(57) [Claim 1] In a pneumatic radial tire in which a belt layer and a belt reinforcing layer are provided outside a carcass layer of a tread, a cord made of an aromatic polyamide is used as a belt layer .
At least one sheet having a thickness of 1.5 to 2.8 times the diameter is used, and the cross-sectional shape of the belt reinforcing layer is a denier having a ratio (a / b) of the major axis a to the minor axis b of 1.5 or more. Number 200
A pneumatic radial tire in which the tread portion is reinforced using 0 to 4000 flat organic fiber monofilaments.