JPS59153605A - Low rolling resistance tire - Google Patents

Abstract

PURPOSE:To reduce rolling resistance in a tire and improve its durability, by specifying a volumetric portion rate, a diameter of each filament and the number of contact points among filaments themselves or the like held in a belt layer of a radial tire. CONSTITUTION:In case of a radial tire interposing a double belt layer 4, which has a reinforced cord consisting of a steel cord, between a carcass 7 and a tread 3, a volumetric portion rate (f) of the steel coard held in the belt layer 4 is set down to 10-35%, while a diameter (d) of a steel filament constituting the steel cord is to 0.06-0.40mm., respectively. The number of contact points among filaments themselves at the section side rectangular to the tire peripheral direction of the belt layer 4 should be set so as to satisfy the specified formula. In addition, the tread rubber 3 is made up of cap and each base tread rubber units C and U, and in this connection, as for each rubber C and U, one that is larger in the dynamic modulus of elasticity in the rubber C than that of the rubber U is used.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pneumatic radial tire.
By increasing the degree of dispersion of the steel filaments that make up the reinforcing steel cords in the belt layer, belt rigidity can be increased with fewer coats, reducing rolling resistance.
The present invention relates to a low rolling resistance tire that has improved fuel efficiency and durability, as well as improved riding comfort by having a tread section with a structure of two or more layers made of different types of rubber.

Generally, it is well known that radial tires exhibit superior maneuverability and superior fuel efficiency compared to bias tires. These features of radial tires are achieved by having a carcass layer with cords arranged in the radial direction, as well as a belt layer surrounding the outer periphery of the crown of the carcass layer. It is even more effective by using steel cord. Therefore, conventionally, steel cords are often used.

However, steel cord has a specific gravity of about 7.86, which is several times heavier than synthetic fiber cords such as rayon 1, polyester, and Kevlar, so the use of steel cord increases the weight of the tire. An increase in tire weight is accompanied by deterioration of tire uniformity and an increase in the unsprung weight of the vehicle, which leads to a decrease in driving performance. Therefore, it is necessary to keep the amount of steel cord to the minimum necessary.

Additionally, radial tires have the disadvantage of inferior ride comfort compared to bias tires. This riding comfort is improved by absorbing and attenuating the impact force from the road surface with the tires, and many attempts have been made to improve the riding comfort. For example, the total number of steel cords in the belt layer may be reduced, or if the belt layer is composed of two or more layers, the angle at which the steel cords in each layer intersect with the tire circumferential direction may be increased, or the number of steel cords in the belt layer may be increased. Measures such as narrowing the belt width are being taken. However, such a method has a problem in that it is accompanied by a decrease in the rigidity of the belt layer, leading to a decrease in the durability of the belt layer.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a pneumatic radial tire with low rolling resistance in which rolling resistance is reduced without deteriorating ride comfort performance.

For this reason, the present invention comprises a carcass made of cords arranged parallel or substantially parallel to the meridional section of the tire, and at least two belt layers arranged between the carcass and the tread, the reinforcing cords being made of steel cords. In the pneumatic radial tire, the volume fraction f of the steel cord in the belt layer is 10 to 35%, and the steel filament c6 diameter d constituting the steel cord is 0.06 to 0.4'OM. , the number N (pieces/cm2) of contact points between steel filaments in a cross section of the belt layer approximately at an angle to the tire circumferential direction is (number of Luni belts, i: the number of steel cords arranged in the i-th belt bridle from the inside of the tire). The dynamic elastic modulus of the camp tread rubber is smaller than the value obtained by the equation expressed by the equation (angle with respect to the tire circumferential direction), and the tread rubber is composed of at least two types of rubber, cap tread rubber and undertread rubber, and the dynamic elastic modulus of the camp tread rubber is ``C'% When the loss tangent is tanδC, the dynamic elastic modulus of the undertread rubber F E'u, and the loss tangent is tanδU, El'c> Biυ tanδC ≧tanδU, and the tread of the undertread rubber It is characterized in that the volume fraction thereof is 10% or more.

Hereinafter, the present invention will be specifically explained based on the drawings.

FIGS. 1 and 2 are partial calf cross-sectional views showing essential parts of an example of the tire of the present invention, in which 1 is a bead part, 2 is a sidewall part, 3 is a tread rubber, and 7 is a tire. The carcass has a radial structure in which cords are arranged parallel or almost parallel to the cross section of the calf, and between the carcass 7 and the tread rubber 6, reinforcing cords are made of steel cords so as to surround the outer periphery of the carcass 7. at least 2
A belt layer 4 of layers is arranged. The tread rubber 3 is composed of at least two types of rubber: cap tread rubber C and undertread rubber U. ,
FIG. 1 shows that the undertread rubber U disposed between the cap tread rubber C and the belt layer 4 is located directly below the tire groove 6, and the same rubber 2 as the rubber constituting the sidewall portion 2 is shown. ' is disposed in the shoulder part 5 intermittently from the sidewall part 2. In addition, in FIG. This is a case in which both sides of the undertread rubber U are covered, and the rubber 2' is disposed in the shoulder portion 5 continuously with the sidewall portion 2.

In the present invention, the volume fraction f of the steel cord in the belt layer 4 is 10 to 35%.

The reason for this limitation is that if the volume fraction f of the steel cord is less than 10%, it will lack strength as a belt reinforcement material for steel radial tires, and there is a great risk that the belt layer will break while the car is running. This is because if the volume fraction f in the belt layer becomes so large as to exceed 35%, the weight of the crown portion increases, resulting in a marked deterioration in the tire uniformity. Therefore, the volume fraction of the steel cord in the belt layer is at least 10% and at most 3%.
It is necessary to limit it to 5%.

Moreover, the volume fraction is defined as follows. That is,
As shown in Fig. 3, when manufacturing a steel radial tire, for example, two rubberized steel cord layers a and b, each having a thickness of hl and h2, are formed at an appropriate intersecting angle with each other. to form a belt layer.

Therefore, the total thickness of the first layer a containing the rubber composition surrounding the steel cord and the second layer is h3.

However, when these two rubberized steel cord layers a and b form a tire, the first layer a is in contact with a carcass layer made of a rubberized synthetic fiber layer, while the second layer a is in contact with a carcass layer consisting of a rubberized synthetic fiber layer.
The layer contacts the undertread rubber layer.

When looking at the two stacked rubberized steel cord layers a and b from a structural mechanics point of view, the area in the thickness direction is determined by h3 shown in the drawing, that is, the total thickness of the steel cord covering rubber layer. Instead, it is more reasonable to define it by the diagonally shaded area j shown in the drawing, that is, the area from the upper end to the lower end where the steel wire exists.

The reason is that the tensile modulus of steel cord is 5000~
22,000 kg/Crn2, whereas the tensile modulus of vulcanized rubber is extremely small, for example, 15 to 80 kg/Crn2 when expressed as a 100% modulus value, so two rubberized steel cord layers are used. This is because the mechanical properties of the composite layer consisting of a and b depend mostly on the spatial arrangement of the steel wires. The area in the thickness direction of the belt layer is defined by a line connecting the points closest to the carcass of the individual steel cords constituting the first layer a and a point closest to the tread of the individual steel cords constituting the second layer. It is defined as the part surrounded by the connecting line. Therefore, the volume fraction f (support) of the steel cord in the belt layer is the area occupied by the steel cord with respect to the area considered to be the belt layer defined above in the cut plane perpendicular to the tire circumferential direction. It is defined as a ratio expressed as a percentage. Note that FIG. 4 is an explanatory plan view of the belt portion from the tire tread side. 1st
Steel cord a1 in layer a is θ with respect to the tire circumferential direction.
The steel cords bx in the second layer are arranged at an angle of θ2 with respect to the tire circumferential direction. θ1 and 02 are respectively 15° to 30
It is preferable that it be within the range of °. This is because if the angle exceeds 30°, not only will the rolling resistance increase significantly, but also the high-speed durability of the tire will decrease, while if the angle is less than 15°, the ride quality will deteriorate, which is not preferable.

However, in the present invention, the diameter d(-) of the steel filament constituting the steel cord is 0.06hu≦d
≦0.40 pieces.

The reason for this is that steel filaments thinner than 0.061 rrm have many difficulties in wire drawing, leading to an increase in cost, which is in fact difficult to commercialize.

On the other hand, steel filaments thicker than 0.040 mm have a significant drop in fatigue resistance and are not favorable in terms of tire durability.

Furthermore, in the present invention, when the number of contact points between steel filaments in a cross section perpendicular to the tire circumferential direction of the belt layer 4 is N (pieces/C1rL2), θi is the same as defined above). This is due to the following reason.

In tires, rolling resistance decreases as belt rigidity increases, and this is expected to improve fuel efficiency.

As described above, it can be seen that an increase in belt rigidity improves fuel efficiency, but tires with increased belt rigidity due to an increase in the amount of steel cord used suffer from poor uniformity as described above.

Therefore, in order to obtain a tire that satisfies all aspects of durability, fuel efficiency, and uniformity, it is necessary to use the minimum number of steel cords necessary to ensure durability, and to obtain as much belt rigidity as possible. is desired. However, when we examined the degree of dispersion of the steel cords in the belt layer, we found that by using a belt layer that satisfies the above formula (1), it is possible to increase durability and improve fuel efficiency without increasing tire weight. They discovered the surprising fact that it is now possible to manufacture steel radial tires with improved performance.

Furthermore, in the present invention, the tread rubber 6 is
It is also composed of at least two types of rubber, namely a cap tread rubber C in contact with the road surface and an anchor rubber U in contact with the belt layer 4. In addition, when the dynamic elastic modulus of the cap tread rubber C is E"c), the loss tangent is tanδC, the dynamic elastic modulus of the undertread rubber U is E"c), and the loss tangent is tanδU, E"c) E"u tan δC≧ tan δU, and the volume fraction of the undertread rubber U in the tread 6 is 10% or more.This is m1iU
This is because if tan δU is larger than tan δC, the ride quality deteriorates, and if tan δU becomes larger than tan δC, the rolling resistance deteriorates, which is not preferable.
%, ride comfort performance will hardly be improved. The dynamic elastic modulus E'%, E- and the loss tangent tan δ, tan δU were measured using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho, using a sample cut from a tire at a frequency of 20 Hz, a temperature of 60°C, an initial strain of 10
% and a dynamic strain of 2%, it can be calculated by a known method. However, cap tread rubber C or undertread rubber U is mainly composed of natural rubber or synthetic impregnated rubber, and is blended with diene rubber and additives commonly used in the rubber industry such as carbon black and sulfur. A mixed rubber composition may be used. As the diene comb, styrene-O-butadiene copolymer rubber is most suitable. Note that the undertrend rubber U is placed between the cap tread rubber C, which has high rigidity, and the belt layer 4, so it is highly deformed, so it is a rubber that generates little heat during compressive deformation at high temperatures. This is because the high-speed durability of The cord of the carcass 7 is preferably a cord made of synthetic fiber such as rayon, nylon, or polyester in order to reduce rolling resistance of the tire.

The effects of the present invention will be specifically explained below with reference to experimental examples.

Experimental Example The radial tire 165 SR13 having the structure as shown in Figure 1 or Figure 2 was trial-produced by changing the belt layer, cap tread rubber, and undertread rubber as shown in Table 1 below. A1-9),
These were evaluated for transfer resistance, protrusion impact force, and high-speed durability. The results are shown in Table 1. In addition, tire 1
1 (y, 1 to 5 are of the structure shown in Fig. 1, tire I (r, 6 to 9 are of the structure shown in Fig. 2) 1, angle θl of the steel cord of the belt layer and 0
2 is 2o0, and the volume fraction of the undertread rubber trend is 20%.

Also, layer Sl, S2. S3
(7) For details, see Table 2. Cap tread rubber C1'
For details on C2 and undertread rubber U1 to U4, see Part 3.
Each is shown in the table.

(Margin below) Jl:) Eaves and tire performance were evaluated as follows.

(a) Transfer resistance: Measured with a 6-inch drum at a running speed of 80 km/hr. Displayed as an index with the conventional tire (tire YTB 1.) set as 100.

Port C) Protrusion impact crab Measured using a drum (diameter 2200φ) equipped with protrusions of protrusion size 10 (m+n) at an air pressure of 1.8 kg/cm2 and a running speed of 59 km/hr. Conventional tire (tire j
Expressed as an index with f;1) set as 100.

High-speed durability: The mileage was measured through JATMA's high-speed durability test.1. Displayed as an index with the conventional tire (tire J61) set as 100.

(Margin below) Table 3 Note 1) High cis 1,4 bond-containing polyisoprene rubber (Nipole IR2200, manufactured by Nippon Zeon Co., Ltd.) 2) Emulsion polymerization S
BR, amount of bound styrene 23°5% (two balls 1500
, Nippon Zeon Co., Ltd.) 3) Solution polymerized SBR, bound styrene content 18.0% (Tuften 1000R, Asahi Kasei Co., Ltd.) 4) High-cis 1,4 bond-containing polybutadiene rubber (Nipole BL 1220, Nippon Zeon Co., Ltd.) )□As is clear from Tables 1 to 3, tire shop 1 (conventional tires)
Tire A is a tire in which the same rubber CI is placed on the cap tread rubber and undertread rubber.
2 (Comparative Example Tire) is a tire in which the belt layer was changed to 82. This shows that although rolling resistance can be reduced by increasing the degree of dispersion of steel filaments, the protrusion impact force increases. Tire A 3
(Tire of the present invention) is a tire in which rubber Ul, which has a smaller dynamic elastic modulus and loss tangent than the cap tread rubber c1, is arranged in the undertread comb, and as a result, according to the present invention, the rolling resistance can be further reduced. It can be seen that the protrusion impact force can also be reduced. Tire shop 5 (tire of the present invention) is a tire with a different belt layer, and tires A6 to A9
is a tire with changed undertread rubber. Note that Tire A 6 (comparative example tire) uses U2 comb as the undertread comb, and it can be seen that the U2 comb has a higher dynamic elastic modulus than C2 rubber, so that the protrusion impact force is larger.

As explained above, the tire of the present invention can reduce rolling resistance without impairing ride quality, so it can be used not only as a pneumatic radial tire for passenger cars, but also as large tires for trucks, buses, etc. It is possible.

[Brief explanation of the drawing]

FIGS. 1 and 2 are partial meridional cross-sectional views showing essential parts of an example of the tire of the present invention, FIG. 3 is a cross-sectional view of the belt layer perpendicular to the tire circumferential direction, and FIG. 4 is a cross-sectional view of the tire tread. FIG. 3 is a plan view of the belt portion seen from the side. 1...Bead part, 2...Side wall part-, 6.
...Tread rubber, 4...Belt layer, 5...Part of shoulder, 6...Tire groove, 7...Carcass, C...
- Cap tread rubber, U... Undertread rubber, a... first layer, b... second layer. □□□□□□□□□□□□□□□□□□□□ Agent Patent attorney Shin Ogawa − Patent attorney Ken Noguchi Patent attorney Kazuhiko Saishita

Claims (1)

[Scope of Claims] A carcass consisting of cords arranged parallel or substantially parallel to the calf cross section of the tire, and at least two belt layers arranged between the carcass and the tread and having reinforcing cords made of steel cords. In the pneumatic radial tire, the volume fraction f of the steel cord in the belt layer is 10 to 35%, and the diameter d of the steel filament constituting the steel cord is 0.06 to 0.4'.
Q mm, and the number N (pieces/crIL2) of contact points between steel filaments in the cross section perpendicular to the tire circumferential direction of the belt layer is (n,: number of belt layers, 1: i-th point from the inside of the tire). belt bris, θ1: the angle of the steel cord arranged in the belt bris of the i1 layer in the circumferential direction of the tire) is smaller than the value obtained by the formula, and the tread rubber is smaller than the value obtained by the formula If the tonnage is made of at least two types of rubber, and the dynamic elastic modulus of the cap tread rubber is expressed as tanδC, and the loss tangent is tanδC, and the dynamic elastic modulus of the undertread rubber is expressed as so, and the loss tangent is tanδU, then
> EU tan δC≧ tan δU, and the volume of the undertread rubber in the tread is 10% or more.