JPS6245081B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a pneumatic radial tire that, when used in a passenger car, can reduce the fuel consumption of the car and also maintains good braking performance and wear resistance on wet road surfaces. Radial tires generally consist of one or more carcass plies that have an angle of 75 degrees or more with respect to the circumferential direction of the tire, but in order to reduce the fuel consumption of passenger cars using this tire, It has been known that it is effective to reduce the rolling resistance of tires. Additionally, the rolling resistance of the tire is 60 at the tread (see Figure 1).
It is well known that ~80% of cases occur. In addition,
Figure 1 shows a partial cross-sectional view of a radial tire, where 1 is the tread part, 2 is the sidewall part,
3 represents the tread portion rubber, 4 represents the belt layer, and 5 represents the carcass. The rolling resistance of a tire is, in principle, proportional to the strain energy that each member of the tire repeatedly receives during rolling, the hysteresis loss coefficient of each member, and the volume of each member. Furthermore, a large amount of material with high strain energy and high hysteresis loss coefficient is used in the tread portion. Therefore, most of the rolling resistance occurs in the tread portion. Conventionally, synthetic rubbers such as non-oil-extended styrene-butadiene rubber, oil-extended styrene-butadiene rubber, or mixtures thereof have been mainly used as the tread rubber of general pneumatic tires for passenger cars, and reinforcing carbon Rubber compositions heavily loaded with black have been used. These synthetic rubbers and rubber compositions have high hysteresis loss coefficients,
Therefore, the rolling resistance of tires using these materials was also high. For this reason, in recent years, attempts have been made to reduce rolling resistance by using a mixture of natural rubber with a small hysteresis loss coefficient and polybutadiene rubber mainly consisting of 1,4 bonds, or a compound with a reduced amount of carbon black as the tread rubber. was proposed (Japanese Patent Application Laid-Open No. 52-118705). However, when a tire made of such a tread rubber material is used in a passenger car and the passenger car is driven on a wet road surface, the braking performance on the wet road surface is lower than that of the conventional tread rubber material described above. It has the disadvantage that it is much lower than when using . Therefore, when using this tread section rubber material, that is, a mixture of natural rubber and polybutadiene rubber mainly composed of 1,4 bonds, or a compound with a reduced amount of carbon black, the tread section should be drained in order to improve the above-mentioned braking performance. Attempts have been made to increase the friction coefficient by increasing the number of grooves to quickly remove water from wet road surfaces (Japanese Patent Application Laid-Open No.
52-69101). However, in this case, the drainage effect is exhibited when driving at relatively high speeds (80 km/h or more), but at low speeds, the effective contact area between the road surface and the tread rubber decreases due to the increase in drainage grooves. The friction coefficient becomes smaller. Therefore, the braking distance until stopping is not necessarily improved. Furthermore, as the tread part rubber, compound rubber is added.
For 100 parts by weight, (a) 5-30% by weight of polyisobutylene/isoprene rubber with a chlorine and/or bromine content of 1.0-2.0% by weight, (b) natural rubber and/or
or 40-95% by weight of polyisoprene rubber, and
(c) It has been proposed to use a mixture containing 50% by weight or less of polybutadiene rubber (Japanese Unexamined Patent Application Publication No. 1983-1999-
No. 135148). However, although this mixture has good impact resilience and wet skid resistance,
There is a problem of poor wear resistance, and a solution to this problem has been awaited. The present invention has been made in view of the above-mentioned circumstances, and is a pneumatic radial tire that has low rolling resistance when used for passenger cars, and also maintains good braking performance and wear resistance on wet road surfaces. The purpose is to provide Therefore, in the present invention, the tread portion rubber is made of polyisobutylene containing (a) 1.0 to 2.0% by weight of chlorine and/or bromine, based on 100 parts by weight of the compounded rubber.
In a radial tire made of a mixture containing 5 to 30% by weight of isoprene rubber, (b) 40 to 95% by weight of natural rubber and/or polyisoprene rubber, and (c) 50% by weight or less of polybutadiene rubber, (1) The tread part drainage groove has an area ratio of 20 to 30% of the total ground contact area, and (2) the belt part has a cord with a single cord Young's modulus of 2500 kg/mm2 ^or more in the tire circumferential direction. The gist of the present invention is a pneumatic radial tire characterized in that the belt portion is arranged at an angle of 15 to 25 degrees, and the circumferential tensile rigidity of the belt portion is 200 times or less of the radial tensile rigidity. Hereinafter, the configuration of the present invention will be explained in detail. The rubber composition used as the tread rubber material in the pneumatic radial tire of the present invention is composed of (a) polyisobutylene/isoprene rubber having a chlorine and/or bromine content of 1.0 to 2.0% by weight per 100 parts by weight of the compounded rubber; (b) 40 to 95% by weight of natural rubber and/or polyisoprene rubber, and (c) 50% by weight or less of polybutadiene rubber. In this rubber composition, (a) polyisobutylene/isoprene rubber having a chlorine and/or bromine content of 1.0 to 2.0% by weight (hereinafter referred to as halogenated butyl rubber) is used in an amount of less than 5% by weight. It becomes difficult to maintain high braking performance on wet road surfaces of the resulting tires;
If the amount exceeds 5% by weight, braking performance on wet road surfaces can be maintained at a high level, but rolling resistance increases and wear resistance decreases, so it must be within the range of 5 to 30% by weight. (b) The amount of natural rubber and/or polyisoprene rubber used is equal to the total amount of compounded rubber.
It must be within the range of 40-95% by weight per 100 parts by weight. This is because if it is less than 40% by weight, the resulting tire will have an unsatisfactory rolling resistance, while if it is more than 95% by weight, it will not be possible to maintain high braking performance on wet road surfaces. Note that the polyisoprene rubber used here preferably has a cis 1,4 bond unit content of 90 mol % or more. Furthermore, (c) polybutadiene rubber,
In order to obtain a tire with desired performance, it is necessary that the amount used be 50% by weight or less per 100 parts by weight of the total compounded rubber. Note that by using this polybutadiene rubber, it is possible to suppress a significant decrease in wear resistance when a high proportion of halogenated butyl rubber is used. In this way, (a), (b) and
A diene-based synthetic rubber such as a styrene-butadiene copolymer obtained by emulsion polymerization or solution polymerization is added to the rubber composition consisting of component (c) (a).
It may be added in an amount of 0 to 20% by weight based on the total amount of components (b) and (c). A radial tire using such a rubber composition has low rolling resistance and high braking performance (ie, high coefficient of friction). In addition, in the pneumatic radial tire of the present invention, the tread drainage groove is 20% of the total ground contact area.
With an area ratio of ~30%. If the area ratio of this drainage groove is less than 20%, the drainage performance during high-speed driving will be poor; if it exceeds 30%, the drainage performance in the high-speed range will be further improved, but the friction coefficient will decrease in the low-speed range. This is unsuitable because the abrasion resistance, which will be described later, will be disadvantageous. The value of this area ratio is based on a tire using the above rubber composition mounted on a JIS standard rim, an arbitrary air pressure, and a JIS tire corresponding to that air pressure.
This is based on the knowledge that under conditions of 80 to 100% of the load, the best braking performance can be achieved when the area ratio of the tread drainage groove to the total ground contact area is 20 to 30%. Furthermore, in the pneumatic radial tire of the present invention, the Young's modulus of a single cord in the belt portion is 2500.
Kg/mm ² or more cord in the circumferential direction of the tire
Values are arranged at an angle of 15 to 25 degrees, and the circumferential tensile rigidity of the belt part is 200% higher than the radial tensile rigidity.
Must be less than double. This is for the following reasons. The above rubber composition used in the present invention can achieve both the two performances of reducing rolling resistance and maintaining wet road braking performance as described above, but it tends to have poor abrasion resistance. Therefore, tires using this rubber composition must be devised to compensate for this weakness. In particular, when the tread portion is subjected to severe deformation or when the degree of curvature of the road surface is extremely large, the tread shoulder portion wears out faster than the tread center portion, a form of so-called shoulder wear. That is the problem. Therefore, in a tire using the above-mentioned rubber composition used in the present invention, it is necessary to provide high rigidity to the belt portion in order to reduce the movement of the tread portion rubber on the road surface. In particular, it is necessary to optimize the balance of rigidity regarding the shoulder portion. Therefore, when we investigated the relationship between the Young's modulus of a single cord constituting the belt layer and the average amount of wear using the treaded rubber material used in the present invention, we found that the higher the Young's modulus, the more the amount of wear. It was found that the Young's modulus reached a saturated state when it was 2500 Kg/mm ² or more. Incidentally, FIG. 2 is an explanatory diagram showing, in a graph, the results of examining the relationship between the Young's modulus and the wear amount of a single cord constituting the belt layer using the rubber composition used in the present invention. Test conditions: Tire size for A, B, C, D, and E
165SR13, tested with tires with the same belt angle and the same belt width, and the belt structure was as follows: A and B are folded structure 4.
Stacked, C is folded structure 3
D and E are two stacked sheets with a step structure, and the vertical axis represents the amount of wear determined from the amount of groove remaining after 20,000 km of actual vehicle wear test. On the other hand, the relationship between the ratio of the amount of wear on the tread shoulder and the tread center and the belt cord angle was investigated using actual vehicle wear tests mainly on winding roads. The results are shown in FIG. In addition, Figure 3 shows the ratio of the amount of wear between the tread shoulder part and the tread center part, the cord angle α of the belt with respect to the circumferential direction of the tire, and the tensile rigidity in the circumferential direction of the tire.
The ratio of E ₁ to the radial tensile stiffness E ₂ (E ₁ /
₂ ) is an explanatory diagram showing the results of an actual vehicle wear test mainly on a curved road as a graph regarding the relationship with E2). Test conditions: The test tire size is 165SR13 with the same belt width, and the belt angle α
are as shown in the figure, and the belt structures A, B, C, D, and E are two-ply steel belts with a step structure.
C' and D' are the tread values determined from the amount of groove remaining after 20,000 km of actual vehicle wear test, conducted using a tire with a three-ply steel belt with a step structure and 0 degree aramid fiber added. The ratio of the amount of wear on the shoulder portion is expressed on the vertical axis. As can be seen from FIG. 3 above, the smaller the belt angle with respect to the circumferential direction of the tire, the more prone it is to shoulder wear, and when the belt cord angle is less than 15 degrees, the shoulder wear resistance is unsatisfactory. In Figure 3,
E ₁ /E ₂ expressed on the horizontal axis considers the belt layer to be a biaxial plane with the circumferential and radial directions of the tire as its axes, and E ₁ is the tensile rigidity in the circumferential direction and E ₂ is the radial direction. It shows the ratio in terms of tensile rigidity. Therefore, to solve the problem of shoulder wear, it is necessary to maintain the radial tensile stiffness E ₂ above a certain range in order to reduce the amount of wear on the shoulder part, rather than simply increasing the rigidity of the belt part. Therefore, the ratio of E ₁ /E ₂ is 200
and the belt cord angle must be at least 15 degrees. In this way, in order to improve the wear resistance of the tire using the rubber composition used in the present invention,
The Young's modulus of a single cord in the belt portion is 2500 kg/mm2 _or more, the belt cord angle is 15° or more, preferably 17° or more with respect to the circumferential direction of the tire, and E ₁ /E ₂ is 200 or less It is preferably 120 or less. Furthermore, as mentioned above, it is also necessary to improve wear resistance by keeping the groove area ratio below 30% and reducing the contact pressure of the tread rubber. Furthermore, rolling resistance and cord angle of the belt layer with respect to the circumferential direction of the tire were tested. The results are shown in FIG. Figure 4 is a graph showing the results of examining the relationship between tire rolling resistance and cord angle of the belt layer in the low speed range (20 to 60 km/h) and high speed range (100 to 150 km/h). FIG. Test conditions: Rolling resistance was measured on a 67-inch drum using a test tire size 165SR13, the same belt width, and a tire with two-ply steel belts with a step structure (load 300Kg, air pressure 1.7Kg/
^cm2 ). As is clear from Figure 4, as the belt cord angle increases, the movement resistance gradually decreases in the relatively low speed range of 20 to 40 km/h, and increases at an accelerating rate in the high speed range of 100 to 150 km/h. . 80% in this low speed range,
Assuming a normal speed with 20% weight added to the high speed range, rolling resistance becomes minimum at a belt cord angle of around 21 degrees, and in the range of 15 to 20 degrees, preferably 17 to
A belt cord angle in the range of 23° is advantageous for reducing rolling resistance. Judging from the results shown in FIGS. 2 to 4 as described above, in the pneumatic radial tire of the present invention, the Young's modulus of a single cord in the belt portion is 2500 Kg/mm ² or more, as described above. The cords were arranged at an angle of 15 to 25 degrees with respect to the circumferential direction of the tire, and the tensile rigidity in the circumferential direction of the belt must be 200 times or less as compared to the tensile rigidity in the radial direction. As described above, according to the present invention, when used in a passenger car, it is possible to reduce the fuel consumption of the passenger car by appropriately combining a specific tread rubber material, a specific tread design, and a specific belt structure. Moreover, it is possible to provide a pneumatic radial tire that has good braking performance and wear resistance on wet road surfaces. EXAMPLES Below, the effects of the present invention will be specifically explained with reference to Examples. Examples Rubber compositions A, B, and C with the following formulations (parts by weight)
(A is within the scope of the present invention, B and C are outside the scope of the present invention) were tested for rolling resistance performance, wet road braking performance, and wear resistance performance of radial tires using rubber for the tread portion. The results are shown in the table below. In the table, No. 1 is the case according to the present invention, and No. 2 to No. 9 are for comparison.

【table】

[Table] Test method (1) Rolling resistance performance The reciprocal of the average rolling resistance value on a 67-inch drum at a speed of 40 to 100 kg/h is expressed as an index. (2) Wet road braking performance This is the coefficient of friction when the brake is locked on a wet road on an asphalt road (skid number approximately 50) expressed as an index. (3) Wear resistance performance This is the reciprocal of the wear amount of each groove in the tread section during actual vehicle driving, expressed as an index.

[Table] As is clear from the above table, none of No. 2 to No. 9 simultaneously satisfies the three performances of rolling resistance performance, wet road braking performance, and wear resistance performance. That is, No. 2 and No. 9 satisfy the requirements within the scope of the present invention in the same manner as No. 1 except that a rubber composition outside the scope of the present invention was used for the tread rubber, but It is inferior to No. 1 in terms of dynamic resistance performance, wet road braking performance, and wear resistance performance. Also, No.3,
No. 4, No. 5, and No. 6 use a rubber composition within the scope of the present invention for the tread rubber, but each lacks one of the other requirements, so it has rolling resistance performance and wet road braking performance. - Inferior to No. 1 in both wear resistance performance. No. 6 and No. 7 use a rubber composition outside the scope of the present invention for the tread rubber, and each lacks one of the other requirements, resulting in rolling resistance performance, wet road braking performance, Inferior to No. 1 in all aspects of wear resistance. Therefore, only the radial tire of the present invention can provide an excellent low fuel consumption tire.

[Brief explanation of the drawing]

Figure 1 is a partial sectional view of a radial tire, Figure 2 is a partial cross-sectional view of a radial tire;
The figure is an explanatory graph showing the relationship between the Young's modulus and the amount of wear of a single cord constituting the belt layer using the rubber composition used in the present invention. Regarding the relationship between the ratio of the wear amount of the rudder part and the tread center part, the cord angle of the belt to the circumferential direction of the tire, and the ratio of the tensile rigidity in the circumferential direction and the tensile rigidity in the radial direction of the tire. Actual vehicle wear mainly on curved roads FIG. 4 is an explanatory diagram showing the test results in a graph. FIG. 4 is an explanatory diagram showing the results of examining the relationship between the rolling resistance of the tire and the cord angle of the belt layer in various speed ranges in the form of a graph. 1...Tread section, 2...Side wall section,
3...Tread section rubber, 4...Belt section, 5...
carcass.

Claims (1)

[Scope of Claims] 1. The tread portion rubber has (a) a chlorine and/or bromine content of 1.0 to 2.0 with respect to 100 parts by weight of compounded rubber;
5% by weight of polyisobutylene/isoprene rubber
-30% by weight, (b) 40 to 95% by weight of natural rubber and/or polyisoprene rubber, and (c) 50% by weight or less of polybutadiene rubber, (1) Tread drainage grooves is 20~ for the total ground contact area
(2) The Young's modulus of a single cord in the belt section is 25 kg/mm.
² or more cords 15 to 25 in the circumferential direction of the tire
The circumferential tensile rigidity of the belt section is 200 degrees relative to the radial tensile rigidity.
A pneumatic radial tire characterized by: