JP2002052906A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire keeping improved snow braking performance and wet braking performance over a long period after proceeding with wear since a new one. SOLUTION: A tread portion is formed of two types of rubbers A, B having the following material properties: (1) the rubber A is superior to the rubber B in storage elastic modulus E' at -20 deg.C, (2) the rubber B is superior to the rubber A in wet face friction resistance at 25 deg.C in measurement with a portable skid tester, (3) the storage elastic modulus E' of the rubber A at -20 deg.C is 65 MPa or less, and (4) the storage elastic modulus E' of the rubber B at -20 deg.C is 55 MPa or less. The rubber A and the rubber B are arranged on the tread portion so that the tread surface area ratio Sb/Sa of the rubber B to the rubber A at which the tread portion is grounded on a road surface gradually increases as a tread surface proceeds with wear from the beginning of wear.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire, and more particularly, to a wet tire performance and a snow braking performance of an all-terrain tire that is frequently used in four-wheel drive vehicles from the initial stage to the time when wear progresses. The present invention relates to a pneumatic tire maintained and improved.

[0002]

2. Description of the Related Art A tire running on a general road surface has a styrene-butadiene copolymer having a relatively high glass transition temperature as a rubber for a tire tread in order to emphasize braking performance (wet skid performance) and steering stability on a wet road surface. A rubber composition mainly comprising coalescing is used. On the other hand, in winter tires, polybutadiene rubber (BR) or natural rubber (NR) having a low glass transition temperature is mainly used to emphasize braking performance (snow skid performance) on snowy roads.
Is used.

[0003] With respect to snow skid performance, it is important to increase the coefficient of friction with the road surface by maintaining the flexibility of the rubber composition in the tread portion at a low temperature (around -20 ° C). At low temperatures, the rubber elasticity increases and cannot follow the road surface irregularities. On a frozen road surface, the surface unevenness is smaller than that of a normal road surface, so the energy dissipation (tan δ) generated between the tread tread surface and the road surface is reduced. ) Contributes less to snow skid performance. Therefore, it is necessary to increase the true contact area between the tread surface and the road surface at a low temperature, and it is more important to lower the storage elastic modulus (E ′) at around −20 ° C. (lower elastic modulus).

[0004] In winter tires, in addition to ground contact on snowy road surfaces, the road surface is "scratched" at the tread block edge.
The braking performance on snow has been improved by forming a tread pattern that improves the braking performance. For this reason, a block pattern composed of a large number of independent block-shaped land portions, in which the circumferential main groove is partitioned by a lateral groove or an oblique groove, has been often used.

[0005] According to the above-mentioned material and structural proposals, the braking performance of snow tires and wet roads has been considerably improved when the tires are new or in the initial stage of progress of wear. For tires that have traveled 20% or more, the above-mentioned materials and structural effects do not work so much that the braking performance on snowy and wet road surfaces is significantly reduced, and this improvement is urgently important. Problem.

[0006] Regarding the all-terrain tires used all year, which are frequently used in four-wheel drive vehicles, this type of tire is conventionally a single tread, and while taking into account the running performance on general dry roads and wet roads, the tires can be used on snowy roads. Tires with a tread configuration and rubber properties that provide braking performance have been used, but as with general passenger car tires, when the tread wears out, wet braking performance (drainage) and snow braking performance decrease. However, there is a concern that an accident may occur, and the use is usually discontinued and removed relatively early, in some cases, when the wear has progressed by about 50%, and there have been many complaints and complaints.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a snow road braking performance and a wet road braking performance that are long from the time of brand new to after the progress of tread wear. An object of the present invention is to provide a pneumatic tire that can be maintained and improved over a period of time.

[0008]

Means for Solving the Problems The present inventors diligently studied the material of the tread rubber and the structure of the tread, and as a result, found that the above problems could be solved, and completed the present invention. That is, means for solving the problems of the present invention are:
The invention resides in each of the following inventions.

The invention according to claim 1 is a pneumatic tire in which a belt layer and a tread portion are disposed radially outside a crown region of a carcass straddling a pair of bead cores in a toroidal manner. , The tread portion,
A and B rubbers having the following material properties, (1) -2
The storage elastic modulus (E ′) at 0 ° C. is larger for rubber A than for rubber B. (2) The wet surface friction resistance at 25 ° C. measured with a portable skid tester is A for B rubber. (3) The storage elastic modulus (E ′) of rubber A at −20 ° C. is 65 MPa or less, and (4) the storage elastic modulus (E ′) of rubber B at −20 ° C. The area ratio Sb / Sa of the rubber B and the rubber A occupying the tread surface which is 55 MPa or less and which is formed and lands on the road surface of the tread portion,
From a certain point in the initial stage of wear of the tread tread, the rubber A and the B are gradually increased with the progress of wear of the tread tread.
A pneumatic tire characterized in that rubber is arranged in a tread portion.

Here, the storage elastic modulus (E ') is defined by JIS
Is a viscoelasticity value measured by a dynamic viscoelasticity test method specified in K7198, and represents a storage elastic modulus (real part) under dynamic deformation of a rubber material. The wet surface friction resistance at 25 ° C. measured with a portable skid tester was measured using a pendulum-type friction tester shown in FIG. 5 in which a shaken rubber test piece rubbed a wet road surface adjusted to 25 ° C. After that, the swinging angle (θ) is measured, and the reciprocal of the angle (θ) is defined as the wet surface friction resistance. The smaller the angle (θ) to be swung after friction and the larger the reciprocal of (θ), the greater the wet surface friction resistance.

Next, the operation of the present invention will be described.

Generally, in winter tires, a block pattern is formed on a tread surface of a tread, and braking performance on a snowy road surface is improved by a "scratching" effect of a sharp edge angle of a block land portion. The "scratching" effect of the block edge works well for a new tire, but the effect decreases as the tread wear of the tire progresses, as the edge angle of the block becomes rounder. Further, regarding the snow skid performance, the coefficient of friction with the road surface is increased by maintaining the flexibility of the rubber composition in the tread portion at a low temperature (around -20 ° C). It is necessary to increase the true contact area between the tread surface and the road surface at low temperatures,
It is important to lower the storage elastic modulus (E ') at around 20 ° C. (low elastic modulus) to improve the snow skid performance.

The tread portion of the pneumatic tire described in this section has A, B2 as shown in cross-sectional examples in FIGS.
It is made of various types of rubber. B rubber has a low storage modulus (E ′) at −20 ° C. and a large wet surface friction resistance at 25 ° C. measured by a portable skid tester.
Although excellent in braking performance on snowy roads and wet roads, rubber A is more advantageous in abrasion resistance. Area ratio of rubber B and rubber A occupying the tread contacting the tread surface with the road surface Sb /
In the example of FIG. 2, Sa gradually increases from the almost initial stage of the start of wear of the tread tread, and in the example of FIG. 3, from a certain point of the initial wear stage where the surface layer (A rubber) of the tread tread is worn away, as the wear progresses. The rubber A and the rubber B are arranged in the tread portion so as to perform the same. Therefore, the pneumatic tire described in this section has a "scratch" of the sharp edge angle of the block land portion.
In the early stage of wear where the effect is effectively acting, the ratio of A rubber with good wear resistance occupying the surface layer is increased, and the wear life of the tire is prolonged during this period. By gradually increasing the ratio of the B rubber having good snow braking performance and wet braking performance as the ceases to be effective, the braking performance can be kept good over a long period from the initial stage to the progress of wear.

According to a second aspect of the present invention, in the pneumatic tire according to the first aspect, the area of the B rubber in the center area of the tread contacting the road surface of the tread portion from the time of the new tread through a wear process of the tread tread surface. Occupies more area than the rubber A area. Here, the center area of the tread tread is an area inward of a 50% line distributed from the center of the maximum contact width when a tire is incorporated into a standard rim, filled with a normal internal pressure and a 100% load is applied. That is.

Next, the operation of the present invention will be described. In general, the braking performance of a tire tends to decrease as the load decreases, because the contact area decreases. The tread of the tire according to the present invention has a low low-temperature elastic modulus (storage elastic modulus E ′ at −20 ° C.) and a wet surface at 25 ° C., particularly in the center region of the tread, from the time of brand new through the wear process of the tread tread. Since the area of the rubber B having a large frictional resistance, that is, excellent in braking performance, occupies more area than the area of the rubber A, even if the contact width becomes small with a light load, the center area occupies a large area. By the effect of B rubber,
Good braking performance is exhibited.

According to a third aspect of the present invention, in the pneumatic tire of the first aspect, when the tire is new, all of the treads that contact the tread portion on the road surface are occupied by A rubber. The purpose of the tire according to the present invention is to maintain the braking performance on a snowy road surface and the wet road surface braking performance in the initial stage of a new article stage mainly by the "scratch" effect of the edge angle of the block pattern of the tread tread surface,
A rubber with relatively good wear resistance prolongs the wear life of the tire, and at the stage where the edge angle is worn out and the above-mentioned "scratch" effect is reduced, the braking performance is maintained and improved by the B rubber exposed on the tread tread surface. That is, it is possible to maintain and improve the braking performance while extending the life of the tire.

[0017] The invention described in claim 4 is the invention according to claims 1 to 3.
In the pneumatic tire, the area ratio Sb / (Sa + S) of the B rubber occupying the tread contacting the tread on the road surface is described.
b) is 0 to 60% when new, and gradually increases as the wear of the tread tread progresses. When the wear progresses by about 80%, the area ratio Sb / (Sa + Sb) of the B rubber is obtained.
Is 60 to 100%. Here, the degree of progress (%) of the wear of the tread tread is indicated by the ratio of the remaining depth of the main groove after the wear to the depth of the main groove of the new tire. When new, the area ratio Sb / (Sa
+ Sb) is set in a suitable range of 0 to 60%, and abrasion is approximately 8%.
Even at the time of progress of 0%, the area ratio of this B rubber Sb / (S
The tread of the present invention, in which a + Sb) is set to a preferable value of 60 to 100%, particularly in a tire for a passenger car, has a high braking performance on a snowy road surface and a wet road surface for a long period of time from the initial stage to the end of the wear life. It can be maintained and improved to a standard.

According to a fifth aspect of the present invention, in the pneumatic tire according to the third aspect, when the tire is new, all of the treads that contact the tread portion on the road surface are occupied by A rubber.
The thickness of the rubber A at the tire equatorial plane is 20 to 50% of the thickness of the entire tread. The aim of the tire of the present invention is the same as that of the invention of claim 3, but the A
By suitably setting the thickness of the rubber on the equatorial plane of the tire within a range of 20 to 50% of the thickness of the entire tread, it is possible to maintain and improve the braking performance while extending the life of the tire, particularly for a tire for a passenger car. The effect is even more pronounced.

The invention according to claim 6 is the invention according to claims 1 to 5
Is characterized in that the tread of the tread portion has a block pattern. The tire according to the present invention, which has a large number of block-shaped land portions defined by circumferentially extending rib grooves and lateral or oblique grooves on the tread surface of the tire, is characterized by "scratching" by the edge of the block-shaped land portion.
The effect and the "drainage" effect by the rib grooves and the lateral grooves or the inclined grooves can greatly improve the braking performance on snowy road surfaces and wet road surfaces.

[0020] The invention according to claim 7 provides the invention according to claims 1 to 6.
In the pneumatic tire of (1), the negative rate of the tread of the tread portion is 35 to 50%. According to the invention of this item in which the negative rate of the tread tread that governs drainage performance is set to a preferable range of 35 to 50%, the steering stability, the (uneven) abrasion resistance and the riding comfort are not impaired.
The braking performance on wet road surfaces and snow road surfaces can be further improved. If the negative rate of the tread tread is less than 35%,
The effect of improving the braking performance on wet road surfaces and snow road surfaces is small. On the other hand, if the groove area is increased beyond 50%, steering stability, (uneven) wear resistance, riding comfort, and the like may be impaired.

[0021] The invention according to claim 8 is the invention according to claims 1 to 7.
The pneumatic tire of the present invention is characterized in that the use of the tire is for an all-terrain four-wheel drive vehicle (4 × 4). Since the pneumatic tire of the present invention has the above-described configuration, it maintains good wet braking performance and snow braking performance over a long period from the time of new product to after the progress of wear. It is particularly suitable for four-wheel drive vehicles (4 × 4 vehicles) for leisure purposes used below.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a pneumatic tire according to the present invention will be described below in detail with reference to FIGS.

FIG. 1 is a sectional view of a plane including a rotation axis of a pneumatic tire, and FIGS. 2 to 4 are enlarged sectional views of a tread portion thereof. The internal structure (case) of the pneumatic tire of the present invention (hereinafter, simply referred to as a tire) is not particularly limited, and as illustrated in FIG. Side wall part 2
And a tread portion 3, and these portions 1 to 3 are reinforced by a carcass layer 5 extending between bead cores 4 embedded in the bead portion, and further, a belt layer 6 is provided outside the crown region of the carcass layer 5 in the tire radial direction. Strengthens the tread portion 3. The tread portion 3 of the tire of the present invention corresponds to FIG.
As shown in the enlarged view of FIG. 2, the conventional tire is usually formed of one type of rubber (here, A) as shown in FIG. .

FIGS. 2 and 3 show the tread portion 3 in FIG.
It is an expanded sectional view of a vicinity.

As shown in FIG. 2, in one preferred embodiment of the present invention, B rubber occupies most or all of the center area of the tread contacting the road surface of the tread portion. Accordingly, the pneumatic tire is characterized in that the area of the B rubber occupies more area than the area of the A rubber in the center region through the wear process of the tread tread.

FIG. 3 shows another preferred embodiment of the present invention, which is a pneumatic tire characterized in that when it is new, all treads that contact the road surface of the tread portion are occupied by A rubber. In this embodiment, from a certain point in the initial stage of the wear of the tread tread, that is, from the time when the A rubber on the surface layer is worn and the B rubber appears on the surface, the B rubber and the A rubber occupy the tread contacting the ground surface on the road surface of the tread portion. Area ratio Sb
A pneumatic tire is characterized in that A rubber and B rubber are arranged in a tread portion so that / Sa increases gradually with the progress of wear on the tread surface.

Here, "the tread on which the tire touches the ground"
A tire is mounted on an applicable rim, is provided with a specified air pressure, is placed perpendicularly to a flat plate in a stationary state, and refers to a tire contact surface when a specified load is applied.
In accordance with the year 2000 YEAR BOOK, the tire is mounted on a standard rim, and the maximum load capacity in the applicable size and ply rating and the corresponding air pressure (maximum air pressure) are used as a reference.

[0028]

EXAMPLES In order to clarify the effects of the present invention,
The present invention will be described with reference to examples, but the present invention is not limited to these examples.

An embodiment of the present invention will be specifically described with reference to FIGS. A radial structure tire for a four-wheel drive vehicle having a size of 265 / 70R16 was manufactured by applying three types of treads having the specifications shown in the tread specification column in Table 1. The tread of Example 1 is of the type shown in FIG. 2, in which most of the center area is occupied by B rubber, and most of the shoulder area is occupied by A rubber, and is a tread divided as shown in the tire width direction. As the tread wears, the area occupied by the B rubber increases. The tread of Example 2 is of the type shown in FIG. 3, in which the surface layer in the center region is initially occupied by A rubber, but B rubber appears as the tread surface layer wears. The tread of the comparative example is the conventional type shown in FIG. 4, and is entirely formed of A rubber.

At the time of new and 50, 80% wear,
Area ratio of Sb / (S
a + Sb) is shown in Table 1 in%. Storage modulus (E ') at -20 DEG C. for rubber A and rubber B
And the wet surface friction resistance (relative index) at 25 ° C. as measured on a portable skid tester are given in the notes below the table.

Four test tires were prepared for the examples and comparative examples, mounted on an actual vehicle and subjected to a braking test. The results are shown in Table 1 below.

[0032]

[Table 1]

From the results in Table 1, it can be seen that the tire to which the tread of the present invention is applied has a wet or new braking performance on a new road which is equal to or higher than that of the conventional tread tire, and the tread wear is low. It has been found that the braking performance on wet and snowy roads at the point when the vehicle travels from 50% to 80% is improved by about 10 to 15 points as compared with the conventional tire.

Incidentally, the evaluation test of the tire in this embodiment is as follows.
This was performed in the following manner.

<Snow road surface braking test> The braking performance on a snow road surface is represented by the acceleration and braking performance on a snow road surface as an index. Four test tires were mounted on a four-wheel drive passenger car having a displacement of 2500 cc at a standard internal pressure, and a braking distance from 40 km / h was measured on a snowy road test course. The snow braking performance was indicated by an index according to the following equation.

Snow braking performance = (braking distance of comparative tire / braking distance of test tire) × 100 The larger the value of this index, the better the snow braking performance.

<Wet Road Braking Test> The braking performance on a wet road is represented by wet skid performance as an index.
Four test tires were mounted on a four-wheel drive vehicle at a standard internal pressure, and a braking distance from 100 km / h was measured on a wet test course for two passengers. Wet skid performance is evaluated to be superior as the index is larger.

[0038]

According to the present invention, it is possible to provide a pneumatic tire having excellent snow braking performance and wet braking performance over a long period of time from the time of new tires to the progress of tire tread wear. In particular, it is suitable as a tire for a four-wheel drive vehicle used for leisure throughout the year.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating one embodiment of a pneumatic tire.

FIG. 2 is an enlarged cross-sectional view of the vicinity of a tread portion of the pneumatic tire of the present invention.

FIG. 3 is an enlarged sectional view of the vicinity of a tread portion of the pneumatic tire of the present invention.

FIG. 4 is an enlarged cross-sectional view near a tread portion of a pneumatic tire of a comparative example.

FIG. 5 is a diagram illustrating the principle of a method for measuring the wet surface frictional resistance of rubber.

[Explanation of symbols]

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

Claims (8)

[Claims] 1. A pneumatic tire having a belt layer and a tread portion disposed radially outside a crown region of a carcass straddling a pair of bead cores in a toroidal manner, wherein the tread portion is as follows: (1) The storage elastic modulus (E ') at -20 ° C is larger for A rubber than for B rubber, and (2) measured with a portable skid tester. The wet surface friction resistance at 25 ° C. is larger for the B rubber than for the A rubber. (3) The storage elastic modulus (E ′) of the A rubber at −20 ° C. is 65.
(4) The storage elastic modulus (E ') of B rubber at -20 ° C is 55
The area ratio Sb / Sa of the rubber B and the rubber A occupying the tread surface which is less than or equal to or less than Mpa and occupies the tread tread surface on the road surface of the tread portion is determined at a certain point in the initial stage of wear of the tread tread surface. A pneumatic tire characterized in that A rubber and B rubber are arranged in a tread portion so as to gradually increase as wear progresses. 2. In the center region of the tread contacting the road surface of the tread portion, the area of the B rubber occupies more than the area of the A rubber through a wear process of the tread tread from the time of new product. The pneumatic tire according to claim 1, wherein 3. The pneumatic tire according to claim 1, wherein, when new, all of the treads that contact the road surface of the tread portion are occupied by A rubber. 4. The area ratio Sb / (Sa + Sb) of B rubber occupying a tread contacting the road surface of the tread portion on a road surface is 0 to 60% when new, and gradually increases as wear of the tread tread progresses, When the wear has progressed by about 80%, the area ratio Sb / (Sa + Sb) of the B rubber is 60 to 100.
% In any one of claims 1 to 3
The pneumatic tire according to the paragraph. 5. When new, all of the treads that contact the road surface of the tread portion are occupied by A rubber, and the thickness of the A rubber on the tire equatorial plane is 20 to 50% of the thickness of the entire tread. The pneumatic tire according to claim 3, wherein: 6. The pneumatic tire according to claim 1, wherein the tread of the tread portion has a block pattern. 7. The pneumatic tire according to claim 1, wherein a negative ratio of a tread surface of the tread portion is 35% to 50%. 8. The air according to claim 1, wherein the tire is used for an all-terrain four-wheel drive vehicle (4 × 4 vehicle). Containing tires.