JP2000052713A - Pneumatic tire for heavy load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a low fuel cost and the biased wear resistance compatible with each other by using comparatively high tanδ rubber excellent in biased wear resistance for cap rubber, using comparatively low tanδ rubber excellent in low fuel cost performance for base rubber and thinning the cap rubber in the central area in the cross direction of the tire hard to cause biased wear. SOLUTION: In two or more main grooves of a tread part 1, a thin part with a thickness of 2.4 mm or less of cap rubber between both outer main grooves 4 in the cross direction of a tire is provided or the base rubber 3 is exposed to the tread surface. The tanδA of cap rubber is 0.10-0.30, tanδB of base rubber is 0.07-0.20 tanδA is larger than tanδB, and the sum of the value obtained by multiplying tanδA by the ratio of cap rubber volume to the tread rubber volume and the value obtained by multiplying tanδB by the ratio of base rubber volume to tread rubber volume is 0.01-0.18. Further, the base rubber composition contains 2-20 wt. parts of silica to 100 wt. parts of rubber component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for improving fuel efficiency of heavy duty pneumatic tires such as trucks and buses having a specific rib pattern and a cap-base structure without impairing uneven wear resistance.

[0002]

2. Description of the Related Art The fact that vehicles have low fuel consumption means that:
Although the rolling resistance is small, the main factor that governs the rolling resistance is the heat build-up of the rubber constituting the tire. In particular, the tread rubber has a low heat generation (low tan δ).
Is effective.

[0003] Tread rubber can be reduced in tan δ by reducing the blending amount of carbon black in a rubber composition constituting the tread or increasing the crosslink density by sulfur. However, when the blending amount of carbon black is simply reduced, the abrasion resistance decreases, while the increase in the crosslinking density causes a decrease in breaking elongation and a decrease in crack propagation resistance.

[0004] Therefore, in order to avoid a decrease in wear resistance and crack propagation resistance while reducing tan δ, carbon black having a specific colloidal property is used to enhance the dispersibility of carbon black or to reduce the hysteresis. There are technologies that utilize loss agents. Also, in order to improve the dispersibility of carbon black, the terminal of the polymer is modified,
Modification of the polymer itself, such as elimination of low-molecular-weight polymers as heat sources and uniformization of the molecular weight distribution, has also been effective.

[0005] By these techniques, low heat generation (low ta) is achieved.
nδ) and abrasion resistance / crack growth resistance can be compatible to some extent.

However, it has not been possible to achieve both low fuel consumption and uneven wear resistance at present. This is because the uneven wear resistance is governed by “tan δ”, like the low rolling resistance. The above-mentioned low heat generation and wear resistance and crack propagation resistance can be moved to some extent independently, whereas uneven wear resistance and low rolling resistance both have tan δ as a main factor, and the improvement direction is exactly opposite. Therefore, if tan δ is reduced to reduce rolling resistance, this directly lowers uneven wear resistance.

Accordingly, the tread rubber is reduced in tan δ,
Even if fuel efficiency is reduced, uneven wear of such tires is promoted, and as a result, the steering stability of the vehicle is significantly reduced, the durability life is shortened, and the economy for the user is rather deteriorated.

[0008] It is well known that uneven wear is particularly likely to occur under the condition that the usage ratio of the highway is high, and in trucks and buses for long-distance transportation, not only low fuel consumption but also long service life is required. There is a high need for

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to achieve both uneven wear resistance and low fuel economy.

[0010]

The uneven wear occurs mainly on the outer side (shoulder side) of the tread surface of the tread in the tire width direction. This is known as differential wear. That is, since the tire has a predetermined curvature with respect to the road surface, a difference in diameter naturally occurs between the center side and the shoulder side, and the circumference of the shoulder side is shorter than that of the center side. Therefore, during rolling, the shoulder having the shorter circumference is dragged (slip occurs), and wear occurs. From this fact, it can be seen that it is effective to prevent uneven wear by increasing uneven wear resistance on the shoulder side.

Further, from the viewpoint of materials, it has been found that rubber having a high tan δ is effective for uneven wear resistance. When rolling, the tread tread repeats adhesion and slipping on the road surface. In the case of rubber having a high tan δ, the ratio of adhesion to the road surface during rolling increases, and the ratio of slip decreases.

From these facts, it has been conceived that in order to prevent uneven wear, it is only necessary to arrange a rubber having a high tan δ at least on the shoulder side.

On the other hand, from the viewpoint of pursuing low fuel consumption, it is needless to say that the tan δ of the tread rubber is preferably low. That is, rubber with a high tan δ leads to high hysteresis loss = high heat generation = high rolling resistance and impairs fuel efficiency and self-heating durability.

Considering the deformation of the rubber at the time of rolling, the portion where the deformation of the rubber is large, that is, the portion where the heat generation is large, has the predetermined curvature as described above. Moreover, it can be seen that it is on the surface layer side. Therefore, from the above considerations, the conventional cap
In the base structure, it can be seen that most of the center side occupied by the cap rubber can be replaced with the base rubber having a lower tan δ, so that the volume itself of the fuel-efficient rubber can be increased, and at the same time, the deformation amount is large. The rubber having low heat generation can be efficiently arranged on the center side and the surface layer side. The present invention has been achieved based on the above considerations, and the specific configuration is as follows.

(1) In a heavy-duty pneumatic tire provided with a tread portion having a cap-base structure and having a rib pattern having two or more main grooves extending in a circumferential direction, the two or more main grooves are provided. at between the main groove located on both outer sides in the tire width direction of the thickness of the cap rubber is exposed to or based rubber tread surface provided below the cap thin portion 2.4 mm, tan [delta _a cap rubber 0.10 ~ 0.30, tan of base rubber
δ _B is 0.07 to 0.20, and tan δ _A is tan
greater than [delta] _B, the value obtained by multiplying the ratio V _A of the cap rubber volume of the tread rubber volume in tan [delta _A and tan [delta _B
The ratio of base rubber volume to tread rubber volume V _{B
A + B} is 0.10 to 0.18, preferably 0.11 to 0.15, and silica is added to the rubber composition of the base rubber and 100 parts by weight of the rubber component. On the other hand, it is characterized by containing 2 to 20 parts by weight. (2) The width in the tire width direction occupied by the base rubber (refer to l in FIG. 2III) at a depth of 2.4 mm from the surface of the tread portion (refer to a broken line in FIG. 2III) is the two. Of the above main grooves, between the main grooves located on both outer sides in the tire width direction, and the entire width of the tread (see:
15-90% of L) in FIG. 2III, preferably 30-80%
%. (3) The rubber composition constituting the cap rubber contains natural rubber and styrene-butadiene copolymer rubber as rubber components, and the rubber composition constituting the base rubber contains natural rubber as a rubber component. Features. (4) The rubber component of the rubber composition of the cap rubber is 25 to 75% by weight of natural rubber and 25 to 75% by weight of styrene / butadiene copolymer rubber, and the rubber component of the rubber composition of the base rubber. It is characterized in that the content of natural rubber is 50 to 100% by weight. (5) The rubber component of the rubber composition of the cap rubber further contains 30% by weight or less of butadiene rubber. Here, tan δ is room temperature, amplitude 2%, frequency 52
It is a value measured in Hz.

That is, the present invention uses a relatively high tan δ rubber excellent in uneven wear resistance for the cap rubber, uses a relatively low tan δ rubber excellent in low fuel consumption for the base rubber, and reduces uneven wear. By reducing the thickness of the cap rubber in the center area in the tire width direction, which is less likely to occur, the volume ratio of the base rubber is increased, while maintaining the effect of preventing uneven wear,
Improved fuel economy was achieved.

Furthermore, in addition to the above-described improvement in the tread cap / base structure, a defense groove (which is narrower than the main groove and has outer shoulders on both outer main grooves) effective for uneven wear resistance. Side groove (a sub-groove provided from the tread end to the buttress portion), the function of effectively preventing the occurrence of uneven wear and suppressing the progress of the generated uneven wear. Thus, it is possible to effectively achieve protection of other portions due to sacrificed uneven wear in this portion. Also, in the main groove, effective for uneven wear resistance,
A protruding rib that descends from the tread surface may be provided.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. FIG. 1 illustrates six types of cross-sectional views of the tread portion according to the present invention. A to C are cases where the thickness of the thin portion of the cap is 0, that is, when the base rubber is exposed, and D to F are cases where the thickness is 2.4 mm or less. 1 is a tread portion, 2 is a cap rubber, 2a is a thin cap portion, 3 is a base rubber, 4 is a main groove, 5 is a defense groove, and 6 is a side groove.

In the present invention, the thickness of the thin portion of the cap is specified to be 2.4 mm or less. However, as can be seen from the above-mentioned consideration, it is most preferably 0 (zero) when the cap is new. Even if it is not zero, if it is 2.4 mm or less, the effect of the present invention can be sufficiently achieved. 2.4mm
Is exceeded, the effect of reducing the rolling resistance is insufficient even if the lower limit of tan δ specified for the base rubber is applied to the base rubber. This is because not only the volume of the base rubber is reduced, but also a large amount of cap rubber having a high tan δ is disposed on the surface layer which generates a large amount of deformation and heat during rolling.

Further, the width of the thin portion in the tire width direction is formed between the main grooves located on both outer sides in the tire width direction among the two or more main grooves, so that the amount of the base rubber can be adjusted in an appropriate shape. Fuel efficiency is ensured.

The tan δ _{A of} the cap rubber is 0.1
0 to 0.30 (room temperature, amplitude 2%, frequency 52 Hz), tan δ _{B of} the base rubber is 0.07 to 0.20 (room temperature, amplitude 2%, frequency 52 Hz), and tan δ _A is t
defining a greater than anδ _B. This is for the following reasons. For example, even if the cap rubber and the base rubber are within the respective specified ranges, if both tan δ values are the same or the magnitude relationship is opposite, uneven wear occurs on the shoulder side as in the past, and the defense groove is If the groove is formed outside the main groove, sacrificial uneven wear applied to the defense groove is large, and there is no improvement effect. In addition, even if the magnitude relationship between both tan δ is maintained, if tan δ _A is less than the lower limit, the above-mentioned adhesive effect cannot be obtained and uneven wear on the shoulder side cannot be prevented. If tan δ _B is less than the lower limit, uneven wear occurs at a location indicated by X in FIG. 1A. Also, t
When both an δ _A and tan δ _B exceed the upper limit,
The rolling resistance increases, which is not preferable. From the same viewpoint as above, preferably, tan δ _A is 0.14 to 0.1.
22 (room temperature, amplitude 2%, frequency 52 Hz) and ta
nδ _B is 0.10 to 0.14 (room temperature, amplitude 2%, frequency 52 Hz). Further, a value obtained by multiplying tan δ _A by a ratio V _A of the cap rubber volume to the tread rubber volume and t
The sum S _{A + B} of a value obtained by multiplying an δ _B by a ratio V _B of a base rubber volume to a tread rubber volume is 0.10 to 0.18.
By doing so, rolling resistance can be reduced without lowering uneven wear resistance. S _{A + B} is 0.10
If it is less than the value, the slip of the entire tread surface increases, and even if a cap rubber having a high tan δ is arranged on the shoulder side, uneven wear cannot be suppressed. When S _{A + B} exceeds 0.18, the rolling resistance increases. . In addition, the reason that silica is blended in an amount of 2 to 20 parts by weight with respect to 100 parts by weight of the rubber component is that rolling resistance is reduced and tear resistance is improved.

Also, 2.4 m from the surface of the tread portion.
m, the width of the base rubber in the tire width direction occupied by the base rubber is between the main grooves located on both outer sides in the tire width direction of the two or more main grooves, and 15 to 15 of the total width of the tread. 90% is preferable, but if it is less than 15%, low rolling resistance becomes insufficient, which is not preferable. If it exceeds 90%, uneven wear occurs near a portion indicated by Y in FIG. 1A, which is not preferable. . From a similar perspective,
Preferably it is 30 to 80%.

In the rubber component of the rubber composition of the cap rubber,
The reason that the natural rubber is 25 to 75% by weight and the styrene / butadiene copolymer rubber is 25 to 75% by weight is that natural rubber ensures the strength of the tread rubber during heavy deformation in a heavy-duty pneumatic tire, This is because the abrasion resistance and uneven wear resistance are ensured by the styrene / butadiene copolymer rubber. Further, in the rubber component of the rubber composition of the cap rubber,
When butadiene rubber is contained in an amount of 30% by weight or less,
Abrasion resistance and tear resistance can be improved,
If the content exceeds 30% by weight, the uneven wear resistance deteriorates. Natural rubber in the rubber component of the rubber composition of the base rubber is 50 to 100.
The reason for the weight percentage is that it is preferable in terms of low rolling resistance, tear resistance, and workability.

[0024]

EXAMPLES In each of the examples and comparative examples, the tire size is 11R22.5, and the track / bus is a rib pattern having four main grooves and no auxiliary grooves such as defense grooves and side grooves. This was done by making a radial tire for use. For measurement of uneven wear resistance, each tire was mounted on the front axle of a 20-ton vehicle, and a highway usage rate of 0.
The test was performed by an actual vehicle test when the vehicle traveled 100,000 km at 5%, and the depth and area of the uneven wear generating portion were measured.
The index is represented as an index of 00, and is shown in Table 1. The larger the value, the better. The low rolling resistance was measured by a drum test on the same tire as described above. Similarly, Comparative Example 1 is set to 100, and an index is shown. The larger the value, the better. The details of the tread portion of these tires depend on the composition and composition shown in Table 1.

FIG. 2 shows five cross-sectional views of the tread portion of the cap / base structure employed in each of the embodiments and the comparative examples. I is the case where the cap rubber is thick even on the center side, and II is the main groove 4 on both outer sides in the tire width direction.
a, 4d, when the base rubber is exposed (the thickness of the thin portion of the cap is 0), and III is when the exposed portion of the base rubber is narrower than the width of the main grooves 4a, 4d.
IV is a case where the thin portion of the cap has a predetermined thickness, and V is a case where the exposed portion of the base rubber is wider than the main grooves 4a and 4d toward the shoulder. In Table 2,
The compounding of the cap rubber and the base rubber in each example and each comparative example is shown. In addition, the tan δ value of each rubber composition at room temperature at an amplitude of 2% and a frequency of 52 Hz is also shown.

[0026]

[Table 1]

[0027]

[Table 2]

The SBR is FS.C1, C3 and C4. HX765 (trade name: Firestone Chemical
C1 and C5 are JSR # 1500 (trade name: manufactured by Nippon Synthetic Rubber Co., Ltd.). Also, BR
It is, BR ¹ Ubeboru 150L: a (trade name, product of Ube Industries Ltd.). The silane coupling agent is ABC-
856 (trade name: manufactured by Shin-Etsu Chemical Co., Ltd.), and the vulcanization accelerator is dibenzothiazyl disulfide, Noxeller D
M (trade name: Ouchi Shinko Chemical Co., Ltd.).

Consider the experimental results. Comparative Examples 1 and 2 are prior art and are used for current tires.
Comparative Example 1 are kept well-balanced uneven wear resistance and low rolling resistance, Comparative Example 2 improves the uneven wear resistance, but to enhance the durability of the tire, the upper limit of the provisions S A _{+ B} , The rolling resistance is large. Example 1 is an optimal example in which the base rubber is exposed on the center side, and Example 1 is an example in which the same composition as that of Comparative Example 1 is used and the cap / base structure is changed to improve the composition. Example 2 had the same base rubber composition as Example 1, and the cap rubber was NR / S
This is an example in which BR / BR is changed to lower tan δ to improve low rolling resistance, while S _{A + B} is set within a specified range near the lower limit, and uneven wear resistance is set within an allowable range. Example 3 is the same as Example 1 except that the base rubber is compounded, and the cap rubber is compounded with silica. In Example 4, the width l in the tire width direction occupied by the base rubber at a depth of 2.4 mm from the surface of the tread portion was changed to 40% of the total width L of the tread by changing the division position of the cap / base structure. This is an example, whereby the uneven abrasion at both ends of the center rib is improved as compared with Example 1, but the low rolling resistance is slightly reduced by the reduced volume of the base rubber. Example 5 is an example in which the thickness d of the thin portion of the cap is 1.8 mm, and the uneven wear resistance is improved, but the low rolling resistance is slightly inferior to Example 1 due to the reduced volume of the base rubber. However, compared with the current product, the uneven wear resistance and the low rolling property are good. Comparative Example 3 is an example in which the rubber of the cap and the base is reversed. Since the rubber having a low tan δ is arranged on the shoulder side, uneven wear is severe. In Comparative Example 4, the tan δ of the cap rubber was too high, and S _{A + B} also exceeded the upper limit of the specified range. Therefore, although the base rubber was exposed, the effect of reducing the rolling resistance was not obtained. In Comparative Example 5, tan δ of the base rubber was too low, and uneven wear occurred at the end of the center rib. In Comparative Example 6, the width l of the base rubber was narrow.
Since the thickness d of the thin portion is too thick and the volume of the base rubber is also small, the effect of reducing the rolling resistance cannot be obtained.
In Comparative Example 8, the exposed width of the base rubber extends to the shoulder side, and uneven wear occurs in this region.

[0030]

As described above, according to the present invention,
Since uneven wear-resistant rubber is arranged in places where uneven wear mainly occurs, the amount of low rolling resistance rubber is increased as much as possible, and furthermore, it is arranged on the center surface layer where the amount of rubber deformation is large,
It is possible to efficiently achieve low fuel consumption while preventing uneven wear.

[Brief description of the drawings]

FIGS. 1A to 1F are cross-sectional views showing a cap base structure of a tread portion according to the present invention.

FIG. 2 is a cross-sectional view showing a cap / base structure of a tret portion employed in the embodiment.

[Explanation of symbols]

 Reference Signs List 1 tread part 2 cap rubber 3 base rubber 4 main groove 5 defense groove 6 side groove

Claims (5)

[Claims] 1. A heavy-duty pneumatic tire provided with a tread portion having a cap-base structure and having a rib pattern having two or more main grooves extending in a circumferential direction. A thin cap portion having a cap rubber thickness of 2.4 mm or less is provided between the main grooves located on both outer sides in the tire width direction, or the base rubber is exposed on the tread surface, and t of the cap rubber is adjusted.
an δ _A is 0.10 to 0.30, tan δ of base rubber
_B is 0.07 to 0.20, and tan δ _A is tan δ
Greater than _B, the sum S _{A + B} is 0 and the value obtained by multiplying the ratio V _B of the base rubber volume of the tread rubber volume values and tan [delta _B multiplied by the ratio V _A of the cap rubber volume of the tread rubber volume in tan [delta _A 0.10 to 0.18, and silica in the rubber composition of the base rubber and rubber component 1
A pneumatic tire for heavy load, comprising 2 to 20 parts by weight with respect to 00 parts by weight. 2. The width of the base rubber occupied by the base rubber at a depth of 2.4 mm from the surface of the tread portion in the tire width direction is a width of the two or more main grooves located on both outer sides in the tire width direction. The pneumatic tire for heavy load according to claim 1, wherein the distance between the grooves is 15 to 90% of the total width of the tread. 3. The rubber composition constituting the cap rubber contains a natural rubber and a styrene-butadiene copolymer rubber as a rubber component, and the rubber composition constituting the base rubber contains a natural rubber as a rubber component. The pneumatic tire for heavy loads according to claim 1 or 2, wherein: 4. The rubber component of the rubber composition of the cap rubber comprises 25 to 75% by weight of a natural rubber and 25 to 75% by weight of a styrene / butadiene copolymer rubber. 50-1 natural rubber in rubber component
The pneumatic tire for heavy load according to claim 3, wherein the content is 00% by weight. 5. The pneumatic tire for heavy loads according to claim 4, wherein the rubber component of the rubber composition of the cap rubber further contains 30% by weight or less of butadiene rubber.