JP3401283B2 - Pneumatic tire - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an all-weather pneumatic tire which is excellent in handling stability on ice and snowy roads, has less wear of the tread rubber even when running on a dry road for a long time, and has excellent durability. In particular, it relates to a heavy duty pneumatic tire used for buses, trucks and the like.

[0002]

2. Description of the Related Art An all-weather pneumatic tire is required to have excellent steering stability and durability even under various road surface conditions such as dry road surface, wet road surface and snowy and snowy road surface. is there. Among these pneumatic tires, studless tires that use foamed rubber as the tread rubber have recently attracted attention.

[0003] Studless tires generally have a tread rubber of a material having a lower rubber hardness than those of tires normally used for road surfaces in order to impart performance on ice.
However, this tire had poor durability because the tread rubber was significantly worn when the tire was running on a road surface other than the icy and snowy road surface.

Further, since the heavy load pneumatic tire has a high average ground contact pressure, the ice and snow road surface is easily melted, and a water film is likely to be formed between the tread ground contact surface and the ice and snow road surface. Therefore, when foamed rubber with reduced rubber hardness is used for the tread rubber,
Its advantage is that driving stability on ice and snow roads cannot be expected as much as that for tires for passenger cars, and permanent distortion, so-called fatigue, is likely to occur in the land portion of the tread, resulting in poor durability. Therefore, in order to solve these problems, improvements have been made in the material and structure of the foamed rubber.

For example, in Japanese Unexamined Patent Publication (Kokai) No. 1-118542, foam rubber is used as a tread rubber of a general pneumatic tire, and the foaming ratio and foam cell diameter are limited to maintain wear resistance. It is described that the steering stability on ice and snowy roads is improved, and dynamic compression permanent deformation (so-called sag) is less likely to occur, resulting in improved durability.

Further, Japanese Patent Laid-Open No. 2-155806 discloses that
Abrasion resistance by using foamed rubber as the tread rubber of heavy duty pneumatic tires, limiting the foaming ratio and foaming bubble diameter, and limiting the rubber hardness of the foamed rubber and the composition of carbon black in the foamed rubber. There is a statement that both of the settling properties are improved.

[0007]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In Japanese Patent Laid-Open No. 2 (1993), although the tread rubber contains carbon black as a reinforcing agent (usually contained in the tread rubber), the content of carbon black in the tread rubber is limited in improving the durability. I haven't. However, in practice, it has been found that the content of carbon black greatly changes the wear resistance and durability. For example, if the carbon black content is increased within the range of the normal usage amount, the wear resistance is improved, but the heat generation amount of the tread rubber is also increased. This fever is
The rubber itself is deteriorated to lower the breaking strength, and the conduction causes a decrease in the adhesive force between the cord of the belt and the rubber, which causes belt separation.

Further, in the case of Japanese Patent Laid-Open No. 2-155806, the carbon black content in the foamed rubber is optimized in order to eliminate the above-mentioned drawback. With this optimization, heat generation due to the inclusion of carbon black can be considerably suppressed. However, heat generation due to other factors has not yet been examined. In addition, studless tires generally have a wider tread width and a larger ground contact area in order to provide on-ice performance, but this causes significant heat generation at the shoulder portion where the amount of rubber is large, and belt separation is more likely to occur. is doing.

Therefore, by optimizing the structure and rubber physical properties of the tread crown portion, heat generated in the tread crown portion is less likely to be transmitted to the reinforcing belt side, and the amount of heat generated in the tread crown rubber is reduced to deteriorate the rubber. It is an object of the present invention to prevent abrasion and improve wear resistance without lowering heat generation durability.

[0010]

Means for Solving the Problems The present invention provides a rubber hardness JIS
A cap in which a cap rubber layer made of foamed rubber of A 45 to 70 ° (according to JIS K6301) and a base rubber layer made of non-foamed rubber of JIS A 45 to 70 ° are laminated-
Equipped with a base structure tread crown, the foam rubber is
With the closed cells having an average bubble diameter of 5 to 100 μm at a foaming rate of 5 to 50%, the ratio of the total number of bubbles having the same bubble diameter of 5 to 30 μm is 0. In the pneumatic tire of 5 or more, the volume ratio of the base rubber layer to the total rubber volume of the tread crown portion is 0.5 or more, the resilience of the cap rubber layer is 30 to 60%, and the resilience of the base rubber layer is 45. ~ 75%, the resilience of the base rubber layer is 5% or more larger than that of the cap rubber layer, and the tread crown portion extends in parallel across the plane including the central peripheral line, and the tread land of the central region and both shoulder regions With two main grooves divided into parts, at least two fine grooves dividing the central region into several, and lateral grooves intersecting these main grooves and fine grooves,
A pneumatic tire having a large number of divided land blocks, each land block having a sipe transversely crossing the land block.

Further, the cap rubber layer contains at least one selected from the group consisting of natural rubber, polybutadiene rubber, and styrene-butadiene copolymer rubber having a glass transition temperature of −45 ° C. or lower with respect to 100 parts by weight of all rubber components. The composition comprises 50 parts by weight or more of rubber, the base rubber is made of natural rubber, and the cap rubber layer and the base rubber layer each contain carbon black having the following physical properties in an amount of 30 to 80 parts with respect to 100 parts by weight of the rubber component. Parts by weight, 30 to 70 parts by weight, (note)

[Table 2] More preferably, the amount of oil contained in each of the cap rubber layer and the base rubber layer is 10 parts by weight or less and 5 parts by weight or less based on 100 parts by weight of the rubber component.

[0012]

In the pneumatic tire of the present invention, the resilience of the cap rubber layer made of foamed rubber and the base rubber layer made of non-foamed rubber forming the tread crown portion is made higher than that of the cap rubber layer. Is
This is because generation of heat is suppressed in the base rubber layer located on the reinforcing belt side of the tread crown portion, and heat transfer to the belt is reduced to prevent deterioration of rubber and improve durability. These resiliences have 3 cap rubber layers.
It is preferable that the resilience of the base rubber layer is larger than that of the cap rubber layer by 5% or more in the range of 0 to 60% and the base rubber layer is 45 to 75%. Resilience of cap rubber layer and base rubber layer is less than 30% each,
This is because if it is less than 45%, the heat generation becomes large, and if it exceeds 60% and 75%, respectively, the wear resistance decreases. The value obtained by subtracting the resilience value of the cap rubber layer from the resilience value of the base rubber layer is 5
If it is less than%, the effect of the cap-base structure for reducing the internal heat generation amount of the tread crown portion becomes unnoticeable.

The volume ratio of the base rubber layer having a relatively high resilience to the total rubber volume of the tread crown portion is set to 0.5 or more because the heat generation amount of the entire tread crown portion is suppressed as much as possible to improve the durability. This is to allow it. When this volume ratio is less than 0.5, the volume ratio of the base rubber layer becomes small, so that the effect of suppressing the internal heat generation amount of the tread crown portion is not remarkable. The upper limit of the practical volume ratio is preferably up to 0.9.

The tread crown portion having the physical properties and structure of the tread rubber as described above requires that the ground contact surface has a block pattern excellent in performance on ice. 2 to 10 show a part of typical block patterns. These treads have two main grooves that extend parallel to each other across a plane including the central circumference line and divide into a tread land portion of the central region and both shoulder regions, and at least two fine grooves that divide the central region into several. It has a large number of land blocks divided by grooves and lateral grooves intersecting these main grooves and narrow grooves, and each land block has a sipe that crosses it in its width direction. It is preferable that the size of each land block is relatively small, and the width in the tire circumferential direction is preferably about 15 to 40 mm. If the block size is less than this range, the block rigidity becomes too small and the driving performance and braking performance deteriorate, and if it exceeds this range, the amount of heat generation cannot be suppressed and the ground pressure also decreases, which is not preferable.

By making the land block relatively small in this way, it is possible to suppress the amount of heat generation and heat storage of the tread rubber and prevent deterioration of durability due to rubber deterioration. Further, since the land edge is increased by forming a relatively small block, the number of sipes in the width direction of each block can be reduced accordingly. If the number of sipes is small, the movement of the block becomes small, and the heat generation amount of the tread rubber becomes small. The number of sipes is preferably 1 to 2, and in particular, only 1 sipes is preferable for heat generation and durability.

The cap rubber layer made of foamed rubber is at least one selected from the group consisting of natural rubber, polybutadiene rubber, and styrene-butadiene copolymer rubber having a glass transition temperature of −45 ° C. or lower with respect to 100 parts by weight of all rubber components. The base rubber layer made of a non-foamed rubber is preferably made of natural rubber. This is because within this range, the rubber has sufficient rubber elasticity even at low temperatures.

It is preferable that the cap rubber layer and the base rubber layer are blended with the above-mentioned carbon black in an amount of 30 to 80 parts by weight and 30 to 70 parts by weight with respect to 100 parts by weight of the rubber component, respectively. If both rubber layers are less than the lower limit, abrasion resistance is deteriorated and settling easily occurs.If the upper limits of both ranges are exceeded, the amount of heat generated tends to be large, and workability is also disadvantageous. Is.

Regarding the physical properties of carbon black,
The cap rubber layer and the base rubber layer have CTAB of 130 m2 / g or more and 100 to 140 m2 / g, respectively, and 24
M4DBP 100ml / 100g or more, 90
It is preferable that the amount is 100 ml / ml or more. CTAB
The reason why the above range is set is that the wear resistance tends to decrease if the lower limit range is not reached, and conversely, if the upper limit of the range is exceeded, heat generation tends to increase.

The amount of oil contained in each of the cap rubber layer and the base rubber layer is preferably 10 parts by weight or less and 5 parts by weight or less with respect to 100 parts by weight of the rubber component. If both rubber layers exceed the upper limits of the ranges, the abrasion resistance tends to decrease and the calorific value tends to increase, which is not preferable.

[0020]

EXAMPLE FIG. 1 shows a widthwise cross section of a typical tire of a pneumatic tire according to the present invention, and FIG. 2 shows a part of its tread pattern developed. 1 pneumatic tire 1
(Tire size: 11R22.5) is a pneumatic tire for heavy loads such as buses and trucks. The pneumatic tire 1 includes a carcass 3 having a rubberized cord arranged substantially parallel to a rotation axis of the tire between a pair of bead portions 2 in a toroidal shape together with an inner liner 4.
At the crown portion of the carcass 3, there are provided a reinforcing belt 5 having a laminated structure and a tread crown portion 6 having a cap-base structure, which are arranged in an intersecting cord arrangement.

The tread crown portion 6 has a two-layer structure of a cap rubber layer 7 in contact with the road surface and a base rubber layer 8 on the reinforcing belt side. The cap rubber layer 7 is foamed rubber and the base rubber layer 8 is non-foamed. Made of rubber. The volume ratio of the base rubber layer 8 to the total rubber volume of the tread crown portion 6 was 0.75. The carbon black contained in the cap rubber layer 7 and the base rubber layer 8 has CTAB of 146 m ² / g and 117 m ² / g, and 24M4DBP of 102 ml / 100 g and 101 ml / 100 g, respectively.
The one with the physical properties of was used. Further, in the cap rubber layer 7 and the base rubber layer 8, the rubber hardness, the rubber composition, the resilience of the rubber, the compounding amount of carbon black and the oil content, and regarding the foamed rubber, the foaming rate and the bubble diameter of 5 μm or more, Bubble diameter 5 to 30 for the total number of closed bubbles
Inventive tires in which the ratio of the total number of bubbles in μm and the like were changed by the composition were tested as Examples 1 to 4. Further, the comparative tires in which the resilience of the cap rubber layer 7 and the base rubber layer 8 were variously shifted from the appropriate range were tested as Comparative Examples 1 to 6. These items are summarized in Table 3 for the cap rubber layer and Table 4 for the base rubber layer. The configuration other than the tread crown portion does not require modification for a general heavy-duty tire, and thus detailed description thereof will be omitted.

[0022]

[Table 3]

[0023]

[Table 4]

Next, a test for evaluating the performance of the above-mentioned test tire was carried out and will be described. Performance evaluation was performed by a wear resistance test and a heat resistance test. For the wear resistance test, 10 test tires were mounted on a truck with a loading capacity of 10 tons,
After traveling about 20,000 km, the traveling distance per 1 mm was obtained from the average value of the groove depth. In the heat resistance test, the running distance until the tread heat destruction was indexed in the high speed drum test. Table 5
The results of these tests are shown in. The larger the numerical value of the performance evaluation in the table, the better. In addition, the compositions of the cap rubber layer and the base rubber layer of the tires used in Comparative Examples and Examples are collectively shown in the table.

[0025]

[Table 5]

According to the test results, compared with Comparative Examples 1 to 6,
It can be seen that Examples 1 to 4 have excellent wear resistance without lowering heat resistance.

[0027]

In this pneumatic tire, the tread crown portion has a composite structure of a cap rubber layer of a specific foamed rubber and a base rubber layer of a non-foamed rubber to increase the volume ratio of the base rubber layer having high resilience. By
The amount of heat generated in the entire tread crown portion can be reduced, and deterioration of rubber due to this heat generation can be prevented, so that durability is improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an inventive tire in the width direction.

2 is a part of a development view of the tread 9 of the inventive tire shown in FIG. 1. FIG.

FIG. 3 is a part of a development view of a tread 10 of an invention tire.

FIG. 4 is a part of a development view of a tread 11 of an invention tire.

FIG. 5 is a part of a development view of the tread 12 of the invention tire.

FIG. 6 is a part of a development view of the tread 13 of the invention tire.

FIG. 7 is a part of a development view of the tread 14 of the invention tire.

FIG. 8 is a part of a development view of the tread 15 of the inventive tire.

FIG. 9 is a part of a development view of the tread 16 of the invention tire.

FIG. 10 is a part of a development view of the tread 17 of the invention tire.

[Explanation of symbols]

1 pneumatic tire 2 bead part 3 carcass 4 Inner liner 5 Reinforcement belt 6 tread crown 7 Cap rubber layer 8 Base rubber layer 9-17 tread

─────────────────────────────────────────────────── --- Continuation of the front page (56) Reference JP-A-1-118542 (JP, A) JP-A-2-155806 (JP, A) JP-A-3-295704 (JP, A) JP-A-1- 297303 (JP, A) JP-A-3-281551 (JP, A) JP-A-55-99403 (JP, A) JP-A-58-116204 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B60C 11 / 00,11 / 11-11 / 12,1 / 00

Claims (4)

(57) [Claims] 1. Rubber hardness JIS A 45 to 70 ° (JIS K63
(According to 01), a cap rubber layer made of foamed rubber and a base rubber layer made of non-foamed rubber having JIS A hardness of 45 to 70 ° are laminated, and a tread crown portion of a cap-base structure is provided. The ratio of the total number of bubbles having the same bubble diameter of 5 to 30 μm is 0.5 with respect to the total number of the independent bubbles having the bubble diameter of 5 μm or more occupying within a certain area. In the pneumatic tire described above, the volume ratio of the base rubber layer to the total rubber volume of the tread crown portion is 0.5 or more, the resilience of the cap rubber layer is 30 to 60%, and the resilience of the base rubber layer is 45 to 75%, the resilience of the base rubber layer is 5% or more larger than that of the cap rubber layer, and the tread crown portion extends in parallel with the plane including the central peripheral line therebetween. By the two main grooves that divide into the central area and the tread land portion of both shoulder areas, at least two narrow grooves that divide the central area into several, and the lateral grooves that intersect these main grooves and narrow grooves. Pneumatic tire having a large number of formed land blocks, each land block having a sipe transversely crossing the land block. 2. The cap rubber layer comprises 10 parts of all rubber components.
A base rubber having a composition containing 50 parts by weight or more of at least one rubber selected from the group consisting of natural rubber, polybutadiene rubber, and styrene-butadiene copolymer rubber having a glass transition temperature of −45 ° C. or less based on 0 parts by weight. The pneumatic tire according to claim 1, wherein the layer is made of natural rubber. 3. A rubber component 100 comprising carbon black having the following physical properties for the cap rubber layer and the base rubber layer.
30-80 parts by weight, 30-70 parts by weight, respectively
The pneumatic tire according to claim 1, wherein the pneumatic tire is mixed with parts by weight. (Note) [Table 1] 4. The pneumatic tire according to claim 3, wherein the amount of oil contained in each of the cap rubber layer and the base rubber layer is 10 parts by weight or less and 5 parts by weight or less based on 100 parts by weight of the rubber component. .