JP7360021B2 - Pneumatic tires for heavy loads - Google Patents

Description

The present invention relates to a pneumatic tire for heavy loads, and more particularly, to a pneumatic tire for heavy loads that can achieve both sufficient wet traction and rolling resistance.

A pneumatic tire is mainly composed of a pair of left and right bead portions and sidewall portions, and a tread portion that is continuous with both sidewall portions and includes a cap tread and an undertread. A carcass layer is provided on the inside of the tire, and both ends of the carcass layer are folded back so as to wrap around the bead core from the inside of the tire to the outside.

On the other hand, as pneumatic tires for heavy loads such as truck or bus tires, safety and economic efficiency are important. Therefore, for heavy-duty pneumatic tires, emphasis is placed on slope start performance (wet traction performance) and low rolling resistance on wet roads such as during rainy weather. In order to improve wet traction, there is a method of lowering the hardness of the cap tread rubber, but this has the problem that the blocks tend to move easily and rolling resistance deteriorates.
In this way, the wet traction properties and rolling resistance of heavy-duty pneumatic tires have a trade-off relationship.

Note that techniques for improving the wet traction properties of heavy-duty pneumatic tires are disclosed, for example, in Patent Documents 1 and 2.

Japanese Patent Application Publication No. 6-48122 Japanese Patent Application Publication No. 1-306304

Therefore, an object of the present invention is to provide a heavy-duty pneumatic tire that can achieve both sufficient wet traction and rolling resistance.

As a result of extensive research, the present inventor has determined the composition of the sidewall rubber, the hardness of the cap tread rubber, the relationship between the hardness of the cap tread rubber and the tan δ of the sidewall rubber at 60°C, and the range of the thickness of the sidewall rubber. It was discovered that the above-mentioned problem could be solved by specificization, and the present invention was completed.
That is, the present invention is as follows.

1. The sidewall rubber contains diene rubber including butadiene rubber and carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 60 to 100 m ² /g,
The blending ratio of the butadiene rubber in 100 parts by mass of the diene rubber is 40 parts by mass or more,
The blending ratio of the carbon black is 30 parts by mass or more with respect to 100 parts by mass of the diene rubber,
The hardness of the cap tread rubber constituting the tire contact surface is 55 or more, and the product of the hardness of the cap tread rubber (CAP hardness) and the tan δ at 60°C of the sidewall rubber (SIDE tan δ 60°C) satisfies the following formula: , and the sidewall rubber has a thickness of 3 mm to 20 mm. A heavy-duty pneumatic tire.
4.0≦(CAP hardness)×(SIDE tanδ60℃)≦7.5
2. 2. The heavy-duty pneumatic tire as described in 1 above, wherein the carbon black is blended in an amount of 35 to 60 parts by mass based on 100 parts by mass of the diene rubber.
3. 3. The heavy-duty pneumatic tire as described in 1 or 2 above, wherein the proportion of the butadiene rubber in 100 parts by mass of the diene rubber is 50 to 70 parts by mass.
4. 4. The heavy-duty pneumatic tire according to any one of items 1 to 3 above, wherein the proportion of syndiotactic-1,2-polybutadiene in the butazine rubber is 10% by mass or more.
5. 5. The heavy-duty pneumatic tire according to any one of 1 to 4 above, wherein the sidewall rubber is disposed outside the carcass layer in the tire width direction.

In the heavy-duty pneumatic tire of the present invention, the sidewall rubber contains a diene rubber including butadiene rubber and carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 60 to 100 m ² /g, and the diene rubber The blending ratio of the butadiene rubber in 100 parts by mass is 40 parts by mass or more, the blending ratio of the carbon black in 100 parts by mass of the diene rubber is 30 parts by mass or more, and the cap constitutes the tire contact surface. The hardness of the tread rubber is 55 or more, and the product of the hardness of the cap tread rubber (CAP hardness) and the tan δ at 60°C (SIDE tan δ 60°C) of the sidewall rubber is 4.0≦(CAP hardness)×(SIDE Since it satisfies tan δ (60° C.)≦7.5 and the thickness of the sidewall rubber is 3 mm to 20 mm, it is possible to achieve both sufficient wet traction properties and rolling resistance.

As mentioned above, there is a method of lowering the hardness of the cap tread rubber to improve wet traction, but this has the problem that the blocks tend to move and rolling resistance deteriorates.
In the present invention, the composition of the sidewall rubber, the hardness of the cap tread rubber, the relationship between the hardness of the cap tread rubber and the tan δ of the sidewall rubber at 60°C, and the thickness range of the sidewall rubber have been specified. The rubber plays a role in improving wet traction, and the sidewall rubber absorbs the heat generated thereby, making it possible to provide a heavy-duty pneumatic tire that has both sufficient wet traction and rolling resistance.

FIG. 1 is a meridian cross-sectional view of a pneumatic tire.

The present invention will be explained in more detail below.
(Sidewall rubber)
The sidewall rubber used in the heavy-duty pneumatic tire (hereinafter sometimes simply referred to as pneumatic tire) of the present invention is disposed outside the carcass layer in the tire width direction. Note that the tire width direction is a direction parallel to the tire rotation axis, and the tire width direction outer side refers to a direction away from the tire rotation axis.
In the present invention, the composition of the sidewall rubber is specified. That is, the sidewall rubber contains diene rubber including butadiene rubber and carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 60 to 100 m ² /g, and the butadiene rubber is contained in 100 parts by mass of the diene rubber. The blending ratio of the rubber is 40 parts by mass or more, and the blending ratio of the carbon black is 30 parts by mass or more with respect to 100 parts by mass of the diene rubber.

When the blending ratio of the butadiene rubber is less than 40 parts by mass, when the blending ratio of the carbon black is less than 30 parts by mass, and/or when the nitrogen adsorption specific surface area (N ₂ SA) of the carbon black is 60 to 100 m ² /g, it is not possible to achieve both sufficient wet traction and rolling resistance.

Here, from the viewpoint of improving the effects of the present invention, the following embodiments are preferable.
(1) The blending ratio of the butadiene rubber (BR) in 100 parts by mass of the diene rubber is preferably 50 to 70 parts by mass.
(2) The diene rubber preferably contains natural rubber (NR), and the blending ratio of NR is preferably 30 to 60 parts by mass in 100 parts by mass of the diene rubber.
(3) The blending ratio of the carbon black to 100 parts by mass of the diene rubber is preferably 35 to 60 parts by mass.
(4) The nitrogen adsorption specific surface area (N ₂ SA) of the carbon black is preferably 65 to 95 m ² /g, more preferably 70 to 90 m ² /g. Note that two or more types of carbon black may be used as a blend.
Note that NR as used in the present invention includes synthetic polyisoprene rubber (IR). Further, the nitrogen adsorption specific surface area (N ₂ SA) is a value measured according to JIS K 6217-2:2001 "Part 2: Determination of specific surface area - Nitrogen adsorption method - Single point method".

In addition to natural rubber (NR) and butadiene rubber (BR), the rubber constituting the sidewall rubber used in the present invention is styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), and styrene-butadiene copolymer rubber (SBR). ) etc. can also be used together. The rubber used in the present invention is not particularly limited in its molecular weight or microstructure, and may be terminally modified with amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl groups, etc., or may be epoxidized.

In the present invention, the proportion of syndiotactic-1,2-polybutadiene (VCR) in the BR can be 10% by mass or more, preferably 25 to 55% by mass. Note that VCRs are well known, and a method for manufacturing them is disclosed in, for example, Japanese Patent Laid-Open No. 2000-44633. It is also commercially available, for example, sold by Ube Industries, Ltd. under the trade name UBEPOL VCR412.

In addition to the above-mentioned ingredients, the sidewall rubber also contains various fillers, various oils, anti-aging agents, plasticizers, zinc oxide, and other additives that are commonly included in sidewall rubbers. can do. Further, during vulcanization, known vulcanization or crosslinking agents and vulcanization or crosslinking accelerators can be used without limitation. The blending amounts of these additives can also be set to conventional and general blending amounts as long as they do not contradict the purpose of the present invention.

In the present invention, the composition of the cap tread rubber is not particularly limited and can be appropriately selected as long as it satisfies the relationship of (CAP hardness) x (SIDE tan δ 60°C) described below.
For example, various ingredients commonly included in cap tread rubber such as diene rubber, various fillers such as silica and carbon black, coupling agents, various oils, anti-aging agents, plasticizers, and zinc oxide are blended. be able to. Further, during vulcanization, known vulcanization or crosslinking agents and vulcanization or crosslinking accelerators can be used without limitation. The blending amounts of these additives can also be set to conventional and general blending amounts as long as they do not contradict the purpose of the present invention.

However, the cap tread rubber needs to have a hardness of 55 or higher. If the hardness is less than 55, it is too soft and the heat generation property deteriorates, making it impossible to obtain low rolling resistance.
The hardness of the cap tread rubber is preferably 58 to 75, more preferably 60 to 70.
Note that the hardness referred to in the present invention is measured at 20° C. in accordance with JIS K6253.

Furthermore, with respect to the members constituting the other members in the pneumatic tire of the present invention, the blending ratio of each component is not particularly limited and can be appropriately selected.
For example, various commonly used components such as diene rubber, various fillers, various oils, anti-aging agents, plasticizers, zinc oxide, etc. can be blended as rubber compositions for other members. Further, during vulcanization, known vulcanization or crosslinking agents and vulcanization or crosslinking accelerators can be used without limitation. The blending amounts of these additives can also be set to conventional and general blending amounts as long as they do not contradict the purpose of the present invention.

In the pneumatic tire of the present invention, the product of the hardness of the cap tread rubber (CAP hardness) and the tan δ at 60°C of the sidewall rubber (SIDE tan δ 60°C) must satisfy the following formula.

4.0≦(CAP hardness)×(SIDE tanδ60℃)≦7.5

If (CAP hardness) x (SIDE tan δ60°C) is outside this range, the effects of the present invention cannot be achieved.
The above (SIDE tan δ 60°C) is measured using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd. under the following conditions: initial strain 10%, amplitude ±2%, frequency 20Hz, and temperature 60°C.

In the present invention, (SIDE tan δ60°C) is preferably 0.05 to 0.12, more preferably 0.06 to 0.11.
Further, from the viewpoint of further improving the effects of the present invention, (CAP hardness) x (SIDE tan δ 60°C) is preferably 4.5 to 7.0.

Note that the above (CAP hardness) and (SIDE tan δ 60°C) can be adjusted by, for example, increasing or decreasing the vulcanizing agent or crosslinking agent, or changing the blending amount or type of carbon black.

FIG. 1 is a meridian cross-sectional view of a pneumatic tire.
As shown in FIG. 1, the pneumatic tire of the present embodiment includes a tread portion 1 extending in the tire circumferential direction and forming an annular shape, a pair of sidewall portions 2 disposed on both sides of the tread portion 1, and a side wall portion 2 disposed on both sides of the tread portion 1. A pair of bead portions 3 are arranged on the inner side of the wall portion 2 in the tire radial direction.

A carcass layer 4 including a plurality of carcass cords extending in the tire radial direction is mounted between the pair of bead portions 3, 3. The carcass layer 4 is rolled up around the bead core 5 from the inside of the tire to the outside. Furthermore, rim cushion rubber 8, which is a rubber layer that forms a contact surface with the rim, is arranged on the inner side in the tire radial direction and the outer side in the tire width direction of the bead core 5.

On the other hand, a plurality of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1 over the entire circumference of the tire. These belt layers 7 include a plurality of reinforcing cords that are inclined with respect to the tire circumferential direction, and are arranged so that the reinforcing cords intersect with each other between layers.

In the present invention, it is necessary that the sidewall rubber constituting the sidewall portion 2 has a thickness of 3 mm to 20 mm. Note that the thickness of the sidewall rubber is the maximum thickness of the sidewall rubber in a direction perpendicular to the carcass layer 4 toward the outside in the tire width direction.

From the viewpoint of improving the effects of the present invention, the thickness of the sidewall rubber is more preferably 5 mm to 17 mm.

Moreover, the pneumatic tire for heavy loads of the present invention can be manufactured according to the conventional manufacturing method of pneumatic tires for heavy loads.

EXAMPLES The present invention will be further explained below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Standard example, Examples 1 to 4 and Comparative examples 1 to 5
In the formulation (parts by mass) shown in Table 1, the components excluding the vulcanization accelerator and sulfur were kneaded for 5 minutes in a 16 liter closed Banbury mixer, and the rubber was discharged outside the mixer and cooled at room temperature. Next, the rubber was put into the same mixer again, a vulcanization accelerator and sulfur were added, and further kneaded to obtain various sidewall rubbers.

On the other hand, cap tread rubbers were prepared according to a conventional method, and cap tread rubbers having various types (CAP hardness) shown in Table 1 were obtained by increasing and decreasing the amounts of vulcanizing agent, crosslinking agent, and filler.

(CAP hardness) and (SIDE tan δ60°C) were measured as described above. The results are shown in Table 1.

(Evaluation of wet traction properties)
Various test tires with tire sizes of 275/80R22.5 and 151/148J were manufactured by incorporating the sidewall rubber and the sidewall rubber. Further, the conditions for the sidewall rubber and each member other than the sidewall rubber were the same among the various test tires.

The various test tires obtained were evaluated as follows. The results are shown in Table 1.

Wet traction performance: The test tires were mounted on a test vehicle (tractor head) with a displacement of 12,770cc, the air pressure was adjusted to 900kPa at the front and 900kPa at the rear, and the tires were run on a paved road surface with a water depth of 1mm, at speeds of 6 to 21km/h. The slip rate of the rear wheels during acceleration was measured. The results were expressed as an index with the value of the standard example set as 100. The larger the index, the better the wet traction properties.

Rolling resistance: The rolling resistance of each test tire was measured at an air pressure of 900 kPa, a load of 28.76 kN, and a speed of 60 km/h. The results were expressed as an index with the standard example as 100. The larger the index, the lower the rolling resistance and the better the fuel efficiency.

*1:NR (RSS#3)
*2: BR (Nipol BR1220 manufactured by Zeon Corporation)
*3: VCR (UBEPOL VCR412 manufactured by Ube Industries, Ltd. Table 1 shows the amount of syndiotactic-1,2-polybutadiene)
*4: Carbon black (product name SEAST 3 manufactured by Tokai Carbon Co., Ltd., N ₂ SA = 80 m ² /g)
*5: Zinc oxide (3 types of zinc oxide manufactured by Seido Kagaku Kogyo Co., Ltd.)
*6: Stearic acid (industrial stearic acid N manufactured by Chiba Fatty Acid Co., Ltd.)
*7: Anti-aging agent (Ozonone 6C manufactured by Seiko Kagaku Co., Ltd.)
*8: Aroma oil (Diana Process NH-60 manufactured by Idemitsu Kosan Co., Ltd.)
*9: Vulcanization accelerator (Noxeler NS-P manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.)
*10: Sulfur (fine powder sulfur with Kinka seal oil manufactured by Tsurumi Chemical Industry Co., Ltd.)

As is clear from Table 1 above, the heavy-duty pneumatic tires prepared in each example had the composition of the sidewall rubber, the hardness of the cap tread rubber, the hardness of the cap tread rubber, and the hardness of the sidewall rubber at 60°C. Since the relationship of tan δ and the range of the thickness of the sidewall rubber have been specified, it is possible to achieve both sufficient wet traction properties and rolling resistance compared to the standard example.
In Comparative Example 1, the hardness of the cap tread rubber was less than the lower limit specified by the present invention, so wet traction properties and rolling resistance were deteriorated.
In Comparative Example 2, (CAP hardness)×(SIDE tan δ60° C.) exceeded the upper limit specified by the present invention, and therefore wet traction properties deteriorated.
In Comparative Example 3, the thickness of the sidewall rubber exceeded the upper limit defined by the present invention, so the wet traction properties deteriorated.
In Comparative Example 4, the thickness of the sidewall rubber was less than the lower limit defined by the present invention, so rolling resistance deteriorated.
In Comparative Example 5, the blending amount of BR was less than the lower limit defined by the present invention, so wet traction properties and rolling resistance deteriorated.

1 Tread portion 2 Sidewall portion 3 Bead portion 4 Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 8 Rim cushion rubber

Claims (4)

The sidewall rubber contains diene rubber including butadiene rubber and carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 60 to 100 m ² /g,
The blending ratio of the butadiene rubber in 100 parts by mass of the diene rubber is 40 parts by mass or more,
The blending ratio of the carbon black is 30 parts by mass or more with respect to 100 parts by mass of the diene rubber,
The hardness of the cap tread rubber constituting the tire contact surface is 55 or more, and the product of the hardness of the cap tread rubber (CAP hardness) and the tan δ at 60°C of the sidewall rubber (SIDE tan δ 60°C) satisfies the following formula: , and the sidewall rubber has a thickness of 3 mm to 20 mm. A heavy-duty pneumatic tire.
4.0≦(CAP hardness)×(SIDE tanδ60℃)≦7.5 The heavy-duty pneumatic tire according to claim 1, wherein the carbon black is blended in an amount of 35 to 60 parts by mass based on 100 parts by mass of the diene rubber. The pneumatic tire for heavy loads according to claim 1 or 2, wherein the proportion of the butadiene rubber is 50 to 70 parts by mass in 100 parts by mass of the diene rubber. The heavy-duty pneumatic tire according to any one of claims 1 to 3 , wherein the sidewall rubber is arranged outside the carcass layer in the tire width direction.

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