JP7275889B2 - pneumatic tire - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire that simultaneously satisfies reduction of road noise, improvement of steering stability and durability.

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

By the way, an electric vehicle that runs using a motor as a power source has significantly reduced vehicle-derived noise compared to a vehicle that runs using an internal combustion engine as a power source. ), there is no difference between the two vehicles. Therefore, there is a demand for a technique for further reducing tire-derived road noise.

In order to reduce road noise, there is known a method of softening a tire member such as a cap tread rubber to reduce spring characteristics. However, softening the cap tread rubber, for example, has the problem of lowering steering stability and durability, and reducing road noise and improving steering stability and durability are in a trade-off relationship.

Techniques for reducing road noise and improving steering stability are disclosed in Patent Documents 1 to 3, for example.

Japanese Patent Application Laid-Open No. 2007-253708 JP 2014-80074 A International publication WO2014/002631 pamphlet

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a pneumatic tire that simultaneously satisfies reduction of road noise, improvement of steering stability and durability.

As a result of intensive research, the inventors of the present invention specified the ratio of the thickness of the undertread rubber, the composition of the undertread rubber, and the ratio of the hardness of the captread rubber to the storage modulus of the undertread rubber. was able to be solved, and the present invention was completed.
That is, the present invention is as follows.

1. A pneumatic tire comprising a cap tread rubber and an undertread rubber disposed radially inward of the cap tread rubber,
The thickness of the undertread rubber is 5% or more of the thickness of the cap tread rubber,
The undertread rubber contains 40 parts by mass or more of natural rubber, 10 to 60 parts by mass of terminal-modified butadiene rubber, 40 parts by mass or more of carbon black, and 20 parts by mass or less of silica with respect to 100 parts by mass of diene rubber. and wherein the hardness (Hs cap) of the cap tread rubber at 20°C and the storage elastic modulus (E'ut) of the undertread rubber at 20°C satisfy the following formula: tire.
3.50≤(Hscap)/(E'ut)≤18.00
2. 2. The pneumatic tire described in 1 above, wherein the terminal group of the terminal-modified butadiene rubber is one or more selected from a hydroxyl group, an amino group, an alkoxyl group and an epoxy group.
3. 3. The pneumatic tire described in 1 or 2 above, wherein the carbon black has a nitrogen adsorption specific surface area (N ₂ SA) of 25 to 50 m ² /g.
4. 4. The pneumatic tire according to any one of 1 to 3 above, wherein the carbon black is mixed in an amount of 40 to 80 parts by mass with respect to 100 parts by mass of the diene rubber.

The pneumatic tire of the present invention includes a cap tread rubber and an undertread rubber arranged inside the cap tread rubber in the tire radial direction, and the thickness of the undertread rubber is 5% of the thickness of the cap tread rubber. The undertread rubber comprises 40 parts by mass or more of natural rubber, 10 to 60 parts by mass of terminal-modified butadiene rubber, 40 parts by mass or more of carbon black, and 20 parts by mass of silica, based on 100 parts by mass of diene rubber. The hardness (Hs cap) of the cap tread rubber at 20°C and the storage elastic modulus (E'ut) of the undertread rubber at 20°C are 3.50 ≤ (Hs cap). /(E'ut)≦18.00 is satisfied, so a pneumatic tire that satisfies reduction of road noise, improvement of steering stability and durability at the same time can be provided.

As described above, softening the cap tread rubber is an effective way to reduce road noise, but on the other hand, it reduces steering stability and durability. In the present invention, by specifying the thickness ratio of the undertread rubber, the composition of the undertread rubber, and the ratio of the hardness of the captread rubber to the storage modulus of the undertread rubber, the captread rubber improves road noise. Even if the steering stability and durability are reduced, the undertread rubber plays the role of complementing the steering stability and durability, resulting in the reduction of road noise and the improvement of steering stability and durability, which are in a trade-off relationship. can be achieved at the same time.

The present invention will now be described in more detail.

(Undertread rubber)
The undertread rubber used in the pneumatic tire of the present invention is a member arranged radially inward of the cap tread rubber forming the tire ground contact surface. In addition, the inner side in the tire radial direction means the side close to the rotation axis in the tire radial direction (the direction orthogonal to the rotation axis of the pneumatic tire).

In the present invention, the thickness of the undertread rubber must be 5% or more of the thickness (maximum thickness) of the cap tread rubber. If the thickness of the undertread rubber is less than 5%, reduction of road noise and improvement of steering stability and durability cannot be achieved at the same time.
The thickness of the undertread rubber with respect to the thickness of the captread rubber is preferably 7 to 20%, more preferably 10 to 15%.

The thickness of the undertread rubber is preferably 0.5 mm to 5 mm.
The thickness of the cap tread rubber is preferably 5 mm to 15 mm.

The present invention specifies the composition of the undertread rubber. That is, the undertread rubber contains 40 parts by mass or more of natural rubber (NR), 10 to 60 parts by mass of terminal-modified butadiene rubber (terminal-modified BR), and 40 parts by mass or more of carbon black with respect to 100 parts by mass of diene rubber. , and 20 parts by mass or less of silica.

When the blending ratio of the NR is less than 40 parts by mass, when the blending ratio of the terminal-modified BR is less than 10 parts by mass or exceeds 60 parts by mass, when the blending ratio of the carbon black is less than 40 parts by mass, and Alternatively, if the silica content exceeds 20 parts by mass, reduction in road noise and improvement in steering stability and durability cannot be achieved at the same time.

Here, from the viewpoint of improving the effects of the present invention, the following forms are preferable.
(1) The mixing ratio of the NR is preferably 40 to 60 parts by mass with respect to 100 parts by mass of the diene rubber.
(2) The compounding ratio of the terminal-modified BR is preferably 40 to 60 parts by mass with respect to 100 parts by mass of the diene rubber.
(3) The nitrogen adsorption specific surface area (N ₂ SA) of the carbon black is preferably 25-50 m ² /g.
(4) The mixing ratio of the carbon black is preferably 40 to 80 parts by mass with respect to 100 parts by mass of the diene rubber.
(5) The mixing ratio of the silica is preferably 0 to 15 parts by mass with respect to 100 parts by mass of the diene rubber. That is, the undertread rubber in the present invention may not contain silica.
In addition, NR as used in the present invention includes synthetic isoprene rubber (IR). 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".

The terminal-modified BR has its terminal modified with a functional group, and by using the terminal-modified BR having such a structure, road noise is further reduced, and steering stability and durability are further improved. There is an effect that it can be improved. From the viewpoint of enhancing this action, the functional group is preferably one or more functional groups selected from hydroxyl groups, amino groups, alkoxyl groups and epoxy groups.
A terminal-modified BR can be prepared by a known technique. For example, 1,3-butadiene polymerization is performed using a saturated hydrocarbon-based compound as a solvent and an organic lithium compound as a polymerization initiator, and a compound having the functional group capable of reacting with the active terminal of the obtained butadiene-based polymer. can be exemplified by a method of obtaining by a denaturation reaction. A commercially available terminal-modified BR can also be used. For example, Nipol BR1250H (trade name, manufactured by Nippon Zeon Co., Ltd.) can be used as a butadiene rubber whose terminal is modified with an amino group.

As the diene rubber used in the present invention, diene rubbers other than NR and terminal-modified BR can be used in combination, if necessary. For example, terminally unmodified butadiene rubber, styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), ethylene-propylene-diene terpolymer (EPDM) and the like may be compounded. The diene rubber used in the present invention is not particularly limited in its molecular weight or microstructure, and may be terminally modified with an amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl group, or the like, or may be epoxidized. good.

The silica used in the present invention is not particularly limited, and for example, any conventionally known silica compounded in rubber compositions for use in tires can be used.
Specific examples of silica include wet silica, dry silica, and fumed silica. As for silica, one type of silica may be used alone, or two or more types of silica may be used in combination.

In addition to the above components, the undertread rubber may contain various additives generally blended in undertread rubber, such as various fillers, various oils, antioxidants, and plasticizers. can. Further, at the time of vulcanization, a known vulcanization or cross-linking agent, vulcanization or cross-linking accelerator can be used without limitation. The blending amount of these additives can also be a conventional general blending amount as long as it does not contradict the object of the present invention.

In the present invention, the composition of the cap tread rubber is not particularly limited as long as the relationship of (Hs cap)/(E'ut) described below can be satisfied, and can be appropriately selected.
For example, various components generally blended in cap tread rubber, such as diene rubbers, various fillers, various oils, anti-aging agents, and plasticizers, can be blended. Further, at the time of vulcanization, a known vulcanization or cross-linking agent, vulcanization or cross-linking accelerator can be used without limitation. The blending amount of these additives can also be a conventional general blending amount as long as it does not contradict the object of the present invention.

Also, in the other members of the pneumatic tire of the present invention, such as members constituting the carcass, bead portions, sidewall portions, etc., the compounding ratio of each component is not particularly limited, and can be appropriately selected.
For example, as the rubber composition of other members, various components generally blended such as diene rubbers, various fillers, various oils, anti-aging agents, and plasticizers can be blended. Further, at the time of vulcanization, a known vulcanization or cross-linking agent, vulcanization or cross-linking accelerator can be used without limitation. The blending amount of these additives can also be a conventional general blending amount as long as it does not contradict the object of the present invention.

In the pneumatic tire of the present invention, the hardness (Hs cap) of the cap tread rubber at 20°C and the storage elastic modulus (E'ut) of the undertread rubber at 20°C must satisfy the following equations. be.

3.50≤(Hscap)/(E'ut)≤18.00

That is, when (Hs cap)/(E'ut) is in the range of 3.50 to 18.00, the cap tread rubber is responsible for improving road noise and reducing steering stability and durability as described above. Undertread rubber plays the role of complementing steering stability and durability even in the case of a tire, and as a result, it is possible to simultaneously achieve reduction of road noise and improvement of steering stability and durability, which are in a trade-off relationship. Become.

The hardness (Hs cap) of the cap tread rubber at 20° C. referred to in the present invention is rubber hardness measured at a temperature of 20° C. with a durometer type A according to JIS K6253.
In addition, the storage elastic modulus (E'ut) at 20 ° C. of the undertread rubber referred to in the present invention conforms to JIS K6394, under the conditions of initial strain 10%, amplitude ± 2%, frequency 20 Hz, manufactured by Toyo Seiki Seisakusho Storage modulus measured at 20° C. with a viscoelastic spectrometer. In this specification, the unit of storage elastic modulus (E'ut) is MPa.

The hardness (Hs cap) of the cap tread rubber at 20° C. can be adjusted, for example, by increasing or decreasing the plasticizer.
Further, the storage elastic modulus (E'ut) of the undertread rubber at 20° C. can be adjusted, for example, by changing the filler amount and particle size.

From the viewpoint of further improving the effects of the present invention, the (Hs cap)/(E'ut) is preferably 5 to 18, more preferably 8 to 18.

Further, the pneumatic tire of the present invention can be manufactured according to a conventional pneumatic tire manufacturing method, and is preferably used for passenger cars, for example.

The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

Standard Example, Examples 1-3 and Comparative Examples 1-2
In the formulation (parts by mass) shown in Table 1, the vulcanization accelerator and components other than sulfur were kneaded for 5 minutes in a 1.7-liter internal Banbury mixer, and the rubber was discharged out of the mixer and cooled to room temperature. Then, the rubber was placed in the same mixer again, a vulcanization accelerator and sulfur were added, and the mixture was further kneaded to obtain various undertread rubber compositions.

Next, cap tread rubbers were prepared according to a conventional method, and cap tread rubbers having various hardnesses shown in Table 1 were obtained by increasing or decreasing the amount of the plasticizer.

The hardness (Hs cap) of the cap tread rubber at 20°C was measured at a temperature of 20°C with a durometer type A according to JIS K6253.
The storage elastic modulus (E'ut) of the undertread rubber composition at 20° C. was determined according to JIS K6394 under conditions of initial strain of 10%, amplitude of ±2%, and frequency of 20 Hz using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho. was measured at 20°C by Table 1 shows the results.

Various pneumatic tires having a tire size of 205/55R16 were produced by incorporating the undertread rubber and the cap tread rubber. The conditions of each member other than the undertread rubber and the cap tread rubber were the same among various pneumatic tires. In each example, the thickness of the cap tread rubber is 8.5 mm, and the thickness of the under tread rubber is 1 mm. (However, the thickness of the cap tread rubber in Comparative Example 1 is 20 mm, and the thickness of the under tread rubber is 0.8 mm.)

The various pneumatic tires obtained were evaluated as follows. Table 1 shows the results.

Road noise: Each test tire was mounted on a wheel with a rim size of 18×8.5J, mounted on a test vehicle, and subjected to sensory evaluation by a test driver for road noise during running under the condition of air pressure of 240 kPa. The score was a relative evaluation with a full score of 3.0 (a clear improvement can be confirmed), and a standard example of 1.0 (an improvement cannot be confirmed). A higher score means less road noise.

Steering stability: Each test tire was mounted on a wheel with a rim size of 18×8.5J, mounted on a test vehicle, and subjected to a sensory evaluation by a test driver on a paved test course at an air pressure of 240 kPa. The score was a relative evaluation with a full score of 3.0 (a clear performance improvement can be confirmed), and the standard example was given a score of 2.0 (no change in performance). The higher the score, the better the steering stability.

Durability: The tire is mounted on a rim with a rim size of 16 x 7JJ, filled with air pressure of 230kPa, loaded with a load of 45kN, and run at a speed of 45km/h on a rotating drum with a diameter of 1707mm until the tire fails. Distance traveled was measured. The running distance of the standard example is set to 100 and shown as an index. The larger the index value, the better the tire durability performance.

*1: NR (TSR20)
*2: End-modified BR (Nipol BR1250H manufactured by Nippon Zeon Co., Ltd.)
*3: Carbon black GPF (trade name: Niteron #G, N ₂ SA = 35 m ² /g, manufactured by Shin Nikka Carbon Co., Ltd.)
*4: Carbon black HAF (trade name: Niteron #10N, N ₂ SA = 40 m ² /g, manufactured by Shin Nikka Carbon Co., Ltd.)
*5: Silica (trade name Ultrasil VN3GR manufactured by EVONIK)
*6: Zinc oxide (Type 3 zinc oxide manufactured by Seido Chemical Industry Co., Ltd.)
*7: Anti-aging agent (SANTOFLEX 6PPD manufactured by FLEXSYS)
*8: Vulcanization accelerator (SANTOCURE CBS manufactured by FLEXSYS)
* 9: Sulfur (Mucron OT-20 manufactured by Shikoku Kasei Co., Ltd.)

As is clear from Table 1 above, the pneumatic tires prepared in Examples 1 to 3 have a thickness ratio of the undertread rubber, a composition of the undertread rubber, a hardness of the cap tread rubber, and a storage of the undertread rubber. Since the elastic modulus ratio was specified, reduction in road noise and improvement in steering stability and durability were recognized compared to the standard example.
In Comparative Example 1, the ratio of the thickness of the undertread rubber was less than the lower limit specified in the present invention, so the steering stability was worse than in the standard example. Moreover, heat was generated due to an increase in the distortion of the cap tread, and the durability deteriorated compared to the standard example.
In Comparative Example 2, (Hs cap)/(E'ut) was less than the lower limit specified in the present invention, so the durability deteriorated.

Claims (4)

A pneumatic tire comprising a cap tread rubber and an undertread rubber disposed radially inward of the cap tread rubber,
The thickness of the undertread rubber is 5% or more of the thickness of the cap tread rubber,
The undertread rubber contains 40 parts by mass or more of natural rubber, 10 to 60 parts by mass of terminal-modified butadiene rubber, 40 parts by mass or more of carbon black, and 0 to 15 parts by mass of silica based on 100 parts by mass of diene rubber. and wherein the hardness (Hs cap) of the cap tread rubber at 20°C and the storage elastic modulus (E'ut) of the undertread rubber at 20°C satisfy the following formula: entered tire.
8 ≤ (Hs cap) / (E'ut) ≤ 18.00 2. The pneumatic tire according to claim 1, wherein the terminal group of the terminal-modified butadiene rubber is one or more selected from a hydroxyl group, an amino group, an alkoxyl group and an epoxy group. 3. The pneumatic tire according to claim 1, wherein the carbon black has a nitrogen adsorption specific surface area (N ₂ SA) of 25 to 50 m ² /g. The pneumatic tire according to any one of claims 1 to 3, wherein the carbon black is added in an amount of 40 to 80 parts by mass with respect to 100 parts by mass of the diene rubber.