JP5617316B2 - Rubber composition for tire tread and pneumatic tire using the same - Google Patents

Description

  The present invention relates to a rubber composition for a tire tread and a pneumatic tire using the same, and more specifically, is excellent in low temperature characteristics typified by performance on ice, wet performance, low rolling resistance, low hysteresis resistance, The present invention relates to a rubber composition for a tire tread excellent in aging property and a pneumatic tire using the same.

Conventionally, many means have been proposed to improve the on-ice characteristics of tires. For example, the amount of reinforcing filler in the rubber composition can be reduced to improve the frictional force by increasing the flexibility, or a special compounding agent that forms pores in the rubber can be blended to add water on the ice surface. There is a method of improving the frictional force by absorbing water and improving the adhesion between rubber and ice.
However, although these conventional techniques improve the frictional force on the road surface on ice, there is a problem that braking / driving performance is not effective on wet road surfaces such as rainy weather.

  Patent Document 1 discloses an essential plasticizer for the present invention described below. However, Patent Document 1 discloses or suggests the technical idea of using the plasticizer to achieve all of low temperature characteristics, wet performance, low rolling resistance, low hysteresis, and aging resistance of the rubber composition. Absent.

JP 2009-108298 A

  Accordingly, an object of the present invention is to provide a tire tread rubber composition excellent in low-temperature characteristics typified by on-ice performance, excellent in wet performance, low rolling resistance, low hysteresis, and aging resistance, and air using the same. The purpose is to provide tires.

The present invention is as follows.
1. For 100 parts by mass of diene rubber having a glass transition temperature of −50 ° C. or lower,
5 to 50 parts by mass of an ester plasticizer having a saturated cyclic structure consisting of the following formula (I) ,
10 to 120 parts by mass of a reinforcing filler containing 10 to 80 parts by mass of silica , and
A rubber composition for a tire tread comprising 0.5 to 20 parts by mass of at least one selected from thermally expandable microcapsules and expanded graphite .

(In the formula, R ¹ and R ² are each independently an alkyl group having 2 to 18 carbon atoms, and may have a branched or cyclic structure .)
2. 2. The rubber composition for a tire tread according to 1, wherein the natural rubber accounts for 30 parts by mass or more in 100 parts by mass of the diene rubber.
3 . A pneumatic tire using the tire tread rubber composition according to 1 or 2 as a tire tread.

  According to the present invention, by adding a specific amount of a specific ester plasticizer and a specific amount of a reinforcing filler containing silica to a diene rubber containing a specific component, performance on ice is represented. A rubber composition for a tire tread excellent in low temperature characteristics, wet performance, low rolling resistance, low hysteresis and aging resistance and a pneumatic tire using the same can be provided.

It is a fragmentary sectional view of an example of a pneumatic tire.

  Hereinafter, the present invention will be described in more detail.

FIG. 1 is a partial cross-sectional view of an example of a pneumatic tire for a passenger car.
In FIG. 1, the pneumatic tire is composed of a pair of left and right bead portions 1 and sidewalls 2, and a tread 3 connected to both sidewalls 2, and a carcass layer 4 in which fiber cords are embedded between the bead portions 1 and 1 is mounted. Then, the end portion of the carcass layer 4 is turned up around the bead core 5 and the bead filler 6 from the tire inner side to the outer side. In the tread 3, a belt layer 7 is disposed over the circumference of the tire outside the carcass layer 4. In the bead portion 1, a rim cushion 8 is disposed at a portion in contact with the rim.
The rubber composition of the present invention described below is particularly useful for the tread 3.

(Diene rubber)
As the diene rubber used in the present invention, any diene rubber that can be blended in the rubber composition can be used, for example, natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR). Styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), and the like. These may be used alone or in combination of two or more. The molecular weight and microstructure are not particularly limited, and may be terminally modified with an amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl group or the like, or may be epoxidized.
However, the diene rubber used in the present invention needs to have a glass transition temperature (Tg) of −50 ° C. or lower. If Tg exceeds -50 ° C, the desired friction performance on ice cannot be obtained. Tg is measured according to ASTM: D-3418-82. Examples of the measuring instrument include a differential thermal analyzer (DSC-EOA) manufactured by Shimadzu Corporation.
Among these diene rubbers, it is preferable that NR accounts for 30 parts by mass or more in 100 parts by mass of the diene rubber from the viewpoint of the effect of the present invention.
Furthermore, more preferable Tg is −60 to −110 ° C.

(Ester plasticizer)
The ester plasticizer used in the present invention is represented by the following formula (I).

In the formula (I), R ¹ and R ² each independently represent a hydrogen atom or an organic group having 1 to 18 carbon atoms. R ¹ and R ² are preferably an alkyl group, more preferably an alkyl group having 2 to 18 carbon atoms, and may have a branched or cyclic (bicyclo) structure. Particularly preferred is an alkyl group having 4 to 12 carbon atoms, and most preferred is an alkyl group having 4 to 9 carbon atoms.
In addition, a C2-C18 alkyl group produces the effect of this invention equally from the reason that compatibility with rubber | gum does not change a lot.

(Reinforcing filler)
Examples of the reinforcing filler used in the present invention include silica, carbon black, and alumina.
In the present invention, silica is blended as an essential component as a reinforcing filler. The silica used in the present invention preferably has, for example, a BET specific surface area (measured in accordance with ISO 5794-1 Annex E) of 60 to 250 m ² / g, and more preferably 80 to 210 m ² / g. .

(Thermally expandable microcapsules and expanded graphite)
In the present invention, it is preferable to further blend at least one selected from thermally expandable microcapsules and expanded graphite from the viewpoint of effects.
The heat-expandable microcapsule is a heat-expandable thermoplastic resin particle in which, for example, a liquid that is vaporized by heat to generate a gas is contained in a thermoplastic resin, and the particle is heated to a temperature higher than its expansion start temperature, for example, 140 to 190. By heating and expanding at a temperature of 150 ° C., preferably 150 to 180 ° C., gas-encapsulated thermoplastic resin particles in which a gas is enclosed in the outer shell made of the thermoplastic resin are obtained. The particle value of the thermally expandable microcapsule is not particularly limited, but is preferably 5 to 300 μm before expansion, more preferably 10 to 200 μm. Such a heat-expandable microcapsule is, for example, trade name “Expancel 091DU-80” or “Expancel 092DU-120” from EXPANCEL, Sweden, or a trade name “Matsumoto Yushi Seiyaku Co., Ltd.” It can be obtained as “Matsumoto Microsphere F-85” or “Matsumoto Microsphere F-100”.
As the thermoplastic resin constituting the outer shell component of the gas-filled thermoplastic resin particles, for example, a polymer of (meth) acrylonitrile and a copolymer having a high (meth) acrylonitrile content are preferably used. As the other monomer (comonomer) of the copolymer, a monomer such as vinyl halide, vinylidene halide, styrene monomer, (meth) acrylate monomer, vinyl acetate, butadiene, vinylpyridine, chloroprene, or the like is used. The thermoplastic resin is divinylbenzene, ethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, allyl. It may be made crosslinkable with a crosslinking agent such as (meth) acrylate, triacryl formal, triallyl isocyanurate or the like. The crosslinked form is preferably uncrosslinked, but may be partially crosslinked so as not to impair the properties as a thermoplastic resin.
Examples of the liquid that is vaporized by the heat contained in the thermally expandable microcapsule to generate a gas include hydrocarbons such as n-pentane, isopentane, neopentane, butane, isobutane, hexane, petroleum ether, methyl chloride, Examples thereof include chlorinated hydrocarbons such as methylene chloride, dichloroethylene, trichloroethane, and trichloroethylene.
Expandable graphite is a powder material having a particle size of 30 to 600 μm, preferably 100 to 350 μm, which encloses a material that is vaporized by heat between the layers of graphite particles, and expands due to heat during vulcanization to expand the graphite ( Expanded Graphite) is preferred.
The expanded graphite is a known material, and its production method is also known. For example, commercially available products such as “Graph Guard 160-50” or “Graph Guard 160-80” manufactured by UCAR Graphtech of the United States from Sakai Industries. Is available.

(Other fillers)
In the present invention, various fillers can be blended in addition to the reinforcing filler. Such a filler is not particularly limited and may be appropriately selected depending on the application. Examples thereof include inorganic fillers such as clay, talc, and calcium carbonate.

(Rubber composition ratio)
The rubber composition of the present invention has 5 to 50 parts by mass of an ester plasticizer having a saturated cyclic structure composed of the above formula (I) with respect to 100 parts by mass of a diene rubber having a glass transition temperature of −50 ° C. or less. It is characterized by comprising 10 to 120 parts by mass of a reinforcing filler containing 10 to 80 parts by mass of silica.
When the blending amount of the ester plasticizer is less than 5 parts by mass, the addition amount is too small to achieve the effects of the present invention. On the other hand, when it exceeds 50 parts by mass, the mixing property deteriorates.
When the amount of silica is less than 10 parts by mass, the amount of addition is too small to achieve the effects of the present invention. Conversely, when it exceeds 80 mass parts, mixing property and workability will deteriorate.
In addition, when the compounding amount of the reinforcing filler exceeds 120 parts by mass, the mixing property and workability deteriorate.

Furthermore, the compounding quantity of the said ester plasticizer is 5-35 mass parts with respect to 100 mass parts of diene rubbers.
A more preferable blending amount of the silica is 20 to 80 parts by mass with respect to 100 parts by mass of the diene rubber.
Further preferable blending amount of the reinforcing filler is 100 parts by mass of the diene rubber.
20 to 90 parts by mass.

  In the rubber composition of the present invention, in addition to the above-described components, various additives generally blended in the rubber composition such as a vulcanization or crosslinking agent, a vulcanization or crosslinking accelerator, various oils, and an antioxidant. An additive can be blended, and such an additive can be kneaded by a general method to form a composition, which can be used for vulcanization or crosslinking. The blending amounts of these additives can be set to conventional general blending amounts as long as the object of the present invention is not violated.

  The rubber composition of the present invention can be used to produce a pneumatic tire according to a conventional method for producing a pneumatic tire.

  EXAMPLES Hereinafter, although an Example and a comparative example further demonstrate this invention, this invention is not restrict | limited to the following example.

Examples 1-2 and Comparative Examples 1-2
Preparation of sample In the composition (parts by mass) shown in Table 1, ingredients other than the vulcanization accelerator, sulfur, thermally expandable microcapsules and expanded graphite were kneaded for 3 to 5 minutes with a 1.8 liter closed mixer, and the temperature Was released to obtain a master batch. A vulcanization accelerator, sulfur, thermally expandable microcapsules, and expanded graphite were kneaded with this masterbatch with an 8-inch open roll to obtain a rubber composition. Next, the obtained unvulcanized rubber composition was press vulcanized at 160 ° C. for 20 minutes in a 15 × 15 × 0.2 cm mold to prepare a vulcanized rubber sheet (test sample). The physical properties of vulcanized rubber were measured by the method.

Hardness: Measured at a temperature of −10 ° C. or 20 ° C. with a durometer type A according to JIS K6253. Further, the hardness at −10 ° C. after the test sample was aged at 70 ° C. for 96 hours was also measured. The results are shown as an index with the value of Comparative Example 1 being 100.
Aging resistance (breaking elongation after aging): A test sample was aged at 70 ° C. for 96 hours, and then subjected to a tensile test according to JIS K6251. The modulus for every 10% strain was recorded and the sum of these values was compared with the test sample before aging. The results are shown as an index with the rate of decrease in breaking elongation measured in Comparative Example 1 as 100. The larger the index, the smaller the rate of decrease in breaking elongation.
The results are also shown in Table 1.

Examples 3 to 4 and Comparative Example 3
This example and a comparative example are examples in which the rubber compounding system is changed as shown in Table 2 (part by mass).
Using the test samples prepared by the same method as in Examples 1 and 2, the physical properties were measured by the following test methods.
Expansion coefficient: The specific gravity of the test sample measured according to JIS K2249 was divided by the calculated specific gravity (theoretical value) obtained from the specific gravity and the blending amount of each compounding agent, and the difference from 1.0 was defined as the expansion coefficient. The results are shown as an index with Comparative Example 3 as 100.
Performance on ice: The test sample was attached to a flat cylindrical base rubber and measured using an inside drum type on-ice friction tester at a measurement temperature of -1.5 ° C, a load of 0.54 MPa, and a drum rotation speed of 25 km / h. The value of Comparative Example 3 was taken as 100 and indicated as an index. Larger values indicate better performance on ice. In addition, about the sample after aging the test sample at 70 degreeC for 96 hours, said test was conducted as performance on aging ice.
Wet performance: Tires using the above test samples as treads are mounted on four wheels of a passenger car, run on a flooded asphalt road surface at an initial speed of 40 km / h, and the braking distance when braking is measured. The index is shown as 100. The larger the value, the better the braking performance.
Rolling resistance: tan δ (60 ° C.) under the conditions of initial strain = 10%, amplitude = ± 2%, frequency = 20 Hz, using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho, in accordance with JIS K6394 The rolling resistance was evaluated with this value. The results are shown as an index with Comparative Example 3 as 100. A lower index indicates better rolling resistance.
The results are also shown in Table 2.

* 1: NR (RSS # 3 Tg = -65 ° C)
* 2: BR (Nipol BR1220 Tg = -107 ° C manufactured by Nippon Zeon Co., Ltd.)
* 3: Carbon black (Showa Black N330 manufactured by Cabot Japan Co., Ltd.)
* 4: Silica (Zeosil 1165MP manufactured by Rhodia, BET specific surface area = 160 m ² / g)
* 5: Silane coupling agent (KBE845 manufactured by Shin-Etsu Chemical Co., Ltd.)
* 6: Zinc flower (3 types of zinc oxide, manufactured by Shodo Chemical Industry Co., Ltd.)
* 7: Stearic acid (beef stearic acid manufactured by NOF Corporation)
* 8: Anti-aging agent (SANTOFLEX 6PPD manufactured by FLEXSYS)
* 9: Wax (Sannok manufactured by Ouchi Shinsei Chemical Co., Ltd.)
* 10: Aroma oil (Aroma 4 from Showa Shell Sekiyu KK)
* 11: Paraffin oil (Process oil 123 manufactured by Showa Shell Sekiyu KK)
* 12: Ester plasticizer (Hexamol Dinch manufactured by BASF, ester plasticizer having a saturated cyclic structure represented by the following formula)

* 13: Sulfur (Hosoi Chemical Co., Ltd., oil-treated sulfur)
* 14: Vulcanization accelerator (NS-P manufactured by Ouchi Shinsei Chemical Co., Ltd.)
* 15: Thermally expandable microcapsules (Matsumoto Yushi Seiyaku Matsumoto Microsphere F100)
* 16: Expanded graphite (Graph Guard 160-50 manufactured by UCAR Graphtech)

As is clear from Table 1 above, the rubber compositions prepared in Examples 1 and 2 contain a specific amount of a specific ester plasticizer and a specific amount of a reinforcing filler containing silica. It can be seen that the hardness at low temperature is lower than that of the conventional representative Comparative Example 1. This means that the frictional force against the road surface on ice is improved. In addition, it can be seen that the hardness at 20 ° C. is equal to or higher than that of Comparative Example 1, excellent wet performance without reducing the frictional force on the road surface on ice, and temperature dependency is also suppressed. It is also excellent in aging resistance.
On the other hand, Comparative Example 2 is an example in which the aroma oil used in Comparative Example 1 is changed to paraffin oil, which is considered to be excellent in low temperature characteristics, but since an ester plasticizer is not used, wet performance is improved. It does not improve and the aging resistance is not improved.

Further, as apparent from Table 2 above, the rubber compositions prepared in Examples 3 to 4 were formulated with a specific amount of a specific ester plasticizer and a specific amount of a reinforcing filler containing silica. Therefore, it can be seen that the performance on ice, the wet performance, the rolling resistance, and the aging resistance are all improved with respect to the conventional representative comparative example 3.
In Comparative Example 4, since the blending amount of the ester plasticizer exceeded the upper limit defined in the present invention, the wet performance and the rolling resistance were deteriorated.
In Comparative Example 5, the on-ice performance and rolling resistance deteriorated because the amount of silica exceeded the upper limit specified in the present invention.

1 Bead part 2 Side wall 3 Tread 4 Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 8 Rim cushion

Claims (3)

For 100 parts by mass of diene rubber having a glass transition temperature of −50 ° C. or lower,
5 to 50 parts by mass of an ester plasticizer having a saturated cyclic structure consisting of the following formula (I) ,
10 to 120 parts by mass of a reinforcing filler containing 10 to 80 parts by mass of silica , and
A rubber composition for a tire tread comprising 0.5 to 20 parts by mass of at least one selected from thermally expandable microcapsules and expanded graphite .

(In the formula, R ¹ and R ² are each independently an alkyl group having 2 to 18 carbon atoms, and may have a branched or cyclic structure .)   The rubber composition for a tire tread according to claim 1, wherein natural rubber accounts for 30 parts by mass or more in 100 parts by mass of the diene rubber. A pneumatic tire using the tire tread rubber composition according to claim 1 for a tire tread.

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