WO2016208537A1 - Rubber composition and pneumatic tire obtained using same - Google Patents

Abstract

The present invention addresses the problem of providing: a rubber composition that gives tires excellent in terms of low heat build-up property and comes to have a high hardness; and a pneumatic tire including a tire tread formed from the rubber composition. The rubber composition according to the present invention comprises a diene-based rubber, silica, and an acid-modified polyolefin having an average particle diameter less than 1,000 µm, the silica being contained in an amount of 1-150 parts by mass per 100 parts by mass of the diene-based rubber and the acid-modified polyolefin being contained in an amount of 1-30 parts by mass per 100 parts by mass of the diene-based rubber. [The average particle diameter is the opening size of a finest sieve through which 50% or more of the particles pass in a sieving method using sieves complying with JIS Z8801:2006.]

Description

Rubber composition and pneumatic tire using the same

The present invention relates to a rubber composition and a pneumatic tire using the same.

In recent years, there has been a demand for reducing tire rolling resistance in order to improve fuel efficiency during vehicle travel. Under these circumstances, silica is added to the “rubber composition containing a diene rubber” used in tire treads to reduce hysteresis loss (particularly tan δ at high temperatures), thereby reducing heat generation and tire rolling resistance. A method for reducing the above is known.
However, since silica has low affinity with diene rubbers and high cohesiveness between silicas, silica is not dispersed even if silica is simply blended with diene rubbers, reducing the rolling resistance of tires. There was a problem that could not be obtained sufficiently.
On the other hand, a technique for improving the dispersibility of silica (hereinafter, “silica dispersibility” is also simply referred to as “silica dispersibility”) by blending a silane coupling agent with silica is known. (For example, patent document 1). In Examples of Patent Document 1, bis (3-triethoxysilylpropyl) tetrasulfide (Si69: manufactured by Evonik Degussa) is used as a silane coupling agent ([0027]).

JP 2000-017107 A

Under such circumstances, the present inventor examined the rubber composition disclosed in Patent Document 1, and the tire obtained from such a rubber composition was improved in low heat build-up, but introduced a silane coupling agent. As a result, it has been found that the hardness tends to decrease. In other words, it has become clear that the hardness does not necessarily satisfy the level required recently.

Therefore, in view of the above circumstances, the present invention provides a rubber composition that is excellent in low heat buildup and high in hardness when made into a tire, and a pneumatic tire using the rubber composition in a tire tread. With the goal.

As a result of intensive studies on the above problems, the present inventors have found that the above problems can be solved by containing a specific amount of powdered acid-modified polyolefin having an average particle diameter of less than a specific value, and have reached the present invention.
That is, the present inventor has found that the above problem can be solved by the following configuration.

(1) containing a diene rubber, silica, and an acid-modified polyolefin having an average particle diameter of less than 1000 μm,
The content of the silica is 1 to 150 parts by mass with respect to 100 parts by mass of the diene rubber,
A rubber composition, wherein the content of the acid-modified polyolefin is 1 to 30 parts by mass with respect to 100 parts by mass of the diene rubber.
[In the sieving method using a sieve conforming to JIS Z8801: 2006, the minimum particle size at which the passing particles are 50% by mass or more is defined as the average particle size. ]
(2) The rubber composition according to (1), wherein the acid-modified polyolefin is a copolymer having two or more repeating units formed from a monomer selected from the group consisting of ethylene and α-olefin.
(3) The rubber composition according to (2), wherein the α-olefin is at least one selected from the group consisting of propylene, 1-butene and 1-octene.
(4) A pneumatic tire using the rubber composition according to any one of (1) to (3) as a tire tread.

According to the present invention, it is possible to provide a rubber composition that is excellent in low heat buildup and high in hardness when used as a tire, and a pneumatic tire using the rubber composition as a tire tread.

It is a typical fragmentary sectional view of the tire showing an example of the embodiment of the pneumatic tire of the present invention.

Below, the rubber composition of this invention and the pneumatic tire using the rubber composition of this invention are demonstrated.
In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

[Rubber composition]
The rubber composition of the present invention contains a diene rubber, silica, and an acid-modified polyolefin having an average particle size of less than 1000 μm.
In the present invention, the average particle diameter of the acid-modified polyolefin refers to the size of the minimum opening at which particles passing therethrough is 50% by mass or more in a sieving method using a sieve according to JIS Z8801: 2006.
The silica content is 1 to 150 parts by mass with respect to 100 parts by mass of the diene rubber, and the acid-modified polyolefin content is 1 to 30 parts by mass with respect to 100 parts by mass of the diene rubber. is there.
Since the rubber composition of the present invention has such a configuration, it is considered that a rubber composition having excellent low heat buildup and high hardness when formed into a tire could be formed.

This is not clear in detail, but is estimated to be as follows.
In other words, the acid-modified polyolefin has a mean particle size of less than 1000 μm and is made into a powder form by reducing the particle size, so that the incorporation of the acid-modified polyolefin into the rubber component is improved and the acid groups of the acid-modified polyolefin have an affinity with it. It is presumed that high hardness was obtained while excellent high low heat generation property (low rolling resistance) because high-silica silica was also more uniformly dispersed in the rubber component.
The above effect is particularly remarkable when acid-modified polyolefin is used as a copolymer, and high hardness can be obtained while being more excellent due to low exothermic property (low rolling resistance).
Below, each component which the rubber composition of this invention contains is demonstrated in detail.

[Diene rubber]
The diene rubber contained in the rubber composition of the present invention is not particularly limited as long as it has a double bond in the main chain. Specific examples thereof include natural rubber (NR), isoprene rubber (IR), butadiene. Rubber (BR), acrylonitrile-butadiene rubber (NBR), aromatic vinyl-conjugated diene copolymer rubber [for example, styrene-butadiene rubber (SBR), styrene-isoprene rubber, styrene-butadiene-isoprene rubber (SBIR), styrene- Isoprene rubber (SIR), styrene-isoprene-butadiene rubber (SIBR)] and the like. These may be used alone or in combination of two or more.
The diene rubber is a derivative in which the end or side chain of each rubber is modified (modified) with an amino group, an amide group, a silyl group, an alkoxy group, a carboxy group, a hydroxy group, an epoxy group, or the like. Also good.

In the present invention, it is preferable to contain 10% by mass or more of aromatic vinyl-conjugated diene copolymer rubber (especially SBR) as a diene rubber from the viewpoint of a balance between low heat build-up and wet grip performance.
Here, the weight average molecular weight of the aromatic vinyl-conjugated diene copolymer rubber is not particularly limited, but in addition to the above-mentioned viewpoint, it is preferably 900,000 to 2,000,000 from the viewpoint of abrasion resistance, More preferably, it is ˜1.8 million. The weight average molecular weight (Mw) is measured in terms of standard polystyrene by gel permeation chromatography (GPC) using tetrahydrofuran as a solvent.

In the present invention, the aromatic vinyl-conjugated diene copolymer rubber can further reduce the heat generation, and from the viewpoint of the balance between the low heat generation property and the wet grip performance, The content is preferably 100% by mass, more preferably 20 to 90% by mass.

In the present invention, the aromatic vinyl-conjugated diene copolymer rubber contains 20 to 50% by mass of aromatic vinyl from the viewpoint of a balance between low heat build-up and wet grip performance, and the amount of vinyl bonds in the conjugated diene. Is preferably contained in an amount of 10 to 65% by mass.

〔silica〕
The silica which the rubber composition of this invention contains is not specifically limited, The conventionally well-known arbitrary silica currently mix | blended with the rubber composition for uses, such as a tire, can be used.
Specific examples of the silica include fumed silica, calcined silica, precipitated silica, pulverized silica, fused silica, colloidal silica, and the like. These may be used alone or in combination of two or more. You may use together.

The silica preferably has a CTAB adsorption specific surface area of 50 to 300 m ² / g, more preferably 80 to 250 m ² / g, from the viewpoint of suppressing silica aggregation.
Here, the CTAB adsorption specific surface area was determined by measuring the amount of n-hexadecyltrimethylammonium bromide adsorbed on the silica surface in accordance with JIS K6217-3: 2001 “Part 3: Determination of specific surface area—CTAB adsorption method”. Value.

In the present invention, the content of the silica is 1 to 150 parts by weight, preferably 10 to 120 parts by weight, and preferably 20 to 100 parts by weight with respect to 100 parts by weight of the diene rubber. More preferred.

[Acid-modified polyolefin]
The acid-modified polyolefin contained in the rubber composition of the present invention is a modified polymer obtained by modifying a polyolefin with an unsaturated carboxylic acid having an average particle size of less than 1000 μm.
Here, in the present invention, the average particle size of the acid-modified polyolefin is the minimum opening size in which particles passing therethrough are 50% by mass or more in a sieving method using a sieve in accordance with JIS Z8801: 2006. Say.

In the present invention, the average particle diameter of the acid-modified polyolefin is preferably 800 μm or less, and more preferably 200 to 700 μm, from the reason that the hardness becomes better while making the low heat build-up good. Although a minimum in particular is not restrict | limited, It is preferable that it is 100 micrometers or more.

In the present invention, a polyolefin having at least one repeating unit formed from a monomer selected from the group consisting of ethylene and α-olefin is preferable from the viewpoint of excellent low heat build-up and excellent workability. Examples of the α-olefin include propylene, 1-butene and 1-octene. The polyolefin may be a homopolymer (homopolymer) or a copolymer having these repeating units.
In the present invention, from the viewpoint of being excellent in low exothermic property, it is preferably a copolymer having two or more repeating units formed from a monomer selected from the group consisting of ethylene and α-olefin, and at least ethylene It preferably contains a repeating unit formed from

(Polyolefin)
As the polyolefin constituting the skeleton of the acid-modified polyolefin, for example,
Homopolymers such as polypropylene, polybutene, polyoctene;
Propylene / ethylene copolymer, propylene / 1-butene copolymer, propylene / 1-hexene copolymer, propylene / 4-methyl-1-pentene copolymer, propylene / 1-octene copolymer, propylene / 1 -Decene copolymer, propylene / 1,4-hexadiene copolymer, propylene / dicyclopentadiene copolymer, propylene / 5-ethylidene-2-norbornene copolymer, propylene / 2,5-norbornadiene copolymer, Propylene / 5-ethylidene-2-norbornene copolymer, 1-octene / ethylene copolymer, 1-butene / ethylene copolymer, 1-butene / propylene copolymer, 1-butene / 1-hexene copolymer 1-butene / 4-methyl-1-pentene copolymer, 1-butene / 1-octene copolymer, 1-butene -Decene copolymer, 1-butene / 1,4-hexadiene copolymer, 1-butene / dicyclopentadiene copolymer, 1-butene / 5-ethylidene-2-norbornene copolymer, 1-butene / 2 Two-component copolymers such as 5-norbornadiene copolymer and 1-butene / 5-ethylidene-2-norbornene copolymer;
Ethylene / propylene / 1-butene copolymer, ethylene / propylene / 1-hexene copolymer, ethylene / propylene / 1-octene copolymer, ethylene / propylene / 1-octene copolymer, ethylene / propylene / 1, 4-hexadiene copolymer, ethylene / propylene / 1,4-hexadiene copolymer, ethylene / propylene / dicyclopentadiene copolymer, ethylene / propylene / dicyclopentadiene copolymer, ethylene / propylene / 5-ethylidene 2-norbornene copolymer, ethylene / propylene / 5-ethylidene-2-norbornene copolymer, ethylene / propylene / 2, 5-norbornadiene copolymer, ethylene / propylene / 2, 5-norbornadiene copolymer, ethylene / propylene Propylene 5-ethylidene-2-no Borene copolymer, ethylene / propylene / 5-ethylidene-2-norbornene copolymer, 1-butene / ethylene / propylene copolymer, 1-butene / ethylene / 1-hexene copolymer, 1-butene / ethylene / copolymer 1-octene copolymer, 1-butene / propylene / 1-octene copolymer, 1-butene / ethylene / 1,4-hexadiene copolymer, 1-butene / propylene / 1,4-hexadiene copolymer, 1-butene / ethylene / dicyclopentadiene copolymer, 1-butene / propylene / dicyclopentadiene copolymer, 1-butene / ethylene / 5-ethylidene-2-norbornene copolymer, 1-butene / propylene / 5 -Ethylidene-2-norbornene copolymer, 1-butene / ethylene / 2,5-norbornadiene copolymer, 1-butene・ Multi-components such as propylene / 2,5-norbornadiene copolymer, 1-butene / ethylene / 5-ethylidene-2-norbornene copolymer, 1-butene / propylene / 5-ethylidene-2-norbornene copolymer And the like.

Among these, polypropylene, polybutene, polyoctene, propylene / ethylene copolymer, 1-butene / ethylene copolymer, 1-butene / propylene copolymer, ethylene / propylene / 1-butene copolymer, 1-octene / It is preferable to use an ethylene copolymer.

(Unsaturated carboxylic acid)
On the other hand, examples of the unsaturated carboxylic acid that modifies the above-described polyolefin include maleic acid, fumaric acid, acrylic acid, crotonic acid, methacrylic acid, itaconic acid, or acid anhydrides of these acids. .
Of these, maleic anhydride, maleic acid, and acrylic acid are preferably used, and maleic anhydride is more preferable.

The acid modification amount (% by mass) in the acid-modified polyolefin is not particularly limited, but is usually 0.1 to 10% by mass, preferably 0.2 to 5% by mass.

The acid-modified polyolefin may be produced by a usual method, for example, a method for graft polymerization of an unsaturated carboxylic acid to the polyolefin under the usual conditions, for example, stirring under heating, or a commercially available product. May be used.
Examples of commercially available products include maleic anhydride-modified propylene / ethylene copolymers such as Tuffmer MA8510 (manufactured by Mitsui Chemicals) and MP0620 (manufactured by Mitsui Chemicals); maleic anhydride modified such as Tuffmer MH7020 (manufactured by Mitsui Chemicals) And ethylene 1-butene copolymer; maleic anhydride-modified polypropylene such as Admer QE060 (manufactured by Mitsui Chemicals); and maleic anhydride-modified polyethylene such as Modic H511 (manufactured by Mitsubishi Chemical).

In the present invention, the content of the acid-modified polyolefin is 1 to 30 parts by weight, preferably 1 to 25 parts by weight, based on 100 parts by weight of the diene rubber, and 3 to 20 parts by weight. Is more preferable.

〔Silane coupling agent〕
The rubber composition of the present invention may contain a silane coupling agent.
The said silane coupling agent is not specifically limited, The conventionally well-known arbitrary silane coupling agents currently mix | blended with the rubber composition for uses, such as a tire, can be used.
Specific examples of the silane coupling agent include bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, Bis (2-triethoxysilylethyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxy Silane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N, N- Methylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropyl Methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis (3-diethoxymethylsilylpropyl) tetrasulfide, dimethoxymethylsilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, dimethoxymethylsilylpropylbenzothiazole tetrasulfide These may be used, and these may be used alone or in combination of two or more. Moreover, you may use what made these 1 type, or 2 or more types oligomerize beforehand.

Specific examples of the silane coupling agent other than the above include γ-mercaptopropyltriethoxysilane, 3- [ethoxybis (3,6,9,12,15-pentaoxaoctacosan-1-yloxy), and the like. ) Silyl] -1-propanethiol and other mercapto silane coupling agents; 3-octanoylthiopropyltriethoxysilane and other thiocarboxylate silane coupling agents; 3-thiocyanate propyltriethoxysilane and other thiocyanate silane cups Ring agents; and the like. These may be used alone or in combination of two or more. Moreover, you may use what made these 1 type, or 2 or more types oligomerize beforehand.

Of these, bis- (3-triethoxysilylpropyl) tetrasulfide and / or bis- (3-triethoxysilylpropyl) disulfide is preferably used from the viewpoint of reinforcing effect. Specifically, For example, Si69 [bis- (3-triethoxysilylpropyl) tetrasulfide; manufactured by Evonik Degussa], Si75 [bis- (3-triethoxysilylpropyl) disulfide; manufactured by Evonik Degussa] and the like can be mentioned.

When the silane coupling agent is contained, the content thereof is preferably 1 part by mass or more and more preferably 1 to 10 parts by mass with respect to 100 parts by mass of the diene rubber.
In addition, the content of the silane coupling agent is preferably 0.1 to 20 parts by mass, and more preferably 0.5 to 15 parts by mass with respect to 100 parts by mass of the silica.

〔Carbon black〕
The rubber composition of the present invention preferably contains carbon black.
Specific examples of the carbon black include furnace carbon blacks such as SAF, ISAF, HAF, FEF, GPE, and SRF. These may be used alone or in combination of two or more. May be.
The carbon black preferably has a nitrogen adsorption specific surface area (N ₂ SA) of 10 to 300 m ² / g, preferably 20 to 200 m ² / g, from the viewpoint of processability when mixing the rubber composition. More preferably.
Here, N ₂ SA is a value obtained by measuring the amount of nitrogen adsorbed on the carbon black surface according to JIS K 6217-2: 2001 “Part 2: Determination of specific surface area—nitrogen adsorption method—single point method”. .

When the carbon black is contained, the content is preferably 1 to 100 parts by mass, and more preferably 5 to 80 parts by mass with respect to 100 parts by mass of the diene rubber.

[Other ingredients]
In addition to the components described above, the rubber composition of the present invention comprises a filler such as calcium carbonate; a chemical foaming agent such as a hollow polymer; a vulcanizing agent such as sulfur; a sulfenamide-based, guanidine-based, thiazole-based, thiourea-based, and thiuram. Vulcanization accelerators such as zinc oxide, vulcanization accelerators such as stearic acid, waxes, aroma oils, paraphenylenediamines (for example, N, N'-di-2-naphthyl-p-phenylenediamine, N 1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine, etc.) and ketone-amine condensates (eg 2,2,4-trimethyl-1,2-dihydroquinoline, etc.) Various other additives generally used in rubber compositions for tires such as an agent; a plasticizer; and the like can be blended.
As long as the amount of these additives is not contrary to the object of the present invention, a conventional general amount can be used. For example, with respect to 100 parts by mass of diene rubber, 0.5 to 5 parts by mass of sulfur, 0.1 to 5 parts by mass of vulcanization accelerator, 0.1 to 10 parts by mass of vulcanization accelerator, The inhibitor may be added in an amount of 0.5 to 5 parts by mass, the wax 1 to 10 parts by mass, and the aroma oil 5 to 30 parts by mass.

[Method for producing rubber composition]
The method for producing the rubber composition of the present invention is not particularly limited, and examples thereof include a method of kneading the above-described components using a known method and apparatus (for example, a Banbury mixer, a kneader, a roll, etc.). It is done. When the rubber composition of the present invention contains sulfur or a vulcanization accelerator, components other than sulfur and the vulcanization accelerator are first mixed at a high temperature and cooled, and then the sulfur or vulcanization accelerator is mixed. Is preferred.
In the present invention, since the acid-modified polyolefin is in the form of a powder having an average particle size of less than 1000 μm, heating is performed at a temperature equal to or higher than the melting point of the acid-modified polyolefin that is normally required when mixing and kneading each component. There is no need. As with other additive components, the powdery acid-modified polyolefin can be incorporated into the rubber component due to the heat history when kneading the diene rubber and silica. In the present invention, since the acid-modified polyolefin is in the form of a powder having an average particle diameter of less than 1000 μm, the components can be mixed and the acid-modified polyolefin can be mixed later.
The rubber composition of the present invention can be vulcanized or crosslinked under conventionally known vulcanization or crosslinking conditions.

[Pneumatic tire]
The pneumatic tire of the present invention (hereinafter also simply referred to as “the tire of the present invention”) is a pneumatic tire using the above-described rubber composition of the present invention as a constituent (rubber) member.
Here, the constituent member using the rubber composition of the present invention is not particularly limited, and examples thereof include a tire tread portion, a sidewall portion, a bead portion, a belt layer covering, a carcass layer covering, an inner liner, etc. The tire tread portion is preferable.
FIG. 1 shows a schematic partial cross-sectional view of a tire representing an example of an embodiment of the tire of the present invention, but the tire of the present invention is not limited to the embodiment shown in FIG.

In FIG. 1, the code | symbol 1 represents a bead part, the code | symbol 2 represents a sidewall part, and the code | symbol 3 represents the tread part comprised from the rubber composition of this invention.
Further, a carcass layer 4 in which fiber cords are embedded is mounted between the pair of left and right bead portions 1, and the end of the carcass layer 4 extends from the inside of the tire to the outside around the bead core 5 and the bead filler 6. Wrapped and rolled up.
In the tire tread 3, a belt layer 7 is disposed over the circumference of the tire on the outside of the carcass layer 4.
Moreover, in the bead part 1, the rim cushion 8 is arrange | positioned in the part which touches a rim | limb.
Further, an inner liner 9 is disposed on the inner surface of the tire in order to prevent air filled in the tire from leaking outside the tire.

For example, when the rubber composition of the present invention is used in a tire tread portion, the tire of the present invention can achieve both excellent low heat generation and hardness, and is excellent in steering stability.
In addition, the tire of the present invention is vulcanized or cured at a temperature corresponding to, for example, the type of diene rubber, vulcanization or crosslinking agent, vulcanization or crosslinking accelerator used in the rubber composition of the present invention, and the blending ratio thereof. It can manufacture by bridge | crosslinking and forming a tire tread part.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these.

<Preparation of acid-modified polyolefins 1-3>
Pulverized acid-modified polyolefin 4 (Tuffmer MH7020 (commercial product), manufactured by Mitsui Chemicals, Inc.) having an average particle diameter of 2000 μm is pulverized using a pulverizer, whereby powdered acid-modified polyolefin 1 to 3 were prepared respectively.
The average particle diameters of the acid-modified polyolefins 1 to 3 were 300 μm, 500 μm, and 800 μm, respectively. The method for obtaining the average particle size is as described above.

<Examples 1 to 4 and Comparative Examples 1 and 2: Production of Rubber Composition>
The components shown in the following table were blended in the proportions (parts by mass) shown in the table.
Specifically, first of all the components shown in the table below, excluding sulfur and vulcanization accelerator, are kneaded for 5 minutes using a 1.7 liter closed Banbury mixer and then cooled to room temperature. A master batch was obtained. Furthermore, using an open roll, sulfur and a vulcanization accelerator were mixed and kneaded into the obtained master batch to obtain a rubber composition.

<Manufacture of vulcanized rubber>
The rubber composition (unvulcanized) produced as described above was press vulcanized at 160 ° C. for 20 minutes in a mold (15 cm × 15 cm × 0.2 cm) to produce a vulcanized rubber sheet.
The physical properties of the obtained vulcanized rubber sheet were evaluated by the following test methods.

<Hardness>
The produced vulcanized rubber sheet was evaluated by measuring the durometer hardness (type A) at 20 ° C. according to JIS K6253-3: 2012.
The measurement results are represented by an index with the value of Comparative Example 1 being 100, and are shown in Table 1 below. It means that it is excellent in hardness, so that this index | exponent is large.

<Low exothermic property (tan δ (60 ° C.))>
Using the viscoelastic spectrometer (manufactured by Iwamoto Seisakusho Co., Ltd.), the loss tangent tan δ (60 ° C.) was measured for the prepared vulcanized rubber sheet under the conditions of an elongation deformation strain rate of 10 ± 2%, a frequency of 20 Hz, and a temperature of 60 ° C. The low exothermic property (rolling resistance) was evaluated by measuring.
The measurement results are represented by an index with the value of Comparative Example 1 being 100, and are shown in Table 1 below. It means that it is excellent in low exothermic property, so that this index | exponent is small.

Each component shown in Table 1 is as follows.
S-SBR: solution polymerized styrene butadiene rubber, vinyl content 70% by weight, non-oil-extended product (Nipol NS116, manufactured by Nippon Zeon Co., Ltd.)
-BR: Nipol BR 1220 (manufactured by Nippon Zeon)
Acid-modified polyolefin prepared above 1: Maleic anhydride-modified ethylene / 1-butene copolymer, average particle size 300 μm (Tuffmer MH7020, manufactured by Mitsui Chemicals)
Acid-modified polyolefin 2 prepared above: Maleic anhydride-modified ethylene / 1-butene copolymer, average particle size 500 μm (Tuffmer MH7020, manufactured by Mitsui Chemicals)
Acid-modified polyolefin 3 prepared above: Maleic anhydride-modified ethylene / 1-butene copolymer, average particle size 800 μm (Tuffmer MH7020, manufactured by Mitsui Chemicals)
Acid-modified polyolefin 4: Maleic anhydride-modified ethylene / 1-butene copolymer, average particle size 2000 μm (Tuffmer MH7020, manufactured by Mitsui Chemicals)
Acid-modified polyolefin 5: acid-modified polyethylene, average particle size 500 μm (Modic H511, manufactured by Mitsubishi Chemical Corporation)
Silane coupling agent: Si69 (Evonik Degussa)
Silica: wet silica (nip seal AQ, CTAB adsorption specific surface area 170 m ² / g, manufactured by Nippon Silica)
・ Carbon black: Show black N339M (manufactured by Showa Cabot)
・ Zinc oxide: 3 kinds of zinc white (made by Shodo Chemical Industry Co., Ltd.)
・ Stearic acid: Beads stearic acid (manufactured by NOF Corporation)
Anti-aging agent: N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine (Antigen 6C, manufactured by Sumitomo Chemical Co., Ltd.)
・ Oil: Extract No. 4 S (made by Showa Shell Sekiyu KK)
・ Sulfur: Oil-treated sulfur (manufactured by Karuizawa Refinery)
・ Sulfur-containing vulcanization accelerator (CZ): N-cyclohexyl-2-benzothiazole sulfenamide (Sunceller CM-PO, manufactured by Sanshin Chemical Industry Co., Ltd.)
・ Vulcanization accelerator (DPG): 1,3-diphenylguanidine (Sunceller DG, manufactured by Sanshin Chemical Industry Co., Ltd.)

As can be seen from Table 1, from the comparison between Comparative Examples 1 and 2 and Examples 1 to 4, Comparative Example 1 in which no acid-modified polyolefin is used and Comparative Example 2 in which an acid-modified polyolefin having an average particle size of 1000 μm or more is used. In comparison, it was confirmed that Examples 1 to 4 using acid-modified polyolefin having an average particle size of less than 1000 μm showed high hardness.
Further, in comparison with Examples 1 to 3 and Example 4, Examples 1 to 3 using an olefin copolymer are more preferable than Example 4 using a homopolymer as the acid-modified polyolefin. However, it was confirmed that a further excellent low heat generation can be achieved.

DESCRIPTION OF SYMBOLS 1 Bead part 2 Side wall part 3 Tire tread part 4 Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 8 Rim cushion 9 Inner liner

Claims (4)

Containing a diene rubber, silica, and an acid-modified polyolefin having an average particle size of less than 1000 μm,
The silica content is 1 to 150 parts by mass with respect to 100 parts by mass of the diene rubber,
A rubber composition, wherein the content of the acid-modified polyolefin is 1 to 30 parts by mass with respect to 100 parts by mass of the diene rubber.
[In the sieving method using a sieve conforming to JIS Z8801: 2006, the minimum particle size at which the passing particles are 50% by mass or more is defined as the average particle size. ] 2. The rubber composition according to claim 1, wherein the acid-modified polyolefin is a copolymer having two or more repeating units formed from a monomer selected from the group consisting of ethylene and α-olefin. The rubber composition according to claim 2, wherein the α-olefin is at least one selected from the group consisting of propylene, 1-butene and 1-octene. A pneumatic tire using the rubber composition according to any one of claims 1 to 3 for a tire tread.

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