JP7535840B2 - Rubber composition and tire - Google Patents

Description

The present invention relates to a rubber composition and a tire.

In recent years, awareness of safety has been increasing as a common issue for automobiles, and further improvements in wet grip performance are required. Various research has been conducted to improve wet grip performance, and many inventions of rubber compositions containing silica have been reported (for example, Patent Document 1). Since wet grip performance is greatly affected by the performance of the rubber composition, particularly in the tread portion that comes into contact with the road surface, technical improvements to rubber compositions for tires, such as treads, have been widely studied and put into practical use.

JP 2008-285524 A

As a result of intensive research by the present inventors, it was found that while significant progress has been made in the wet grip performance of tires due to technical improvements in rubber compositions for treads that use silica, the change in grip performance when the road surface changes, for example, from a dry road surface to a wet road surface, or from a wet road surface to a dry road surface, remains an important technical issue and there is room for improvement.
As a result of extensive research by the inventors on this point, it was found that conventional rubber has the property of not changing its volume when it changes from a dry state (not wet with water) to a so-called wet state (when wet with water), and therefore does not provide sufficient drainage performance on wet road surfaces, and as a result, wet grip performance tends to be inferior to dry grip performance.
Furthermore, as a result of extensive research by the present inventors, it was found that one method for improving wet grip performance is to soften the rubber by blending a softener such as oil, but softening the rubber has the disadvantage that fuel economy deteriorates.
As described above, it has become clear that there is room for improvement in the conventional technology in terms of improving the overall performance of wet grip performance, dry grip performance, and fuel economy.
An object of the present invention is to provide a rubber composition and a tire which can solve the above problems and improve the overall performance of wet grip performance, dry grip performance, and fuel economy.

The present invention relates to a rubber composition that undergoes a reversible volume change due to water and satisfies the following formulas (1) and (2).
Volume when wet/Volume when dry>1.00 (1)
(In the formula, the volume is the volume of the rubber composition at 25° C.)
tan δ at 70°C when dry < 0.14 (2)
(In the formula, tan δ at 70° C. is the loss tangent measured under the conditions of 70° C., initial strain of 10%, dynamic strain of 2%, and frequency of 10 Hz.)

In the above formula (1), it is preferable that the volume when wet with water/volume when dry is 1.03 or more, more preferably 1.06 or more, and even more preferably 1.10 or more.

In the above formula (2), tan δ at 70°C when dry is preferably 0.13 or less, more preferably 0.12 or less, and even more preferably 0.11 or less.

The rubber composition preferably contains a diene rubber and a polymer having a carbon-carbon double bond and a heteroatom.

It is preferable that the heteroatom is at least one atom selected from the group consisting of an oxygen atom, a nitrogen atom, a silicon atom, a sulfur atom, a phosphorus atom, and a halogen atom.

It is preferable that the insoluble matter of the above polymer is 5% by mass or more when 1 g is suspended in 10 mL of water.

It is preferable that the insoluble matter of the above polymer is 5% by mass or more when 1 g is suspended in 10 mL of tetrahydrofuran.

The rubber composition preferably contains 5 parts by mass or more of the above polymer per 100 parts by mass of the rubber component.

The rubber composition preferably contains isoprene-based rubber.

The rubber composition preferably contains butadiene rubber.

The rubber composition preferably contains 95% by mass or less of styrene butadiene rubber in 100% by mass of the rubber component.

The rubber composition is preferably a rubber composition for treads.

The present invention also relates to a tire having tire components at least partially composed of the above rubber composition.

It is preferable that the tire components are the components that are located on the outermost surface when new or during operation.

It is preferable that the tire component is a tread.

The present invention provides a rubber composition that reversibly changes volume in response to water and satisfies the above formulas (1) and (2), improving the overall performance of wet grip performance, dry grip performance, and fuel economy.

The rubber composition of the present invention reversibly changes in volume in response to water and satisfies the following formulas (1) and (2), thereby improving the overall performance of wet grip performance, dry grip performance, and fuel economy.
Volume when wet/Volume when dry>1.00 (1)
(In the formula, the volume is the volume of the rubber composition at 25° C.)
tan δ at 70°C when dry < 0.14 (2)
(In the formula, tan δ at 70° C. is the loss tangent measured under the conditions of 70° C., initial strain of 10%, dynamic strain of 2%, and frequency of 10 Hz.)

The above-mentioned rubber composition provides the above-mentioned effects, and although the reason why such effects are obtained is not entirely clear, it is presumed to be as follows.
On dry roads, shallower tire grooves are desirable in order to increase the contact area between the road surface and the tire surface, while on wet roads, deeper tire grooves are desirable in order to expel water that is between the road surface and the tire surface.
Furthermore, because the volume of rubber used in conventional tires does not change whether water is present or not, tire grooves remain constant regardless of road surface conditions. The inventors' research has revealed that this makes it difficult to achieve both wet grip performance and dry grip performance in a tire.
On the other hand, the rubber composition of the present invention reversibly changes in volume due to water and satisfies the above formula (1). Here, the above formula (1) means that the volume when wetted with water is larger than the volume when dry. That is, the rubber composition of the present invention reversibly changes in volume due to water and satisfies the above formula (1), which means that the volume when wetted with water is larger than the volume when dry, and the volume changes reversibly in the presence of water.
Therefore, when the road surface changes from dry to wet, the rubber composition is wetted with water and the volume of the rubber composition increases, the tire grooves become deeper, and good grip performance (wet grip performance) is obtained.
On the other hand, when the road surface changes from wet to dry, the rubber composition moistened with water dries and the volume of the rubber composition decreases, the tire grooves become shallower, and good grip performance (dry grip performance) is obtained.
In this way, the volume changes reversibly with water and the above formula (1) is satisfied, so that an appropriate groove depth can be obtained according to the water condition on the road surface (wet road surface, dry road surface). This makes it possible to achieve both the contact area on dry road surfaces and the drainage performance on wet road surfaces, thereby improving the overall wet grip performance and dry grip performance.
Furthermore, the rubber composition of the present invention can improve fuel economy by satisfying the above formula (2).
Therefore, the rubber composition of the present invention reversibly changes in volume due to water, and by satisfying the above formulas (1) and (2), the overall performance of wet grip performance, dry grip performance, and fuel economy can be improved.
In this specification, the volume, tan δ, of a rubber composition means the volume, tan δ, of a rubber composition after vulcanization. Also, tan δ is a value obtained by carrying out a viscoelasticity test on the rubber composition after vulcanization.

In this specification, "the volume changes reversibly due to water" means that the volume of the rubber composition (after vulcanization) reversibly increases or decreases due to the presence of water. For example, when the volume changes from dry to wet to dry, it is sufficient that the volume changes reversibly, and the volume does not have to be the same at the first dry time and the second dry time, or the volume may be the same at the first dry time and the second dry time.

In this specification, the term "dry volume" refers to the volume of a rubber composition (after vulcanization) in a dry state, and specifically refers to the volume of a rubber composition (after vulcanization) dried by the method described in the examples.
In this specification, the volume when wet with water means the volume of the rubber composition (after vulcanization) in a state wet with water, and specifically means the volume of the rubber composition (after vulcanization) wetted with water by the method described in the examples.

In this specification, the volume of the rubber composition (after vulcanization) means the volume calculated by the method described in the examples.

In this specification, tan δ at 70°C when dry means tan δ at 70°C of the rubber composition in a dry state (after vulcanization), specifically, tan δ at 70°C of the rubber composition (after vulcanization) dried by the method described in the examples.

In this specification, tan δ at 70°C of a rubber composition (after vulcanization) is the loss tangent measured under the conditions of 70°C, initial strain of 10%, dynamic strain of 2%, and frequency of 10 Hz.

As shown in the above formula (1), (volume when wet with water/volume when dry (volume of rubber composition (after vulcanization) when wet with water/volume of rubber composition (after vulcanization) when dry)) is more than 1.00, preferably 1.03 or more, more preferably 1.06 or more, even more preferably 1.10 or more, particularly preferably 1.16 or more, most preferably 1.23 or more, even more preferably 1.30 or more, even more preferably 1.36 or more, especially most preferably 1.40 or more, even more preferably 1.46 or more, even more preferably 1.53 or more, even more preferably 1.70 or more, and the upper limit is not particularly limited, but is preferably 3.00 or less, more preferably 2.80 or less, even more preferably 2.60 or less, especially preferably 2.40 or less, most preferably 2.20 or less, and even more preferably 2.00 or less. When it is within the above range, the effect can be obtained more suitably.

As shown in the above formula (2), tan δ at 70°C when dry (tan δ at 70°C of the rubber composition (after vulcanization) when dry) is less than 0.14, preferably 0.13 or less, more preferably 0.12 or less, and even more preferably 0.11 or less. There is no particular lower limit, but it is preferably 0.01 or more, more preferably 0.02 or more. When it is within the above range, the effect can be obtained more suitably.

The volume change of the rubber composition represented by the above formula (1) and the reversible volume change caused by water can be achieved by compounding a compound capable of forming reversible molecular bonds with water, such as hydrogen bonds and ionic bonds. More specifically, the volume change of the rubber composition represented by the above formula (1) and the reversible volume change caused by water can be achieved by using a rubber component containing a diene rubber in combination with a polymer having a carbon-carbon double bond and a heteroatom. This is because the heteroatom is capable of forming reversible molecular bonds with water, such as hydrogen bonds and ionic bonds, in the rubber composition, and the volume of the rubber composition increases when wet with water as a result of the formation of these molecular bonds.
Furthermore, by using the above-mentioned combination, the polymer is crosslinked to the rubber component by the carbon-carbon double bonds during vulcanization and is fixed to the rubber component, so that liberation of the polymer from the rubber component can be suppressed, precipitation of the polymer on the rubber surface can be suppressed, and deterioration of grip performance (wet grip performance, dry grip performance) can also be suppressed.

The tan δ at 70°C when dry can be adjusted by the type and amount of chemicals (particularly rubber components, fillers, softeners, sulfur, vulcanization accelerators, and silane coupling agents) compounded into the rubber composition. For example, the tan δ at 70°C tends to decrease when a softener that is highly compatible with the rubber components is used, when modified rubber is used, when silica is used as a filler, when oil as a plasticizer is reduced, when sulfur is increased, when the vulcanization accelerator is increased, or when the silane coupling agent is increased.

More specifically, by using a rubber component containing a diene rubber in combination with a polymer having a carbon-carbon double bond and a heteroatom, it is possible to achieve the volume change of the rubber composition represented by the above formula (1), a reversible volume change due to water, and it is also possible to adjust the tan δ at 70°C when dry to within the desired range.

As another means for achieving the volume change of the rubber composition represented by the above formula (1) and the reversible volume change due to water, a rubber component containing a diene rubber is used in combination with a polymer having a carbon-carbon double bond and a heteroatom. During vulcanization, the polymer is crosslinked to the rubber component by the carbon-carbon double bond and fixed to the rubber component, thereby preventing the polymer from being liberated from the rubber component, and the volume change of the rubber composition represented by the above formula (1) and the reversible volume change due to water can be achieved.
If the rubber composition does not have a carbon-carbon double bond, it may be liberated into water when it comes into contact with water, and a reversible volume change may not be obtained.

Another way to keep the tan δ at 70°C when dry within the above range is to use a rubber component containing a diene rubber in combination with a polymer having a carbon-carbon double bond and a heteroatom. This crosslinks the polymer to the rubber component via the carbon-carbon double bond during vulcanization, and fixes it to the rubber component. This prevents the polymer from being released from the rubber component, and reduces the tan δ at 70°C.

The following describes the chemicals that can be used.

The rubber component may be, for example, diene-based rubber such as isoprene-based rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), or butyl rubber (IIR). The rubber component may be used alone or in combination of two or more. Among these, diene-based rubber is preferred, with isoprene-based rubber, BR, and SBR being more preferred, and SBR being even more preferred. A combination of isoprene-based rubber and SBR, a combination of BR and SBR, or a combination of isoprene-based rubber, BR, and SBR is also preferred.

Here, the rubber component is preferably a rubber having a weight average molecular weight (Mw) of 150,000 or more, more preferably 350,000 or more. There is no particular upper limit for Mw, but it is preferably 4 million or less, more preferably 3 million or less.

The content of diene rubber in 100% by mass of the rubber component is preferably 20% by mass or more, more preferably 50% by mass or more, even more preferably 70% by mass or more, particularly preferably 80% by mass or more, and most preferably 90% by mass or more, and may be 100% by mass. When it is within the above range, the effect tends to be better obtained.

The SBR is not particularly limited, and for example, emulsion-polymerized SBR (E-SBR), solution-polymerized SBR (S-SBR), and other SBRs commonly used in the tire industry can be used. These may be used alone or in combination of two or more types.

The styrene content of SBR is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. Within the above range, the effect tends to be more favorably obtained.

The vinyl content of the SBR is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, particularly preferably 40% by mass or more, and most preferably 50% by mass or more, and is preferably 75% by mass or less, more preferably 65% by mass or less. If it is within the above range, the compatibility with the BR will be good, and the effect will tend to be more favorably obtained.

The SBR may be an unmodified SBR or a modified SBR.
The modified SBR may be any SBR having a functional group that interacts with a filler such as silica, and examples thereof include terminally modified SBR (terminally modified SBR having the above-mentioned functional group at the terminal) in which at least one terminal of SBR has been modified with a compound (modifying agent) having the above-mentioned functional group, main-chain modified SBR having the above-mentioned functional group in the main chain, main-chain terminal-modified SBR having the above-mentioned functional group in the main chain and at least one terminal (for example, main-chain terminal-modified SBR having the above-mentioned functional group in the main chain and at least one terminal modified with the above-mentioned modifier), and terminal-modified SBR modified (coupled) with a polyfunctional compound having two or more epoxy groups in the molecule and having a hydroxyl group or epoxy group introduced therein. These may be used alone or in combination of two or more types.

The functional groups include, for example, amino groups, amide groups, silyl groups, alkoxysilyl groups, isocyanate groups, imino groups, imidazole groups, urea groups, ether groups, carbonyl groups, oxycarbonyl groups, mercapto groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, thiocarbonyl groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, carboxyl groups, nitrile groups, pyridyl groups, alkoxy groups, hydroxyl groups, oxy groups, and epoxy groups. These functional groups may have a substituent. Among them, amino groups (preferably amino groups in which the hydrogen atoms of the amino groups are substituted with alkyl groups having 1 to 6 carbon atoms), alkoxy groups (preferably alkoxy groups having 1 to 6 carbon atoms), alkoxysilyl groups (preferably alkoxysilyl groups having 1 to 6 carbon atoms), and amide groups are preferred.

As SBR, for example, SBR manufactured and sold by Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Co., Ltd., etc. can be used.

The content of SBR in 100% by mass of the rubber component is preferably 20% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more, and is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less. Within the above range, the effect tends to be better obtained.

The BR is not particularly limited, and any BR commonly used in the tire industry can be used. These may be used alone or in combination of two or more types.

The cis content of BR is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 97% by mass or more. There is no particular upper limit, and it may be 100% by mass. When it is within the above range, the effect tends to be more favorably obtained.

BR may be either unmodified BR or modified BR. Modified BR includes modified BR into which the above-mentioned functional groups have been introduced. The preferred embodiments are the same as those of modified SBR.

For example, products from Ube Industries, Ltd., JSR Corporation, Asahi Kasei Corporation, Zeon Corporation, etc. can be used as BR.

The BR content in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, and is preferably 70% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. Within the above range, the effect tends to be more favorably obtained.

Isoprene-based rubbers include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, modified IR, etc. NR can be, for example, SIR20, RSS#3, TSR20, etc., which are common in the tire industry. IR is not particularly limited, and can be, for example, IR2200, etc., which are common in the tire industry. Modified NR can be, for example, deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), etc. Modified NR can be, for example, epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, etc. Modified IR can be, for example, epoxidized isoprene rubber, hydrogenated isoprene rubber, grafted isoprene rubber, etc. These can be used alone or in combination of two or more. Of these, NR is preferred.

The content of isoprene-based rubber in 100% by mass of the rubber component is preferably 3% by mass or more, more preferably 5% by mass or more, and is preferably 60% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less. Within the above range, the effect tends to be more favorably obtained.

In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) can be determined in terms of standard polystyrene based on measurements obtained using a gel permeation chromatograph (GPC) (GPC-8000 series, manufactured by Tosoh Corporation; detector: differential refractometer; column: TSKGEL SUPERMULTIPORE HZ-M, manufactured by Tosoh Corporation).
The cis content (amount of cis-1,4-bonded butadiene units) and the vinyl content (amount of 1,2-bonded butadiene units) can be measured by infrared absorption spectroscopy, and the styrene content can be measured by ¹ H-NMR measurement.

The rubber composition preferably contains a polymer having a carbon-carbon double bond and a heteroatom.

The carbon-carbon double bonds are necessary for crosslinking with diene rubber, and there is no particular limit to the number of carbon-carbon double bonds.

The heteroatom means an atom other than carbon and hydrogen atoms, and is not particularly limited as long as it can form a reversible molecular bond with water, such as a hydrogen bond or an ionic bond, but is preferably at least one atom selected from the group consisting of an oxygen atom, a nitrogen atom, a silicon atom, a sulfur atom, a phosphorus atom, and a halogen atom, more preferably an oxygen atom, a nitrogen atom, or a silicon atom, and even more preferably an oxygen atom. The heteroatom is preferably present in the main chain (skeleton) of the polymer, and more preferably in the repeating unit of the polymer.

Examples of structures and groups containing an oxygen atom include an ether group, an ester group, a carboxy group, a carbonyl group, an alkoxy group, a hydroxy group, etc. Among these, an ether group is preferable, and an oxyalkylene group is more preferable.
Examples of structures and groups containing a nitrogen atom include amino groups (primary amino groups, secondary amino groups, tertiary amino groups), amide groups, nitrile groups, nitro groups, etc. Among these, amino groups are preferred, and tertiary amino groups are more preferred.
Examples of structures and groups containing silicon atoms include silyl groups, alkoxysilyl groups, silanol groups, etc. Among these, silyl groups are preferred, and alkoxysilyl groups are more preferred.
Examples of the structure or group containing a sulfur atom include a sulfide group, a sulfate group, a sulfate ester, and a sulfo group.
Examples of structures and groups containing a phosphorus atom include a phosphate group and a phosphate ester.
Examples of structures and groups containing a halogen atom include halogeno groups such as a fluoro group, a chloro group, a bromo group, and an iodo group.

The oxyalkylene group is a group represented by -(AO)-, and is preferably a group represented by -(AO) _n - (n is the number of repeating units).
The number of carbon atoms in the alkylene group A in the oxyalkylene group AO is preferably 1 or more, more preferably 2 or more, and is preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. When it is within the above range, the effect tends to be more suitably obtained.

The alkylene group A in the oxyalkylene group AO may be either linear or branched, but is preferably branched since this results in a bulkier structure and the effect can be more suitably obtained.
For reasons in which the effect can be more suitably obtained, AO is preferably an oxyalkylene group having 2 to 3 carbon atoms (oxyethylene group (EO), oxypropylene group (PO)) or a group in which a branched chain R ⁴ (R ⁴ represents a hydrocarbon group which may have a heteroatom) is bonded to an oxyalkylene group having 2 to 3 carbon atoms, and it is more preferable to use an oxyalkylene group having 2 to 3 carbon atoms or a group in which a branched chain R ⁴ is bonded to an oxyalkylene group having 2 to 3 carbon atoms in combination. The branched chain R ⁴ is preferably bonded to a carbon atom adjacent to an oxygen atom.

The hydrocarbon group which may have a heteroatom of ^R4 is not particularly limited. The number of carbon atoms in the hydrocarbon group is preferably 1 or more, more preferably 2 or more, and preferably 10 or less, more preferably 6 or less, and even more preferably 4 or less. When it is within the above range, the effect tends to be more suitably obtained.
As the hydrocarbon group for ^R4 which may have a heteroatom, a group represented by the following formula is preferable.

The group represented by -(AO)- is more preferably a group represented by the following formula (B), particularly preferably a group represented by the following formulas (A) to (B), and can also be used in combination with a group represented by the following formula (C):

When the above polymer contains two or more types of oxyalkylene groups, the arrangement of the oxyalkylene groups may be block or random.

The above polymer is preferably a polymer containing a group (structural unit) represented by the above formula (B), and more preferably a polymer consisting of groups (structural units) represented by the above formulas (A) and (B).
The content of the group (structural unit) represented by the above formula (B) in 100 mol% of the above polymer is preferably 2 mol% or more, more preferably 5 mol% or more, and is preferably 50 mol% or less, more preferably 40 mol% or less, even more preferably 30 mol% or less, and particularly preferably 20 mol% or less.

The weight average molecular weight (Mw) of the above polymer is preferably 10,000 or more, more preferably 50,000 or more, even more preferably 100,000 or more, and particularly preferably 500,000 or more, and is preferably 3 million or less, more preferably 2.5 million or less, even more preferably 2 million or less, particularly preferably 1.5 million or less, and most preferably 1 million or less.

The above polymer preferably has an insoluble matter (water-insoluble matter) of 5% by mass or more when 1 g of the polymer is suspended in 10 mL of water, more preferably 10% by mass or more, even more preferably 30% by mass or more, particularly preferably 50% by mass or more, most preferably 70% by mass or more, further most preferably 80% by mass or more, and even more preferably 90% by mass or more, with no particular upper limit.
The insoluble matter can be measured by the method described in the Examples.
The more the insoluble matter is, the more the amount of the polymer that dissolves in water when the rubber is wetted with water can be reduced, and the more suitably the reversible volume change can be achieved.

The above polymer preferably has an insoluble matter (THF insoluble matter) of 5% by mass or more when 1 g of the polymer is suspended in 10 mL of tetrahydrofuran, more preferably 10% by mass or more, even more preferably 30% by mass or more, particularly preferably 50% by mass or more, most preferably 70% by mass or more, and even more preferably 90% by mass or more, with no particular upper limit.
The insoluble matter can be measured by the method described in the Examples.
Since diene rubbers are soluble in tetrahydrofuran, the greater the amount of the polymer that is insoluble in tetrahydrofuran, the more likely it is that the polymer will be incompatible with the diene rubber and will be able to fully achieve the effect of increasing its volume when wet with water.

The above polymer may be a commercially available product, or may be produced by preparing a polymer from a monomer having a hetero atom.
The monomer having a hetero atom is not particularly limited, and examples of the monomer having an oxygen atom include ethers such as vinyl ether, alkoxystyrene, allyl glycidyl ether, ethylene oxide, propylene oxide, and tetrahydrofuran, (meth)acrylic acid and esters thereof, and acid anhydrides. Examples of the monomer having a nitrogen atom include acrylonitrile, N-vinylcarbazole, carbamic acid, and caprolactam. Examples of the monomer having a silicon atom include alkoxysilylstyrene and alkoxysilylvinyls.
When the monomer having a heteroatom does not contain an unsaturated bond, a monomer having a carbon-carbon double bond (for example, a conjugated diene monomer such as butadiene or isoprene, or a vinyl polymer such as styrene) may be polymerized together with the monomer having a heteroatom.
The polymerization method is not particularly limited, and can be carried out by a known method.

The content of the above polymer is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 20 parts by mass or more, particularly preferably 30 parts by mass or more, most preferably 40 parts by mass or more, even more preferably 50 parts by mass or more, even more preferably 60 parts by mass or more, particularly most preferably 70 parts by mass or more, and is preferably 150 parts by mass or less, more preferably 100 parts by mass or less, per 100 parts by mass of the rubber component. Within the above range, the effect tends to be better obtained.

The rubber composition may contain silica.
Examples of silica include dry silica (anhydrous silicic acid) and wet silica (hydrated silicic acid), among which wet silica is preferred because it has a large number of silanol groups. These may be used alone or in combination of two or more.

The nitrogen adsorption specific surface area ( _N2SA ) of silica is ^40m2 /g or more, preferably ^60m2 /g or more, more preferably ^80m2 /g or more, and even more preferably ^160m2 /g or more. The _N2SA is preferably ^600m2 /g or less, more preferably ^300m2 /g or less, even more preferably ^250m2 /g or less, and particularly preferably ^200m2 /g or less. Within the above range, the effect tends to be more favorably obtained.
The N ₂ SA of silica is a value measured by the BET method in accordance with ASTM D3037-81.

For example, products from Degussa, Rhodia, Tosoh Silica, Solvay Japan, Tokuyama, etc. can be used as silica.

The content of silica is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 150 parts by mass or less, more preferably 100 parts by mass or less, even more preferably 80 parts by mass or less, particularly preferably 60 parts by mass or less, and most preferably 40 parts by mass or less. Within the above range, the effect tends to be better obtained.

In the above rubber composition, the content of silica in 100% by mass of the filler (reinforcing filler) is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. There is no particular upper limit, but it is preferably 90% by mass or less, more preferably 70% by mass or less, and even more preferably 50% by mass or less. Within the above range, the effect tends to be more favorably obtained.

When the rubber composition contains silica, it is preferable that the rubber composition further contains a silane coupling agent.
The silane coupling agent is not particularly limited, and examples thereof include bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(2-triethoxysilylethyl)trisulfide, bis(4-trimethoxysilylbutyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)disulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxysilylbutyl)disulfide, 3-trimethoxysilylpropyl-N , N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide and other sulfide-based compounds; mercapto-based compounds such as 3-mercaptopropyltrimethoxysilane and 2-mercaptoethyltriethoxysilane; vinyl-based compounds such as vinyltriethoxysilane and vinyltrimethoxysilane; amino-based compounds such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; glycidoxy-based compounds such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based compounds such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based compounds such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. As commercially available products, for example, products from Degussa, Momentive, Shin-Etsu Silicone Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azumax Co., Ltd., Dow Corning Toray Co., Ltd., etc. can be used. These may be used alone or in combination of two or more. Among them, sulfide-based silane coupling agents and mercapto-based silane coupling agents are preferred because they tend to provide better effects, and disulfide-based silane coupling agents having a disulfide bond such as bis(3-triethoxysilylpropyl) disulfide are more preferred.

The content of the silane coupling agent is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, per 100 parts by mass of silica. Within the above range, the effect tends to be better.

The rubber composition may contain carbon black.
The carbon black is not particularly limited, and examples thereof include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. These may be used alone or in combination of two or more kinds.

The nitrogen adsorption specific surface area ( _N2SA ) of the carbon black is preferably 80 ^m2 /g or more, more preferably ¹⁰⁰ m2/g or more, and is preferably 150 ^m2 /g or less, more preferably 130 ^m2 /g or less. Within the above range, the effect tends to be better.
In this specification, the N ₂ SA of carbon black is a value measured in accordance with JIS K6217-2:2001.

As carbon black, for example, products from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Shin-Nichika Carbon Co., Ltd., Columbia Carbon Co., Ltd., etc. can be used.

The carbon black content is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 20 parts by mass or more, and particularly preferably 30 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 150 parts by mass or less, more preferably 100 parts by mass or less, even more preferably 80 parts by mass or less, particularly preferably 60 parts by mass or less, and most preferably 50 parts by mass or less. Within the above range, the effect tends to be better obtained.

The rubber composition may contain oil.
Examples of the oil include process oil, vegetable oil, and mixtures thereof. Examples of the process oil include paraffin-based process oil, aromatic process oil, and naphthenic process oil. Examples of the vegetable oil include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil. These may be used alone or in combination of two or more. Among them, process oil is preferred because it provides good effects, and aromatic process oil is more preferred.

As oils, products from, for example, Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., Japan Energy Co., Ltd., Orisoi Co., Ltd., H&R Co., Ltd., Toyokuni Oil Mills Co., Ltd., Showa Shell Sekiyu K.K., Fuji Kosan Co., Ltd., etc. can be used.

The oil content is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 20 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 50 parts by mass or less, and more preferably 35 parts by mass or less. Within the above range, the effect tends to be better obtained. Note that the oil content also includes the amount of oil contained in the rubber (oil-extended rubber).

The rubber composition may contain a resin.
The resin is not particularly limited as long as it is one that is commonly used in the tire industry, and examples thereof include rosin-based resins, coumarone-indene resins, α-methylstyrene-based resins, terpene-based resins, p-t-butylphenol acetylene resins, acrylic resins, C5 resins, C9 resins, etc. Commercially available products include those from Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical Co., Ltd., Nippon Paint Chemical Co., Ltd., Nippon Shokubai Co., Ltd., JX Nippon Energy Corporation, Arakawa Chemical Industries Co., Ltd., Taoka Chemical Co., Ltd., Toagosei Co., Ltd., etc. These may be used alone or in combination of two or more kinds.

The resin content is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, per 100 parts by mass of the rubber component. Within the above range, the effect tends to be better.

The rubber composition may contain a wax.
The wax is not particularly limited, and examples thereof include petroleum waxes such as paraffin wax and microcrystalline wax; natural waxes such as vegetable wax and animal wax; and synthetic waxes such as polymers of ethylene, propylene, etc. These may be used alone or in combination of two or more. Among them, petroleum waxes are preferred, and paraffin wax is more preferred.

As wax, for example, products from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., Seiko Chemical Co., Ltd., etc. can be used.

The wax content is preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, and is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, per 100 parts by mass of the rubber component. Within the above range, the effect tends to be better.

The rubber composition may contain an antioxidant.
Examples of the antioxidant include naphthylamine-based antioxidants such as phenyl-α-naphthylamine; diphenylamine-based antioxidants such as octylated diphenylamine and 4,4'-bis(α,α'-dimethylbenzyl)diphenylamine;N-isopropyl-N'-phenyl-p-phenylenediamine,N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, and N,N'-di-2-naphthyl-p-phenylenediamine. Examples of the antioxidant include p-phenylenediamine antioxidants such as quinoline-based antioxidants such as polymers of 2,2,4-trimethyl-1,2-dihydroquinoline; monophenol-based antioxidants such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis-, tris-, and polyphenol-based antioxidants such as tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. These antioxidants may be used alone or in combination of two or more. Among these, p-phenylenediamine-based antioxidants and quinoline-based antioxidants are preferred.

As anti-aging agents, for example, products from Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Co., Ltd., Flexis, etc. can be used.

The content of the anti-aging agent is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component. Within the above range, the effect tends to be better.

The rubber composition may contain stearic acid.
As the stearic acid, any of the conventionally known products can be used, for example, products available from NOF Corporation, NOF Corporation, Kao Corporation, Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., and the like.

The content of stearic acid is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component. Within the above range, the effect tends to be better.

The rubber composition may contain zinc oxide.
As the zinc oxide, any known zinc oxide can be used, for example, products available from Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc.

The zinc oxide content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component. Within the above range, the effect tends to be better.

The rubber composition may contain sulfur.
Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, soluble sulfur, etc., which are generally used in the rubber industry. These may be used alone or in combination of two or more kinds.

As sulfur, for example, products from Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flexis Corporation, Nippon Kanzatsu Kogyo Co., Ltd., Hosoi Chemical Industry Co., Ltd., etc. can be used.

The sulfur content is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less, per 100 parts by mass of the rubber component. If it is within the above range, the effect tends to be better.

The rubber composition may contain a vulcanization accelerator.
Examples of the vulcanization accelerator include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, and N-cyclohexyl-2-benzothiazyl sulfenamide; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazole sulfenamide, N-tert-butyl-2-benzothiazole sulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, and N,N'-diisopropyl-2-benzothiazole sulfenamide; and guanidine-based vulcanization accelerators such as diphenyl guanidine, di-orthotolyl guanidine, and orthotolyl biguanidine. These may be used alone or in combination of two or more. Among them, sulfenamide-based vulcanization accelerators and guanidine-based vulcanization accelerators are preferred because they provide more suitable effects.

As vulcanization accelerators, for example, products manufactured by Kawaguchi Chemical Co., Ltd. and Ouchi Shinko Chemical Co., Ltd. can be used.

The content of the vulcanization accelerator is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, per 100 parts by mass of the rubber component. If it is within the above range, the effect tends to be better.

In addition to the above components, the rubber composition may further contain additives commonly used in the tire industry, such as organic peroxides; fillers such as calcium carbonate, talc, alumina, clay, aluminum hydroxide, and mica; etc. The content of these additives is preferably 0.1 to 200 parts by mass per 100 parts by mass of the rubber component.

The rubber composition can be produced, for example, by kneading the components using a rubber kneading device such as an open roll or a Banbury mixer, and then vulcanizing the mixture.

As for kneading conditions, in the base kneading process where additives other than the vulcanizing agent and vulcanization accelerator are kneaded, the kneading temperature is usually 100 to 180°C, preferably 120 to 170°C. In the finish kneading process where the vulcanizing agent and vulcanization accelerator are kneaded, the kneading temperature is usually 120°C or lower, preferably 80 to 110°C. Furthermore, the composition kneaded with the vulcanizing agent and vulcanization accelerator is usually subjected to a vulcanization treatment such as press vulcanization. The vulcanization temperature is usually 140 to 190°C, preferably 150 to 185°C. The vulcanization time is usually 5 to 15 minutes.

The rubber composition can be used (as a rubber composition for tires) for tire components such as treads (cap treads), sidewalls, base treads, under treads, shoulders, clinches, bead apex, breaker cushion rubber, carcass cord covering rubber, insulation, chafers, inner liners, and side reinforcing layers of run-flat tires. In particular, it is preferably used for components that may come into contact with water (treads, sidewalls, shoulders), and more preferably for treads. In the case of a tread that is composed of a cap tread and a base tread, it can be preferably used for the cap tread.
Examples of components that may come into contact with water include components (tread, sidewall, shoulder) that are located on the outermost surface of a tire when it is new or during running when the tire wears.

The tire (pneumatic tire, etc.) of the present invention is manufactured by a conventional method using the above rubber composition. That is, the rubber composition, which contains various additives as necessary, is extruded to match the shape of each tire component (particularly the tread (cap tread)) while still unvulcanized, molded by a conventional method on a tire building machine, and laminated together with other tire components to form an unvulcanized tire, which is then heated and pressurized in a vulcanizer to manufacture the tire.

Note that the tire components (e.g., the tread) of the tire may be at least partially made of the rubber composition, or may be entirely made of the rubber composition.

The above tires are suitable for use as passenger car tires, large passenger car tires, large SUV tires, truck and bus tires, motorcycle tires, racing tires, studless tires (winter tires), all-season tires, run-flat tires, aircraft tires, mining tires, etc.

The present invention will be specifically explained based on examples, but the present invention is not limited to these.

(Production Example 1)
Hexane, 1,3-butadiene, styrene, tetrahydrofuran, and ethylene glycol diethyl ether were charged into an autoclave reactor whose atmosphere had been replaced with nitrogen. Next, bis(diethylamino)methylvinylsilane and n-butyllithium were charged as a cyclohexane solution and an n-hexane solution, respectively, to initiate polymerization.
The stirring speed was set to 130 rpm, the temperature inside the reactor was set to 65°C, and copolymerization of 1,3-butadiene and styrene was carried out for 3 hours while continuously feeding monomers into the reactor. Next, the obtained polymer solution was stirred at a stirring speed of 130 rpm, N-(3-dimethylaminopropyl)acrylamide was added, and the reaction was carried out for 15 minutes. After the polymerization reaction was completed, 2,6-di-tert-butyl-p-cresol was added. Next, the solvent was removed by steam stripping, and the mixture was dried with a heated roll adjusted to 110°C to obtain a modified styrene butadiene rubber (SBR).

(Production Example 2) Synthesis of Polymer 1 (Epoxide-Allyl Glycidyl Ether Copolymer) 500 mL of diethyl ether was added to a nitrogen-substituted glass flask, and the internal temperature was cooled to 0° C. or less. Then, 10 mL of a 0.55 mol/L triisobutylaluminum/hexane solution was added, and then a 0.55 mol/L ethanol/diethyl ether solution was added dropwise so that the internal temperature did not exceed 10° C. Next, a solution in which ethylene oxide and allyl glycidyl ether were mixed in a molar ratio of 9/1 to a total weight of 200 g was added dropwise so that the internal temperature did not exceed 10° C., and the mixture was stirred for 8 hours. Next, the solvent was distilled off under reduced pressure at an external temperature of 50° C./internal pressure of 1.0 kPa or less, and the remaining residue was suspended in water and filtered. The filtered residue was washed with THF and then dried under reduced pressure at 50° C./1 kPa or less until a constant weight was reached, thereby obtaining Polymer 1 in an 80% yield (an ether group derived from Formula (A) above and a carbon-carbon peak derived from Formula (B) above were confirmed in the infrared absorption spectrum; the weight average molecular weight (Mw) was 780,000, and the content of the group (structural unit) represented by Formula (B) above in 100 mol % of the polymer was 8 mol %).

(Production Example 3) Synthesis of Polymer 2 (Amine-Allylglycidyl Ether Copolymer) The same procedure as in Production Example 2 was repeated, except that ethylene oxide was changed to triglycidylamine, to obtain Polymer 2 of triglycidylamine and allylglycidyl ether in 80% yield. (The same analysis as in Production Example 2 was performed to confirm the absorption of amine and the peak derived from the carbon-carbon double bond, the weight average molecular weight was 980,000, and the content of the group (structural unit) represented by the above formula (B) in 100 mol % of the polymer was 8 mol %).

(Production Example 4) Synthesis of Polymer 3 (Silyl-Allyl Glycidyl Ether Copolymer) The same procedure as in Production Example 2 was repeated, except that ethylene oxide was changed to triethoxysilyl glycidyl ether, to obtain Polymer 3 of triethoxysilyl glycidyl ether and allyl glycidyl ether in an 80% yield. (The same analysis as in Production Example 2 was carried out to confirm the absorption of silanol and the peak derived from the carbon-carbon double bond, the weight average molecular weight was 640,000, and the content of the group (structural unit) represented by the above formula (B) in 100 mol % of the polymer was 8 mol %).

The following evaluations were carried out on the obtained polymers 1 to 3.

<Measurement of water insoluble matter>
1 g of polymer was weighed into a glass flask, 10 mL of water was poured, and the mixture was stirred for 10 minutes at an internal temperature of 66° C., and then stirred until the internal temperature reached 25° C. or lower. The mixture was then filtered through a filter paper made of cellulose and having a mesh size of 5C. The residue remaining on the filter paper was dried for 8 hours at a temperature of 80° C. and an internal pressure of 0.1 kPa or lower, and the weight was measured. The water-insoluble portion was calculated using the following formula.
Water-insoluble matter (mass%)=dry weight of residue (g)/initial weight of polymer (g)×100

<Measurement of THF insoluble matter>
1 g of polymer was weighed into a glass flask, 10 mL of tetrahydrofuran was poured, and the mixture was stirred for 10 minutes at an internal temperature of 66° C., and then stirred until the internal temperature reached 25° C. or lower. The mixture was then filtered through a filter paper made of cellulose and having a mesh size of 5C. The residue remaining on the filter paper was dried for 8 hours at a temperature of 80° C. and an internal pressure of 0.1 kPa or lower, and the weight was measured. The THF insoluble content was calculated using the following formula.
THF insoluble matter (mass%)=dry weight of residue (g)/initial weight of polymer (g)×100

Various chemicals used in the examples and comparative examples will be collectively described below.
SBR: SBR synthesized by the above method (modified S-SBR, styrene content: 25% by mass, vinyl content: 59% by mol, non-oil extended product)
BR: BR150B manufactured by Ube Industries, Ltd. (cis content: 97% by mass)
NR: TSR20
Polymer 1: Polymer 1 synthesized by the above method (water insoluble: 96% by mass, THF insoluble: 96% by mass)
Polymer 2: Polymer 2 synthesized by the above method (water insoluble matter: 82% by mass, THF insoluble matter: 96% by mass)
Polymer 3: Polymer 3 synthesized by the above method (water insoluble: 92% by mass, THF insoluble: 92% by mass)
Silica: ZEOSIL 1165MP ( _N2SA : ^160m2 /g) manufactured by Rhodesia Corporation
Carbon black: SEAT 9H manufactured by Tokai Carbon Co., Ltd. (DBP oil absorption: 115 ml/100 g, N ₂ SA: 110 m ² /g)
Silane coupling agent: Si75 (bis(3-triethoxysilylpropyl)disulfide) manufactured by Evonik Degussa
Oil: Process X-140 (aromatic process oil) manufactured by Japan Energy Co., Ltd.
Wax: Ozoace 0355 manufactured by Nippon Seiro Co., Ltd.
Antioxidant: Santoflex 13 (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD)) manufactured by Flexis Co., Ltd.
Stearic acid: NOF Corporation's "Tsubaki" stearic acid
Zinc oxide: zinc oxide type 2 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: powdered sulfur vulcanization accelerator 1 manufactured by Tsurumi Chemical Industry Co., Ltd. Noccela NS (N-tert-butyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Vulcanization accelerator 2: Noccelaer D (1,3-diphenylguanidine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

Examples and Comparative Examples
According to the compounding recipe shown in Table 1, chemicals other than sulfur and vulcanization accelerator were kneaded for 4 minutes at 160°C using a 1.7L Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a kneaded product. Next, sulfur and vulcanization accelerator were added to the kneaded product obtained, and the mixture was kneaded for 4 minutes at 80°C using an open roll to obtain an unvulcanized rubber composition.
The resulting unvulcanized rubber composition was press-vulcanized at 170° C. for 12 minutes to obtain a vulcanized rubber composition.

The obtained vulcanized rubber composition was evaluated as follows. The results are shown in Table 1.

(Volume Measurement Method)
In a place controlled at room temperature of 25° C., 300 mL of water was accurately measured into a 1000 mL measuring cylinder with a measurement error of ±0.2%, and the measurement sample was placed in it, and the increase in the volume of the water was recorded as the volume.
The volume change rate was calculated by the following calculation method.
Volume change rate = (volume when wet) / (volume when dry)

(Volume when wet with water)
The vulcanized rubber composition (cylinder shape with a radius of 25 mm and a height of 51 mm) was immersed in 500 ml of water at 25° C. for 12 hours to obtain a vulcanized rubber composition after wetting with water. The volume of the obtained vulcanized rubber composition after wetting with water was measured by the above-mentioned method and was defined as the volume when wetted with water. The volume of the vulcanized rubber composition (volume of vulcanized rubber) was expressed as an index with the volume of the vulcanized rubber composition (volume of vulcanized rubber) set to 100.

(Volume when dry)
The vulcanized rubber composition after wetting with water was dried under reduced pressure at 80°C and 1 kPa or less until it reached a constant weight, to obtain a dried vulcanized rubber composition. The temperature of the obtained dried vulcanized rubber composition was returned to 25°C, and the volume of the dried vulcanized rubber composition was measured by the above method and was taken as the volume when dried. The volume of the vulcanized rubber was expressed as an index, with the volume of the vulcanized rubber being 100.

(Volume when rewetted)
The dried vulcanized rubber composition (cylinder shape with a radius of 25 mm and a height of 51 mm) was immersed in 500 ml of water at 25° C. for 12 hours to obtain a vulcanized rubber composition after rewetting with water. The volume of the obtained vulcanized rubber composition after rewetting with water was measured by the above-mentioned method and was taken as the volume at the time of rewetting with water. The volume of the vulcanized rubber was expressed as an index with the volume of the vulcanized rubber being 100.

(tan δ when dry)
The tan δ of the dried vulcanized rubber composition at 70° C. was measured using a viscoelasticity spectrometer VES manufactured by Iwamoto Seisakusho Co., Ltd. The measurement conditions were as follows:
Measurement temperature: 70°C, initial strain: 10%, dynamic strain: 2%, frequency: 10Hz

(Fuel Efficiency Index)
The obtained unvulcanized rubber composition sheet was molded into a tread shape, laminated with other tire components, and press-vulcanized at 170°C/12 minutes to prepare a test tire (size: 195/65R15). Using a rolling resistance tester, the rolling resistance of the test tire was measured when it was run on a rim (15x6JJ), with an internal pressure (230kPa), a load (3.43kN), and a speed (80km/h), and the rolling resistance was expressed as an index (fuel economy index) with Comparative Example 1 taken as 100. The higher the index, the better the fuel economy.

(Wet grip performance index)
The obtained unvulcanized rubber composition sheet was molded into a tread shape, laminated with other tire components, and press-vulcanized at 170° C./12 minutes to prepare a cart tire (tire size: 11×1.10-5). The cart tire was mounted on a cart and driven around a test course with a 2 km lap length on a road surface that had been watered in advance, and the test driver evaluated the grip performance on a scale of 100 to 200, with Comparative Example 1 being 100.

(Dry grip performance index)
The obtained unvulcanized rubber composition sheet was molded into a tread shape, laminated with other tire components, and press-vulcanized at 170° C./12 minutes to prepare a cart tire (tire size: 11×1.10-5). The cart tire was mounted on a cart and driven around a test course with a dry surface and a circumference of 2 km for 8 laps. The test driver evaluated the grip performance on a scale of 100 to 200, with Comparative Example 1 being 100.

From Table 1, it can be seen that the embodiment in which the volume changes reversibly with water and satisfies the above formulas (1) and (2) can improve the overall performance of wet grip performance, dry grip performance, and fuel economy.

Claims (14)

a diene-based rubber containing an isoprene-based rubber, a butadiene rubber, and a styrene-butadiene rubber;
a polymer having a carbon-carbon double bond and a heteroatom ,
the carbon-carbon double bond is capable of crosslinking with the diene rubber,
the polymer has an insoluble content of 5% by mass or more when 1 g of the polymer is suspended in 10 mL of water, and an insoluble content of 5% by mass or more when 1 g of the polymer is suspended in 10 mL of tetrahydrofuran;
A rubber composition that undergoes a reversible volume change due to water and satisfies the following formulas (1) and (2):
Volume when wet/Volume when dry>1.00 (1)
(In the formula, the volume is the volume of the rubber composition at 25° C.)
tan δ at 70°C when dry < 0.14 (2)
(In the formula, tan δ at 70° C. is the loss tangent measured under the conditions of 70° C., initial strain of 10%, dynamic strain of 2%, and frequency of 10 Hz.) The rubber composition according to claim 1, wherein in formula (1), the ratio of wet volume to dry volume is 1.03 or more. The rubber composition according to claim 1, wherein in formula (1), the ratio of wet volume to dry volume is 1.06 or more. The rubber composition according to claim 1, wherein in formula (1), the ratio of wet volume to dry volume is 1.10 or more. The rubber composition according to any one of claims 1 to 4, wherein in formula (2), tan δ at 70°C in a dry state is 0.13 or less. The rubber composition according to any one of claims 1 to 4, wherein in formula (2), tan δ at 70°C in a dry state is 0.12 or less. The rubber composition according to any one of claims 1 to 4, wherein in formula (2), tan δ at 70°C in a dry state is 0.11 or less. The rubber composition according to any one of claims 1 to 7, wherein the heteroatom is at least one atom selected from the group consisting of an oxygen atom, a nitrogen atom, a silicon atom, a sulfur atom, a phosphorus atom, and a halogen atom. The rubber composition according to any one of claims 1 to 8 , comprising 5 parts by mass or more of the polymer per 100 parts by mass of the rubber component. The rubber composition according to any one of claims 1 to 9 , wherein the content of the styrene-butadiene rubber in 100% by mass of the rubber component is 95% by mass or less. The rubber composition according to any one of claims 1 to 10 , which is a rubber composition for a tread. A tire having a tire component at least partly constituted by the rubber composition according to any one of claims 1 to 11 . The tire according to claim 12 , wherein the tire component is a component located on the outermost surface when new or during running. 13. The tire of claim 12 , wherein said tire component is a tread.