JP7243067B2 - tire - Google Patents

Description

The present invention relates to tires.

In recent years, as a common issue for automobiles, awareness of safety is increasing more and more, and further improvement of wet grip performance is required. Until now, various studies have been made to improve wet grip performance, and many inventions of rubber compositions containing silica have been reported (for example, Patent Document 1). 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. Therefore, technical improvements in tire rubber compositions such as treads have been extensively studied and put into practical use.

JP 2008-285524 A

As a result of intensive studies by the present inventors, technical improvements in tread rubber compositions using silica have made significant progress in the wet grip performance of tires. Regarding the change in grip performance when the road surface changes, etc., it remains an important technical issue, and it was found that there is room for improvement.
Regarding this point, the present inventors have made intensive studies and found that the conventional rubber does not change its hardness when it changes from a dry state in which it is not wet with water to a so-called wet state in which it is wet with water, or when it is cooled by water. As a result, wet grip performance tends to be lower than dry grip performance.
From the viewpoint of the tire pattern, grooves are formed on the tread surface for the purpose of improving drainage performance as a method of improving wet grip performance. In the case of a pattern with continuous grooves, drainage performance is improved, but the contact area on dry roads tends to decrease and dry grip performance tends to decrease, so hard rubber with high dry grip performance is used preferentially. need, and soft rubber with good wet grip performance may not be available. In the case of patterns with discontinuous grooves, contrary to the above, dry grip performance improves, but sufficient wet grip tends not to be obtained, so soft rubber with high wet grip performance is preferentially used. There are cases where hard rubber with high dry grip performance cannot be used.
As described above, it has been found that the conventional technology has room for improvement in terms of comprehensively improving wet grip performance and dry grip performance.
An object of the present invention is to solve the above problems and to provide a tire capable of improving the overall wet grip performance and dry grip performance.

The present invention has a tread made of a rubber composition whose hardness reversibly changes with water and satisfies the following formula (1),
It relates to a tire in which the land ratio of the tread is 30% or more.
Hardness when dry - hardness when wet with water ≥ 1 (1)
(In the formula, the hardness is the JIS-A hardness of the rubber composition at 25°C.)

In the above formula (1), the ratio of hardness when dry - hardness when wet with water is preferably 2 or more, more preferably 3 or more, and even more preferably 4 or more.

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

The heteroatom 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.

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

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

The rubber composition preferably contains 5 parts by mass or more of the polymer with respect to 100 parts by mass of the rubber component.

The rubber composition preferably contains an 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 tread preferably has grooves that are continuous in the tire circumferential direction and/or grooves that are discontinuous in the tire circumferential direction.

According to the present invention, the tire has a tread made of a rubber composition that reversibly changes hardness with water and satisfies the above formula (1), and the land ratio of the tread is within a predetermined range. Therefore, the overall performance of wet grip performance and dry grip performance can be improved.

The tire of the present invention reversibly changes hardness with water, has a tread made of a rubber composition that satisfies the following formula (1), and has a land ratio of 30% or more.
Hardness when dry - hardness when wet with water ≥ 1 (1)
(In the formula, the hardness is the JIS-A hardness of the rubber composition at 25°C.)

Although the above-mentioned tire can obtain the above effects, the reason why such effects are obtained is not necessarily clear, but it is speculated as follows.
The rubber composition that constitutes the tread of the tire reversibly changes in hardness with water and satisfies the above formula (1). Here, the above formula (1) means that the hardness when wet with water is smaller than the hardness when dry. That is, the rubber composition reversibly changes its hardness with water and satisfies the above formula (1). , meaning that the hardness changes reversibly in the presence of water.
Therefore, when a dry road surface changes to a wet road surface, the rubber composition is wetted by water, the hardness of the rubber composition is lowered, the deterioration of grip performance (wet grip performance) can be suppressed, and good grip performance (wet grip performance ) is obtained. This is because it is easy to slip on wet road surfaces, so sufficient grip performance cannot be obtained with the hardness suitable for dry road surfaces. grip performance) can be suppressed, and good grip performance (wet grip performance) can be obtained.
On the other hand, when a wet road surface changes to a dry road surface, the rubber composition moistened with water is dried and the hardness of the rubber composition increases, which suppresses the deterioration of the grip performance (dry grip performance) and improves the grip performance ( dry grip performance) can be obtained. This is because it is difficult to slip on a dry road surface, so sufficient grip performance cannot be obtained with the hardness suitable for wet road surfaces. performance) can be suppressed, and good grip performance (dry grip performance) can be obtained.
In this way, the hardness reversibly changes with water, and by satisfying the above formula (1), an appropriate hardness corresponding to the state of water on the road surface (wet road surface, dry road surface) can be obtained. Overall performance of grip performance and dry grip performance can be improved.
Furthermore, the tread improves the dry grip performance by increasing the land ratio, and improves the wet grip performance by decreasing the land ratio. By being within the range, the overall performance of dry grip performance and wet grip performance is improved.
Therefore, in the above tire, the rubber composition constituting the tread reversibly changes in hardness with water, satisfies the above formula (1), and further has a land ratio of the tread within a predetermined range, Overall performance of wet grip performance and dry grip performance can be improved.
In addition, by using rubber whose hardness reversibly changes with water, it is possible to obtain grip performance according to the road surface conditions, and the range of rubber hardness that can be used for the tread is expanded, so tread design can be improved. The degree of freedom can be improved.
In addition, in this specification, the hardness of the rubber composition means the hardness of the rubber composition after vulcanization.

In this specification, when the tire is a pneumatic tire, the land ratio is calculated from the ground contact shape under normal rim, normal internal pressure, and normal load conditions. Non-pneumatic tires can be similarly measured without the need for regular internal pressure.
"Regular rim" means a rim defined for each tire in a standard system that includes the standard on which the tire is based. For example, JATMA standard rim, TRA "Design Rim", or ETRTO. If there is, it means "Measuring Rim".
"Regular internal pressure" is the air pressure specified for each tire by the above-mentioned standards, the maximum air pressure for JATMA, the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and ETRTO. If there is, it means "INFLATION PRESSURE", but in the case of passenger car tires, it is 180 kPa.
"Regular load" is the load defined for each tire by the above standards, maximum load capacity for JATMA, maximum value described in table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, ETRTO If so, it means the load obtained by multiplying "LOAD CAPACITY" by 0.88.
As for the shape of the ground contact, the tire tread surface was painted with ink after being assembled on a regular rim, applying regular internal pressure, and allowed to stand at 25°C for 24 hours. obtained by transferring to
The tire is rotated by 72° in the circumferential direction and transferred at five locations. That is, the ground shape is obtained five times.
Let L be the average value of the maximum length in the axial direction of the tire, and W be the average value of the length in the direction perpendicular to the axial direction of the five ground contact shapes.
The land ratio is calculated as the average area of the five ground shapes (black portions) transferred to the cardboard/(L×W)×100(%).
Here, the average value of length and area is a simple average of five values.

As used herein, the reversible change in hardness by water means that the presence of water reversibly increases or decreases the hardness of the rubber composition (after vulcanization). It should be noted that, for example, if the hardness changes reversibly in the case of a change from drying → water wetting → drying, the hardness may not be the same during the previous drying and the subsequent drying. Alternatively, the hardness may be the same during the previous drying and the subsequent drying.

As used herein, the term "dry hardness" means the hardness of a rubber composition in a dry state (after vulcanization). Specifically, the rubber composition dried by the method described in Examples ( (after vulcanization).
As used herein, the water-wet hardness means the hardness of the rubber composition (after vulcanization) in a state of being wet with water. It refers to the hardness of the wet rubber composition (after vulcanization).

In this specification, the hardness (JIS-A hardness) of the rubber composition (after vulcanization) is defined in JIS K6253-3 (2012) "Vulcanized rubber and thermoplastic rubber-How to determine hardness-Part 3: Durometer Hardness” is measured at 25° C. by a Type A durometer.

As shown in the above formula (1), (hardness when dry - hardness when wet with water (hardness of rubber composition when dry (after vulcanization) - hardness of rubber composition when wet with water (after vulcanization))) is 1 or more, preferably 2 or more, more preferably 3 or more, still more preferably 4 or more, particularly preferably 5 or more, most preferably 6 or more, most preferably 8 or more, still most preferably 11 or more, especially Most preferably 15 or more, more preferably 18 or more, still more preferably 21 or more, still more preferably 24 or more, the upper limit is not particularly limited, but preferably 50 or less, more preferably 40 or less, still more preferably 30 or less, particularly preferably 28 or less, most preferably 26 or less. Within the above range, the effect can be obtained more favorably.

The hardness when dry (hardness of the rubber composition (after vulcanization) when dry) can be appropriately adjusted within the range satisfying the above formula (1), preferably 20 or more, more preferably 25 or more, and further It is preferably 30 or more, particularly preferably 40 or more, preferably 95 or less, more preferably 90 or less, still more preferably 85 or less, and particularly preferably 75 or less. When the hardness is within the above range, the effect can be obtained more preferably.

The hardness when wet with water (hardness of the rubber composition (after vulcanization) when wet with water) can be appropriately adjusted within the range satisfying the above formula (1), but is preferably 20 or more, more preferably 25 or more. , more preferably 30 or more, preferably 70 or less, more preferably 65 or less, and still more preferably 60 or less. When the hardness is within the above range, the effect can be obtained more suitably.

In addition, the hardness change represented by the above formula (1) of the rubber composition and the reversible hardness change due to water are compounded with a compound capable of reversible molecular bonding such as hydrogen bonding and ionic bonding with water. This can be achieved by More specifically, by using a rubber component containing a diene rubber and a polymer having a carbon-carbon double bond and a heteroatom in combination, the hardness change represented by the above formula (1) of the rubber composition , can realize reversible hardness change by water. This is because heteroatoms are capable of reversible molecular bonds such as hydrogen bonds and ionic bonds with water in the rubber composition, and as a result of the formation of these molecular bonds, the rubber composition when wet with water This is because the hardness of the object is lowered.
Furthermore, by using the above combination, the polymer is crosslinked to the rubber component by carbon-carbon double bonds during vulcanization and fixed to the rubber component, so that the liberation of the polymer from the rubber component can be suppressed, and the rubber surface can be prevented. Precipitation of the polymer can be suppressed, and deterioration of grip performance (wet grip performance, dry grip performance) can also be suppressed.

In addition, the hardness at the time of drying can be adjusted by the type and amount of chemicals (particularly rubber components, fillers, and softeners such as oils) blended in the rubber composition. When the amount of sulfur is increased, the dry hardness tends to decrease, when the amount of filler is increased, the dry hardness tends to increase, and when the amount of sulfur is decreased, the dry hardness tends to decrease. Also, the hardness at the time of drying can be adjusted by adjusting the blending amounts of sulfur and vulcanization accelerator. More specifically, increasing the sulfur content tends to increase the dry hardness, and increasing the vulcanization accelerator tends to increase the dry hardness.

As another means for achieving the hardness change represented by the above formula (1) of the rubber composition and the reversible hardness change by water, a rubber component containing a diene rubber, a carbon-carbon double bond and a hetero atom By using a polymer having It is possible to achieve the hardness change represented by the above formula (1) of the rubber composition and the reversible hardness change by water.
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, making it impossible to obtain a reversible change in hardness.

In addition, as another means for achieving the hardness change represented by the above formula (1) of the rubber composition and the reversible hardness change by water, for example, ionic bonds between rubber molecules are changed by adding water and drying. A method of reversibly cutting and rejoining is also included. More specifically, by using a rubber containing halogen or oxygen together with a compound containing a metal, a semimetal or nitrogen, the hardness change represented by the above formula (1) of the rubber composition, reversible by water hardness change can be realized. This is because cations derived from metals, metalloids, and nitrogen and anions derived from halogens and oxygen form ionic bonds between rubber molecules by the combined use, and ionic bonds are formed between rubber molecules by adding water. This is because, as a result of recombination of ionic bonds due to cleavage and drying of water, the hardness decreases when wet with water and increases when dried.

Usable chemicals are described below.

Examples of rubber components include isoprene-based rubber, butadiene rubber (BR), styrene-butadiene rubber (SBR), styrene-isoprene-butadiene rubber (SIBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), and the like. diene rubber. A rubber component may be used independently and may use 2 or more types together. Among them, diene rubber is preferable, isoprene rubber, BR, and SBR are more preferable, and SBR is still more preferable. A combination of isoprene rubber and SBR, a combination of BR and SBR, and a combination of isoprene rubber, BR and SBR are also preferred.

Here, the rubber component preferably has a weight average molecular weight (Mw) of 150,000 or more, more preferably 350,000 or more. Although the upper limit of Mw is not particularly limited, it is preferably 4,000,000 or less, more preferably 3,000,000 or less.

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

The SBR is not particularly limited, and those commonly used in the tire industry, such as emulsion polymerization SBR (E-SBR) and solution polymerization SBR (S-SBR), can be used. These may be used alone or in combination of two or more.

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

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

SBR may be unmodified SBR or modified SBR.
The modified SBR may be an SBR having a functional group that interacts with a filler such as silica. SBR (end-modified SBR having the above functional group at the end), main chain-modified SBR having the above-mentioned functional group in the main chain, main chain end-modified SBR having the above-mentioned functional group in the main chain and end (for example, the main chain Main chain end-modified SBR having the above functional group and at least one end modified with the above modifier), or modified (coupled) with a polyfunctional compound having two or more epoxy groups in the molecule, hydroxyl group and terminal-modified SBR into which an epoxy group is introduced. These may be used alone or in combination of two or more.

Examples of the functional groups include amino group, amido group, silyl group, alkoxysilyl group, isocyanate group, imino group, imidazole group, urea group, ether group, carbonyl group, oxycarbonyl group, mercapto group, sulfide group, disulfide group, sulfonyl group, sulfinyl group, thiocarbonyl group, ammonium group, imide group, hydrazo group, azo group, diazo group, carboxyl group, nitrile group, pyridyl group, alkoxy group, hydroxyl group, oxy group, epoxy group and the like. . In addition, these functional groups may have a substituent. Among them, an amino group (preferably an amino group in which the hydrogen atom of the amino group is substituted with an alkyl group having 1 to 6 carbon atoms), an alkoxy group (preferably an alkoxy group having 1 to 6 carbon atoms), an alkoxysilyl group ( An alkoxysilyl group having 1 to 6 carbon atoms is preferable), and an amide group is preferable.

As SBR, for example, SBR manufactured and sold by Sumitomo Chemical Co., Ltd., JSR Co., Ltd., Asahi Kasei Co., Ltd., 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, still more preferably 60% by mass or more, and preferably 95% by mass or less, more preferably It is 90% by mass or less, more preferably 80% by mass or less. Within the above range, the effect tends to be obtained more favorably.

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

The cis amount of BR is preferably 90% by mass or more, more preferably 95% by mass or more, and still more preferably 97% by mass or more. The upper limit is not particularly limited, and may be 100% by mass. Within the above range, the effect tends to be obtained more favorably.

BR may be either non-denatured BR or denatured BR. Examples of modified BR include modified BR into which the aforementioned functional groups have been introduced. Preferred embodiments are the same as for modified SBR.

As BR, for example, products of Ube Industries, Ltd., JSR Corporation, Asahi Kasei Co., Ltd., Nippon Zeon Co., Ltd., etc. can be used.

The content of BR 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 still more preferably It is 30% by mass or less. Within the above range, the effect tends to be obtained more favorably.

The isoprene rubber includes natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, modified IR, and the like. As NR, for example, those commonly used in the tire industry, such as SIR20, RSS#3, and TSR20, can be used. The IR is not particularly limited, and for example IR2200 or the like commonly used in the tire industry can be used. Modified NR includes deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), etc. Modified NR includes epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, etc. Examples of modified IR include epoxidized isoprene rubber, hydrogenated isoprene rubber, grafted isoprene rubber, and the like. These may be used alone or in combination of two or more. Among them, 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 further Preferably, it is 20% by mass or less. Within the above range, the effect tends to be obtained more favorably.

In the present specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are defined by gel permeation chromatograph (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: It can be obtained by standard polystyrene conversion based on the measured value by TSKGEL SUPERMULTIPORE HZ-M manufactured by Tosoh Corporation.
In addition, the cis amount (cis-1,4-bonded butadiene unit amount) and vinyl amount (1,2-bonded butadiene unit amount) can be measured by infrared absorption spectrometry, and the styrene amount can be measured by ¹ H-NMR measurement. can be measured by

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

A carbon-carbon double bond is necessary for cross-linking with the diene rubber, and the number thereof is not particularly limited.

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

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

The oxyalkylene group is a group represented by -(AO)-, preferably a group represented by -(AO) _n - (where 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 still more preferably 6 or less. Within the above range, the effect tends to be obtained more favorably.

The alkylene group A in the oxyalkylene group AO may be linear or branched, but is preferably branched because it has a bulkier structure and more favorable effects.
AO is branched into an oxyalkylene group having 2 to 3 carbon atoms (oxyethylene group (EO), oxypropylene group (PO)) and an oxyalkylene group having 2 to 3 carbon atoms for the reason that the effect can be obtained more preferably. It is preferably a group to which a chain R ⁴ (R ⁴ represents a hydrocarbon group which may have a heteroatom) is bonded, such as an oxyalkylene group having 2 to 3 carbon atoms, an oxy It is more preferable to use a group in which a branched chain ^R4 is bonded to an alkylene group. The branched chain ^R4 is preferably attached to the carbon atom adjacent to the oxygen atom.

The hydrocarbon group optionally having a heteroatom for ^R4 is not particularly limited. The number of carbon atoms in the hydrocarbon group is preferably 1 or more, more preferably 2 or more, preferably 10 or less, more preferably 6 or less, still more preferably 4 or less. Within the above range, the effect tends to be obtained more favorably.
As the hydrocarbon group optionally having a heteroatom for R ⁴ , groups represented by the following formulas are 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), A group represented by the following formula (C) can also be used in combination.

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

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

The weight average molecular weight (Mw) of the polymer is preferably 10,000 or more, more preferably 50,000 or more, still more preferably 100,000 or more, particularly preferably 500,000 or more, preferably 3,000,000 or less, more preferably 250. 10,000 or less, more preferably 2,000,000 or less, particularly preferably 1,500,000 or less, and most preferably 1,000,000 or less.

The polymer preferably has an insoluble content (water-insoluble content) of 5% by mass or more, more preferably 10% by mass or more, and still more preferably 30% by mass or more when 1 g of the polymer is suspended in 10 mL of water. It is particularly preferably 50% by mass or more, most preferably 70% by mass or more, most preferably 80% by mass or more, and most preferably 90% by mass or more, and the upper limit is not particularly limited.
The insoluble matter can be measured by the method described in Examples.
As the insoluble content increases, the amount of the polymer eluted into water can be reduced when the rubber is wetted with water, and reversible hardness change can be achieved more favorably.

The polymer preferably has an insoluble content (THF-insoluble content) of 5% by mass or more, more preferably 10% by mass or more, and still more preferably 30% by mass or more when 1 g of the polymer is suspended in 10 mL of tetrahydrofuran. It is particularly preferably 50% by mass or more, most preferably 70% by mass or more, and most preferably 90% by mass or more, and the upper limit is not particularly limited.
The insoluble matter can be measured by the method described in Examples.
Since the diene rubber is soluble in tetrahydrofuran, the greater the insoluble content of the polymer in tetrahydrofuran, the more incompatible it is with the diene rubber, and the harder it is to reduce the hardness when wet with water.

Commercially available products may be used for the above polymers, but they may also be produced by preparing a polymer from a monomer having a heteroatom.
The heteroatom-containing monomer is not particularly limited, but examples of the oxygen atom-containing monomer include vinyl ether, alkoxystyrene, allyl glycidyl ether, ethylene oxide, propylene oxide, ethers such as tetrahydrofuran, (meth ) Acrylic acid and their esters, acid anhydrides, nitrogen atom-containing monomers such as acrylonitrile, N-vinylcarbazole, carbamic acid and caprolactam, silicon atom-containing monomers such as alkoxysilylstyrene and alkoxysilylvinyls is mentioned.
If the monomer having a heteroatom does not contain an unsaturated bond, the monomer having a heteroatom and a monomer having a carbon-carbon double bond (e.g., conjugated diene monomers such as butadiene and isoprene, vinyl polymers such as styrene) ) can be polymerized.
The polymerization method is not particularly limited, and can be carried out by a known method.

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

The rubber composition may contain silica.
Examples of silica include dry silica (anhydrous silicic acid) and wet silica (hydrated silicic acid), but wet silica is preferred because it contains many silanol groups. These may be used alone or in combination of two or more.

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

As silica, for example, products of Degussa, Rhodia, Tosoh Silica, Solvay Japan, Tokuyama, etc. can be used.

The silica content is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, still more preferably 15 parts by mass or more, and preferably 150 parts by mass or less, or more, relative to 100 parts by mass of the rubber component. It is preferably 100 parts by mass or less, 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 obtained more favorably.

In the 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 still more preferably 30% by mass or more, Although the upper limit is not particularly limited, 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 obtained more favorably.

When the rubber composition contains silica, it preferably 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, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3- sulfides such as triethoxysilylpropyl methacrylate monosulfide; mercaptos such as 3-mercaptopropyltrimethoxysilane and 2-mercaptoethyltriethoxysilane; vinyls such as vinyltriethoxysilane and vinyltrimethoxysilane; Amino compounds such as propyltriethoxysilane and 3-aminopropyltrimethoxysilane, glycidoxy compounds such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane, 3-nitropropyltrimethoxysilane, Nitro-based agents such as 3-nitropropyltriethoxysilane and chloro-based agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane can be mentioned. Commercially available products such as Degussa, Momentive, Shin-Etsu Silicone Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azumax Co., Ltd., Dow Corning Toray Co., Ltd., and the like 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 obtain better effects, and disulfide-based agents having a disulfide bond such as bis(3-triethoxysilylpropyl) disulfide. A silane coupling agent is 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 preferably 20 parts by mass or less, more preferably 15 parts by mass or less, relative to 100 parts by mass of silica. is. Within the above range, the effect tends to be obtained more favorably.

The rubber composition may contain carbon black.
Examples of carbon black include, but are not limited to, N134, N110, N220, N234, N219, N339, N330, N326, N351, N550 and N762. These may be used alone or in combination of two or more.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 80 m ² /g or more, more preferably 100 m ² /g or more, and preferably 150 m ² /g or less, more preferably 130 m ² /g. It is below. Within the above range, the effect tends to be obtained more favorably.
In this specification, the N ₂ SA of carbon black is a value measured according to JIS K6217-2:2001.

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

The content of carbon black is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, still more preferably 20 parts by mass or more, and particularly preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component, and , preferably 150 parts by mass or less, more preferably 100 parts by mass or less, still 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 obtained more favorably.

The rubber composition may contain oil.
Oils include, for example, process oils, vegetable oils, or mixtures thereof. As the process oil, for example, paraffinic process oil, aromatic process oil, naphthenic process oil, etc. can be used. Vegetable oils 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 bran oil, safflower oil, sesame oil, Olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, tung oil and the like. These may be used alone or in combination of two or more. Of these, process oils are preferred, and aroma-based process oils are more preferred, because they are more effective.

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

The content of the oil is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, still more preferably 20 parts by mass or more, and preferably 50 parts by mass or less, or more, relative to 100 parts by mass of the rubber component. Preferably, it is 35 parts by mass or less. Within the above range, the effect tends to be obtained more favorably. The content of oil 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 commonly used in the tire industry, and includes rosin-based resin, coumarone-indene resin, α-methylstyrene-based resin, terpene-based resin, pt-butylphenolacetylene resin, and acrylic resin. resin, C5 resin, C9 resin, and the like. Commercially available products include Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical, Nichinuri Chemical Co., Ltd., Japan. Catalysts, products of JX Nippon Oil & Energy Corporation, Arakawa Chemical Industries, Ltd., Taoka Chemical Industries, Ltd., Toagosei Co., Ltd., etc. can be used. These may be used alone or in combination of two or more.

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

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

As the wax, for example, products of Ouchi Shinko Kagaku Kogyo Co., Ltd., Nippon Seiro Co., Ltd., Seiko Kagaku 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 preferably 20 parts by mass or less, more preferably 10 parts by mass, based on 100 parts by mass of the rubber component. It is below the department. Within the above range, the effect tends to be obtained more favorably.

The rubber composition may contain an antioxidant.
Examples of anti-aging agents include naphthylamine-based anti-aging agents such as phenyl-α-naphthylamine; diphenylamine-based anti-aging agents such as octylated diphenylamine and 4,4′-bis(α,α′-dimethylbenzyl)diphenylamine; -Isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, etc. p-phenylenediamine-based antioxidants; quinoline-based antioxidants such as polymers of 2,2,4-trimethyl-1,2-dihydroquinoline; 2,6-di-t-butyl-4-methylphenol, monophenolic anti-aging agents such as styrenated phenol; inhibitors and the like. These may be used alone or in combination of two or more. Among them, p-phenylenediamine antioxidants and quinoline antioxidants are preferred.

As the anti-aging agent, products of Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Kagaku Kogyo Co., Ltd., Flexis, etc. can be used, for example.

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 preferably 10 parts by mass or less, more preferably 5 parts by mass, relative to 100 parts by mass of the rubber component. It is below the department. Within the above range, the effect tends to be obtained more favorably.

The rubber composition may contain stearic acid.
Conventional stearic acid can be used, for example, NOF Corporation, NOF Corporation, Kao Corporation, Wako Pure Chemical Industries, Ltd., Chiba Fatty Acids Co., Ltd. products can be used.

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

The rubber composition may contain zinc oxide.
As the zinc oxide, conventionally known ones can be used, for example, products of Mitsui Kinzoku Mining Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc. can be used.

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

The rubber composition may contain sulfur.
Sulfur includes powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, soluble sulfur and the like commonly used in the rubber industry. These may be used alone or in combination of two or more.

As sulfur, for example, products of Tsurumi Chemical Industry Co., Ltd., Karuizawa Io Co., Ltd., Shikoku Kasei Kogyo Co., Ltd., Flexis Co., Ltd., Nippon Kantan 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 preferably 10 parts by mass or less, more preferably 5 parts by mass, based on 100 parts by mass of the rubber component. parts or less, more preferably 3 parts by mass or less. Within the above range, the effect tends to be obtained more favorably.

The rubber composition may contain a vulcanization accelerator.
Vulcanization accelerators include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, and N-cyclohexyl-2-benzothiazylsulfenamide; tetramethylthiuram disulfide (TMTD ), tetrabenzylthiuram disulfide (TBzTD), tetrakis (2-ethylhexyl) thiuram disulfide (TOT-N) and other thiuram vulcanization accelerators; N-cyclohexyl-2-benzothiazolesulfenamide, N-tert-butyl- 2-benzothiazolylsulfenamide, N-oxyethylene-2-benzothiazolesulfenamide, N-oxyethylene-2-benzothiazolesulfenamide, N,N'-diisopropyl-2-benzothiazolesulfenamide, etc. and guanidine-based vulcanization accelerators such as diphenylguanidine, diorthotolylguanidine and orthotolylbiguanidine. These may be used alone or in combination of two or more. Among them, sulfenamide-based vulcanization accelerators and guanidine-based vulcanization accelerators are preferable because they are more suitable for obtaining effects.

As the vulcanization accelerator, for example, products manufactured by Kawaguchi Kagaku Co., Ltd., Ouchi Shinko Kagaku Co., etc. 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 preferably 10 parts by mass or less, more preferably 7 parts by mass, relative to 100 parts by mass of the rubber component. It is below. Within the above range, the effect tends to be obtained more favorably.

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

The rubber composition can be produced, for example, by kneading the above components using a rubber kneading device such as an open roll mixer or a Banbury mixer, followed by vulcanization.

As for the kneading conditions, the kneading temperature is usually 100 to 180°C, preferably 120 to 170°C in the base kneading step in which additives other than the vulcanizing agent and the vulcanization accelerator are kneaded. In the finishing kneading step of kneading the vulcanizing agent and the vulcanization accelerator, the kneading temperature is usually 120°C or lower, preferably 80 to 110°C. A composition obtained by kneading a vulcanizing agent and a vulcanization accelerator is usually subjected to vulcanization treatment such as press vulcanization. The vulcanization temperature is generally 140-190°C, preferably 150-185°C. Vulcanization time is usually 5 to 15 minutes.

The rubber composition can be used for treads. A tread composed of a cap tread and a base tread can be suitably used for the cap tread.

In the above tire, the land ratio of the tread may be 30% or more, but from the viewpoint of dry grip performance, it is preferably 40% or more, more preferably 50% or more, and still more preferably 75% or more. From the viewpoint of wet grip performance, the upper limit is preferably 95% or less, more preferably 90% or less, and even more preferably 85% or less.
Further, when the rubber composition constituting the tread has a land ratio of 30% or more and less than 60%, it preferably has a hardness of 60 to 75 when dry and a hardness of 55 to 70 when wet with water, and a land ratio of 60% to 95. %, the hardness is preferably 55 to 70 when dry and 30 to 55 when wet.

The tread of the tire may have circumferentially continuous grooves and/or circumferentially discontinuous grooves. Patterns having such grooves include rib type, lug type, rib lug type, and block type.

The tire (pneumatic tire, etc.) is manufactured by a conventional method using the rubber composition. That is, a rubber composition blended with various additives as necessary is extruded according to the shape of a tread (cap tread) in an unvulcanized stage, and molded by a normal method on a tire molding machine. , and other tire members to form an unvulcanized tire, which is then heated and pressurized in a vulcanizer to manufacture a tire.

At least a portion of the tread of the tire may be composed of the rubber composition, and the entire tread may be composed of the rubber composition.

The above tires include tires for passenger cars, tires for large passenger cars, tires for large SUVs, tires for trucks and buses, tires for motorcycles, racing tires, studless tires (winter tires), all-season tires, run-flat tires, and aircraft tires. , mining tires and the like. The tire may be a pneumatic tire or a non-pneumatic tire.

EXAMPLES The present invention will be specifically described based on Examples, but the present invention is not limited to these.

(Production example 1)
A nitrogen purged autoclave reactor was charged with hexane, 1,3-butadiene, styrene, tetrahydrofuran, and ethylene glycol diethyl ether. Bis(diethylamino)methylvinylsilane and n-butyllithium were then introduced as cyclohexane and n-hexane solutions, respectively, to initiate polymerization.
The stirring speed was 130 rpm, the temperature inside the reactor was 65° C., and the copolymerization of 1,3-butadiene and styrene was carried out for 3 hours while continuously supplying the monomers into the reactor. Next, the resulting polymer solution was stirred at a stirring speed of 130 rpm, N-(3-dimethylaminopropyl)acrylamide was added, and the reaction was allowed to proceed for 15 minutes. After completion of the polymerization reaction, 2,6-di-tert-butyl-p-cresol was added. Then, the solvent was removed by steam stripping and dried with a hot 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-purged glass flask, the internal temperature was cooled to 0°C or less, and then 0.55 mol/L was added. 10 mL of a triisobutylaluminum/hexane solution of 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 at a molar ratio of 9/1 and 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, after the solvent was distilled off under reduced pressure at an external temperature of 50°C/internal pressure of 1.0 kPa or less, the remaining residue was suspended in water and filtered. It is dried under reduced pressure at 1 kPa or less until it reaches a constant weight, and the polymer 1 (in the infrared absorption spectrum, the ether group derived from the above formula (A) and the carbon-carbon derived from the above formula (B) is obtained with a yield of 80%. A peak was confirmed, the weight average molecular weight (Mw) was 780,000, 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 3) Synthesis of Polymer 2 (Amine-Allyl Glycidyl Ether Copolymer) The procedure was carried out in the same manner as in Production Example 2, except that ethylene oxide was changed to triglycidylamine. Polymer 2 of glycidylamine and allyl glycidyl ether (Analysis in the same manner as in Production Example 2 was performed to confirm the absorption of amine and the peak derived from the carbon-carbon double bond, and the weight average molecular weight was 980,000. The content of the group (structural unit) represented by the formula (B) was 8 mol %).

(Production Example 4) Synthesis of Polymer 3 (silyl-allyl glycidyl ether copolymer) The same procedure as in Production Example 2 was carried out, except that ethylene oxide was changed to triethoxysilyl glycidyl ether, and the yield was 80%. Polymer 3 of triethoxysilyl glycidyl ether and allyl glycidyl ether (Analysis in the same manner as in Production Example 2 was performed 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 polymer was 100 mol. % of the group (structural unit) represented by the above formula (B) was 8 mol %).

In addition, the following evaluations were performed on the obtained polymers 1 to 3.

<Measurement of water-insoluble content>
Weigh 1 g of polymer into a glass flask, pour 10 mL of water, stir at an internal temperature of 66 ° C. for 10 minutes, continue stirring until the internal temperature is 25 ° C. or less, and filter with a filter paper of cellulose material and mesh size 5C. Then, the residue remaining on the filter paper was dried at a temperature of 80° C. and an internal pressure of 0.1 kPa or less for 8 hours, weighed, and the water-insoluble matter was calculated according to the following formula.
Water-insoluble content (% by mass) = dry weight of residue (g) / initial weight of polymer (g) x 100

<Measurement of THF-insoluble content>
Weigh 1 g of polymer into a glass flask, pour 10 mL of tetrahydrofuran, stir at an internal temperature of 66 ° C. for 10 minutes, continue stirring until the internal temperature is 25 ° C. or less, and filter with a filter paper of cellulose material and mesh size 5C. Then, the residue remaining on the filter paper was dried at a temperature of 80° C. and an internal pressure of 0.1 kPa or less for 8 hours, weighed, and the THF-insoluble matter was calculated by the following formula.
THF insoluble content (% by mass) = dry weight of residue (g) / initial weight of polymer (g) x 100

Various chemicals will be collectively described below.
SBR: SBR synthesized by the above method (modified S-SBR, styrene content: 25% by mass, vinyl content: 59 mol%, non-oil-extended product)
BR: BR150B (cis amount: 97% by mass) manufactured by Ube Industries, Ltd.
NR: TSR20
Polymer 1: Polymer 1 synthesized by the above method (water-insoluble content: 96% by mass, THF-insoluble content: 96% by mass)
Polymer 2: Polymer 2 synthesized by the above method (water-insoluble content: 82% by mass, THF-insoluble content: 96% by mass)
Polymer 3: Polymer 3 synthesized by the above method (water-insoluble content: 92% by mass, THF-insoluble content: 92% by mass)
Silica: ZEOSIL 1165MP (N ₂ SA: 160 m ² /g) manufactured by Rhodesia
Carbon black: SEAST 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.
Antiaging agent: Santoflex 13 (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD)) manufactured by Flexis Co., Ltd.
Stearic acid: stearic acid "Tsubaki" manufactured by NOF Corporation
Zinc oxide: Type 2 zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator 1: Noxcellar NS (N-tert- butyl-2-benzothiazolylsulfenamide)
Vulcanization accelerator 2: Noxceler D (1,3-diphenylguanidine) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.

(Formulation example)
According to the compounding recipe shown in Table 1, using a 1.7 L Banbury mixer manufactured by Kobe Steel, Ltd., chemicals other than sulfur and vulcanization accelerators were kneaded at 160°C for 4 minutes to obtain a kneaded product. got Next, sulfur and a vulcanization accelerator were added to the resulting kneaded material, and the mixture was kneaded at 80° C. for 4 minutes 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. Table 1 shows the results.

(Hardness of vulcanized rubber (Hs))
According to JIS K6253-3 (2012) "Vulcanized rubber and thermoplastic rubber-Determination of hardness-Part 3: Durometer hardness", Shore hardness of vulcanized rubber composition (test piece) by type A durometer (Hs) was measured (JIS-A hardness). Measurements were made at 25°C.

(Hardness when wet with water)
A vulcanized rubber composition after being wetted with water was obtained by immersing the vulcanized rubber composition (having a rectangular parallelepiped shape of 30 mm×30 mm×4 mm) in 20 ml of water at 25° C. for 6 hours. The hardness of the obtained vulcanized rubber composition after being wetted with water was measured by the above-described method, and was defined as the hardness when wetted with water.

(Dry hardness)
The water-moistened vulcanized rubber composition was dried under reduced pressure under conditions of 80° C. and 1 kPa or less until a constant weight was obtained to obtain a dried vulcanized rubber composition. After the temperature of the obtained vulcanized rubber composition after drying was returned to 25° C., the hardness of the vulcanized rubber composition after drying was measured by the method described above, and the hardness at the time of drying was obtained.

(Hardness when re-wet)
The dried vulcanized rubber composition (30 mm×30 mm×4 mm rectangular parallelepiped) was immersed in 20 ml of water at 25° C. for 6 hours to obtain a rewatered vulcanized rubber composition. The hardness of the obtained vulcanized rubber composition after rewetting with water was measured by the above-described method, and was defined as the hardness upon rewetting with water.

(Preparation of tires)
The obtained unvulcanized rubber composition was molded into a tread shape, laminated with another tire member, and press-vulcanized at 170° C./12 minutes to prepare a test tire (size: 195/65R15). Examples 1 to 18 and Comparative Examples 1 to 3 are block pattern tires, and Examples 19 to 36 and Comparative Examples 4 to 6 are lug pattern tires.

(Measurement of land ratio)
The land ratio (%) was measured using the JATMA standard according to the land ratio measurement method described in this specification. Tables 2 and 3 show the measurement results.

(Wet Grip Performance Index)
The test tire was mounted on a vehicle, and the tire was run 8 times on a 2 km test course on which water had been sprinkled in advance. Tables 2 and 3 show the evaluation results.

(Dry grip performance index)
The test tire was mounted on a vehicle, and the tire was run 8 laps on a 2 km test course on a dry road surface. Tables 2 and 3 show the evaluation results.

From Tables 1 to 3, examples in which the hardness reversibly changes with water, have a tread composed of a rubber composition that satisfies the above formula (1), and the land ratio of the tread is within a predetermined range , wet grip performance, and dry grip performance can be improved.

Claims (12)

Having a tread made of a rubber composition whose hardness reversibly changes with water and satisfies the following formula (1),
The rubber composition comprises a rubber component containing styrene-butadiene rubber,
The content of styrene-butadiene rubber in 100% by mass of the rubber component is 95% by mass or less,
A tire in which the land ratio of the tread is 30% or more.
Hardness when dry - hardness when wet with water ≥ 1 (1)
(In the formula, the hardness is the JIS-A hardness of the rubber composition at 25°C.) 2. The tire according to claim 1, wherein in the formula (1), the ratio of dry hardness-water-wet hardness is 2 or more. 2. The tire according to claim 1, wherein in the formula (1), the ratio of dry hardness-water-wet hardness is 3 or more. 2. The tire according to claim 1, wherein in the formula (1), the ratio of hardness when dry to hardness when wet with water is 4 or more. The tire according to any one of claims 1 to 4, wherein the rubber composition contains a diene rubber and a polymer having a carbon-carbon double bond and a heteroatom. 6. The tire of claim 5, wherein said heteroatom is at least one atom selected from the group consisting of oxygen, nitrogen, silicon, sulfur, phosphorus and halogen atoms. The tire according to claim 5 or 6, wherein 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. The tire according to any one of claims 5 to 7, wherein the polymer has an insoluble content of 5% by mass or more when 1 g of the polymer is suspended in 10 mL of tetrahydrofuran. The tire according to any one of claims 5 to 8, wherein the rubber composition contains 5 parts by mass or more of the polymer with respect to 100 parts by mass of the rubber component. The tire according to any one of claims 1 to 9, wherein the rubber composition contains an isoprene-based rubber. The tire according to any one of claims 1 to 10, wherein the rubber composition contains butadiene rubber. The tire according to any one of claims 1 to 11 , wherein the tread comprises circumferentially continuous grooves and/or circumferentially discontinuous grooves.