阅读说明：本技术 无钉轮胎用橡胶组合物和使用了其的无钉轮胎 (Rubber composition for studless tire and studless tire using same ) 是由 佐藤正树 高桥坚一郎 于 2020-05-12 设计创作，主要内容包括：本发明为了提供冰上性能、湿路性能、滚动阻力性能和耐磨损性能同时提高了的无钉轮胎,在无钉轮胎用橡胶组合物中,相对于包含天然橡胶和/或合成异戊二烯橡胶30质量份以上、且包含丁二烯橡胶和/或苯乙烯-丁二烯共聚物橡胶50质量份以上的二烯系橡胶100质量份,混配了二氧化硅40质量份以上、特定的四嗪化合物0.7～5质量份、和热膨胀性微胶囊0.5～20质量份。(In order to provide a studless tire having improved on-ice performance, wet performance, rolling resistance performance, and abrasion resistance, a rubber composition for studless tires is obtained by compounding 40 parts by mass or more of silica, 0.7 to 5 parts by mass of a specific tetrazine compound, and 0.5 to 20 parts by mass of a thermally expandable microcapsule to 100 parts by mass of a diene rubber containing 30 parts by mass or more of a natural rubber and/or a synthetic isoprene rubber and 50 parts by mass or more of a butadiene rubber and/or a styrene-butadiene copolymer rubber.)

1. A rubber composition for studless tires, characterized by comprising:

100 parts by mass of a diene rubber containing 30 parts by mass or more of a natural rubber and/or a synthetic isoprene rubber and 50 parts by mass or more of a butadiene rubber and/or a styrene-butadiene copolymer rubber,

more than 40 parts by mass of silicon dioxide,

0.7 to 5 parts by mass of a tetrazine compound represented by the following formula (1), and

0.5 to 20 parts by mass of a thermally expandable microcapsule,

in the formula, X¹And X²The same or different, represents a hydrogen atom, an alkyl group, an alkylthio group, an arylthio group, a heterocyclic group or an amino group, and each of these groups may have 1 or more substituents.

2. The rubber composition for studless tires according to claim 1, characterized by comprising: the diene rubber comprises, by mass, 35 to 50 parts of the natural rubber and/or the synthetic isoprene rubber and 50 to 65 parts of the butadiene rubber and/or the styrene-butadiene copolymer rubber per 100 parts of the diene rubber.

3. The rubber composition for studless tires according to claim 1, characterized by comprising: the diene rubber comprises 45 to 50 parts by mass of the natural rubber and/or the synthetic isoprene rubber and 50 to 60 parts by mass of the butadiene rubber and/or the styrene-butadiene copolymer rubber per 100 parts by mass of the diene rubber.

4. The rubber composition for studless tires according to claim 1, characterized by comprising: the compounding amount of the silica is 45 to 110 parts by mass per 100 parts by mass of the diene rubber.

5. The rubber composition for studless tires according to claim 1, characterized by comprising: the nitrogen adsorption specific surface area of the silica is N₂SA of 100 to 220m²/g。

6. The rubber composition for studless tires according to claim 1, characterized by comprising: the rubber composition further comprises 2 to 30 parts by mass of a liquid rubber which is liquid at 23 ℃ per 100 parts by mass of the diene rubber.

7. The rubber composition for studless tires according to claim 6, characterized in that: the liquid rubber is liquid polybutadiene.

8. A studless tire using the rubber composition for a tire according to claim 1 for a cap tread.

Technical Field

The present invention relates to a rubber composition for studless tires (studless tire) and a studless tire using the same, and more particularly, to a rubber composition for studless tires capable of improving on-ice performance, wet performance, rolling resistance performance, and abrasion resistance performance at the same time and a studless tire using the same.

Background

Conventionally, in order to improve the on-ice performance (braking property on ice) and the wet performance (braking property on a wet road surface) of studless tires, a technique of compounding silica into a rubber composition for studless tires has been known. However, silica has a problem that it has low affinity for rubber and poor dispersibility, and thus cannot obtain desired physical properties.

On the other hand, increasing the surface roughness of the tread is effective for improving the on-ice performance, and for example, the following methods are known: by mixing hard foreign matter and hollow particles in the rubber, fine irregularities are formed on the rubber surface, and a water film generated on the ice surface is removed, thereby increasing the friction on ice. However, only by such a method, there is a problem that the wear resistance is lowered.

For the purpose of improving the dispersibility of silica and improving fuel economy, for example, patent document 1 below discloses a technique of compounding a specific tetrazine compound.

However, the technique disclosed in patent document 1 cannot improve the on-ice performance, the wet performance, the rolling resistance performance, and the wear resistance performance at the same time.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 6148799

Disclosure of Invention

Problems to be solved by the invention

Accordingly, an object of the present invention is to provide a rubber composition for studless tires capable of improving on-ice performance, wet performance, rolling resistance performance, and abrasion resistance performance at the same time, and a studless tire using the same.

Means for solving the problems

The present inventors have conducted intensive studies and as a result, have found that the above problems can be solved by blending a specific amount of silica, a specific tetrazine compound and a heat-expandable microcapsule in a diene rubber having a specific composition, and have completed the present invention.

The invention provides a rubber composition for a studless tire, which is characterized in that: the rubber composition is characterized by comprising a diene rubber which comprises at least 30 parts by mass of a natural rubber and/or a synthetic isoprene rubber and at least 50 parts by mass of a butadiene rubber and/or a styrene-butadiene copolymer rubber, and at least 40 parts by mass of silica, 0.7 to 5 parts by mass of a tetrazine compound represented by the following formula (1), and 0.5 to 20 parts by mass of a thermally expandable microcapsule, the weight of the diene rubber being 100 parts by mass.

[ in the formula, X¹And X²The same or different, represents a hydrogen atom, an alkyl group, an alkylthio group, an arylthio group, a heterocyclic group or an amino group. Each of these groups may have 1 or more substituents.]

The present invention also provides a studless tire using the rubber composition for a tire in a cap tread (cap tread).

ADVANTAGEOUS EFFECTS OF INVENTION

The invention provides a rubber composition for studless tires, which is characterized in that: the rubber composition is characterized by comprising 40 parts by mass or more of silica, 0.7 to 5 parts by mass of a tetrazine compound represented by the formula (1), and 0.5 to 20 parts by mass of a thermally expandable microcapsule per 100 parts by mass of a diene rubber containing 30 parts by mass or more of Natural Rubber (NR) and/or synthetic Isoprene Rubber (IR) and 50 parts by mass or more of Butadiene Rubber (BR) and/or styrene-butadiene copolymer rubber (SBR).

In general, NR and BR are used to improve low-temperature characteristics and wear resistance, but silica is likely to be unevenly distributed in NR.

The present inventors have studied a rubber composition containing a tetrazine compound represented by the above formula (1), and as a result, have found that the tetrazine compound represented by the above formula (1) reacts more easily with a butadiene structure than with an isoprene structure.

Therefore, by specifying the composition of the diene rubber, the dispersibility of silica in NR or IR and the dispersibility of silica in BR or SBR due to the tetrazine compound represented by the above formula (1) are optimally balanced, and thus the silica can be dispersed well in the rubber composition containing NR and/or IR and BR and/or SBR. Thus, it is possible to provide a rubber composition for studless tires, which can improve the performance on ice, the wet performance and the rolling resistance performance by the high dispersibility of silica and can improve the abrasion resistance performance even when a thermally expandable microcapsule is compounded, and a studless tire using the same.

Detailed Description

The present invention is described in more detail below.

(diene rubber)

The diene rubber used in the present invention is required to contain not less than 30 parts by mass of Natural Rubber (NR) and/or synthetic Isoprene Rubber (IR) and not less than 50 parts by mass of Butadiene Rubber (BR) and/or styrene-butadiene copolymer rubber (SBR) when the whole is 100 parts by mass.

If the relationship between NR and IR and the amount of BR and SBR is not satisfied, the dispersibility of silica is not improved, and the desired effect of the present invention cannot be exhibited.

The amount of NR and/or IR is preferably 35 to 50 parts by mass, more preferably 40 to 50 parts by mass, per 100 parts by mass of the diene rubber. Further, the amount of BR and/or SBR is preferably 50 to 65 parts by mass, more preferably 50 to 60 parts by mass, based on 100 parts by mass of the diene rubber.

(silica)

As the silica used in the present invention, 2 or more of the following may be used alone or in combination: any silica conventionally used in rubber compositions is known, such as dry silica, wet silica, colloidal silica, and precipitated silica.

From the viewpoint of further improving the on-ice performance and the wet performance, the nitrogen adsorption specific surface area (N) of silica₂SA) is preferably 100 to 220m²/g。

The nitrogen adsorption specific surface area (N)₂SA) was determined in accordance with JIS K6217-2.

The amount of the silica is 40 parts by mass or more, preferably 45 to 110 parts by mass, and more preferably 50 to 100 parts by mass per 100 parts by mass of the diene rubber. If the compounding amount of silica is less than 40 parts by mass, the effects of the present invention cannot be exerted.

(tetrazine Compound)

The tetrazine compound used in the present invention is represented by the following formula (1) and is disclosed in patent document 1, and is well known.

[ in the formula, X¹And X²The same or different, represents a hydrogen atom, an alkyl group, an alkylthio group, an arylthio group, a heterocyclic group or an amino group. Each of these groups may have 1 or more substituents.]

In the present specification, the "alkyl group" is not particularly limited, and examples thereof include linear, branched or cyclic alkyl groups, and specific examples thereof include: a linear or branched alkyl group having 1 to 6 carbon atoms (particularly 1 to 4 carbon atoms) such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a 1-ethylpropyl group, an n-pentyl group, a neopentyl group, an n-hexyl group, an isohexyl group, or a 3-methylpentyl group; a cyclic alkyl group having 3 to 8 carbon atoms (particularly 3 to 6 carbon atoms) such as a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, or a cyclooctyl group; and so on. The preferred alkyl group is a linear or branched alkyl group having 1 to 6 carbon atoms, more preferably a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group or an n-pentyl group, and particularly preferably a methyl group or an ethyl group.

In the present specification, the "alkylthio group" is not particularly limited, and examples thereof include a straight-chain, branched or cyclic alkylthio group, and specifically include: straight-chain or branched alkylthio groups having 1 to 6 carbon atoms (particularly 1 to 4 carbon atoms), such as methylthio, ethylthio, n-propylthio, isopropylthio, n-butylthio, isobutylthio, sec-butylthio, tert-butylthio, 1-ethylpropylthio, n-pentylthio, neopentylthio, n-hexylthio, isohexylthio, and 3-methylpentylthio; a C3-8 (especially C3-6) cyclic alkylthio group such as cyclopropylthio, cyclobutylthio, cyclopentylthio, cyclohexylthio, cycloheptylthio, cyclooctylthio and the like; and so on. As the preferred alkylthio group, a methylthio group, an ethylthio group, an isopropylthio group or an isobutylthio group is preferable, and a methylthio group or an ethylthio group is more preferable.

In the present specification, the "aralkyl group" is not particularly limited, and examples thereof include a benzyl group, a phenethyl group, a trityl group, a 1-naphthylmethyl group, a 2- (1-naphthyl) ethyl group, a 2- (2-naphthyl) ethyl group and the like. As a more preferred aralkyl group, a benzyl group or a phenethyl group is preferred, and a benzyl group is more preferred.

In the present specification, the "aryl group" is not particularly limited, and examples thereof include phenyl, biphenyl, naphthyl, indanyl, and 9H-fluorenyl groups. As a more preferred aryl group, a phenyl group or a naphthyl group is preferable, and a phenyl group is more preferable.

In the present specification, the "arylthio group" is not particularly limited, and examples thereof include a phenylthio group, a biphenylthio group, and a naphthylthio group.

In the present specification, the "heterocyclic group" is not particularly limited, and examples thereof include 2-pyridyl, 3-pyridyl, 4-pyridyl, 2-pyrazinyl, 2-pyrimidinyl, 4-pyrimidinyl, 5-pyrimidinyl, 3-pyridazinyl, 4- (1,2, 3-triazinyl), 5- (1,2, 3-triazinyl), 2- (1,3, 5-triazinyl), 3- (1,2, 4-triazinyl), 5- (1,2, 4-triazinyl), 6- (1,2, 4-triazinyl), 2-quinolyl, 3-quinolyl, 4-quinolyl, 5-quinolyl, 6-quinolyl, 7-quinolyl, 8-quinolyl, and the like, 1-isoquinolinyl, 3-isoquinolinyl, 4-isoquinolinyl, 5-isoquinolinyl, 6-isoquinolinyl, 7-isoquinolinyl, 8-isoquinolinyl, 2-quinoxalinyl, 3-quinoxalinyl, 5-quinoxalinyl, 6-quinoxalinyl, 7-quinoxalinyl, 8-quinoxalinyl, 3-cinnolinyl, 4-cinnolinyl, 5-cinnolinyl, 6-cinnolinyl, 7-cinnolinyl, 8-cinnolinyl, 2-quinazolinyl, 4-quinazolinyl, 5-quinazolinyl, 6-quinazolinyl, 7-quinazolinyl, 8-quinazolinyl, 1-phthalazinyl, 4-phthalazinyl, 5-phthalazinyl, 6-phthalazinyl, 7-phthalazinyl, 8-phthalazinyl group, 1-tetrahydroquinolyl group, 2-tetrahydroquinolyl group, 3-tetrahydroquinolyl group, 4-tetrahydroquinolyl group, 5-tetrahydroquinolyl group, 6-tetrahydroquinolyl group, 7-tetrahydroquinolyl group, 8-tetrahydroquinolyl group, 1-pyrrolyl group, 2-pyrrolyl group, 3-pyrrolyl group, 2-furyl group, 3-furyl group, 2-thienyl group, 3-thienyl group, 1-imidazolyl group, 2-imidazolyl group, 4-imidazolyl group, 5-imidazolyl group, 1-pyrazolyl group, 3-pyrazolyl group, 4-pyrazolyl group, 5-pyrazolyl group, 2-oxazolyl group, 4-oxazolyl group, 5-oxazolyl group, 2-thiazolyl group, 4-thiazolyl group, 5-thiazolyl group, 3-isoxazolyl group, 3-pyridyl group, and the like, 4-isoxazolyl, 5-isoxazolyl, 3-isothiazolyl, 4-isothiazolyl, 5-isothiazolyl, 4- (1,2, 3-thiadiazolyl), 5- (1,2, 3-thiadiazolyl), 3- (1,2, 5-thiadiazolyl), 2- (1,3, 4-thiadiazolyl), 4- (1,2, 3-oxadiazolyl), 5- (1,2, 3-oxadiazolyl), 3- (1,2, 4-oxadiazolyl), 5- (1,2, 4-oxadiazolyl), 3- (1,2, 5-oxadiazolyl), 2- (1,3, 4-oxadiazolyl), 1- (1,2, 3-triazolyl), 4- (1,2, 3-triazolyl), 5- (1,2, 3-triazolyl), 1- (1,2, 4-triazolyl), 3- (1,2, 4-triazolyl), 5- (1,2, 4-triazolyl), 1-tetrazolyl, 5-tetrazolyl, 1-indolyl, 2-indolyl, 3-indolyl, 4-indolyl, 5-indolyl, 6-indolyl, 7-indolyl, 1-isoindolyl, 2-isoindolyl, 3-isoindolyl, 4-isoindolyl, 5-isoindolyl, 6-isoindolyl, 7-isoindolyl, 1-benzimidazolyl, 2-benzimidazolyl, 4-benzimidazolyl, 5-benzimidazolyl, etc, 6-benzimidazolyl, 7-benzimidazolyl, 2-benzofuranyl, 3-benzofuranyl, 4-benzofuranyl, 5-benzofuranyl, 6-benzofuranyl, 7-benzofuranyl, 1-isobenzofuranyl, 3-isobenzofuranyl, 4-isobenzofuranyl, 5-isobenzofuranyl, 6-isobenzofuranyl, 7-isobenzofuranyl, 2-benzothienyl, 3-benzothienyl, 4-benzothienyl, 5-benzothienyl, 6-benzothienyl, 7-benzothienyl, 2-benzoxazolyl, 4-benzoxazolyl, 5-benzoxazolyl, 6-benzoxazolyl, 7-benzoxazolyl, 2-benzothiazolyl, 3-benzofuranyl, 4-isobenzofuranyl, 4-benzothiazolyl, 5-benzothiazolyl, 6-benzothiazolyl, 7-benzothiazolyl, 1-indazolyl, 3-indazolyl, 4-indazolyl, 5-indazolyl, 6-indazolyl, 7-indazolyl, 2-morpholinyl, 3-morpholinyl, 4-morpholinyl, 1-piperazinyl, 2-piperazinyl, 1-piperidinyl, 2-piperidinyl, 3-piperidinyl, 4-piperidinyl, 2-tetrahydropyranyl, 3-tetrahydropyranyl, 4-tetrahydropyranyl, 2-tetrahydrothiopyranyl, 3-tetrahydrothiopyranyl, 4-tetrahydrothiopyranyl, 1-pyrrolidinyl, 2-pyrrolidinyl, 3-pyrrolidinyl, 2-tetrahydrofuranyl, 1-pyrrolidinyl, 2-morpholinyl, 1-piperazinyl, 2-piperazinyl, 1-piperidinyl, 2-piperidinyl, 3-piperidinyl, 4-piperidinyl, 2-tetrahydropyranyl, 2-tetrahydrothiopyranyl, 2-pyrrolidinyl, 3-pyrrolidinyl, 2-tetrahydrofuranyl, 2-thiazolyl, etc, 3-tetrahydrofuranyl, 2-tetrahydrothienyl, 3-tetrahydrothienyl, and the like. Among them, preferred as the heterocyclic group is a pyridyl group, a furyl group, a thienyl group, a pyrimidinyl group or a pyrazinyl group, and more preferred is a pyridyl group.

In the present specification, "amino" includes not only-NH₂The amino group shown also includes, for example, the following substituted amino groups: a linear or branched monoalkylamino group having 1 to 6 carbon atoms (particularly, having 1 to 4 carbon atoms), such as a methylamino group, an ethylamino group, a n-propylamino group, an isopropylamino group, a n-butylamino group, an isobutylamino group, a sec-butylamino group, a tert-butylamino group, a 1-ethylpropylamino group, a n-pentylamino group, a neopentylamino group, a n-hexylamino group, an isohexylamino group, or a 3-methylpentylamino group; a dialkylamino group having a linear or branched alkyl group having 2 carbon atoms of 1 to 6 (particularly 1 to 4 carbon atoms) such as a dimethylamino group, an ethylmethylamino group, or a diethylamino group; and so on.

Each of these alkyl group, alkylthio group, aralkyl group, aryl group, arylthio group, heterocyclic group and amino group may have 1 or more substituents, respectively. The "substituent" is not particularly limited, and examples thereof include a halogen atom, an amino group, an aminoalkyl group, an alkoxycarbonyl group, an acyl group, an acyloxy group, an amide group, a carboxyl group, a carboxyalkyl group, a formyl group, a nitrile group, a nitro group, an alkyl group, a hydroxyalkyl group, a hydroxyl group, an alkoxy group, an aryl group, an aryloxy group, a heterocyclic group, a thiol group, an alkylthio group, and an arylthio group. Preferably 1 to 5, more preferably 1 to 3 substituents are present.

In the present specification, examples of the "halogen atom" include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a chlorine atom, a bromine atom and an iodine atom are preferable.

In the present specification, the "aminoalkyl group" is not particularly limited, and examples thereof include an aminoalkyl group such as an aminomethyl group, a 2-aminoethyl group, and a 3-aminopropyl group.

In the present specification, the "alkoxycarbonyl group" is not particularly limited, and examples thereof include a methoxycarbonyl group and an ethoxycarbonyl group.

In the present specification, the "acyl group" is not particularly limited, and examples thereof include a linear or branched alkylcarbonyl group having 1 to 4 carbon atoms such as an acetyl group, a propionyl group, and a pivaloyl group.

In the present specification, the "acyloxy group" is not particularly limited, and examples thereof include acetoxy, propionyloxy, and n-butyryloxy.

In the present specification, the "amide group" is not particularly limited, and examples thereof include: carboxamide groups such as an acetamido group and a benzamido group; thioamide groups such as thioacetamide groups and thiobenzamide groups; n-substituted amide groups such as N-methylacetamide group and N-benzylacetamide group; and so on.

In the present specification, the "carboxyalkyl group" is not particularly limited, and examples thereof include carboxyalkyl groups (preferably alkyl groups having 1 to 6 carbon atoms having a carboxyl group) such as a carboxymethyl group, a carboxyethyl group, a carboxyl-n-propyl group, a carboxyl-n-butyl group, and a carboxyl-n-hexyl group.

In the present specification, the "hydroxyalkyl group" is not particularly limited, and examples thereof include hydroxyalkyl groups (preferably alkyl groups having 1 to 6 carbon atoms and a hydroxyl group) such as a hydroxymethyl group, a hydroxyethyl group, a hydroxy-n-propyl group, and a hydroxy-n-butyl group.

In the present specification, the "alkoxy group" is not particularly limited, and examples thereof include: examples of the linear, branched or cyclic alkoxy group include linear or branched alkoxy groups having 1 to 6 carbon atoms (particularly 1 to 4 carbon atoms) such as a methoxy group, an ethoxy group, a n-propoxy group, an isopropoxy group, a n-butoxy group, a tert-butoxy group, a n-pentoxy group, a neopentoxy group and a n-hexoxy group; a C3-8 (particularly C3-6) cyclic alkoxy group such as a cyclopropyloxy group, a cyclobutyloxy group, a cyclopentyloxy group, a cyclohexyloxy group, a cycloheptyloxy group, or a cyclooctyloxy group; and so on.

In the present specification, the "aryloxy group" is not particularly limited, and examples thereof include a phenoxy group, a biphenyloxy group, and a naphthyloxy group.

The "salt" of the tetrazine compound represented by the formula (1) is not particularly limited, and may include all kinds of salts. Examples of such salts include: inorganic acid salts such as hydrochloride, sulfate, and nitrate; organic acid salts such as acetate and methanesulfonate; alkali metal salts such as sodium salt and potassium salt; alkaline earth metal salts such as magnesium salts and calcium salts; quaternary ammonium salts such as dimethylammonium and triethylammonium; and so on.

Of these tetrazine compounds (1), the preferred compound is X¹And X²The same or different, and is an alkyl group which may have a substituent, an aralkyl group which may have a substituent, an aryl group which may have a substituent, or a heterocyclic group which may have a substituent.

More preferred tetrazine compounds (1) are X¹And X²The same or different, and is an aralkyl group which may have a substituent, an aryl group which may have a substituent, or a heterocyclic group which may have a substituent.

Further preferred tetrazine compounds (1) are X¹And X²The same or different and is a benzyl group which may have a substituent, a phenyl group which may have a substituent, a 2-pyridyl group which may have a substituent, a 3-pyridyl group which may have a substituent, a 4-pyridyl group which may have a substituent, a 2-furyl group which may have a substituent, a thienyl group which may have a substituent, a 1-pyrazolyl group which may have a substituent, a 2-pyrimidinyl group which may have a substituent or a 2-pyrazinyl group which may have a substituent, among theseOf the compounds, X is particularly preferred¹And X²The same or different, and is a 2-pyridyl group which may have a substituent, a 3-pyridyl group which may have a substituent, or a 2-furyl group which may have a substituent.

Specifically, examples of the tetrazine compound (1) include 1,2,4, 5-tetrazine, 3, 6-bis (2-pyridyl) -1,2,4, 5-tetrazine, 3, 6-bis (3-pyridyl) -1,2,4, 5-tetrazine, 3, 6-bis (4-pyridyl) -1,2,4, 5-tetrazine, 3, 6-diphenyl-1, 2,4, 5-tetrazine, 3, 6-dibenzyl-1, 2,4, 5-tetrazine, 3, 6-bis (2-furyl) -1,2,4, 5-tetrazine, 3-methyl-6- (3-pyridyl) -1,2,4, 5-tetrazine, 3, 6-bis (3, 5-dimethyl-1-pyrazolyl) -1,2,4, 5-tetrazine, 3, 6-bis (2-thienyl) -1,2,4, 5-tetrazine, 3-methyl-6- (2-pyridyl) -1,2,4, 5-tetrazine, 3, 6-bis (4-hydroxyphenyl) -1,2,4, 5-tetrazine, 3, 6-bis (3-hydroxyphenyl) -1,2,4, 5-tetrazine, 3, 6-bis (2-pyrimidinyl) -1,2,4, 5-tetrazine, 3, 6-bis (2-pyrazinyl) -1,2,4, 5-tetrazine, and the like.

Among them, preferred tetrazine compounds (1) are 3, 6-bis (2-pyridyl) -1,2,4, 5-tetrazine, 3, 6-bis (3-pyridyl) -1,2,4, 5-tetrazine, 3, 6-bis (2-furyl) -1,2,4, 5-tetrazine, 3-methyl-6- (3-pyridyl) -1,2,4, 5-tetrazine, and 3-methyl-6- (2-pyridyl) -1,2,4, 5-tetrazine, further preferred tetrazine compounds (1) are 3, 6-bis (2-pyridyl) -1,2,4, 5-tetrazine, and 3, 6-bis (3-pyridyl) -1,2,4, 5-tetrazine.

In the present invention, the compounding amount of the tetrazine compound is 0.7 to 5 parts by mass, preferably 1.0 to 4.0 parts by mass, per 100 parts by mass of the diene rubber.

If the compounding amount of the tetrazine compound is less than 0.7 part by mass, the compounding amount is too small, and the effects of the present invention cannot be exerted. On the contrary, if it exceeds 5 parts by mass, the on-ice performance deteriorates.

(silane coupling agent)

In the present invention, a silane coupling agent may be compounded to further improve the dispersibility of silica. The silane coupling agent to be used is not particularly limited, but is preferably a sulfur-containing silane coupling agent, and examples thereof include bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, 3-trimethoxysilylpropylbenzothiazoletetrasulfide, γ -mercaptopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane, and the like.

The amount of the silane coupling agent is preferably 1 to 20% by mass based on the mass of silica. If the compounding amount of the silane coupling agent is less than 1% by mass relative to the mass of silica, the compounding amount is too small to improve the dispersibility of silica. On the other hand, if it exceeds 20 mass%, the workability and elongation at break may deteriorate.

The amount of the silane coupling agent is preferably 5 to 15% by mass based on the mass of the silica.

(Heat-expandable microcapsules)

The rubber composition of the present invention is compounded with a heat-expandable microcapsule from the viewpoint of improving the performance on ice.

In the present invention, the heat-expandable microcapsule has a structure in which a heat-expandable substance is contained in a shell material made of a thermoplastic resin. The shell material of the thermally expandable microcapsule may be formed of a nitrile polymer.

The heat-expandable substance contained in the shell material of the microcapsule has a property of being vaporized or expanded by heat, and examples thereof include at least one selected from hydrocarbons such as isoparaffin and normal paraffin. Examples of the isoalkane include isobutane, isopentane, 2-methylpentane, 2-methylhexane, and 2,2, 4-trimethylpentane, and examples of the n-alkane include n-butane, n-propane, n-hexane, n-heptane, and n-octane. These hydrocarbons may be used alone or in combination of two or more. As a preferred embodiment of the thermally expandable substance, a hydrocarbon mixture obtained by dissolving a hydrocarbon which is gaseous at normal temperature in a hydrocarbon which is liquid at normal temperature is preferable. By using such a hydrocarbon mixture, a sufficient expansion force can be obtained in a range from a low temperature region to a high temperature region in a vulcanization molding temperature range (150 ℃ C. to 190 ℃ C.) of an unvulcanized tire.

As such heat-expandable microcapsules, for example: スェーデン trade name "EXPANCEL 091 DU-80" or "EXPANCEL 092 DU-120" manufactured by エクスパンセル of China; or "マツモトマイクロスフェアー F-85D" or "マツモトマイクロスフェアー F-100D" manufactured by Songbu oil & fat pharmacy.

The proportion of the thermally expandable microcapsules is 0.5 to 20 parts by mass, preferably 2 to 16 parts by mass, per 100 parts by mass of the diene rubber.

(other Components)

In the rubber composition of the present invention, in addition to the above-mentioned components, a vulcanizing agent or a crosslinking agent may be compounded; a vulcanization accelerator or a crosslinking accelerator; various fillers such as zinc oxide, carbon black, clay, talc, and calcium carbonate; an anti-aging agent; various additives such as plasticizers are generally blended in rubber compositions, and such additives can be kneaded by a conventional method to prepare a composition for vulcanization or crosslinking. The compounding amounts of these additives may be conventional ones unless the object of the present invention is not impaired.

(liquid rubber)

In the present invention, from the viewpoint of improving the effect of the present invention and from the viewpoint of suppressing a change in performance over time on ice, it is preferable to blend a liquid rubber.

Examples of the liquid rubber include liquid polyisoprene (liquid IR), liquid polybutadiene (liquid BR), and liquid styrene-butadiene copolymer (liquid SBR), and the liquid BR is preferable from the viewpoint of improving the effect. The liquid rubber may be, for example, one having a weight average molecular weight of 1000 to 100000, preferably 2000 to 80000. The weight average molecular weight in the present invention means a weight average molecular weight in terms of polystyrene obtained by analysis by Gel Permeation Chromatography (GPC).

The liquid rubber used in the present invention is liquid at 23 ℃. Therefore, it is distinguished from the above-mentioned diene rubber which is solid at this temperature.

The amount of the liquid rubber is preferably 2 to 30 parts by mass, and more preferably 4 to 20 parts by mass, per 100 parts by mass of the diene rubber.

The rubber composition of the present invention is suitable for producing a pneumatic tire according to a conventional method for producing a pneumatic tire, and is preferably used for a tread, particularly a cap tread, to produce a studless tire.

Examples

The present invention will be further illustrated by the following examples and comparative examples, but the present invention is not limited to the following examples.

Examples 1 to 6 and comparative examples 1 to 7

In the compounding (parts by mass) shown in table 1, components other than the vulcanization accelerator and sulfur were kneaded in a 1.7L internal banbury mixer for 5 minutes, and then the vulcanization accelerator and sulfur were added thereto and further kneaded to obtain a rubber composition. Subsequently, the obtained unvulcanized rubber composition was press-vulcanized in a predetermined mold at 160 ℃ for 20 minutes to obtain a vulcanized rubber test piece, and the physical properties of the vulcanized rubber test piece were measured by the test methods shown below.

Performance on ice: the vulcanized rubber test piece thus obtained was stuck to a flat cylindrical base rubber, and a friction tester was used on ice with an inner roller type, at a measurement temperature of-1.5 ℃ and a load of 5.5kg/cm²And the friction coefficient on ice was measured at a drum rotation speed of 25 km/h. The resulting on-ice friction coefficient is expressed in an exponential form with the value of comparative example 1 as 100. The larger the index is, the larger the frictional force on ice is, and the more excellent the performance on ice is.

Wet performance: using the vulcanized rubber test piece thus obtained, the maximum wet friction coefficient was measured using an outside type friction tester under the conditions of a measurement temperature of 25 ℃, a surface pressure of 180kPa, and a drum rotation speed of 30km/h, in a state where water was sprayed on the road surface. The maximum value of the obtained wet friction coefficient is expressed in an exponential form with the value of comparative example 1 as 100. The larger the index is, the more excellent the wet performance is.

Rolling resistance performance: tan δ (60 ℃) was measured according to JIS K6394:2007 using a viscoelastometer (manufactured by tokyo seiki) under the conditions of a tensile strain rate of 10 ± 2%, a frequency of 20Hz, and a temperature of 60 ℃. The results are expressed in an exponential form with the value of comparative example 1 as 100. The larger the index, the lower the heat generation property and the lower the rolling resistance.

Wear resistance: the abrasion resistance of the vulcanized rubber test piece was evaluated by using a lambbourne abrasion tester in accordance with JIS K6264. The obtained results are represented by an index with the value of comparative example 1 as 100. The larger the index is, the more excellent the abrasion resistance is.

The results are shown in table 1.

[ Table 1]

*1：NR(RSS#3)

*2: SBR (Nipol 1502 manufactured by Nippon ゼオン Co., Ltd.)

*3: BR (Nipol BR1220 manufactured by Japan ゼオン K.K.)

*4: carbon black (キャボットジャパン type ショウブラック N339 manufactured by Kyowa Kagaku Co., Ltd.)

*5: silica (1165 MP manufactured by ローディア, nitrogen adsorption specific surface area (N)₂SA)＝160m²/g)

*6: zinc white (3 kinds zinc oxide produced by Zhengassimilation chemical industry Co., Ltd.)

*7: stearic acid (stearic acid YR manufactured by Nichigan oil Co., Ltd.)

*8: anti-aging agent 6C (オゾノン 6C manufactured by Seiko chemical Co., Ltd.)

*9: antioxidant RD (Daneixing chemical industry Co., Ltd. ノクラック 224)

*10: silane coupling agent (Si 69, manufactured by エボニックデグッサ Co., Ltd., bis (3-triethoxysilylpropyl) tetrasulfide)

*11: tetrazine Compound (3, 6-bis (2-pyridyl) -1,2,4, 5-tetrazine available from Otsuka chemical Co., Ltd.)

*12: aromatic oil (S エキストラクト 4 Zhao シェル oil K.K.)

*13: heat-expandable microcapsule (Songban oil & fat pharmaceuticals マツモトマイクロスフェア F100)

*14: sulfur (Jinhua stamp-pad ink, produced by Hejia chemical industries, Ltd., micronised sulfur)

*15: vulcanization accelerator CZ (ノクセラー CZ-G manufactured by Danei Kagaku Kogyo Co., Ltd.)

*16: vulcanization accelerator DPG (Perkacit DPG manufactured by Flexsys Co., Ltd.)

*17: liquid BR (LBR 305 from Kuraray Co., Ltd.; 26,000 weight average molecular weight)

From the results shown in table 1, the rubber compositions of the examples each contain silica, a specific tetrazine compound and a heat-expandable microcapsule in specific amounts in a diene rubber having a specific composition, and therefore, the on-ice performance, wet performance, rolling resistance performance and abrasion resistance performance were improved as compared with those of comparative example 1.

In contrast, comparative example 2 does not contain the tetrazine compound and the thermally expandable microcapsules, and therefore the on-ice performance and the rolling resistance performance are inferior to those of comparative example 1.

Comparative example 3 has no thermal expansion microcapsules incorporated therein, and therefore has deteriorated on-ice performance as compared with comparative example 1.

Comparative example 4 has deteriorated on-ice performance compared to comparative example 1 because the blending amount of BR and/or SBR is less than the lower limit specified in the present invention.

In comparative example 5, the wet performance was deteriorated as compared with comparative example 1 because the compounding amount of NR and/or IR was less than the lower limit specified in the present invention.

Comparative example 6 shows substantially the same results as in comparative example 1, since the compounding amount of the tetrazine compound is less than the lower limit specified in the present invention.

Comparative example 7 the on-ice performance was deteriorated as compared with comparative example 1 because the compounding amount of the tetrazine compound exceeded the upper limit specified in the present invention.