JP7243148B2 - Rubber composition and pneumatic tire using the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a rubber composition and a pneumatic tire using the same. More specifically, the present invention relates to a rubber composition and a pneumatic tire using it. The present invention relates to a rubber composition having excellent stability and a pneumatic tire using the same.

In general, the performance required for pneumatic tires for competitions varies widely, and in addition to excellent steering stability (dry grip performance and wet grip performance) on dry and wet roads at high speeds, It is required to suppress changes in tire performance (wear skin and heat sagging) when performing for a long time. Therefore, techniques for blending silica into tires are known. Although the abrasion resistance can be improved by blending silica, there is a problem that silica is extremely difficult to disperse in rubber. Although the industry has attempted to disperse silica by developing various silane couplings, sufficient silica dispersion has not yet been achieved.

Patent Document 1 below discloses that a glycerin fatty acid ester is composed of a glycerin fatty acid ester, the glycerin fatty acid ester is an ester of glycerin and two or more fatty acids, and the most An additive composition for a silica-blended rubber composition is disclosed which contains 10 to 90% by mass of fatty acid components in total fatty acids and 50 to 100% by mass of monoester components in glycerin fatty acid esters.
Further, in Patent Document 2 below, a rubber component containing two or more diene rubbers and a glycerol fatty acid triester derived from a non-petroleum resource are included, and the rubber component contains natural rubber, epoxidized natural rubber, and butadiene rubber. The glycerol fatty acid triester has an oleic acid content of 45% by mass or more, and the total of natural rubber and butadiene rubber in 100% by mass of the rubber component A sidewall or base tread rubber composition is disclosed having a content of 50% by mass or more, or a total content of natural rubber and epoxidized natural rubber in 100% by mass of the rubber component of 50% by mass or more.
However, the technologies disclosed in Patent Documents 1 and 2 provide a pneumatic tire that improves the dispersibility of silica and has excellent steering stability during high-speed driving and excellent tire performance stability during high-speed driving for a long time. Not yet.

International publication WO2016/139916 pamphlet Japanese Patent No. 5679798

Accordingly, an object of the present invention is to provide a rubber composition that enhances the dispersibility of silica and exhibits excellent steering stability during high-speed driving and stability of tire performance during high-speed driving for a long time, and a pneumatic tire using the same. to provide.

As a result of extensive research, the present inventors have found that a specific amount of silica and a silane coupling agent are blended with a diene rubber, and a specific polyglycerin fatty acid ester is blended in a specific amount, and a composition The present inventors have found that the above-mentioned problems can be solved by setting the average glass transition temperature of to a specific range, and have completed the present invention.
That is, the present invention is as follows.

1. 150 to 300 parts by mass of silica per 100 parts by mass of diene rubber, 1 to 20% by mass of silane coupling agent based on the mass of silica, and a polyglycerin fatty acid ester derived from a fatty acid having 6 to 24 carbon atoms A rubber composition comprising 0.5 to 20 parts by mass of and having an average glass transition temperature of -20 ° C. or higher.
2. 2. The rubber composition as described in 1 above, wherein the fatty acid is stearic acid, oleic acid, linoleic acid or linolenic acid.
3. 3. The rubber composition as described in 1 or 2 above, wherein the polyglycerol fatty acid ester is represented by the following formula (1).

In formula (1), R represents a carbon chain derived from the fatty acid, and n represents 0-8.
4. 3. The rubber composition as described in 3 above, wherein n is 0 or 1 in the formula (1).
5. 5. The rubber composition according to any one of 1 to 4 above, which is used for a tire cap tread.
6. A pneumatic tire using the rubber composition according to any one of 1 to 4 above for a cap tread.

According to the present invention, a specific amount of silica and a silane coupling agent are blended into a diene rubber, and a specific amount of a specific polyglycerin fatty acid ester is added to the diene rubber, and the average glass transition temperature of the composition is Since it is defined in a specific range, the dispersibility of silica is increased, and the rubber composition and the pneumatic tire using the same have excellent steering stability during high-speed driving and tire performance stability during high-speed driving for a long time. can be provided.

The present invention will now be described in more detail.

(Diene rubber)
As the diene rubber used in the present invention, any diene rubber that can be blended in a normal rubber composition can be used. Examples include natural rubber (NR), isoprene rubber (IR), butadiene rubber ( BR), styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), ethylene-propylene-diene terpolymer (EPDM), and the like. These may be used alone or in combination of two or more. Further, its molecular weight and microstructure are not particularly limited, and it may be terminally modified with an amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl group or the like, or epoxidized.
Among these, it is preferable to use SBR from the viewpoint of easily exhibiting dry and wet grip performance.

(silica)
The silica used in the present invention preferably has a CTAB specific surface area of 150 m ² /g or more. In the present invention, even if silica having such a high specific surface area is blended into rubber, good dispersion is possible. In the present invention, even silica having a CTAB specific surface area of 180 m ² /g or more, particularly 200 m ² /g or more, which is an ultra-high specific surface area, can be well dispersed in the rubber.
The CTAB specific surface area of silica is measured according to ISO5794/1.

(Silane coupling agent)
The silane coupling agent used in the present invention is not particularly limited, but is preferably a silane coupling agent having a mercapto group and/or a thiol ester group (hereinafter sometimes referred to as a "thiol-based coupling agent"). ). By blending a thiol-based coupling agent together with silica, the dispersibility of silica can be improved and the performance of silica can be fully exhibited. A thiol-based coupling agent is a mercaptosilane compound that always contains at least one of a mercapto group (--SH) and a thiol ester group in its chemical structure. This mercaptosilane compound has a Si—O bond in its chemical structure. Examples of the Si—O bond include structures in which a hydrogen atom, a halogen atom, a carbon atom, a nitrogen atom, a silicon atom, or the like is bonded to an oxygen atom of Si—O—. Bonds having a structure of Si--O--H or Si--O--C are particularly preferable.

The silane coupling agent having a mercapto group is not particularly limited as long as it is a silane compound having a mercapto group (--SH). The silane coupling agent having a thiol ester group is preferably a silane compound in which the hydrogen of the mercapto group (--SH) of the silane compound having a mercapto group is substituted with a hydrocarbon group. As the hydrocarbon group, an alkanoyl group having 2 to 10 carbon atoms is preferable, and --CO--(CH ₂ ) ₆ CH ₃ is particularly preferable.

In the present invention, the thiol-based coupling agent is preferably a silane compound having a mercapto group represented by the following formula (10), or a copolymer having a structure represented by the following formulas (20) and (30). .

(In formula (10), R ¹ , R ² and R ³ are each independently hydrogen, an alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a straight chain having a chain length of 4 to 30 is selected from a polyether group and an aryl group having 6 to 30 carbon atoms, at least one of which is the alkoxy group and at least one of which is the linear polyether group; and R ⁴ is an alkylene group of 1 to 30 carbon atoms. be.)

(In formula (20), R ⁵ and R ⁶ may form a ring structure, and R ⁵ is hydrogen, halogen, an alkyl group or alkylene group having 1 to 30 carbon atoms, an alkenyl group having 2 to 30 carbon atoms, or an alkenylene group, an alkynyl group or an alkynylene group having 2 to 30 carbon atoms, or a group in which the terminal of the alkyl or alkenyl group is substituted with a hydroxyl group or a carboxyl group, and R ⁶ is an alkylene group having 1 to 30 carbon atoms; It is selected from an alkenylene group having 2 to 30 carbon atoms and an alkynylene group having 2 to 30 carbon atoms, and x is an integer of 1 or more.)

(In formula (30), R ⁷ and R ⁸ may form a ring structure, and R ⁷ is hydrogen, halogen, an alkyl group or alkylene group having 1 to 30 carbon atoms, an alkenyl group having 2 to 30 carbon atoms, or an alkenylene group, an alkynyl group or an alkynylene group having 2 to 30 carbon atoms, or a group in which the terminal of the alkyl or alkenyl group is substituted with a hydroxyl group or a carboxyl group, and R ⁸ is an alkylene group having 1 to 30 carbon atoms; It is selected from an alkenylene group having 2 to 30 carbon atoms and an alkynylene group having 2 to 30 carbon atoms, and y is an integer of 1 or more.)

In the thiol-based coupling agent represented by the formula (10), R ¹ , R ² and R ³ are each independently hydrogen, an alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, It is a linear polyether group with a chain length of 4-30 and an aryl group with a carbon number of 6-30. Preferred are hydrogen, an alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, and a linear polyether group having a chain length of 10 to 29. Linear polyether groups are preferably represented by the formula —O—(R ¹¹ —O)pR ¹² . In the polyether portion (R ¹¹ --O)p, R ¹¹ is an alkylene group having 2 to 4 carbon atoms, preferably an ethylene group, a trimethylene group (--CH ₂ CH ₂ CH ₂ --) or a propylene group. R ¹¹ may be of one type or multiple types. p is the average number of repetitions of the ether moiety and is a number from 2 to 15, preferably from 3 to 10, more preferably from 3.5 to 8. R ¹² is an alkyl group having 10 to 16 carbon atoms, preferably 11 to 15 carbon atoms. Alkylpolyether groups may be mixtures of species, for example -O-( _{CH2CH2 -} O) _5- ( _CH2 ) _{10CH3 ,} -O-( _{CH2CH2 -} O) _5- ( _{CH2 ) 11CH3 ,} -O-(CH2CH2 _- O) _5- ( _CH2 ) _12CH3 , -O- _{( CH2CH2 -} O) _5- ( _CH2 ) _{13CH3 ,} -O-( _{CH2CH2 - O} ) _5- ( _CH2 ) _{14CH3 ,} -O-( _{CH2CH2- O} ) _3- ( _CH2 ) _12CH3 , _-O- ( _CH2CH2 -O) _4- ( _{CH2 ) 12CH3} , -O-(CH2CH2 _- O) _6- ( _CH2 ) _{12CH3 ,} -O-( _{CH2CH2 -} O _{) 7-} ( _CH2 ) ₁₂ CH ₃ and the like are exemplified.

In formula (10), at least one of R ¹ , R ² and R ³ is an alkoxy group having 1 to 8 carbon atoms and at least one is a linear polyether group having a chain length of 4 to 30; A thiol-based coupling agent represented by (10) always has an alkoxy group and a linear polyether group.

R ⁴ is an alkylene group having 1 to 30 carbon atoms, preferably an alkylene group having 1 to 12 carbon atoms.

_The mercaptosilane compound represented by the formula (10) preferably used in the present _invention includes, for _example , [ _C11H23O ( _CH2CH2O ) ₅ ]( _CH2CH2O ) _2Si (CH ₂ ) _3SH ,
_{[ C12H25O} ( _CH2CH2O ) _{3 ]} ( _CH2CH2O ) _{2Si ( CH2} ) _3SH ,
[ _C12H25O ( _{CH2CH2O )4 ]} ( _CH2CH2O ) _{2Si ( CH2} ) _{3SH ,}
[ _C12H25O ( _CH2CH2O ) _{5 ]} ( _CH2CH2O ) _{2Si ( CH2} ) _{3SH ,
[ C12H25O} ( _CH2CH2O ) _{6 ]} ( _CH2CH2O ) _{2Si ( CH2} ) _3SH ,
_{[ C13H27O} ( _CH2CH2O ) _{3 ]} ( _CH2CH2O ) _{2Si ( CH2} ) _3SH ,
[ _C13H27O ( _CH2CH2O ) _{4 ]} ( _CH2CH2O ) _{2Si ( CH2} ) _{3SH ,}
[ _C13H27O ( _CH2CH2O ) _{5 ]} ( _CH2CH2O ) _{2Si ( CH2} ) _{3SH ,
[ C13H27O} ( _CH2CH2O ) _{6 ]} ( _CH2CH2O ) _{2Si ( CH2} ) _3SH ,
_{[ C14H29O} ( _CH2CH2O ) _{3 ]} ( _CH2CH2O ) _{2Si ( CH2} ) _3SH ,
[ _C14H29O ( _CH2CH2O ) _{4 ]} ( _CH2CH2O ) _{2Si ( CH2} ) _{3SH ,}
[ _C14H29O ( _CH2CH2O ) _{5 ]} ( _CH2CH2O ) _{2Si ( CH2} ) _{3SH ,
[ C14H29O} ( _CH2CH2O ) _{6 ]} ( _CH2CH2O ) _{2Si ( CH2} ) _3SH ,
[ _C15H31O ( _CH2CH2O ) _{5 ]} ( _CH2CH2O ) _{2Si ( CH2} ) _{3SH ,}
[ _C11H23O ( _{CH2CH2O ) 5 ] 2} ( _CH2CH2O )Si( _CH2 ) _{3SH ,}
[ _C12H25O ( _{CH2CH2O ) 3} ] ₂ ( _CH2CH2O ) _Si ( _CH2 ) _{3SH ,
[ C12H25O} ( _{CH2CH2O ) 4} ] ₂ ( _CH2CH2O )Si( _{CH2 ) 3SH} ,
[ _C12H25O ( _CH2CH2O ) _{5 ] 2} ( _CH2CH2O )Si( _{CH2 ) 3SH ,}
[ _C12H25O ( _CH2CH2O ) _{6 ] 2} ( _CH2CH2O ) _Si ( _CH2 ) _{3SH ,}
[ _C13H27O ( _CH2CH2O ) _{3 ] 2} ( _CH2CH2O ) _Si ( _CH2 ) _{3SH ,}
[ _C13H27O ( _{CH2CH2O ) 4} ] ₂ ( _CH2CH2O )Si( _{CH2 ) 3SH ,}
[ _C13H27O ( _CH2CH2O ) _{5 ] 2} ( _CH2CH2O )Si( _{CH2 ) 3SH ,}
[ _C13H27O ( _{CH2CH2O ) 6 ] 2} ( _CH2CH2O )Si( _CH2 ) _{3SH ,}
[ _C14H29O ( _CH2CH2O ) _{3 ] 2} ( _CH2CH2O ) _Si ( _CH2 ) _{3SH ,}
[ _C14H29O ( _{CH2CH2O ) 4} ] ₂ ( _CH2CH2O )Si( _{CH2 ) 3SH ,}
[ _C14H29O ( _CH2CH2O ) _{5 ] 2} ( _CH2CH2O )Si( _{CH2 ) 3SH ,}
[ _C14H29O ( _CH2CH2O ) _{6 ] 2 ( CH2CH2O} )Si( _CH2 ) _{3SH ,}
[ _C15H31O ( _CH2CH2O ) _{5 ] 2} ( _CH2CH2O )Si( _{CH2 ) 3SH} and the like are _exemplified .
Among them, [C ₁₃ H ₂₇ O--(CH ₂ CH ₂ O) ₅ ] ₂ (CH ₂ CH ₂ O) Si(CH ₂ ) ₃ SH, [C ₁₃ H ₂₇ O--(CH ₂ CH ₂ O) ₅ ] ( _CH2CH2O ) _2Si ( _CH2 ) _3SH is _preferred .

A silane coupling agent having a thiol ester group is represented by -S-(C=O)-R (wherein R represents a hydrocarbon group), and the compound represented by the above formula (1) As a silane compound having a thiol ester group based on, for example, (CH ₃ CH ₂ O) ₃ Si(CH ₂ ) ₃ S--(C=O)--(CH ₂ ) ₆ CH ₃ (NXT manufactured by Momentive Performance Materials, Inc.) ) are exemplified.

In the mercaptosilane compound having segments represented by the general formulas (20) and (30), R ⁵ and R ⁶ may form a ring structure, and R ⁷ and R ⁸ may form a ring structure. . R ⁵ and R ⁷ are hydrogen, halogen, an alkyl or alkylene group having 1 to 30 carbon atoms, an alkenyl or alkenylene group having 2 to 30 carbon atoms, an alkynyl or alkynylene group having 2 to 30 carbon atoms, the alkyl group or It is selected from groups in which the terminal of an alkenyl group is substituted with a hydroxyl group or a carboxyl group. The alkyl group, alkynyl group, alkynylene group, alkylene group, alkenylene group and alkynylene group described above may each be branched or unbranched.

R ⁶ and R ⁸ are selected from an alkylene group having 1 to 30 carbon atoms, an alkenylene group having 2 to 30 carbon atoms and an alkynylene group having 2 to 30 carbon atoms. The alkylene group, alkenylene group and alkynylene group described above may each be branched or unbranched.

The content of the segment represented by the above formula (20) is preferably 20 to 99 mol%, preferably 30 to 95 mol%.

The content of the segment represented by the above formula (30) is preferably 1-80 mol %, preferably 5-70 mol %.

In the present invention, thiol-based coupling agents having segments represented by general formulas (20) and (30) that are preferably used include, for example, NXT-Z30 (R ⁵ , R ⁷ : ethyl group, R ⁶ , R ⁸ : ethylene group, 70 mol % of segment represented by formula (20), 30 mol % of segment represented by formula (30), content of mercapto group: 4%) , NXT-Z45 (R ⁵ , R ⁷ : ethyl group, R ⁶ , R ⁸ : ethylene group, 55 mol % of segment represented by formula (20), 45 mol % of segment represented by formula (30), mercapto group content: 6%), NXT-Z60 (R ⁵ , R ⁷ : ethyl group, R ⁶ , R ⁸ : ethylene group, 40 mol % of the segment represented by formula (20), segment containing 60 mol %, content of mercapto group: 9%), and the like.

As the thiol-based coupling agent used in the present invention, a mercaptosilane compound other than the mercaptosilane compound represented by the above formula (10) and the copolymer having the structures of formulas (20) and (30) can be used. . Examples of such thiol-based coupling agents include 3-mercaptopropyl (trimethoxysilane), 3-mercaptopropyl (triethoxysilane), 3-mercaptopropyl (diethoxymethoxysilane), 3-mercaptopropyl (tripropoxysilane), ), 3-mercaptopropyl (dipropoxymethoxysilane), 3-mercaptopropyl (tributoxysilane), 3-mercaptopropyl (dibutoxymethoxysilane), 3-mercaptopropyl (dimethoxymethylsilane), 3-mercaptopropyl (methoxy dimethylsilane), 3-mercaptopropyl (diethoxymethylsilane), 3-mercaptopropyl (ethoxydimethylsilane), 3-mercaptopropyl (dipropoxymethylsilane), 3-mercaptopropyl (propoxydimethylsilane), 3-mercaptopropyl (diisopropoxymethylsilane), 3-mercaptopropyl (isopropoxydimethylsilane), 3-mercaptopropyl (dibutoxymethylsilane), 3-mercaptopropyl (butoxydimethylsilane), 2-mercaptoethyl (trimethoxysilane), 2-mercaptoethyl (triethoxysilane), mercaptomethyl (trimethoxysilane), mercaptomethyl (triethoxysilane), 3-mercaptobutyl (trimethoxysilane), 3-mercaptobutyl (triethoxysilane), etc. can be done. Among them, 3-mercaptopropyl (trimethoxysilane) and 3-mercaptopropyl (triethoxysilane) are preferred.

As the silane coupling agent used in the present invention, one represented by the following formula (100) can also be suitably used.

(A) _a (B) _b (C) _c (D) _d (R1) _e SiO _{(4-2a-bcde)/2} (100)

(In formula (100), A is a divalent organic group containing a sulfide group, B is a monovalent hydrocarbon group having 5 to 10 carbon atoms, C is a hydrolyzable group, and D is an organic group containing a mercapto group. group, R1 represents a monovalent hydrocarbon group having 1 to 4 carbon atoms, 0≦a<1, 0<b<1, 0<c<3, 0<d<1, 0≦e<2, and It satisfies the relationship 0<2a+b+c+d+e<4.)

A sulfur-containing silane coupling agent (polysiloxane) represented by formula (100) and a method for producing the same are disclosed, for example, in International Publication WO2014/002750 and are publicly known.

In the above formula (100), A represents a divalent organic group containing a sulfide group. Among them, a group represented by the following formula (120) is preferable.
^* -( _CH2 ) _n - _Sx- ( _CH2 ) _n- ^* (120)
In the above formula (120), n represents an integer of 1-10, preferably an integer of 2-4.
In the above formula (120), x represents an integer of 1-6, preferably an integer of 2-4.
In the above formula (120), * indicates a bonding position.
Specific examples of the group represented by formula (120) include ^* -CH ₂ -S ₂ -CH ₂ - ^* , ^* -C ₂ H ₄ -S ₂ -C ₂ H ₄ - ^* , ^* - _C3H6 - _{S2 - C3H6-} ^* , ^* _-C4H8 - _S2 - _C4H8- ^* _, ^* _{-CH2- S4 - CH2- *} ^{, *} _{-C2H 4} - _{S4 - C2H4-} ^* , ^* _{-C3H6 - S4 - C3H6-} ^* , ^* _{-C4H8 - S4 - C4H8-} ^* and the like.

In the above formula (100), B represents a monovalent hydrocarbon group having 5 to 20 carbon atoms, and specific examples thereof include hexyl group, octyl group and decyl group. B is preferably a monovalent hydrocarbon group having 5 to 10 carbon atoms.

In formula (100) above, C represents a hydrolyzable group, and specific examples thereof include an alkoxy group, a phenoxy group, a carboxyl group, an alkenyloxy group, and the like. Among them, a group represented by the following formula (130) is preferable.
^* -OR ² (130)
In the above formula (130), R ² is an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aralkyl group having 6 to 10 carbon atoms (arylalkyl group) or an alkenyl group having 2 to 10 carbon atoms. Among them, an alkyl group having 1 to 5 carbon atoms is preferable. Specific examples of the alkyl group having 1 to 20 carbon atoms include methyl group, ethyl group, propyl group, butyl group, hexyl group, octyl group, decyl group and octadecyl group. Specific examples of the aryl group having 6 to 10 carbon atoms include a phenyl group and a tolyl group. Specific examples of the aralkyl group having 6 to 10 carbon atoms include benzyl group and phenylethyl group. Specific examples of the alkenyl group having 2 to 10 carbon atoms include vinyl group, propenyl group and pentenyl group.
In the above formula (130), * indicates a bonding position.

In formula (100) above, D represents an organic group containing a mercapto group. Among them, a group represented by the following formula (140) is preferable.
^* -( _CH2 ) _m -SH (140)
In the above formula (140), m represents an integer of 1-10, preferably an integer of 1-5.
In the above formula (140), * indicates a bonding position.
Specific examples of the group represented by the above formula (140) include ^* --CH ₂ SH, ^* --C ₂ H ₄ SH, ^* --C ₃ H ₆ SH, ^* --C ₄ H ₈ SH, and ^* --C _{5 . H10SH ,} ^* _{-C6H12SH ,} ^* _{-C7H14SH ,} ^* _{-C8H16SH ,} ^* _-C9H18SH , and ^* _{-C10H20SH .}

In the above formula (100), R1 represents a monovalent hydrocarbon group having 1 to 4 carbon atoms.

In the above formula (100), the relationships of 0≦a<1, 0<b<1, 0<c<3, 0<d<1, 0≦e<2, and 0<2a+b+c+d+e<4 are satisfied.

In the above formula (100), a preferably satisfies 0<a≦0.50 for the reason that the effect of the present invention is improved.
In the above formula (100), b preferably satisfies 0<b, and more preferably satisfies 0.10≦b≦0.89 for the reason that the effect of the present invention is improved.
In the above formula (100), c preferably satisfies 1.2≦c≦2.0 for the reason that the effects of the present invention are improved.
In the above formula (100), d preferably satisfies 0.1≦d≦0.8 for the reason that the effect of the present invention is improved.

The weight average molecular weight of the polysiloxane is preferably 500 to 2,300, more preferably 600 to 1,500, for the reason that the effect of the present invention is improved. The molecular weight of the above polysiloxane in the present invention is determined in terms of polystyrene by gel permeation chromatography (GPC) using toluene as a solvent.
The mercapto equivalent of the polysiloxane obtained by the acetic acid/potassium iodide/potassium iodate addition-sodium thiosulfate solution titration method is preferably 550 to 700 g/mol, more preferably 600 to 650 g, from the viewpoint of excellent vulcanization reactivity. /mol is more preferred.

The above polysiloxane preferably has 2 to 50 siloxane units (--Si--O--) for the reason that the effects of the present invention are improved.

Metals other than silicon atoms (for example, Sn, Ti, Al) are not present in the skeleton of the polysiloxane.

Methods for producing the polysiloxane are known, and can be produced, for example, according to the method disclosed in International Publication WO2014/002750.

In addition, sulfur-containing silane coupling agents other than those described above can also be used as the silane coupling agent used in the present invention. For example, bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, 3-trimethoxysilylpropylbenzothiazoletetrasulfide, γ-mercaptopropyltriethoxysilane, 3-octanoylthiopropyltrisulfide, Ethoxysilane and the like can be exemplified.

(Polyglycerol fatty acid ester)
The polyglycerin fatty acid ester used in the present invention is an ester derived from fatty acid having 6 to 24 carbon atoms.
Specific examples of fatty acids include caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, oleic acid, arachidic acid, and behenic acid. and straight-chain fatty acids such as lignoceric acid.
Polyglycerol fatty acid esters may be used alone or in combination of two or more.
In addition, from the viewpoint of increasing the dispersibility of silica and further increasing the stability of tire performance during high-speed driving and steering stability during high-speed driving for a long time, the fatty acids include stearic acid, oleic acid, and linoleic acid. Or linolenic acid is preferred.
In the polyglycerin fatty acid ester used in the present invention, the —OH group derived from glycerin adsorbs to the silanol group on the silica surface, and at the same time, the repeating unit of glycerin enters the pores of silica aggregates having a particularly high specific surface area and stays. contributes to the dispersibility of silica in rubber. As a result, steering stability during high-speed running and stability of tire performance during high-speed running for a long period of time can be improved. In addition, the said effect is a function effect which is not exhibited by the monoglycerol fatty acid ester.

In addition, from the viewpoint of further improving the steering stability during high-speed driving and the stability of tire performance during high-speed driving for a long time, the polyglycerol fatty acid ester used in the present invention is represented by the following formula (1). It is preferably a mono fatty acid ester that is used.

In formula (1), R represents a carbon chain derived from the fatty acid, n represents 0 to 8, preferably 0 to 3, particularly preferably 0 or 1.
In addition, in the glycerin ester compound obtained by selectively esterifying the secondary hydroxy group of polyglycerin, compared to the mono fatty acid ester represented by the above formula (1), silica dispersibility, steering stability during high-speed driving, and The degree of improvement in the effect of enhancing the stability of tire performance when running at high speed for a long period of time is poor.

The polyglycerin fatty acid ester used in the present invention can be commercially available, and examples of the mono-fatty acid ester represented by formula (1) include DS100A (diglycerin monostearate) manufactured by Riken Vitamin Co., Ltd. , DO100V (diglycerin monooleate), S71D (diglycerin stearate), Poem J-4081V (tetraglycerin stearate), J-0021 (decaglycerin laurate), J-0081HV (decaglycerin stearate), J- 0381V (decaglycerin oleate) and the like.

(Mixing ratio of rubber composition)
The rubber composition of the present invention comprises 100 parts by mass of diene rubber, 150 to 300 parts by mass of silica, 1 to 20% by mass of a silane coupling agent based on the mass of the silica, and a fatty acid having 6 to 24 carbon atoms. 0.5 to 20 parts by mass of polyglycerol fatty acid ester derived from
When the silica content is less than 150 parts by mass, the wet grip performance is deteriorated.
If the amount of the silane coupling agent to be blended is less than 1% by mass with respect to the mass of silica, the amount to be blended is too small and the effects of the present invention cannot be obtained. Conversely, if it exceeds 20% by mass, the wear resistance deteriorates.
If the blending amount of the polyglycerin fatty acid ester is less than 0.5 parts by mass, the blending amount is too small and the effects of the present invention cannot be obtained. On the other hand, if it exceeds 20 parts by mass, the wear resistance deteriorates, heat sagging occurs, and the stability of tire performance during high-speed running for a long time becomes poor.

Further, in the rubber composition of the present invention, the amount of silica compounded is preferably 150 to 250 parts by mass with respect to 100 parts by mass of the diene rubber.
The amount of the silane coupling agent compounded is preferably 5 to 15% by mass based on the mass of silica.
The amount of the polyglycerin fatty acid ester compounded is preferably 1 to 20 parts by mass with respect to 100 parts by mass of the diene rubber.

(Other ingredients)
In addition to the components described above, the rubber composition of the present invention includes a vulcanizing or cross-linking agent; a vulcanizing or cross-linking accelerator; various fillers such as zinc oxide, carbon black, clay, talc, and calcium carbonate; agent; various additives that are generally blended in rubber compositions such as plasticizers can be blended. can be used. The blending amount of these additives can also be a conventional general blending amount as long as it does not contradict the object of the present invention.

Further, in the present invention, it is preferable to add a resin having a temperature of 60 to 150° C. from the viewpoint of enhancing wet grip performance. Specifically, an aromatic modified terpene resin having a softening point of 60 to 150° C. is preferably blended.
Examples of aromatic modified terpene resins include those obtained by polymerizing terpene resins such as α-pinene, β-pinene, dipentene, and limonene with aromatic compounds such as styrene, α-methylstyrene, vinyltoluene, and indene. Aromatically modified terpene resins are effectively used. The content of the aromatic compound in the aromatic modified terpene resin is preferably 10 to 50% by mass.
The blending ratio of the resin is, for example, 1 to 30 parts by mass, preferably 3 to 20 parts by mass, per 100 parts by mass of the diene rubber.

Further, the rubber composition of the present invention has an average glass transition temperature (average Tg) of -20°C or higher. By defining the average Tg in this way, the dry grip performance is improved.
The average Tg referred to in this specification is the sum of products obtained by multiplying the glass transition temperature of each component by the weight fraction of each component, that is, the value calculated based on the weighted average. Note that the sum of the weight fractions of each component is assumed to be 1.0 when calculating. Further, the glass transition temperature is measured by differential scanning calorimetry (DSC) under the condition of a temperature increase rate of 20° C./min and measuring a thermogram, and taken as the temperature at the middle point of the transition region.
Further, each of the above components means diene rubber, oil and resin. Note that the oil and resin may not be included in the rubber composition.
A more preferable average Tg is, for example, -30°C or higher, more preferably -30°C to -5°C.

Further, the rubber composition of the present invention is suitable for manufacturing pneumatic tires according to conventional pneumatic tire manufacturing methods, and is preferably applied to cap treads, particularly cap treads of racing pneumatic tires.

The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

Standard Example, Examples 1-4 and Comparative Examples 1-5
Preparation of samples In the formulation (parts by mass) shown in Table 1, the vulcanization accelerator and components other than sulfur were kneaded for 5 minutes in a 1.7-liter internal Banbury mixer, and the rubber was discharged out of the mixer and cooled to room temperature. . Then, the rubber was placed in the same mixer again, a vulcanization accelerator and sulfur were added, and the mixture was further kneaded to obtain a rubber composition. Next, the obtained rubber composition is press-vulcanized in a predetermined mold at 160 ° C. for 20 minutes to obtain a vulcanized rubber test piece, and the unvulcanized rubber composition and the vulcanized rubber are tested by the following test methods. Physical properties of the test piece were measured.

Payne effect (silica dispersibility): G' (0.56% strain) was measured at RPA2000 according to ASTM P6204 using unvulcanized compositions. The results were indexed with the value of the standard example set to 100. A smaller index means higher dispersibility of silica.

Wet grip performance: According to JIS K6394: 2007, using a viscoelastic spectrometer (manufactured by Toyo Seiki Seisakusho), tan δ (0 ° C.) under conditions of extensional deformation strain rate of 10 ± 2%, frequency of 20 Hz, and temperature of 0 ° C. was measured. The results were indexed with the value of the standard example set to 100. A larger index indicates better wet grip performance.

Abrasion resistance: Using a Lambourn abrasion tester manufactured by Iwamoto Seisakusho Co., Ltd., the wear loss was determined by measuring under the conditions of a load of 5 kg (49 N), a slip rate of 25%, a time of 4 minutes, and room temperature. The results are indexed with the value of the standard example set to 100. A larger index indicates better wear resistance.

Heat sagging: 195/65R15 tires were made using the same vulcanized rubber as the vulcanized rubber test piece for the cap tread, and measured by measuring the lap time difference after running a 3 km circuit for 10 weeks on an actual vehicle. Evaluation criteria are as follows.
3: Lap time difference is within 0.5s.
2.5: Lap time difference is 0.5~1.0s.
2: Lap time difference is 1.0~1.5s.
1.5: Lap time difference is 1.5~2.0s.
1: Lap time difference is 2.5s or more.
The results are also shown in Table 1.

*1: SBR1 (E680 manufactured by Asahi Kasei Chemicals Co., Ltd., solution polymerization SBR, styrene content = 36% by mass, vinyl content = 64%, Tg = -13°C, weight average molecular weight of 1,470,000, 100 parts by mass of SBR with an oil component of 37. Oil extended product with 5 parts by mass added (Table 1 shows the actual SBR amount))
* 2: SBR2 (E581 manufactured by Asahi Kasei Chemicals, Tg = -27 ° C., oil extended product obtained by adding 37.5 parts by mass of oil component to 100 parts by mass of SBR (Table 1 shows the actual amount of SBR))
*3: Monoglycerin monostearate (S100 manufactured by Riken Vitamin Co., Ltd.)
* 4: diglycerin monostearate (DS100A manufactured by Riken Vitamin Co., Ltd., n = 0 in the formula (1), and R-COO is derived from stearic acid)
* 5: Diglycerin monooleate (DO100V manufactured by Riken Vitamin Co., Ltd., n = 0 in the above formula (1), and R-COO is derived from oleic acid)
* 6: Diglycerin stearate (S71D manufactured by Riken Vitamin Co., Ltd., n = 0 in the formula (1), and R-COO is derived from stearic acid)
*7: Silica (manufactured by Solvay, trade name 1165MP, CTAB specific surface area = 160 m ² /g)
*8: Silane coupling agent 1 (Si69 manufactured by Evonik Degussa)
*9: Silane coupling agent 2 (compound satisfying formula (100) above. Composition formula = (-C ₃ H ₆ -S ₄ -C ₃ H ₆ -) _0.071 (-C ₈ H ₁₇ ) _0.571 (-OC ₂ H ₅ ) _1.50 (-C ₃ H ₆ SH) _0.286 SiO _0.75 )
*10: Carbon black (N339 manufactured by Cabot Japan Co., Ltd.)
*11: Resin (Yasuhara Chemical Co., Ltd. YS resin TO-125, terpene styrene resin, Mw = 2000, softening point 120-130°C, Tg = 70°C)
*12: Stearic acid (bead stearic acid YR manufactured by NOF Corporation)
*13: Zinc white (Three types of zinc oxide manufactured by Seido Chemical Industry Co., Ltd.)
*14: Antiaging agent (Santoflex 6PPD manufactured by Solutia Europe)
*15: Process oil (Extract No. 4S, manufactured by Showa Shell Sekiyu K.K., Tg = -40°C)
*16: Sulfur (Sulfur from Karuizawa Refining Co., Ltd.)
* 17: Vulcanization accelerator CBS (Ouchi Shinko Chemical Industry Co., Ltd. Noxcellar CZ-G)
*18: Vulcanization accelerator TOT-N (Ouchi Shinko Chemical Industry Co., Ltd. Noxceller TOT-N)

The average Tg in Table 1 is a value calculated based on the weighted average of Tg of the diene rubber, resin and oil.

From the results in Table 1, the rubber compositions of Examples 1 to 4 are compounded with specific amounts of silica and a silane coupling agent with respect to the diene rubber, and further with a specific amount of a specific polyglycerol fatty acid ester. In addition, since the average glass transition temperature of the composition is set to a specific range, the dispersibility of silica is improved compared to the standard example, and the steering stability (wet grip performance) during high-speed driving and high-speed driving for a long time. It can be seen that the stability of tire performance (wear resistance, heat sag) is excellent when the test is performed.
On the other hand, since Comparative Example 1 is an example in which monoglycerol monofatty acid ester is blended, the heat sagging is worse than that of the standard example.
In Comparative Example 2, the amount of polyglycerol fatty acid ester blended was less than the lower limit specified in the present invention, so the result was almost the same as that of the standard example.
In Comparative Example 3, the amount of the polyglycerin fatty acid ester blended exceeds the upper limit specified in the present invention, so the wear resistance and heat sag are worse than in the standard example.
In Comparative Example 4, the amount of silica compounded is less than the lower limit specified in the present invention, so the wet grip performance is worse than in the standard example.
In Comparative Example 5, the content of silica exceeds the upper limit specified in the present invention, so the dispersibility and wear resistance of silica are worse than in the standard example.

Claims (6)

150 to 300 parts by mass of silica per 100 parts by mass of diene rubber, 1 to 20% by mass of silane coupling agent based on the mass of silica, and a polyglycerin fatty acid ester derived from a fatty acid having 6 to 24 carbon atoms and having an average glass transition temperature of -20°C or higher (provided that the silica is added to 100 parts by mass of the diene rubber except when the amount is 150 mass) . 2. The rubber composition according to claim 1, wherein said fatty acid is stearic acid, oleic acid, linoleic acid or linolenic acid. 3. The rubber composition according to claim 1, wherein the polyglycerol fatty acid ester is represented by the following formula (1).

In formula (1), R represents a carbon chain derived from the fatty acid, and n represents 0-8. 4. The rubber composition according to claim 3, wherein n is 0 or 1 in the formula (1). The rubber composition according to any one of claims 1 to 4, which is used for tire cap treads. A pneumatic tire using the rubber composition according to any one of claims 1 to 4 for a cap tread.