JP5776356B2 - Rubber composition for tire tread - Google Patents

Description

  The present invention relates to a rubber composition for a tire tread, and more particularly to a rubber composition for a tire tread that is improved in low rolling resistance, steering stability, and processability.

  In general, a pneumatic tire is required to have excellent fuel efficiency and steering stability. For this reason, by adding silica to the rubber composition for a tire tread constituting the tread portion, rolling resistance is lowered to improve fuel efficiency. In addition, in order to improve steering stability, it is necessary to increase the tire rigidity by increasing the reinforcing property of the rubber composition for a tire tread with a filler.

  In order to increase the reinforcement performance of rubber with silica, it is necessary to add silica having a small particle diameter or increase the amount of the silica. However, since silica having a small particle diameter has a strong cohesive force, it is difficult to disperse it well in a diene rubber, and there is a problem that the viscosity of the rubber composition increases and processability deteriorates. In order to improve steering stability, it is conceivable to increase the rubber hardness by reducing the blending amount of a softening agent such as oil, but in this case also, the viscosity of the rubber composition increases and the processability deteriorates. There was a problem.

  Patent Document 1 improves rolling dispersibility (tan δ at 60 ° C.) by improving the dispersibility of silica by using a rubber composition in which silica is blended with terminal-modified solution-polymerized styrene butadiene rubber whose terminal is modified with polyorganosiloxane or the like. Propose that. Although this rubber composition has an effect of reducing rolling resistance, there is a problem that when the amount of bound rubber is excessive, the viscosity of the rubber composition increases and processability deteriorates.

  For this reason, it has not been achieved that all of the three factors of low rolling resistance, steering stability and workability are improved beyond the conventional level.

JP 2009-91498 A

  An object of the present invention is to provide a rubber composition for a tire tread in which low rolling resistance, steering stability and processability are improved to a level higher than that of the conventional level.

The rubber composition for a tire tread of the present invention that achieves the above object comprises 20-45% by weight of a terminal-modified solution-polymerized styrene-butadiene rubber (modified S-SBR) and an unmodified solution-polymerized styrene-butadiene rubber (S-SBR). 30 to 70% by weight, emulsion polymerized styrene butadiene rubber (E-SBR) 10 parts by weight to 100 parts by weight of rubber component, total oil amount is 30 parts by weight or less, silica and carbon black are blended together total a rubber composition is 60 to 120 parts by weight, hydroxyl group-containing polyorganosiloxane structure with functional groups of the modified S-SBR is closed reactive with the silanol groups of the silica surface, alkoxysilyl group, hydroxyl is at least one selected from the group, the modified weight average molecular weight of S-SBR is 300,000 to 600,000, before The weight average molecular weight of S-SBR is 900,000 to 1.3 million, the weight average molecular weight of E-SBR is 700,000 to 1.3 million, and the silica ratio in the total of the silica and carbon black is 85% by weight or more, Silica has a DBP absorption of 190 ml / 100 g or more, a nitrogen adsorption specific surface area (N ₂ SA) of 194 to 225 m ² / g, a CTAB specific surface area (CTAB) of 170 to 210 m ² / g, and the ratio of N ₂ SA to CTAB. (N ₂ SA / CTAB) is 0.9 to 1.4.

The rubber composition for a tire tread of the present invention is prepared by blending the above-mentioned small particle size silica having the specific particle properties so that the total amount with the carbon black is 60 to 120 wt. Since the amount of oil is 30 parts by weight or less, the rubber hardness is increased and the steering stability can be improved. Further, reactivity there with silanol groups Ri hydroxyl group-containing polyorganosiloxane structure of the silica surface, an alkoxysilyl group, a functional group which Ru is selected from hydroxyl groups and a weight average molecular weight of 300000 to 600000 of the modified S -Since SBR is blended in an amount of 20 to 45% by weight, the dispersibility of silica is improved by increasing the affinity with silica having a small particle diameter, and the molecular weight is lowered. Since the concentration of the functional group is increased, the effect can be exhibited highly. Moreover, since the compounding quantity was kept to 20 to 45 weight%, it can also prevent that the amount of bound rubber becomes high too much and the viscosity of a rubber composition increases too much. Further, as other rubber components, although they do not have a functional group having high affinity with silica, 30 to 70% by weight of S-SBR having a weight average molecular weight of 900,000 to 1,300,000 and a weight average molecular weight of 700,000 to Since 1.3 million E-SBR is blended with SBR having a high molecular weight such as 10 to 25% by weight, the exothermic property is reduced by reducing the density of the end of the rubber molecule and the fuel efficiency is improved. Since the rubber component is composed entirely of styrene butadiene rubber, the handling stability can be improved. In particular, by adding E-SBR, the rubber hardness can be increased to further improve the steering stability.

The functional group of the modified S-SBR, hydroxyl group-containing polyorganosiloxane structure, an alkoxysilyl group, Ri least 1 Tanedea selected hydroxyl group or al, is reactive with silanol groups of the silica surface excellent.

  The E-SBR preferably has a viscosity of 65 or more when 37.5 parts by weight of oil-extended oil is contained with respect to 100 parts by weight of the E-SBR. Thereby, the rubber strength can be further increased.

  The pneumatic tire using the rubber composition for a tire tread of the present invention can improve the low rolling resistance, the steering stability and the workability from the conventional level.

  In the rubber composition for a tire tread of the present invention, the rubber component is composed of styrene butadiene rubber. The styrene-butadiene rubber is a terminal-modified solution-polymerized styrene-butadiene rubber (hereinafter referred to as “modified S-SBR”), an unmodified solution-polymerized styrene-butadiene rubber (hereinafter referred to as “S-SBR”), and an emulsion-polymerized styrene-butadiene rubber. The total of the three types of rubber (hereinafter referred to as “E-SBR”) is 100% by weight.

In the present invention, when modified S-SBR is blended, when silica having a small particle diameter is blended, the exothermic property of the rubber composition is reduced by increasing the affinity with silica and improving the dispersibility. Thus, rolling resistance can be reduced. Modified S-SBR is a solution-polymerized styrene butadiene rubber in which both or one of its molecular ends is modified with a functional group reactive with silanol groups on the silica surface. The functional group capable of reacting with silanol groups is at least one heat Dorokishiru group-containing polyorganosiloxane structure, an alkoxysilyl group, selected hydroxyl group or al.

  In the present invention, the modified S-SBR is a solution-polymerized styrene butadiene rubber having the above-described modifying group, and a conjugated diene monomer and an aromatic vinyl using an organic active metal compound as an initiator in a hydrocarbon solvent. An active conjugated diene polymer chain copolymerized with a monomer has a terminal-modified group obtained by reacting at least one compound having a functional group capable of reacting with the active terminal of the polymer chain; The terminal modification group includes a functional group having an interaction with silica.

  The conjugated diene polymer is prepared by copolymerizing the conjugated diene monomer and the aromatic vinyl monomer described above in a hydrocarbon solvent using an organic active metal compound as an initiator. As a hydrocarbon solvent, what is necessary is just a solvent used normally, for example, cyclohexane, n-hexane, benzene, toluene etc. are illustrated.

  As the organic active metal catalyst to be used, an organic alkali metal compound is preferably used. Organic polyvalent lithium compounds such as 1,4-dilithiobutane, 1,4-dilithio-2-ethylcyclohexane, 1,3,5-trilithiobenzene; organic sodium compounds such as sodium naphthalene; organic potassium compounds such as potassium naphthalene Is mentioned. In addition, 3,3- (N, N-dimethylamino) -1-propyllithium, 3- (N, N-diethylamino) -1-propyllithium, 3- (N, N-dipropylamino) -1- Propyllithium, 3-morpholino-1-propyllithium, 3-imidazole-1-propyllithium and organolithium compounds in which these are chain-extended with 1 to 10 units of butadiene, isoprene or styrene can also be used.

  Also, in the polymerization reaction, diethyl ether, diethylene glycol dimethyl ether, tetrahydrofuran, 2,2-bis (2-oxolanyl) propane, etc. for the purpose of randomly copolymerizing aromatic vinyl monomers with conjugated diene monomers. It is also possible to add aprotic polar compounds such as amines such as ethers, triethylamine and tetramethylethylenediamine.

  By binding at least one compound having a reactive functional group to the active end of an active conjugated diene polymer chain obtained by copolymerizing a conjugated diene monomer and an aromatic vinyl monomer, Terminally modified groups can be generated. Here, the compound having a functional group capable of reacting with the active terminal of the active conjugated diene polymer chain may be bonded to at least one active conjugated diene polymer chain, and one or more active conjugates may be bonded to one compound. Diene polymer chains can be bonded. That is, a modified styrene butadiene rubber is a modified rubber having modified groups at both ends of a conjugated diene polymer, a modified rubber in which the modified group is bonded to one or more other conjugated diene polymers, and a plurality of these A mixture of modified rubbers can be included. In addition, the reaction between the active terminal of the active conjugated diene polymer chain and the compound having a functional group capable of reacting with this active terminal can be reacted in one stage or multiple stages. The same or different compounds can be reacted sequentially.

  Examples of the compound having a functional group capable of reacting with the active terminal of the active conjugated diene polymer chain include a tin compound, a silicon compound, a silane compound, an amide compound and / or an imide compound, an isocyanate and / or an isothiocyanate compound, and a ketone compound. , Ester compounds, vinyl compounds, oxirane compounds, thiirane compounds, oxetane compounds, polysulfide compounds, polysiloxane compounds, polyorganosiloxane compounds, polyether compounds, polyene compounds, halogen compounds, and fullerenes. Of these, polyorganosiloxane compounds are preferred. These compounds can be bonded to a polymer by combining one type of compound or a plurality of compounds.

（上記式（Ｉ）において、Ｒ¹〜Ｒ⁸は、炭素数１〜６のアルキル基または炭素数６〜１２のアリール基であり、これらは互いに同一であっても相違してもよい。Ｘ¹およびＸ⁴は、活性共役ジエン系重合体鎖の活性末端と反応する官能基を有する基、または炭素数１〜６のアルキル基もしくは炭素数６〜１２のアリール基であり、Ｘ¹およびＸ⁴は互いに同一であっても相違してもよい。Ｘ²は、活性共役ジエン系重合体鎖の活性末端と反応する官能基を有する基である。Ｘ³は、２〜２０のアルキレングリコールの繰返し単位を含有する基であり、Ｘ³の一部は２〜２０のアルキレングリコールの繰返し単位を含有する基から導かれる基であってもよい。ｍは３〜２００の整数、ｎは０〜２００の整数、ｋは０〜２００の整数である。）
一般式（ＩＩ）

（上記式（ＩＩ）において、Ｒ⁹〜Ｒ¹⁶は、炭素数１〜６のアルキル基または炭素数６〜１２のアリール基であり、これらは互いに同一であっても相違してもよい。Ｘ⁵〜Ｘ⁸は、活性共役ジエン系重合体鎖の活性末端と反応する官能基を有する基である。）
一般式（ＩＩＩ）：

（上記式（ＩＩＩ）において、Ｒ¹⁷〜Ｒ¹⁹は、炭素数１〜６のアルキル基または炭素数６〜１２のアリール基であり、これらは互いに同一であっても相違してもよい。Ｘ⁹〜Ｘ¹¹は、活性共役ジエン系重合体鎖の活性末端と反応する官能基を有する基である。）
上記一般式（Ｉ）で表されるポリオルガノシロキサンにおいて、Ｒ¹〜Ｒ⁸、Ｘ¹およびＸ⁴を構成する炭素数１〜６のアルキル基としては、例えば、メチル基、エチル基、ｎ−プロピル基、イソプロピル基、ブチル基、ペンチル基、ヘキシル基、シクロヘキシル基などが挙げられる。炭素数６〜１２のアリール基としては、例えば、フェニル基、メチルフェニル基などが挙げられる。これらのアルキル基およびアリール基の中では、メチル基が特に好ましい。 As the polyorganosiloxane compound, compounds represented by the following general formulas (I) to (III) are preferable. That is, the compound having a functional group capable of reacting with the active terminal of the active conjugated diene polymer chain may contain at least one selected from these polyorganosiloxane compounds, and a plurality of types may be combined. Moreover, you may combine these polyorganosiloxane compounds and the other compound which has a functional group which can react with an active terminal.
Formula (I)

(In the above formula (I), R ^{1 to} R ⁸ are an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, and these may be the same or different from each other. X ¹ and X ⁴ are the active conjugated diene polymer chain groups having a functional group capable of reacting with the active terminal of an alkyl group or an aryl group having 6 to 12 carbon atoms having 1 to 6 carbon atoms,, X ¹ and X ⁴ may be the same as or different from each other, X ² is a group having a functional group that reacts with the active end of the active conjugated diene polymer chain, and X ³ is an alkylene glycol of 2 to 20 It is a group containing a repeating unit, and a part of X ³ may be a group derived from a group containing a repeating unit of 2 to 20 alkylene glycol, m is an integer of 3 to 200, and n is 0 to 0. 200 is an integer, and k is an integer of 0 to 200.)
Formula (II)

(In the above formula (II), R ^{9 to} R ¹⁶ are an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, and these may be the same as or different from each other. ^{5 to} X ⁸ are groups having a functional group that reacts with the active terminal of the active conjugated diene polymer chain.
General formula (III):

(In the above formula (III), R ^{17 to} R ¹⁹ are an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, and these may be the same as or different from each other. ^{9 to} X ¹¹ are groups having a functional group that reacts with the active terminal of the active conjugated diene polymer chain.
In the polyorganosiloxane represented by the above general formula (I), examples of the alkyl group having 1 to 6 carbon atoms constituting R ^{1 to} R ⁸ , X ¹ and X ⁴ include, for example, methyl group, ethyl group, n- Examples include propyl group, isopropyl group, butyl group, pentyl group, hexyl group, cyclohexyl group and the like. Examples of the aryl group having 6 to 12 carbon atoms include a phenyl group and a methylphenyl group. Among these alkyl groups and aryl groups, a methyl group is particularly preferable.

In the polyorganosiloxane of the general formula (I), the group having a functional group that reacts with the active terminal of the polymer chain constituting X ¹ , X ² and X ⁴ includes an alkoxyl group having 1 to 5 carbon atoms, 2- A hydrocarbon group containing a pyrrolidonyl group and a group having 4 to 12 carbon atoms containing an epoxy group are preferred.

The alkoxyl group having 1 to 5 carbon atoms constituting the X ^1, X ² and X ^4, for example, a methoxy group, an ethoxy group, a propoxy group, isopropoxy group, butoxy group. Of these, a methoxy group is preferable. When at least one of X ¹ , X ² and X ⁴ is an alkoxyl group having 1 to 5 carbon atoms, when a polyorganosiloxane having an alkoxyl group at the active end of the active conjugated diene polymer chain is reacted, a silicon atom and an alkoxyl The bond with the oxygen atom of the group is cleaved, and the active conjugated diene polymer chain is directly bonded to the silicon atom to form a single bond.

（式（ＩＶ）中、ｊは２〜１０の整数である。特にｊは２であることが好ましい。） Preferred examples of the hydrocarbon group containing a 2-pyrrolidonyl group constituting X ¹ , X ² and X ⁴ include groups represented by the following general formula (IV).

(In the formula (IV), j is an integer of 2 to 10. In particular, j is preferably 2.)

When polyorganosiloxane containing a hydrocarbon group in which at least one of X ¹ , X ² and X ⁴ contains a 2-pyrrolidonyl group is reacted with the active end of the active conjugated diene polymer chain, 2-pyrrolidonyl is obtained. The carbon-oxygen bond of the carbonyl group constituting the group is cleaved to form a structure in which the polymer chain is bonded to the carbon atom.

Preferred examples of the group having 4 to 12 carbon atoms having an epoxy group constituting X ¹ , X ² and X ⁴ include groups represented by the following general formula (V).
Formula (V): ZYE

  In said formula (V), Z is a C1-C10 alkylene group or alkylarylene group, Y is a methylene group, a sulfur atom, or an oxygen atom, E is carbon number C2-C10 which has an epoxy group. It is a hydrogen group. Among these, Y is preferably an oxygen atom, more preferably Y is an oxygen atom and E is a glycidyl group, Z is an alkylene group having 3 carbon atoms, Y is an oxygen atom, and E is a glycidyl group. Those are particularly preferred.

In the polyorganosiloxane represented by the general formula (I), when at least one of X ¹ , X ² and X ⁴ is a group having 4 to 12 carbon atoms containing an epoxy group, the activity of the active conjugated diene polymer chain When polyorganosiloxane is reacted at the terminal, the carbon-oxygen bond constituting the epoxy ring is cleaved to form a structure in which a polymer chain is bonded to the carbon atom.

In the polyorganosiloxane represented by the general formula (I), X ¹ and X ⁴ are preferably an epoxy group-containing group having 4 to 12 carbon atoms or an alkyl group having 1 to 6 carbon atoms, X ² is preferably a group having 4 to 12 carbon atoms containing an epoxy group.

In the polyorganosiloxane represented by the general formula (I), X ³ is a group containing 2 to 20 alkylene glycol repeating units. The group containing 2 to 20 alkylene glycol repeating units is preferably a group represented by the following general formula (VI).

In the formula (VI), t is an integer of 2 to 20, R ¹ is an alkylene group or alkylarylene group having 2 to 10 carbon atoms, R ³ is a hydrogen atom or a methyl group, and R ² is a carbon number. 1-10 alkoxyl groups or aryloxy groups. Among these, it is preferable that t is an integer of 2 to 8, R ¹ is an alkylene group having 3 carbon atoms, R ³ is a hydrogen atom, and R ² is a methoxy group.

In the polyorganosiloxane represented by the general formula (II), R ^{9 to} R ¹⁶ are an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, and these may be the same or different from each other. You may do it. X ^{5 to} X ⁸ are groups having a functional group that reacts with the active end of the polymer chain.

In the polyorganosiloxane represented by the general formula (III), R ^{17 to} R ¹⁹ are an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, and these may be the same or different from each other. You may do it. X ^{9 to} X ¹¹ are groups having a functional group that reacts with the active end of the polymer chain. s is an integer of 1-18.

  In the polyorganosiloxane represented by the general formula (II) and the general formula (III), it reacts with an alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, and an active end of a polymer chain. The group having a functional group is the same as that described for the polyorganosiloxane of the general formula (I).

  Furthermore, the terminal modified group produced | generated by the said reaction has a functional group which has an interaction with a silica. The functional group having an interaction with silica may be a functional group included in the structure of the compound described above. Moreover, the functional group which could be produced by reaction with the said compound and active terminal may be sufficient. The functional group having an interaction with silica is not particularly limited. For example, an organosiloxane group, a hydroxyl group-containing polyorganosiloxane structure, an alkoxysilyl group, a hydroxyl group, an aldehyde group, a carboxyl group, an amino group, Examples include imino group, epoxy group, amide group, thiol group, ether group and the like. Of these, an organosiloxane group, an alkoxysilyl group, and a hydroxyl group-containing polyorganosiloxane structure are preferable. Thus, when a terminal modification group contains the functional group which has an interaction with a silica, affinity with a silica can be made higher and a dispersibility can be improved significantly.

  The concentration of the terminal modifying group possessed by the modified S-SBR is determined in relation to the weight average molecular weight (Mw) of the modified S-SBR. The weight average molecular weight of the modified S-SBR is 300,000 to 600,000, preferably 350,000 to 550,000. If the weight average molecular weight of the modified S-SBR is less than 300,000, the molecular weight of the modified S-SBR is low, so that the effect of improving the strength and rigidity cannot be sufficiently obtained, and the steering stability is insufficient when the tire is used. May end up. On the other hand, if the weight average molecular weight of the modified S-SBR exceeds 600,000, the concentration of the functional group at the molecular end will be low and the affinity with silica having a small particle diameter will be low. The weight average molecular weight (Mw) of the modified S-SBR is measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

  The blending amount of the modified S-SBR is 20 to 45% by weight, preferably 25 to 40% by weight, based on 100% by weight of the rubber component. By setting the blending amount of the modified S-SBR having the above-mentioned weight average molecular weight within this range, the concentration of terminal modified groups in the rubber composition having a total oil amount of 30 parts by weight or less is optimized, and While having good affinity, the amount of bound rubber does not increase too much and good workability can be obtained.

  The modified S-SBR preferably has a styrene unit content of 10 to 40% by weight, more preferably 15 to 35% by weight, and still more preferably 15 to 30% by weight. By setting the styrene unit content of the modified S-SBR within such a range, it is possible to bring the balance of viscoelastic properties to an optimum region in terms of both grip performance and rolling resistance performance. The styrene unit content of the modified S-SBR is measured by infrared spectroscopic analysis (Hampton method).

  The glass transition temperature (Tg) of the modified S-SBR is not particularly limited, but is preferably -80 to -10 ° C. By setting the Tg of the modified S-SBR within such a range, the steering stability can be ensured and the rolling resistance can be reduced. The glass transition temperature (Tg) of the modified S-SBR is determined by differential scanning calorimetry (DSC) with a thermogram measured at a temperature increase rate of 20 ° C./min to obtain the temperature at the midpoint of the transition region. Moreover, when modified | denatured S-SBR is an oil-extended article, it is set as the glass transition temperature of modified | denatured S-SBR in the state which does not contain an oil-extended component (oil).

  In the present invention, the rubber hardness can be increased and the steering stability of the tire can be increased by blending unmodified S-SBR having a high molecular weight. The S-SBR used has a weight average molecular weight of 900,000 to 1,300,000, preferably 950,000 to 1,200,000. If the weight average molecular weight of S-SBR is less than 900,000, the concentration at the end of the rubber molecules increases, so the heat build-up increases and the rolling resistance when tires are increased. On the other hand, if the weight average molecular weight of S-SBR exceeds 1.3 million, the rubber viscosity of the rubber composition increases and the processability deteriorates. The weight average molecular weight of S-SBR is measured in the same manner as the weight average molecular weight of the modified S-SBR described above.

  The glass transition temperature (Tg) of S-SBR is not particularly limited, but is preferably -40 to -15 ° C. By making the Tg of the S-SBR within such a range, it is possible to ensure steering stability and reduce rolling resistance. The Tg of S-SBR is measured in the same manner as the Tg of the modified S-SBR described above.

  The amount of S-SBR is 30 to 70% by weight, preferably 35 to 60% by weight, based on 100% by weight of the rubber component. When the blending amount of S-SBR is less than 30% by weight, the strength of the rubber is insufficient and high steering stability cannot be exhibited. On the other hand, if the blending amount of S-SBR exceeds 70% by weight, the ratio of other SBRs is relatively reduced, and it becomes impossible to balance good performance and workability.

  In this invention, rubber | gum intensity | strength can be made high by mix | blending E-SBR, and the steering stability of a tire can be made high. The E-SBR used has a weight average molecular weight of 700,000 to 1,300,000, preferably 700,000 to 1,200,000. If the weight average molecular weight of E-SBR is less than 700,000, the rubber strength cannot be sufficiently increased. In addition, since the concentration of the end portion of the rubber molecule is increased, the heat generation is increased and the rolling resistance when the tire is formed is increased. When the weight average molecular weight of E-SBR exceeds 1.3 million, the rubber viscosity of the rubber composition increases and the processability deteriorates.

  E-SBR preferably has a viscosity of 65 or more when 37.5 parts by weight of oil-extended oil is contained with respect to 100 parts by weight of E-SBR. By setting the viscosity of E-SBR to 65 or more, the rubber strength of the rubber composition can be further increased, and the steering stability when the tire is formed can be further increased. In the present invention, the viscosity of E-SBR is the Mooney viscosity measured at 100 ° C. based on JIS K 6300.

  E-SBR used in the present invention is a styrene butadiene rubber produced by emulsion polymerization, and the styrene content is preferably 25 to 50% by weight, more preferably 30 to 45% by weight. By setting the styrene content of E-SBR within such a range, it is possible to increase the rubber hardness and improve the steering stability when the tire is made. E-SBR has a Tg of preferably −50 to −20 ° C., more preferably −45 to −25 ° C. In addition, a weight average molecular weight, a styrene content, and a glass transition temperature (Tg) shall each be measured by the method similar to modified | denatured S-SBR mentioned above.

  The rubber composition for a tire tread of the present invention suppresses the exothermic property of the rubber composition by blending silica and reduces rolling resistance when formed into a tire. In particular, by incorporating silica having a small particle diameter having a specific particle property, which will be described later, the reinforcing property of the rubber composition is increased to ensure steering stability. Further, by blending carbon black, the rubber hardness is increased to ensure steering stability.

  In the present invention, the total amount of silica and carbon black is 60 to 120 parts by weight, preferably 70 to 120 parts by weight based on 100 parts by weight of the rubber component consisting of the total of the above-described modified S-SBR, S-SBR and E-SBR. 100 parts by weight. When the blending amount of silica and carbon black is less than 60 parts by weight, the rubber strength is insufficient, so that the steering stability when the tire is made cannot be ensured. If the blending amount of silica and carbon black exceeds 120 parts by weight, the rubber viscosity increases and the processability deteriorates, and at the same time, the fuel efficiency becomes insufficient.

  The ratio of silica to the total of silica and carbon black is 85% by weight or more, preferably 90 to 98% by weight. When the ratio of silica is less than 85% by weight, rolling resistance cannot be reduced.

  As the silica used in the present invention, those having a DBP absorption of 190 ml / 100 g or more are used. When the DBP absorption amount of silica is less than 190 ml / 100 g, the dispersibility of silica deteriorates, and the workability and the strength of rubber deteriorate. In addition, the DBP absorption amount of silica shall be calculated | required based on JISK6217-4 oil absorption amount A method.

Silica has a nitrogen adsorption specific surface area of 194 to 225 m ² / g. When the nitrogen adsorption specific surface area of silica is less than 194 m ² / g, the reinforcing property for the rubber composition is insufficient and the steering stability is insufficient. On the other hand, when the nitrogen adsorption specific surface area of silica exceeds 225 m ² / g, the dispersibility of silica is lowered and rolling resistance is increased. In addition, the nitrogen adsorption specific surface area of a silica shall be calculated | required based on JISK6217-2.

Silica has a CTAB specific surface area (CTAB) of 170 to 210 m ² / g, preferably 185 to 205 m ² / g. When the CTAB of silica is less than 170 m ² / g, the reinforcing property for the rubber composition is insufficient and the steering stability is insufficient. On the other hand, when the CTAB of silica exceeds 210 m ² / g, the dispersibility of silica is lowered and the rolling resistance is increased. In addition, CTAB of a silica shall be calculated | required based on JISK6217-3.

Further, the above-described ratio of N ₂ SA to CTAB (N ₂ SA / CTAB) is set to 0.9 to 1.4. When the characteristic ratio of silica (N ₂ SA / CTAB) is less than 0.9, the reinforcing property for the rubber composition is insufficient and the steering stability is insufficient. On the other hand, when the characteristic ratio of silica (N ₂ SA / CTAB) exceeds 1.4, the dispersibility of silica is lowered and rolling resistance is increased.

  The silica used in the present invention is not limited as long as it has the above-described characteristics, and may be appropriately selected from those manufactured, or may be manufactured to have the above-described characteristics by a normal method. . As the type of silica, for example, wet method silica, dry method silica, or surface-treated silica can be used. Examples of commercially available silica products include Zeosil Premium 200MP manufactured by Rhodia, Ultrasil 9000GR manufactured by Evonik Degussa, and Nipsil AQ manufactured by Tosoh Silica.

  In the rubber composition of the present invention, it is preferable to blend a silane coupling agent together with silica, so that the dispersibility of silica can be improved and the reinforcement to styrene butadiene rubber can be further enhanced. The silane coupling agent is preferably added in an amount of 3 to 15% by weight, more preferably 5 to 12% by weight, based on the amount of silica. When the silane coupling agent is less than 3% by weight of the silica weight, the effect of improving the dispersibility of silica cannot be sufficiently obtained. On the other hand, when the silane coupling agent exceeds 15% by weight, the silane coupling agents are condensed with each other, and a desired effect cannot be obtained.

  Although it does not restrict | limit especially as a silane coupling agent, A sulfur containing silane coupling agent is preferable, for example, bis- (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide. , 3-trimethoxysilylpropylbenzothiazole tetrasulfide, γ-mercaptopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane, and the like.

  The rubber composition for a tire tread of the present invention can increase the rubber strength by blending a filler other than silica and carbon black. Examples of such fillers include clay, mica, talc, calcium carbonate, aluminum hydroxide, and aluminum oxide.

  In addition to the fillers described above, the tire tread rubber composition is generally a tire tread rubber composition such as a vulcanization or crosslinking agent, a vulcanization accelerator, an anti-aging agent, a plasticizer, and a processing aid. Various additives to be used can be blended, and such additives can be kneaded by a general method to form a rubber composition, which can be used for vulcanization or crosslinking. As long as the amount of these additives is not contrary to the object of the present invention, a conventional general amount can be used. Such a rubber composition can be produced by mixing each of the above components using a known rubber kneading machine, for example, a Banbury mixer, a kneader, a roll or the like.

  The rubber composition for a tire tread of the present invention can be suitably used for a pneumatic tire. A pneumatic tire using a rubber composition having excellent processability can be stably manufactured with high quality, and in addition to low rolling resistance and excellent fuel efficiency, steering stability is excellent.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, the scope of the present invention is not limited to these Examples.

  15 types of rubber compositions for tire treads (Examples 1 to 4 and Comparative Examples 1 to 11) each having the composition shown in Tables 1 and 2 were combined with 1.8 L of a closed-type mixer excluding sulfur and a vulcanization accelerator. The mixture was prepared by adding sulfur and a vulcanization accelerator to the master batch that was kneaded and released for 5 minutes and kneading with an open roll. In Tables 1 and 2, since the modified S-SBR3, S-SBR1,2 and E-SBR1,2 are rubbers containing 37.5 parts by weight of oil-extended oil, the description in the compounding amount column is actual. Along with the blending amount, the SBR net blending amount excluding the oil-extended oil is shown in parentheses. Further, the total amount of oil-extended oil and post-added oil contained in these SBRs is shown in parentheses in the total oil amount column.

  The Mooney viscosity of the obtained 15 types of rubber compositions for tire treads was measured by the method shown below and used as an index of workability.

Processability: Mooney viscosity (ML _{1 + 4} )
In accordance with JIS K6300, the obtained rubber composition was subjected to a Mooney viscometer using an L-shaped rotor (38.1 mm diameter, 5.5 mm thickness), preheating time 1 minute, rotor rotation time 4 minutes, 100 The measurement was performed under the conditions of 2 ° C. and ° C. The obtained results are shown in Tables 1 and 2 as an index with the value of Comparative Example 1 as 100. The smaller the index, the smaller the rubber viscosity and the better the workability.

  The obtained 15 types of rubber compositions for tire treads were press vulcanized at 160 ° C. for 25 minutes in a mold having a predetermined shape to prepare a vulcanized rubber sample, and tan δ (60 ° C.) by the method described below. Was used as an index of rolling resistance.

Rolling resistance: tan δ (60 ° C)
Using the viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd., tan δ (60 ° C.) of the obtained vulcanized rubber sample was subjected to conditions of an initial strain of 10%, an amplitude of ± 2%, a frequency of 20 Hz, and a temperature of 60 ° C. Measured with The obtained results are shown in Tables 1 and 2 as an index with Comparative Example 1 as 100. The smaller this index is, the lower the heat is generated, the lower the rolling resistance when the tire is made, and the better the fuel efficiency.

  Next, four pneumatic tires having a tire size of 225 / 50R17 were manufactured by using the 15 types of rubber compositions for tire treads described above in the tread portion. The steering stability of the obtained 15 types of pneumatic tires was evaluated by the following method.

Steering stability The obtained pneumatic tire is assembled on a wheel with a rim size of 7 x J, mounted on a domestic 2.5 liter class test vehicle, and a test course of 2.6 km per lap consisting of a dry road surface under the condition of air pressure of 230 kPa. The driving stability at that time was scored by a sensitive evaluation by three expert panelists. The obtained results were evaluated by a 10-point method and shown in Tables 1 and 2. The larger this index, the better the steering stability.

The types of raw materials used in Tables 1 and 2 are shown below.
Modified S-SBR1: Solution-polymerized styrene butadiene rubber having a hydroxyl group-containing polyorganosiloxane structure at the end, Nipol NS616, manufactured by Nippon Zeon Co., Ltd., weight average molecular weight 510,000, non-oil-extended modified S-SBR2: N-methyl- at the end Solution polymerized styrene butadiene rubber having 2-pyrrolidone group, Nipol NS116 manufactured by Nippon Zeon Co., Ltd., weight average molecular weight 450,000, non-oil-extended modified S-SBR3: solution polymerized styrene butadiene rubber having a hydroxyl group at the terminal, manufactured by Asahi Kasei Chemicals Toughden E581, weight average molecular weight 1.26 million, oil-extended product S-SBR 1 containing 37.5 parts by weight of oil with respect to 100 parts by weight of rubber component, unmodified solution polymerized styrene butadiene rubber, SLR6430 by Dow Chemical Co., weight average molecular weight Is 10.1 million, rubber Oil-extended product S-SBR2 containing 37.5 parts by weight of oil with respect to 100 parts by weight of component: Unmodified solution-polymerized styrene butadiene rubber, Nipol NS460 manufactured by Nippon Zeon Co., Ltd. Oil-extended E-SBR containing 37.5 parts by weight of oil: Emulsion-polymerized styrene butadiene rubber, Nipol 1739 manufactured by Nippon Zeon Co., Ltd., weight average molecular weight of 760,000, and 37.5 parts by weight of oil for 100 parts by weight of rubber component Oil exhibition, including Mooney viscosity 54
E-SBR2: emulsion-polymerized styrene butadiene rubber, Nipol 9548 manufactured by Nippon Zeon Co., Ltd., an oil-extended product containing 37.5 parts by weight of oil with respect to 100 parts by weight of the rubber component, Mooney viscosity of 69
E-SBR3: emulsion polymerized styrene butadiene rubber, Nipol 1502 manufactured by Nippon Zeon Co., Ltd., weight average molecular weight of 400,000, non-oil-extended product, Mooney viscosity when 37.5 parts by weight of oil is oil-extended with respect to 100 parts by weight of rubber component 50
Silica 1: Rhodia Zeosil Premium 200MP, DBP absorption 203 ml / 100 g, nitrogen adsorption specific surface area (N ₂ SA) 200 m ² / g, CTAB specific surface area (CTAB) 197 m ² / g, N ₂ SA and CTAB Ratio (N ₂ SA / CTAB) is 1.02.
Silica 2: Rhodia Zeosil 1165MP, DBP absorption 200 ml / 100 g, nitrogen adsorption specific surface area (N ₂ SA) of 160 m ² / g, CTAB specific surface area (CTAB) of 159 m ² / g, N ₂ SA and CTAB The ratio (N ₂ SA / CTAB) is 1.01
Silica 3: Nipsil AQ manufactured by Tosoh Silica Corporation, DBP absorption amount is 205 ml / 100 g, nitrogen adsorption specific surface area is 205 m 2 / g, CTAB specific surface area is 179 m 2 / g, and the ratio of N 2 SA to CTAB (N 2 SA / CTAB) is 1.15.
Carbon black: Seast KH made by Tokai Carbon
Zinc oxide: Zendo Chemical Industries, Ltd. Zinc oxide, 3 types of stearic acid: NOF Beads stearic acid YR
Anti-aging agent: Santoflex 6PPD manufactured by Flexis
Wax: Sunnock processing aid manufactured by Ouchi Shinsei Chemical Co., Ltd .: SCHILL & SEILACHER Gmbh. & CO. STRUKTOL A50P
Silane coupling agent: Sulfur-containing silane coupling agent, Si69 manufactured by Degussa
Oil: Extract 4 S, Showa Shell Sekiyu
Sulfur: Fine powder sulfur vulcanization accelerator containing Jinhua seal oil manufactured by Tsurumi Chemical Co., Ltd. 1: CBS accelerator, Noxeller CZ-G manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Vulcanization accelerator 2: Vulcanization accelerator DPG, Noxeller D manufactured by Ouchi Shinsei Chemical Co., Ltd.

  As is apparent from Table 1, it was confirmed that the rubber compositions for tire treads of Examples 1 to 4 maintained and improved processability (Mooney viscosity), low rolling resistance (tan δ at 60 ° C.), and steering stability. It was done. In the rubber composition of Comparative Example 1, the compounding amount of the modified S-SBR1 exceeds 45 parts by weight, so that the steering stability is inferior compared with Examples 1-5. The rubber composition of Comparative Example 2 is different in the functional group (terminal modified group) of the modified S-SBR2, and therefore the rolling resistance is deteriorated. In the rubber composition of Comparative Example 3, since the weight average molecular weight of the modified S-SBR3 exceeds 600,000 and the total oil amount exceeds 30 parts by weight, the rolling resistance increases and the steering stability deteriorates.

As is apparent from Table 2, the rubber composition of Comparative Example 4 has both S-SBR2 having a weight average molecular weight of less than 900,000, so both rolling resistance and steering stability are deteriorated. Since the rubber composition of Comparative Example 5 was blended with modified S-SBR3 instead of S-SBR1, the amount of modified S-SBR becomes excessive, and the processability deteriorates. In the rubber composition of Comparative Example 6, since the blending amount of E-SBR1 exceeds 25 parts by weight, the rolling resistance increases and the processability deteriorates. In the rubber composition of Comparative Example 7, the weight average molecular weight of E-SBR1 is less than 700,000, so that the rolling resistance increases and the steering stability cannot be improved. Since the rubber composition of Comparative Example 8 was formulated with S-SBR1 instead of E-SBR1, the steering stability could not be improved sufficiently. In the rubber composition of Comparative Example 9, since the blending amount of S-SBR1 is less than 30 parts by weight and the blending amount of E-SBR1 exceeds 25 parts by weight, the rolling resistance is greatly deteriorated. In the rubber composition of Comparative Example 10, since the ratio of silica in the total of silica and carbon black is less than 85% by weight, rolling resistance is deteriorated. In the rubber composition of Comparative Example 11, since N ₂ SA of silica 2 is less than 190 m ² / g and CTAB is less than 170 m ² / g, rolling resistance increases and steering stability can be sufficiently improved. Can not.

Claims (3)

End-modified solution polymerized styrene butadiene rubber (modified S-SBR) 20 to 45 wt%, unmodified solution polymerized styrene butadiene rubber (S-SBR) 30 to 70 wt%, emulsion polymerized styrene butadiene rubber (E-SBR) 100 parts by weight of a rubber component consisting of 10 to 25% by weight, a total oil amount of 30 parts by weight or less, and a total of 60 to 120 parts by weight of silica and carbon black, hydroxyl group-containing polyorganosiloxane structure with functional groups of the modified S-SBR is closed reactive with the silanol groups of the silica surface, alkoxysilyl group, at least one selected from hydroxyl groups, of the modified S-SBR The weight average molecular weight is 300,000 to 600,000, the weight average molecular weight of the S-SBR is 900,000 to 1.3 million, the E- With a weight average molecular weight of BR is 700,000 to 1,300,000, the silica and silica ratio of the total in the carbon black 85 wt% or more, the DBP absorption amount of silica is 190 ml / 100 g or more, a nitrogen adsorption specific surface area (N ₂ SA) is 194 to 225 m ² / g, CTAB specific surface area (CTAB) is 170 to 210 m ² / g, and the ratio of N ₂ SA to CTAB (N ₂ SA / CTAB) is 0.9 to 1.4. A rubber composition for a tire tread characterized by the above. The rubber composition for a tire tread according to claim 1, wherein the E-SBR has a viscosity of 65 or more when 37.5 parts by weight of oil-extended oil is contained with respect to 100 parts by weight of the E-SBR. . A pneumatic tire using the rubber composition for a tire tread according to claim 1.