JP4405849B2 - Rubber composition for tire tread and tire using the same - Google Patents

Description

  The present invention relates to a rubber composition for a tire tread and a tire using the same.

  In recent years, various measures have been taken to reduce the rolling resistance of tires for the purpose of energy saving (low fuel consumption) of vehicles. For example, a method using silica as a filler used in a tire rubber composition, or a method of reducing the amount of carbon black used as a filler can be given. However, these methods have a problem that the steering stability is deteriorated because the wet grip performance is lowered even if the fuel consumption can be reduced.

  In order to solve these problems, Patent Document 1 uses a styrene-butadiene rubber introduced with a functional group capable of being chemically bonded to silica at the end, and improves the dispersion of silica, so that A method for achieving both low fuel consumption and steering stability is disclosed. However, by improving the dispersion of silica, the generation of secondary particles (primary aggregates) of silica is suppressed, resulting in a problem that the rubber hardness obtained is reduced.

JP 2003-155398 A

  An object of the present invention is to provide a rubber composition for a tire tread that suppresses a reduction in rubber hardness and improves vehicle fuel efficiency and driving stability.

The present invention has a molecular weight distribution (Mw / Mn) of 2.3 or less, a diene rubber component containing 30% by weight or more of styrene-butadiene rubber terminal-modified for silica, and a BET specific surface area of 120 m ² / g or more. Further, silica having a dibutyl phthalate (DBP) oil absorption of 200 ml / 100 g or more and satisfying the following formula, a cetyltrimethylammonium bromide (CTAB) adsorption specific surface area of 170 m ² / g or more, and a content of 100 parts by weight of the rubber component The present invention relates to a rubber composition for a tire tread containing 5 parts by weight or more of carbon black.
(DBP oil absorption) / (BET specific surface area) ≧ 1.8

The carbon black preferably satisfies the following formula.
(CTAB adsorption specific surface area) / (iodine adsorption amount) ≧ 0.90

  The rubber composition preferably contains 50 to 90 parts by weight of the silica with respect to 100 parts by weight of the rubber component, and further contains 3 to 15 parts by weight of a silane coupling agent with respect to 100 parts by weight of the silica.

  The present invention also relates to a tire using the rubber composition.

  According to the present invention, a rubber component containing terminal-modified SBR is blended with silica having a large primary particle size and primary aggregate and carbon black having a specific CTAB, thereby reducing rubber hardness. It is possible to suppress the fuel consumption and improve the driving stability of a vehicle equipped with a tire obtained from the rubber composition.

  The rubber composition of the present invention comprises a diene rubber component, silica and carbon black.

  The diene rubber component contains styrene-butadiene rubber (terminal-modified SBR for silica) modified for silica. Here, the terminal-modified SBR for silica refers to SBR in which a functional group chemically bonded to silica is introduced into a polymer terminal in order to improve adhesion to silica.

  The terminal-modified SBR for silica is easy to control the molecular weight distribution and can remove low molecular weight components that cause the rolling resistance to deteriorate, and because it is a living polymerization, it is easy to introduce a functional group at the terminal. Those obtained by introducing a functional group into SBR obtained by solution polymerization are preferred.

  Examples of the functional group introduced into the terminal-modified SBR for silica include an amino group, a hydroxyl group, an epoxy group, an alkylsilyl group, an alkoxysilyl group, a carboxyl group, a lactam group, and a polysiloxane. Are particularly preferred, and an alkylsilyl group, an alkoxysilyl group, an epoxy group, and an amino group are preferred because the rolling resistance of a tire made of the obtained rubber composition is sufficiently reduced.

  The modification rate of the functional group of the terminal-modified SBR for silica is preferably 30% or more, and more preferably 50% or more. If the modification rate is less than 30%, the amount of bonding with silica is small, and thus there is a tendency that the rolling resistance cannot be sufficiently reduced. The modification rate is preferably 80% or less, and more preferably 70% or less. If it exceeds 80%, the interaction with silica becomes too strong, so that the workability during rubber kneading tends to decrease.

  The diene rubber component contains 30% by weight or more, preferably 45% by weight or more, more preferably 50% by weight or more of the terminal-modified SBR for silica in the rubber component. If the content is less than 30% by weight, it is difficult to reduce rolling resistance. Further, the diene rubber component preferably contains 80% by weight or less of terminal-modified SBR in the rubber component, and more preferably 70% by weight or less. When the content exceeds 80% by weight, the polymer has a strong reaction with silica, so that the physical properties of the rubber after kneading tend to deteriorate or the viscosity during extrusion tends to increase.

  The molecular weight distribution (Mw / Mn) of the terminal-modified SBR for silica is 2.3 or less, preferably 2.2 or less. When Mw / Mn exceeds 2.3, the molecular weight distribution becomes wide, that is, the low molecular weight component increases, so that the rolling resistance deteriorates.

  The amount of styrene units in the terminal-modified SBR for silica is preferably 10 to 40% by weight. When the styrene unit amount is less than 10% by weight, the grip under dry conditions tends to decrease, and the wear resistance also tends to decrease. On the other hand, when the styrene unit amount exceeds 40% by weight, rolling resistance tends to deteriorate.

  The vinyl content of the terminal-modified SBR for silica is preferably 30 to 70% by weight. If the vinyl content is less than 30% by weight, the balance between wet grip and rolling resistance tends to deteriorate. On the other hand, if the vinyl content exceeds 70% by weight, the wear resistance is remarkably deteriorated, and the vulcanization time tends to occur.

  As the rubber component of the present invention, natural rubber (NR), butadiene rubber (BR), butyl rubber (IIR), and the like can be used in addition to the above-mentioned terminal-modified SBR for silica. Among them, it is preferable to use NR because the balance between the wet grip and the rolling resistance can be achieved in a high order while maintaining the wear resistance.

  The silica used in the present invention has a primary particle size larger than that of generally used silica. In the present invention, the hardness of the rubber composition obtained by increasing the primary particle size of silica and increasing the size of the primary aggregate of silica when mixing silica and the terminal-modified polymer for silica. Can be suppressed, and the dispersibility of silica can be improved. Here, the primary aggregate indicates secondary particles formed by aggregation of primary particles.

  In general, silica is obtained by dissolving silica in an alkaline aqueous solution to prepare a water glass, precipitating the silica while neutralizing it with sulfuric acid, once drying, pulverizing, and compacting. Silica used in the present invention can be increased in primary particle size by reacting for a long time while being appropriately stirred in the production process, and further, the size as a primary aggregate is increased. be able to.

  The silica used in the present invention has a specific BET specific surface area and DBP oil absorption. Here, the BET specific surface area indicates the size of the primary particle diameter, and the larger the BET specific surface area, the smaller the particle diameter of the silica. Further, the DBP oil absorption indicates a standard (structure) of the aggregation state of the particles, and the larger the DBP oil absorption, the larger the primary aggregate.

Silica has a BET specific surface area of 120 m ² / g or more. If the BET specific surface area is less than 120 m ² / g, the Mooney viscosity can be kept low and the rolling resistance can be reduced, but it is inferior in terms of wear resistance and steering stability. Further, the BET specific surface area is preferably 150 m ² / g or less, and more preferably 130 m ² / g or less. When the BET specific surface area exceeds 150 m ² / g, in the process of dispersing silica in the rubber, the primary aggregate of silica becomes large and the silica particle size is small. Therefore, the load tends to be excessively applied in the rubber kneading process and the extrusion process.

  Silica has a DBP oil absorption of 200 ml / 100 g or more. When the DBP oil absorption is less than 200 ml / 100 g, it is difficult to maintain the hardness of the rubber, and the steering stability is poor. Further, the DBP oil absorption is preferably 400 ml / 100 g or less, and more preferably 350 ml / 100 g or less. When the DBP oil absorption exceeds 400 ml / 100 g, the viscosity of the kneaded rubber increases, and even if the particle diameter of the silica is increased, the extrusion process tends to be overloaded.

In the rubber composition of the present invention, the ratio of the DBP oil absorption to the BET specific surface area of silica satisfies the following formula.
(DBP oil absorption) / (BET specific surface area) ≧ 1.8

  Furthermore, the ratio of oil absorption is preferably 2.2 or more, more preferably 2.3 or more, and further preferably 2.5 or more. If the ratio of oil absorption is less than 1.8, the balance between rolling resistance and steering stability is poor. The ratio of oil absorption is preferably 4.0 or less, and more preferably 3.5 or less. If it exceeds 4.0, there is a tendency that a load is applied in the extrusion process.

  The content of silica is preferably 50 parts by weight or more and more preferably 60 parts by weight or more with respect to 100 parts by weight of the diene rubber component. When the content of silica is less than 50 parts by weight, the rolling resistance is improved, but the wear resistance is lowered, and it tends to be difficult to maintain the steering stability. The silica content is preferably 90 parts by weight or less, and more preferably 85 parts by weight or less. When the silica content exceeds 90 parts by weight, rolling resistance tends to deteriorate.

  The carbon black used in the present invention is preferably one having a specific cetyltrimethylammonium bromide (CTAB) adsorption specific surface area and iodine adsorption amount. Here, the CTAB adsorption specific surface area indicates the size of the particle diameter, and the larger the CTAB adsorption specific surface area, the smaller the particle diameter of the carbon black. Further, the iodine adsorption amount indicates the size of the particle diameter, and the difference between the CTAB adsorption specific surface area and the iodine adsorption amount indicates a difference in surface activity.

Carbon black has a CTAB adsorption specific surface area of 170 m ² / g or more, preferably 175 m ² / g or more. When the CTAB adsorption specific surface area is less than 170 m ² / g, the wear resistance is deteriorated. Further, the CTAB adsorption specific surface area is preferably 250 m ² / g or less, more preferably 230 m ² / g or less. When the CTAB adsorption specific surface area exceeds 250 m ² / g, the dispersion of carbon black at the time of kneading deteriorates, or the viscosity increases even when rubber is kneaded so that the dispersion state is good, and the process tends to be loaded. There is.

In the rubber composition of the present invention, the ratio of the CTAB adsorption specific surface area to the iodine adsorption amount of carbon black satisfies the following formula.
(CTAB adsorption specific surface area) / (iodine adsorption amount) ≧ 0.90

  Furthermore, the ratio of the CTAB adsorption specific surface area is preferably 0.92 or more, and more preferably 0.95 or more. If it is less than 0.90, the surface activity of the carbon black is lowered and it becomes difficult to bond with the polymer, so that the rolling resistance tends to deteriorate. The ratio of the CTAB adsorption specific surface area is preferably 1.2 or less. Above 1.2, the cost of producing carbon black tends to be high.

  The compounding amount of carbon black is 5 parts by weight or more, preferably 13 parts by weight or more with respect to 100 parts by weight of the diene rubber component. If the blending amount is less than 5 parts by weight, the abrasion resistance is deteriorated and the blackness of the rubber is lowered to deteriorate the weather resistance. The blending amount is more preferably 50 parts by weight or less, and further preferably 40 parts by weight or less. When the amount exceeds 50 parts by weight, the rolling resistance tends to be greatly deteriorated.

  In the present invention, the silane coupling agent can be used in combination with silica. Specific examples of the silane coupling agent include bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (4-triethoxysilylbutyl) tetrasulfide, and bis ( 3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, bis (4-trimethoxysilylbutyl) tetrasulfide, bis (3-methyldiethoxysilylpropyl) tetrasulfide, bis (2 -Methyldimethoxysilylethyl) tetrasulfide, bis (4-methyldimethoxysilylbutyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (2-triethoxysilylethyl) trisulfide, bis (4-tri Toxisilylbutyl) trisulfide, bis (3-trimethoxysilylpropyl) trisulfide, bis (2-trimethoxysilylethyl) trisulfide, bis (4-trimethoxysilylbutyl) trisulfide, bis (3-triethoxysilyl) Propyl) disulfide, bis (2-triethoxysilylethyl) disulfide, bis (4-triethoxysilylbutyl) disulfide, bis (3-trimethoxysilylpropyl) disulfide, bis (2-trimethoxysilylethyl) disulfide, bis ( 4-trimethoxysilylbutyl) disulfide, bis (3-methyldiethoxysilylpropyl) disulfide, bis (2-methyldiethoxysilylpropyl) disulfide, bis (4-methyldiethoxysilylpropyl) disulfide Bis (3-methyldimethoxysilylpropyl) disulfide, bis (2-methyldimethoxysilylpropyl) disulfide, bis (4-methyldimethoxysilylptyl) disulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2 -Mercaptoethyltrimethoxysilane, 2-mercaptotriethyltriethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltomethoxysilane, 3- (2-aminoethyl) aminopropyltriethoxysilane, 3- (2- Aminoethyl) aminopropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycyl Such as de propyl methyl dimethoxysilane and the like. Bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, and bis (3-tri) Methoxysilylpropyl) disulfide, bis (3-methyldiethoxysilylpropyl) disulfide, bis (3-methyldimethoxysilylpropyl) disulfide and the like are preferably used. These silane coupling agents may be used alone or in combination of two or more.

  It is preferable that the compounding quantity of a silane coupling agent is 3-15 weight part with respect to 100 weight part of said silica. If the blending amount is less than 3 parts by weight, there is a tendency that a sufficient coupling effect to silica cannot be obtained, and if it exceeds 15 parts by weight, the cost tends to be high.

  In addition to the rubber component, silica, carbon black, and silane coupling agent, the rubber composition of the present invention includes softeners such as oils commonly used in the rubber industry, waxes, anti-aging agents, stearic acid, and zinc oxide. Further, a vulcanizing agent such as sulfur and a vulcanization accelerator can be appropriately blended.

  The tire of the present invention is produced by an ordinary method using the rubber composition of the present invention. That is, if necessary, the rubber composition of the present invention blended with the various chemicals is extruded according to the shape of the tread at the unvulcanized stage, and molded by a normal method on a tire molding machine, Form an unvulcanized tire. This unvulcanized tire is heated and pressurized in a vulcanizer to obtain a tire.

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

Below, the various chemical | medical agents used in the Example and the comparative example are demonstrated.
Terminal modified SBR for carbon: SL574 (solution polymerization, styrene unit content: 15% by weight, vinyl content: 57% by weight) manufactured by JSR Corporation
End-modified SBR for silica 1: E10 manufactured by Asahi Kasei Corporation (solution polymerization, styrene unit amount: 39%, vinyl content: 31%)
End-modified SBR2 for silica: HRR260 (prototype SBR) manufactured by JSR Corporation (solution polymerization, styrene unit content: 26%, vinyl content: 72%)
NR: RSS # 3
Carbon black 1: prototype carbon black manufactured by Mitsubishi Chemical Corporation (CTAB adsorption specific surface area: 180 m ² / g, iodine adsorption amount: 188 mg / g)
Carbon black 2: Carbon black ISAF manufactured by Showa Cabot Co., Ltd. (CTAB adsorption specific surface area: 107 m ² / g, iodine adsorption amount: 120 mg / g)
Silica 1: Silica 115Gr manufactured by Rhodia (BET specific surface area: 112 m ² / g, DBP oil absorption: 250 ml / 100 g, DBP oil absorption / BET specific surface area: 2.23)
Silica 2: EP7012 (Micropearl) manufactured by Degussa (BET specific surface area: 144 m ² / g, DBP oil absorption: 273 ml / 100 g, DBP oil absorption / BET specific surface area: 1.90)
Silica 3: Silica VN3 manufactured by Degussa (BET specific surface area: 175 m ² / g, DBP oil absorption: 162 ml / 100 g, DBP oil absorption / BET specific surface area: 0.93)
Silane coupling agent: Si-75 manufactured by Degussa
Process oil: Diana Process PS24 manufactured by Idemitsu Kosan Co., Ltd.
Wax: Sannoc Wax manufactured by Ouchi Shinsei Chemical Co., Ltd. Anti-aging agent: Santoflex 13 manufactured by Flexis
Stearic acid: Tungsten zinc oxide manufactured by Nippon Oil & Fats Co., Ltd .: Zinc Hua No. 2 manufactured by Mitsui Kinzoku Mining Co., Ltd. DPG manufactured by
Vulcanization accelerator 2: Noxeller NS manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

Examples 1-2 and Comparative Examples 1-5
The mixture which knead | mixed the mixing | blending content shown in Table 1 using the 1.7L Banbury by Kobe Steel, Ltd., and then kneaded it by adding sulfur and a vulcanization accelerator to the kneaded material obtained on the open roll. Was vulcanized at 150 ° C. for 30 minutes to obtain a rubber composition. The characteristic test shown below was done using the obtained rubber composition.

(Test method)
<Measurement of viscoelasticity>
Using a VES-F-3 manufactured by Iwamoto Seisakusho, the complex elastic modulus (E *) and loss tangent (tan δ) at 60 ° C. were measured at a frequency of 10 Hz, an initial strain of 10%, and a dynamic strain of 2%.

  The larger the E * value, the higher the rigidity and the better the steering stability. Further, the smaller the value of tan δ, the lower the rolling resistance, which is better.

<Hardness>
The prepared rubber composition was measured at 25 ° C. using a JIS-A hardness meter.

<Extruded dough>
In the production of the rubber composition, visually judge the extruded skin of the unvulcanized rubber composition extruded from the roll after kneading, `` good '' if the surface can not be seen uneven, the surface is uneven, A case where a hole was formed in the rubber fabric was evaluated as “bad”.

<Steering stability>
A tire of 195 / 60R15 size manufactured by using the rubber composition of the present invention on a tread is manufactured by a conventional method, and a sensory test is performed on a test course with a normal passenger car equipped with the tire, and steering stability is excellent. The case was evaluated as “◯” and the case other than that was evaluated as “X”.

  Further, in the abrasion resistance at the time of steering, the case where abrasion wear was large was evaluated as “X”, and the case where it was not so was evaluated as “◯”.

<Rolling resistance>
Using a tire of 195 / 60R15 size manufactured using the rubber composition of the present invention for the tread, the rolling resistance value of the tire was measured on a table. The rolling resistance index was calculated by setting the value of Comparative Example 2 to 100 according to the following formula. It shows that it is so favorable that rolling resistance is small.
Rolling resistance index = (Rolling resistance value of each tire) / (Rolling resistance value of tire in Comparative Example 2) × 100

  The test results are shown in Table 1.

Claims (4)

A diene rubber component having a molecular weight distribution (Mw / Mn) of 2.3 or less and containing 30% by weight or more of styrene-butadiene rubber terminal-modified for silica;
A silica having a BET specific surface area of 120 m ² / g or more, a dibutyl phthalate (DBP) oil absorption of 200 ml / 100 g and satisfying the following formula, and a cetyltrimethylammonium bromide (CTAB) adsorption specific surface area of 170 m ² / g or more, and A rubber composition for a tire tread containing carbon black whose content is 5 parts by weight or more with respect to 100 parts by weight of the rubber component.
(DBP oil absorption) / (BET specific surface area) ≧ 1.8 The rubber composition according to claim 1, wherein the carbon black satisfies the following formula.
(CTAB adsorption specific surface area) / (iodine adsorption amount) ≧ 0.90 The rubber composition according to claim 1 or 2, comprising 50 to 90 parts by weight of the silica with respect to 100 parts by weight of the rubber component, and further 3 to 15 parts by weight of a silane coupling agent with respect to 100 parts by weight of the silica. A tire using the rubber composition according to claim 1, 2 or 3.