JP4975356B2 - Rubber composition for tire tread - Google Patents

Description

  The present invention relates to a rubber composition for a tire tread.

  In recent years, for example, to reduce the rolling resistance of tires in order to save energy (reducing fuel consumption) in vehicles, various means have been studied.

  For example, a method using silica as a filler is known. However, in this case, there is a problem that Mooney viscosity increases, workability deteriorates, rigidity further decreases, and steering stability deteriorates.

  A method for reducing the amount of carbon black used as a filler is also known. However, even in this case, there is a problem that the rubber strength is lowered, the rigidity is further lowered, and the steering stability is deteriorated.

  Patent Document 1 discloses a tire tread that contains a predetermined amount of a predetermined rubber component, a predetermined carbon black, and a predetermined silica, thereby suppressing reduction in rubber hardness and improving fuel economy and driving stability. A rubber composition and a tire using the same are disclosed. However, it is not possible to sufficiently improve both fuel efficiency and steering stability, and there is still room for improvement, particularly in terms of fuel efficiency.

JP 2005-325206 A

  An object of this invention is to provide the rubber composition for tire treads which can improve both low-fuel-consumption property and steering stability.

  The present invention relates to a tire tread rubber comprising a diene rubber component having a molecular weight distribution (Mw / Mn) of 2.3 or less and containing 30% by weight or more of a styrene butadiene rubber terminal-modified for silica, and a paper fiber. Relates to the composition.

  The tire tread rubber composition preferably contains 0.5 to 20 parts by weight of paper fibers with respect to 100 parts by weight of the diene rubber component.

  ADVANTAGE OF THE INVENTION According to this invention, the rubber composition for tire treads which can improve both low-fuel-consumption property and steering stability can be provided by containing a predetermined | prescribed rubber component and paper fiber.

  The rubber composition for tire treads of the present invention contains a diene rubber component and paper fibers.

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

  The modified SBR is easy to control the molecular weight distribution, can remove low molecular weight components that cause deterioration in fuel economy, and is also a living polymerization, so 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 modified SBR include an amino group, a hydroxyl group, an epoxy group, an alkylsilyl group, an alkoxysilyl group, a carboxyl group, and a lactam group, and the adhesion to silica is particularly excellent. An alkylsilyl group, an alkoxysilyl group, an epoxy group, and an amino group are preferable, and an amino group is more preferable because the fuel efficiency of a tire using the obtained rubber composition can be sufficiently improved.

  The modification rate of the functional group of the modified SBR is preferably 30% by weight or more, and more preferably 50% by weight or more. When the modification rate of the functional group of the modified SBR is less than 30% by weight, the amount of bonding with silica is small, and thus there is a tendency that the fuel efficiency is not sufficiently improved. Further, the modification rate of the functional group of the modified SBR is preferably 80% by weight or less, and more preferably 70% by weight or less. When the modification rate of the functional group of the modified SBR exceeds 80% by weight, the interaction with silica becomes too strong, and the workability during rubber kneading tends to be lowered.

  The molecular weight distribution (Mw / Mn) of the modified SBR is 2.3 or less, preferably 2.2 or less. When the Mw / Mn of the modified SBR exceeds 2.3, the molecular weight distribution becomes wide, that is, the low molecular weight component increases, so the fuel efficiency deteriorates. Further, the Mw / Mn of the modified SBR is preferably 1 or more.

  The styrene content of the modified SBR is preferably 10% by weight or more, and more preferably 15% by weight or more. When the styrene content of the modified SBR is less than 10% by weight, grip performance under dry conditions tends to be lowered, and wear resistance tends to be lowered. The styrene content of the modified SBR is preferably 45% by weight or less, more preferably 40% by weight or less. If the styrene content of the modified SBR exceeds 45% by weight, the fuel efficiency tends to deteriorate.

  The amount of vinyl bonds in the modified SBR is preferably 25% by weight or more, and more preferably 30% by weight or more. If the vinyl bond content of the modified SBR is less than 25% by weight, the balance between wet grip performance and fuel efficiency tends to deteriorate. The vinyl bond content of the modified SBR is preferably 70% by weight or less, and more preferably 65% by weight or less. When the vinyl bond content of the modified SBR exceeds 70% by weight, the wear resistance is remarkably deteriorated and the vulcanization time tends to increase.

  The content of the modified SBR in the diene rubber component is 30% by weight or more, preferably 45% by weight or more, more preferably 50% by weight or more. If the content of the modified SBR is less than 30% by weight, it is difficult to improve fuel efficiency. Further, the content of the modified SBR is preferably 80% by weight or less, and more preferably 70% by weight or less. When the content of the modified SBR 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.

  In addition to the modified SBR, the diene rubber component of the present invention includes natural rubber (NR), butadiene rubber (BR), styrene butadiene rubber (SBR) other than modified SBR, butyl rubber (IIR), halogenated butyl rubber (X- IIR), chloroprene rubber (CR), ethylene propylene diene rubber (EPDM), a halide of a copolymer of isomonoolefin and paraalkylstyrene, and the like can be used. Among these, it is preferable to use NR because the balance between wet grip performance and fuel efficiency can be achieved in a high order while maintaining wear resistance.

  Paper fibers are cellulose fibers that are made into fibers by pulverizing and beating wood, pulp, waste paper, etc., and these paper fibers may be used alone or in combination of two or more. May be used. Among these, waste paper is preferred because it can be recycled and is low in cost. Specific examples of paper fibers include Neofiber (new paper used by Oji Bags Co., Ltd.), KC Flock (manufactured by Nippon Paper Chemicals Co., Ltd.), and Mill Five (manufactured by Sankyo Seiko Co., Ltd.). can give.

  Similar to silica and the like, many hydroxyl groups are present on the surface of the paper fiber, and by binding to the modified SBR, it is possible to suppress the movement of the rubber molecules and improve the fuel economy and the handling stability.

  The average fiber length (L) of the paper fibers is preferably 10 μm or more, and more preferably 50 μm or more. If the L of the paper fiber is less than 10 μm, the effect of improving the rigidity by adding the paper fiber tends to be small. The paper fiber L is preferably 1000 μm or less. When the L of the paper fiber exceeds 1000 μm, the paper fiber tends to be poorly dispersed.

  The average fiber diameter (D) of the paper fibers is preferably 0.5 μm or more, and more preferably 1 μm or more. If the D of the paper fiber is less than 0.5 μm, the paper fiber tends to be poorly dispersed. Further, D of the paper fiber is preferably 100 μm or less, and more preferably 90 μm or less. When D of the paper fiber exceeds 100 μm, the reinforcing effect tends to be not obtained.

  The ratio of the average fiber length to the average fiber diameter of the paper fibers (average aspect ratio, L / D) is preferably 10 or more, and more preferably 20 or more. If the L / D of the paper fiber is less than 10, there is a tendency that the reinforcing effect cannot be obtained. The L / D of the paper fiber is preferably 2000 or less, and more preferably 1800 or less. When the L / D of the paper fiber exceeds 2000, the paper fiber tends to be poorly dispersed.

  The content of the paper fiber is preferably 0.5 parts by weight or more, more preferably 1 part by weight or more with respect to 100 parts by weight of the rubber component. When the content of the paper fiber is less than 0.5 parts by weight, the effect of adding the paper fiber tends to be small. Further, the content of paper fiber is preferably 20 parts by weight or less, and more preferably 15 parts by weight or less. When the content of the paper fiber exceeds 20 parts by weight, the wear resistance tends to deteriorate.

  It is preferable that 80% or more of the paper fibers are oriented in the thickness direction of the tire tread. As described above, by orienting the paper fibers substantially in the thickness direction of the tire tread, an effect that both ride comfort and steering stability are excellent can be obtained.

  The rubber composition for a tire tread of the present invention preferably contains a filler.

  The filler is not particularly limited, and examples thereof include carbon black, silica, calcium carbonate, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, alumina, clay, talc, and magnesium oxide. These fillers can be used alone. You may use, and may use it in combination of 2 or more type. In particular, carbon black and / or silica are preferable, and carbon black and silica are more preferable.

The carbon black has a cetyltrimethylammonium bromide adsorption specific surface area (CTAB) of preferably 120 m ² / g or more, and more preferably 125 m ² / g or more. When the CTAB of carbon black is less than 120 m ² / g, the wear resistance tends to deteriorate. Further, CTAB of the carbon black is preferably 250 meters ² / g or less, more preferably 230 m ² / g. If the carbon black CTAB exceeds 250 m ² / g, the dispersibility of the carbon black at the time of kneading tends to deteriorate, and even if the rubber is kneaded so that the dispersion state is good, the viscosity increases, and the workability However, the process tends to be burdened.

  The iodine adsorption amount (IA) of carbon black is preferably 130 mg / g or more, and more preferably 135 mg / g or more. When the IA of carbon black is less than 130 mg / g, the wear resistance tends to deteriorate. The IA of carbon black is preferably 200 mg / g or less, and more preferably 195 mg / g or less. When the IA of carbon black exceeds 200 mg / g, processability tends to deteriorate.

  The ratio of the cetyltrimethylammonium bromide adsorption specific surface area (CTAB / IA) to the iodine adsorption amount of carbon black is preferably 0.90 or more, more preferably 0.92 or more, and further preferably 0.95 or more. If the CTAB / IA of the carbon black is less than 0.90, the surface activity of the carbon black is lowered and it becomes difficult to bond with the polymer, so the fuel efficiency tends to deteriorate. Further, CTAB / IA of carbon black is preferably 1.2 or less, and more preferably 1.15 or less. If CTAB / IA of carbon black exceeds 1.2, the cost for producing carbon black tends to be high.

  When carbon black is contained, the content of carbon black is preferably 5 parts by weight or more and more preferably 10 parts by weight or more with respect to 100 parts by weight of the diene rubber component. When the carbon black content is less than 5 parts by weight, the wear resistance tends to deteriorate, and the blackness of the rubber tends to decrease and the weather resistance tends to deteriorate. The carbon black content is preferably 50 parts by weight or less, more preferably 40 parts by weight or less. If the carbon black content exceeds 50 parts by weight, the fuel efficiency tends to be greatly deteriorated.

  There is no restriction | limiting in particular as a silica, The thing prepared by the wet method or the dry method can be used.

Silica has a BET specific surface area (BET) of preferably 100 m ² / g or more, and more preferably 110 m ² / g or more. When the BET of silica is less than 100 m ² / g, the Mooney viscosity is reduced to improve processability and improve fuel efficiency, but there is a tendency for wear resistance and steering stability to be reduced. Further, BET of silica is preferably 150 meters ² / g or less, more preferably 130m ² / g. If the BET of silica exceeds 150 m ² / g, the Mooney viscosity increases, so that the processability is deteriorated and the load tends to be excessively applied in the rubber kneading process and the extrusion process.

  The DBP oil absorption (DBP) of silica is preferably 200 ml / 100 g or more, more preferably 210 ml / 100 g or more. When the DBP of silica is less than 200 ml / 100 g, it is difficult to maintain the hardness of the rubber and the steering stability tends to be inferior. Further, the DBP of silica is preferably 400 ml / 100 g or less, and more preferably 350 ml / 100 g or less. When the DBP of silica exceeds 400 ml / 100 g, the viscosity of the kneaded rubber increases, and the load of the extrusion process tends to be excessive.

  The ratio of DBP oil absorption to the BET specific surface area of silica (DBP / BET) is preferably 1.8 or more, and more preferably 2.2 or more. If DBP / BET of silica is less than 1.8, the balance between fuel efficiency and steering stability tends to deteriorate. Further, the DBP / BET of silica is preferably 4.0 or less, and more preferably 3.5 or less. When DBP / BET of silica exceeds 4.0, there is a tendency that a load is applied in the extrusion process.

  When silica is contained, 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 silica content is less than 50 parts by weight, the fuel efficiency is improved, but the wear resistance is lowered and it tends to be difficult to maintain the steering stability. Moreover, 90 weight part or less is preferable and, as for content of a silica, 85 weight part or less is more preferable. If the silica content exceeds 90 parts by weight, the fuel efficiency tends to deteriorate.

  When silica is contained, it is preferable to use a silane coupling agent in combination with silica.

  The silane coupling agent is not particularly limited, and specifically, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (4-triethoxysilylbutyl) Tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, bis (4-trimethoxysilylbutyl) tetrasulfide, bis (3-methyldiethoxysilylpropyl) tetra Sulfide, bis (2-methyldimethoxysilylethyl) tetrasulfide, bis (4-methyldimethoxysilylbutyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (2-triethoxysilylethyl) trisulfide Bis (4-triethoxysilylbutyl) trisulfide, bis (3-trimethoxysilylpropyl) trisulfide, bis (2-trimethoxysilylethyl) trisulfide, bis (4-trimethoxysilylbutyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, bis (triethoxysilylpropyl) 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 Rufide, bis (4-methyldiethoxysilylpropyl) disulfide, bis (3-methyldimethoxysilylpropyl) disulfide, bis (2-methyldimethoxysilylpropyl) disulfide, bis (4-methyldimethoxysilylptyl) disulfide, 3-mercapto Propyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptotriethyltriethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltomethoxysilane, 3- (2- Aminoethyl) aminopropyltriethoxysilane, 3- (2-aminoethyl) aminopropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltrimeth Sisilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropylmethyldimethoxysilane and the like can be mentioned, and these silane coupling agents can be used alone or in combination of two or more. Good. Especially, since the coupling agent addition effect and cost can be compatible, bis (triethoxysilylpropyl) disulfide, bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, bis (3 -Trimethoxysilylpropyl) tetrasulfide, bis (3-trimethoxysilylpropyl) disulfide, bis (3-methyldiethoxysilylpropyl) disulfide, bis (3-methyldimethoxysilylpropyl) disulfide and the like are preferably used.

  When the silane coupling agent is contained, the content of the silane coupling agent is preferably 3 parts by weight or more and more preferably 5 parts by weight or more with respect to 100 parts by weight of silica. When the content of the silane coupling agent is less than 3 parts by weight, there is a tendency that a sufficient coupling effect on silica cannot be obtained. Further, the content of the silane coupling agent is preferably 15 parts by weight or less, and more preferably 13 parts by weight or less. When the content of the silane coupling agent exceeds 15 parts by weight, the coupling effect due to the inclusion of the silane coupling agent is not improved, and the cost tends to increase.

  The rubber composition for a tire tread of the present invention includes, in addition to the rubber component, paper fiber, carbon black, silica and silane coupling agent, a softener such as oil generally used in the rubber industry, a wax, and various anti-aging agents. A vulcanizing agent such as an agent, stearic acid, zinc oxide and sulfur, various vulcanization accelerators, and the like can be appropriately contained.

  The tire of the present invention is produced by an ordinary method using the rubber composition for a tire tread of the present invention. That is, if necessary, the rubber composition of the present invention blended with the above various chemicals is extruded in accordance with the shape of the tread at an unvulcanized stage and bonded together with other tire members on a tire molding machine. Then, it is molded by a usual method to form an unvulcanized tire. This unvulcanized tire is heated and pressurized in a vulcanizer to obtain the tire of the present invention.

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

Below, the various chemical | medical agents used by the Example and the comparative example are demonstrated.
NR: RSS # 3
Terminal modified styrene butadiene rubber for silica (modified SBR): E10 manufactured by Asahi Kasei Corporation (solution polymerization, terminal group: amino group, styrene content: 39% by weight, vinyl bond content: 31% by weight, Mw / Mn: 2 .1)
Styrene butadiene rubber (SBR): SBR1502 manufactured by Sumitomo Chemical Co., Ltd. (emulsion polymerization, styrene content: 23.5 wt%, vinyl bond content: 18 wt%)
Paper fiber: Neofiber manufactured by Oji Bag Co., Ltd. (average fiber diameter: 10 μm, average fiber length: 1000 μm, average aspect ratio: 100)
Carbon black: Prototype carbon black manufactured by Mitsubishi Chemical Corporation (CTAB: 180 m ² / g, IA: 188 mg / g)
Silica: 115 Gr silica manufactured by Rhodia (BET: 112 m ^{2 /} g, DBP: 250 ml / 100 g, DBP / BET: 2.23)
Silane coupling agent: Si75 (bis (triethoxysilylpropyl) disulfide (TESPD)) manufactured by Degussa
Process oil: Diana Process PS24 manufactured by Idemitsu Kosan Co., Ltd.
Wax: Sunnock wax (paraffin wax) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Anti-aging agent: Santoflex 13 (N-phenyl-N ′-(1,3-dimethylbutyl) -p-phenylenediamine) 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. Sulfur, oil content: 10%)
Vulcanization accelerator 1: Noxeller D (diphenylguanidine) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Vulcanization accelerator 2: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Co., Ltd.

Example 1 and Comparative Examples 1-3
According to the formulation shown in Table 1, using a 1.7 L Banbury mixer manufactured by Kobe Steel, Ltd., the mixture was kneaded for 5 minutes at 150 ° C. to obtain a kneaded product. Next, using an open roll, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and kneaded for 5 minutes at 90 ° C. to obtain an unvulcanized rubber composition. Furthermore, the vulcanized rubber composition of Example 1 and Comparative Examples 1-3 was obtained by press-vulcanizing the obtained unvulcanized rubber composition for 30 minutes at 150 ° C.

(Viscoelasticity test)
A 4 mm × 30 mm × 1.5 mm strip sample was cut from the vulcanized rubber composition, and using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho, the frequency was 10 Hz, the initial strain was 10%, and the dynamic strain was 1%. Under the conditions, the complex elastic modulus (E ^* ) and loss tangent (tan δ) at 70 ° C. were measured. In addition, it shows that rigidity is high and steering stability is excellent, so that E ^* is large, and it shows that it is excellent in low-fuel-consumption property, so that tan-delta is small.

(Maneuvering stability)
The unvulcanized rubber composition is molded into a tread shape, bonded together with other tire members, an unvulcanized tire is molded, and the unvulcanized tire is press vulcanized at 150 ° C. for 30 minutes. Thus, a tire (tire size: 195 / 60R15) was manufactured.

  The manufactured tire was mounted on a normal passenger car and the vehicle was run on a dry asphalt road test course. At that time, the steering stability index of Comparative Example 1 was set to 100, and the test driver evaluated the steering stability of each formulation by sensory evaluation. In addition, it shows that it is excellent in steering stability and riding comfort, so that a steering stability index | exponent is large.

  The evaluation results of the above test are shown in Table 1.

Claims (2)

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, and 0.5 to 20 with respect to 100 parts by weight of the rubber component A rubber composition for tire treads, which contains paper fibers having an average fiber length of 10 to 1000 μm, an average fiber diameter of 0.5 to 100 μm, and a ratio of the average fiber length to the average fiber diameter of 10 to 2000 in parts by weight. The rubber composition for a tire tread according to claim 1, wherein the ratio of the average fiber length to the average fiber diameter of the paper fibers is 100 to 2,000.