JP2010018757A - Rubber composition and run-flat tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition used for a side reinforcement layer or a bead part reinforcement layer of a run-flat tire, wherein the composition reduces the reduction of rigidity, improves run-flat durability, and improves mileage and speed even when the temperature of the side reinforcement layer or the like is increased accompanying the run-flat running at the time of puncture. <P>SOLUTION: The rubber composition comprises 100 parts by mass of a rubber component containing more than 70% by mass of a styrene-butadiene rubber containing 30 to 60% by mass of a 1,2-syndiotactic polybutadiene crystal and 10 to 80 parts by mass of carbon black. The rubber component is preferably a mixture of a styrene-butadiene rubber and a polyisoprene rubber. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a rubber composition that can suppress heat generation and maintain rigidity even at a high temperature, and further relates to a run-flat tire using the rubber composition as a side reinforcing layer or a bead portion reinforcing layer.

  A conventional run-flat tire has a structure having a high-strength side-reinforcing rubber disposed on the inner side of the sidewall portion, and can travel a predetermined distance to a service station even when the internal pressure is reduced by puncture. . By installing this run flat tire, there is no need to always have a spare tire, and weight reduction of the entire vehicle can be expected. However, the running speed and the running distance when the run flat tire is punctured are not sufficient, and it is desired to improve the durability of the run flat tire.

  As an effective means for improving the durability of the run-flat tire, there is a method of suppressing deformation by increasing the thickness of the reinforcing rubber and preventing destruction due to the deformation. However, since the mass of the tire becomes large, it is not possible to achieve the weight reduction that is the original purpose of the run-flat tire.

  Further, as an effective means for improving the durability of the run-flat tire, there is a method of increasing the hardness of the reinforcing rubber by increasing the amount of reinforcing filler such as carbon black and blending them to suppress deformation. However, the load on the processes such as kneading and extruding is large, and the heat generation becomes high in physical properties after vulcanization.

  In order to improve the durability of run-flat tires, attempts have been made to use a large amount of a vulcanizing agent and a vulcanization accelerator without increasing the amount of carbon black. Although this technique can increase the vulcanization density and suppress deformation and heat generation, it tends to reduce the elongation of rubber and lower the fracture strength. On the other hand, a technique has also been proposed in which a lamellar natural ore such as mica is blended with tire sidewall rubber. However, since the rubber composition is required to have bending resistance, its hardness is low, so even if it is used as a side reinforcing rubber, it is insufficient to support a load.

  Further, during the run-flat running at the time of puncture, the side reinforcing layer generates heat due to repeated deformation of the tire and the temperature rises. As a result, the rigidity of the side reinforcing layer is lowered and the run flat performance is remarkably impaired. Therefore, it is important to develop a rubber composition that maintains high rigidity even at high temperatures.

  Patent Document 1 discloses a rubber composition containing a polybutadiene rubber containing 2.5 to 20% by weight of syndiotactic 1,2-polybutadiene crystals as a rubber composition for a base tread for a tire. This is a syndiotactic 1,2-polybutadiene crystal component graft-polymerized to polybutadiene rubber.

Patent Document 2 discloses a rubber composition containing a polybutadiene rubber containing 2.5 to 20% by weight of syndiotactic 1,2-polybutadiene crystals as a rubber composition for tire clinch. This is also a syndiotactic 1,2-polybutadiene crystal component graft-polymerized on polybutadiene rubber.
JP 2006-124503 A JP 2006-63143 A

  The present invention relates to a rubber composition suitable for a side reinforcing layer or a bead portion reinforcing layer of a run flat tire having low heat buildup and high strength, and more particularly, the rubber composition is used for reinforcing a side reinforcing layer or a bead portion of a run flat tire. Even if the temperature of the side reinforcement layer rises during run flat running during puncture, the run flatness is improved by reducing the decrease in rigidity and improving the run flat durability. Provide flat tires.

  In the present invention, 10 to 80 parts by mass of carbon black is added to 100 parts by mass of a rubber component in which a styrene-butadiene copolymer rubber containing 30 to 60% by mass of 1,2 syndiotactic polybutadiene crystals exceeds 70% by mass. The present invention relates to a rubber composition. The rubber component is preferably a mixture of styrene-butadiene copolymer rubber and polyisoprene rubber. Furthermore, it is preferable that the styrene-butadiene copolymer rubber has a styrene content of 10 mol% or more and 35 mol% or less.

  Further, the styrene-butadiene copolymer rubber containing 30 to 60% by mass of 1,2 syndiotactic polybutadiene crystals in the rubber component preferably exceeds 80% by mass. The present invention relates to a run flat tire using the rubber composition as a side reinforcing layer or a bead portion reinforcing layer.

  According to the present invention, a rubber composition having low heat build-up and high strength can be obtained, and the rubber composition can be used for a side reinforcing layer or a bead portion reinforcing layer of a run flat tire, so In addition, even when the temperature of the side reinforcing layer or the like rises, it is possible to obtain a run-flat tire that maintains rigidity and has excellent run-flat durability.

  The present invention relates to 100 parts by mass of a rubber component in which a styrene-butadiene copolymer rubber containing 30 to 60% by mass of 1,2-syndiotactic polybutadiene crystals (hereinafter also referred to as “SPBd crystals”) exceeds 70% by mass. A rubber composition containing 10 to 80 parts by mass of carbon black.

<SPBd crystal SBR>
The syndiotactic 1,2-polybutadiene crystal (SPBd crystal) is a highly crystalline resin in which ethylene components are regularly arranged in the opposite direction alternately in the 1,2 polybutadiene main chain. It is a resin having a melting point. In the present invention, the melting point of syndiotactic 1,2-polybutadiene is preferably 180 ° C. or higher, and more preferably 190 ° C. or higher. If the melting point is less than 180 ° C, the crystal melts during vulcanization of the tire by pressing, the crystal state changes, the dispersibility of the crystal deteriorates, the crystallinity decreases, the melting point decreases, and the heat resistance is inferior. There is. In the present invention, SPBd crystalline SBR refers to crystalline SPBd chemically bonded to SBR (for example, graft polymerization). The content of the SPBd crystal in the SPBd crystal SBR is 30 to 60% by mass, preferably 30 to 50% by mass. When the SPBd crystal content is in the range of 30 to 60% by mass, the strength and workability of the rubber composition can be improved in a well-balanced manner.

  Moreover, SPBd crystal | crystallization SBR is mix | blended exceeding 70 mass% in a rubber component. When the SPBd crystal SBR is mixed with the rubber component in an amount of 70% by mass or less, sufficient rigidity cannot be maintained in the rubber composition, and more preferably 80% by mass or more.

  In the present invention, the styrene content of the styrene-butadiene copolymer rubber is preferably 10 mol% or more and 35 mol% or less. When the rubber composition is used for the side reinforcing layer or the bead portion reinforcing layer of the run-flat tire, these reinforcing layers are repeatedly deformed by high-speed rotation during running of the tire, and the temperature rises due to heat generation of the reinforcing layer. As a result, the reinforcing layer softens and the characteristics deteriorate, but it is important to reduce the deterioration due to the temperature rise.

<Rubber component>
Polyisoprene rubber (IR) is preferred as the other rubber component to be mixed with the SPBd crystalline styrene-butadiene copolymer rubber. The content is preferably less than 30% by mass. When the content of polyisoprene rubber (IR) is less than 30% by mass, the loss tangent (tan δ) can be kept low, heat generation during run-flat running can be suppressed, and the temperature rises due to tire heat generation. Also, the deterioration of the rubber composition is reduced and the run-flat performance is maintained.

  In the present invention, the rubber component is blended with a rubber component other than isoprene rubber within a range of 20% by mass or less of the rubber component. Here, as rubber components, styrene-butadiene copolymer rubber (SBR), polybutadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), isobutylene-isoprene rubber (IIR), acrylonitrile-butadiene copolymer rubber (NBR). Chloroprene rubber (CR), styrene-isoprene-butadiene copolymer rubber (SIBR), styrene-isoprene copolymer rubber, isoprene-butadiene copolymer rubber and the like can be used. These rubber components are preferably mixed in one kind or two or more kinds.

<Reinforcing agent>
The rubber composition can use carbon black as a reinforcing agent. The type of carbon black is not particularly limited, but soft carbon such as FEF and FPF is preferable in order to maintain the rubber composition with low heat generation. For example, the nitrogen adsorption specific surface area (N ₂ SA) is 30 m ² / g or more, preferably 35 m ² / g or more. If N ₂ SA is less than 30 m ² / g, the reinforcing property is insufficient and sufficient durability cannot be obtained. Further, the N ₂ SA of the carbon black is 100 m ² / g or less, preferably 80 m ² / g or less, more preferably 60 m ² / g or less. When N ₂ SA exceeds 100 m ² / g, exothermicity increases.

  The carbon black has a dibutyl phthalate oil absorption (DBP oil absorption) of 50 ml / 100 g or more, preferably 80 ml / 100 g or more. When the DBP oil absorption is less than 50 ml / 100 g, it is difficult to obtain sufficient reinforcement.

  Although the content of the carbon black varies depending on the blending amount of SPBd, it is 80 parts by mass or less, preferably 60 parts by mass or less with respect to 100 parts by mass of the rubber component. When the amount of carbon black increases, the viscosity of the rubber composition increases, it becomes difficult to knead and extrude the rubber, and heat generation during run-flat running increases.

  In the rubber composition of the present invention, silica generally used for general-purpose rubber can be used. For example, dry method white carbon, wet method white carbon, colloidal silica and the like used as a reinforcing material can be used. Among these, wet method white carbon mainly containing hydrous silicic acid is preferable.

  Furthermore, this invention can also mix | blend lamellar natural ores, for example, mica such as kaolinite, serinite, phlogopite and muscovite. Here, the aspect ratio (ratio of the maximum diameter to the thickness) of the lamellar natural ore is preferably 3 or more from the viewpoint of increasing the rubber hardness. The average particle diameter of the lamellar natural ore is preferably 2 μm or more and 30 μm or less. The compounding quantity can be mixed in 5 mass parts-120 mass parts with respect to 100 mass parts of rubber components.

<Combination agent>
The sulfur or sulfur compound used in the rubber composition of the present invention is preferably insoluble sulfur from the viewpoint of suppressing sulfur surface precipitation. Insoluble sulfur has an average molecular weight of 10,000 or more, particularly 100,000 or more and 500,000 or less, particularly preferably 300,000 or less. If the average molecular weight is less than 10,000, decomposition at low temperature tends to occur and surface precipitation tends to occur, and if it exceeds 500,000, the dispersibility in rubber tends to decrease.

  The compounding amount of sulfur or sulfur compound is preferably 2 parts by mass or more, more preferably 3 parts by mass or more, and preferably 10 parts by mass or less, more preferably 8 parts by mass or less. If the sulfur or sulfur compound is less than 2 parts by mass, sufficient hardness tends not to be obtained, and if it exceeds 10 parts by mass, the storage stability of the unvulcanized rubber tends to be impaired.

  Further, the rubber composition for side reinforcement of the present invention contains zinc oxide, wax, stearic acid, oil, anti-aging agent, vulcanization accelerator and the like used in ordinary rubber compounding within a range not impairing the effects of the present invention. May be included.

  As the vulcanization accelerator, for example, a sulfenamide accelerator is most often used as a delayed vulcanization accelerator because it hardly burns during the production process and has excellent vulcanization characteristics. In addition, rubber compounding using a sulfenamide accelerator improves the durability of the run-flat tire because the heat properties of the rubber properties after vulcanization are low with respect to deformation due to external force.

Examples of the sulfenamide accelerator include TBBS (N-tert-butyl-2-benzothiazolylsulfenamide), CBS (N-cyclohexyl-2-benzothiazolylsulfenamide), DZ (N, N '-Dicyclohexyl-2-benzothiazolylsulfenamide) and the like. As other vulcanization accelerators, for example, MBT (mercaptobenzothiazole), MBTS (dibenzothiazyl disulfide), DPG (diphenylguanidine) and the like can be used.

<Silane coupling agent>
In the present invention, a silane coupling agent can be added in combination with the silica or the lamellar natural ore. Examples of the silane coupling agent include bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylpropyl) tetrasulfide, and 3-mercaptopropyl. Examples include triethoxysilane and 2-mercaptoethyltrimethoxysilane. The compounding quantity of the said silane coupling agent is mix | blended in the range of 2 mass parts-20 mass parts with respect to 100 mass parts of silica and / or lamellar natural ore.

<Viscoelastic properties of rubber composition>
The dynamic elastic modulus (E ′ ₇₀ ) at 70 ° C. of the rubber composition is a ratio of the dynamic elastic modulus (E ′ ₁₅₀ ) at 150 ° C. to 20 MPa or more and the dynamic elastic modulus (E ′ ₂₀₀ ) at 200 ° C. ( E ′ ₂₀₀ ) / (E ′ ₁₅₀ ) is desirably 0.5 or more. By adjusting to such a value, run-flat durability can be maintained even if the temperature rises due to heat generated by repeated deformation during run-flat.

<Run flat tire>
The rubber composition of the present invention is used for a side reinforcing layer of a run flat tire or a bead portion reinforcing layer such as a bead apex. Here, the side reinforcing layer is a rubber layer disposed inside the sidewall portion of the run flat tire, and the bead apex is a rubber layer extending in the sidewall direction from the upper side of the bead core. The presence of the side reinforcing layer and / or the bead apex in the run-flat tire enables the vehicle to be supported without the tire coming off the rim even when the internal pressure is reduced, and excellent run-flat durability is obtained.

  FIG. 1 shows a right half of a cross-sectional view of a run-flat tire according to the present invention. In FIG. 1, a run-flat tire 1 is disposed around a pair of bead cores 2, a toroid-like carcass 3 that is folded and engaged at both ends, and outside the crown portion of the carcass 3. A breaker 4 is arranged so that the cords intersect two breaker plies in which the cords are arranged at an angle of ˜30 degrees, and a tread portion 5 is provided outside the breaker. A side reinforcing layer 6 that gradually decreases in thickness in the both end directions from the central portion of the sidewall is disposed over the sidewall region adjacent to the carcass 3 on the tire lumen side. Further, a hard rubber bead apex 7 is arranged from the upper side of the bead core 2 to the side wall. The present invention employs the specific rubber composition described above for the side reinforcing layer.

  In FIG. 1, the side reinforcing layer is disposed inside the carcass ply 3, but may be disposed outside the carcass ply 3, that is, adjacent to the sidewall. In this case, the side reinforcing layer and the bead apex can be integrated into a side reinforcing layer extending from the upper side of the bead core to the vicinity of both ends of the breaker.

  EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited to these. The materials used in the examples and comparative examples are collectively shown below.

Examples 1-3 and Comparative Examples 1-10
<Synthesis of SPBd crystal SBR (1)>
250 g of 1,3 butadiene was dissolved in 8000 ml of hexane solution, and 165 g of SBR (SL574 manufactured by JSR) was added and dissolved sufficiently. As a polymerization catalyst, 500 ml of 0.2M triisopropylaluminum, 20 ml of 0.042M cobalt octylate solution, and 15 ml of carbon disulfide were added and reacted at 40 ° C. for 8 hours, followed by drying under reduced pressure. And 300g of SPBd whose crystal content rate is 45.4 mass% was obtained.

  The melting point of the SPBd crystal was determined by the glass transition temperature measured at a heating rate of 10 ° C./min using an automatic differential scanning calorimeter Q2000 manufactured by TA Instruments.

Melting point of SPBd crystal: 205 ° C
Content of SPBd crystals in SBR: 45.4% by mass.

<Synthesis of SPBd crystal SBR (2)>
The SPBd crystal SBR (2) was synthesized according to the synthesis method of the SPBd crystal SBR (1). As synthesis conditions, the amount of 1,3 butadiene was changed.

Melting point of SPBd crystal: 204 ° C.
Content of SPBd crystals in SBR: 50% by mass.

<Synthesis of SPBd crystal SBR (3)>
The SPBd crystal SBR (3) was synthesized according to the synthesis method of the SPBd crystal SBR (1). As synthesis conditions, the amount of 1,3 butadiene was changed.

Melting point of SPBd crystal: 205 ° C.
Content of SPBd crystals in SBR: 30% by mass.

<Synthesis of SPBd crystal SBR (4)>
The SPBd crystal SBR (4) was synthesized according to the synthesis method of the SPBd crystal SBR (1). As the synthesis conditions, the type of SBR and the amount of 1,3 butadiene were changed.

Melting point of SPBd crystal: 204 ° C.
Content of SPBd crystals in SBR: 15% by mass.

<Synthesis of SPBd crystal SBR (5)>
The SPBd crystal SBR (5) was synthesized according to the synthesis method of the SPBd crystal SBR (1). As the synthesis conditions, the type of SBR and the amount of 1,3 butadiene were changed.

Melting point of SPBd crystal: 203 ° C.
Content of SPBd crystals in SBR: 25% by mass.

<Synthesis of SPBd crystal SBR (6)>
The SPBd crystal SBR (6) was synthesized according to the synthesis method of the SPBd crystal SBR (1). As the synthesis conditions, the type of SBR and the amount of 1,3 butadiene were changed.

Melting point of SPBd crystal: 203 ° C.
Content of SPBd crystals in SBR: 52% by mass.

<Adjustment of rubber composition>
In accordance with the formulation shown in Table 1, components other than insoluble sulfur and a vulcanization accelerator were kneaded at 160 ° C. for 5 minutes using a Banbury mixer. Insoluble sulfur and a vulcanization accelerator were added to the resulting kneaded product and kneaded at 120 ° C. for 2 minutes using a Banbury mixer to obtain an unvulcanized rubber composition. Further, the unvulcanized rubber composition was extruded into a sheet having a predetermined shape, and press vulcanized at 175 ° C. for 20 minutes to prepare a test piece.

  The following evaluations were made. The evaluation results are shown in Table 1.

(Note 1) SBR (1): “SL574” (styrene content: 15 mol%) manufactured by JSR Corporation.
Melting point of SPBd crystal: 205 ° C.

Content of SPBd crystal in SBR: 45.4% by mass
(Note 2) SBR (2): “SL574” manufactured by JSR (styrene content: 15 mol%).

Melting point of SPBd crystal: 204 ° C.
Content of SPBd crystals in SBR: 50% by mass.
(Note 3) SBR (3): “SL574” (styrene content: 15 mol%) manufactured by JSR Corporation.

Melting point of SPBd crystal: 205 ° C.
Content of SPBd crystals in SBR: 30% by mass.
(Note 4) SBR (4): “NS312S” manufactured by Zeon Corporation (styrene content: 40 mol%).

Melting point of SPBd crystal: 204 ° C.
Content of SPBd crystals in SBR: 15% by mass.
(Note 5) SBR (5): “NS312S” manufactured by Zeon Corporation (styrene content: 40 mol%).

Melting point of SPBd crystal: 203 ° C.
Content of SPBd crystals in SBR: 25% by mass.
(Note 6) SBR (6): “NS312S” manufactured by Zeon Corporation (styrene content: 40 mol%).

Melting point of SPBd crystal: 203 ° C.
Content of SPBd crystals in SBR: 52% by mass.
(Note 7) IR: “IR2200” manufactured by JSR Corporation.
(Note 8) Carbon black (FEF): “Diamond Black E” (N ₂ SA: 41 m ² / g, DBP oil absorption 115 ml / 100 g) manufactured by Mitsubishi Chemical Corporation.
(Note 9) Stearic acid: “Koji” manufactured by NOF Corporation.
(Note 10) Zinc oxide: “Zinc oxide type 2” manufactured by Mitsui Mining & Smelting Co., Ltd.
(Note 11) Anti-aging agent: “Antigen 6C” (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
(Note 12) Insoluble sulfur: “Muclon OT” manufactured by Shikoku Kasei Kogyo Co., Ltd.
(Note 13) Vulcanization accelerator: “Noxeller NS” (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

<Viscoelastic properties>
A rubber test piece (width 0.4 cm, thickness 2 mm) of a predetermined size was produced from the rubber composition, and measured using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd., at a measurement temperature of 70 ° C., an initial strain of 10%, E ′ (dynamic elastic modulus) and tan δ (loss tangent) were measured at a dynamic strain of ± 1% and a frequency of 10 Hz.

<Evaluation results>
From Table 1, in order to maintain the heat resistance and elastic modulus required for the run-flat tire at a predetermined level, the SPBd crystal needs to be 40% by mass or more with respect to 100 parts by mass of the SBR component (Comparative Example). 3, Example 5). In addition, when the SPBd crystal SBR exceeds 70% by mass in the rubber component, a decrease in physical properties can be reduced even at a high temperature of 200 ° C. (Comparative Example 4, Example 1).

  In the compounding system filled with carbon black (Comparative Examples 5 to 8), even when the rubber temperature is measured at about 170 ° C. for several minutes, the elastic modulus is changed due to the molecular chain breakage of the rubber, the cross-linked structure change, etc. Decrease was observed. In the case of Comparative Example 8, the dynamic elastic modulus (E ′) is 13.4 MPa even when 80 parts by mass of carbon black is blended in isoprene rubber (IR), and viscoelasticity is increased. Then, kneading became difficult, and it was impossible to produce a rubber compound.

  In the system in which SPBd was blended, SPBd was able to obtain about four times the strength of the same blend of carbon black. For this reason, compared with carbon, the big dynamic elastic modulus was able to be obtained by mix | blending a small amount (comparative example 7, Examples 1-4).

  In FIG. 2, the measurement result of the temperature dispersion | distribution of E 'of a rubber composition is shown. Each of Examples 1 to 5 has a high E ′ value, and since no decrease in the value is observed even at a high temperature of 200 ° C., high rigidity is maintained even during heat generation and temperature rise during run-flat. You can see that

  The present invention is a rubber composition suitable for a side reinforcing layer and a bead portion reinforcing layer excellent in run-flat performance, and a run-flat tire using the same, and is not limited to a tire for passenger cars, but for light truck tires and truck buses. It can also be applied to tires.

The right half of sectional drawing of the run flat tire of this invention is shown. The temperature dispersion measurement result of the viscoelasticity of a rubber composition is shown.

Explanation of symbols

  1 tire, 2 bead core, 3 carcass, 4 breaker, 5 tread, 6 side reinforcement layer, 7 bead apex.

Claims (5)

  The styrene-butadiene copolymer rubber containing 30 to 60% by mass of 1,2 syndiotactic polybutadiene crystals is blended with 10 to 80 parts by mass of carbon black with respect to 100 parts by mass of the rubber component exceeding 70% by mass. Rubber composition.   The rubber composition according to claim 1, wherein the rubber component is a mixture of a styrene-butadiene copolymer rubber and a polyisoprene rubber.   The rubber composition according to claim 1, wherein the styrene content of the styrene-butadiene copolymer rubber is 10 mol% or more and 35 mol% or less.   The rubber composition according to claim 1, wherein the styrene-butadiene copolymer rubber containing 30 to 60% by mass of 1,2 syndiotactic polybutadiene crystals in the rubber component exceeds 80% by mass.   A run flat tire using the rubber composition according to claim 1 or 2 for a side reinforcing layer or a bead portion reinforcing layer.

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