JP5174502B2 - Run flat tire - Google Patents

Description

  The present invention relates to a run-flat tire, particularly a run-flat tire using a rubber composition capable of improving processability without reducing run-flat durability.

  Conventionally, a side reinforcing rubber layer with a crescent-shaped cross section is arranged on the sidewall of the tire as a so-called run-flat tire that can safely travel a certain distance even when the internal pressure of the tire is reduced by puncture or the like A side-reinforcing type run-flat tire with improved sidewall rigidity is known. However, in the so-called run-flat running in a state where the internal pressure of the tire is reduced, the deformation of the side reinforcing rubber layer increases as the deformation of the sidewall portion of the tire increases. In some cases, the rubber component itself in the side reinforcing rubber layer is cut or crosslinked between the rubber components formed by vulcanization. The part may be cut. In this case, the elastic modulus of the side reinforcing rubber layer decreases, the deflection of the tire further increases, the heat generation of the side wall portion proceeds, and finally the side reinforcing rubber layer exceeds its failure limit, and the tire is compared. There is a risk of failure at an early stage.

  As a means of delaying the time to failure, the elastic modulus of the side reinforcing rubber layer can be increased by changing the composition of the rubber composition applied to the side reinforcing rubber layer of the tire, or the loss of the side reinforcing rubber layer can be increased. There is known a technique for reducing the tangent (tan δ) and suppressing the heat generation of the side reinforcing rubber layer itself.

  On the other hand, from the viewpoint of improving the workability of the rubber composition, a rubber composition containing a softening agent such as oil to lower the viscosity of the rubber composition or a tackifier (tackifier) such as a resin. Techniques for improving the tackiness of objects are known (see, for example, Patent Documents 1 to 3 and Non-Patent Document 1). However, when the rubber composition having improved processability by these methods is applied to the side reinforcing rubber layer, there is a problem that the loss tangent (tan δ) of the side reinforcing rubber layer is increased and the run flat durability is lowered.

Japanese Patent Application Laid-Open No. 11-302459 Japanese Patent Laid-Open No. 2003-213040 Special table 2007-510004 gazette F. F. WOLNY and J.W. J. et al. LAMB, in Kautsch, Gummi Kunstoffe (1984) 37/7, p601-603.

  Accordingly, an object of the present invention is to provide a run-flat tire using a rubber composition that can solve the problems of the prior art and can improve processability without reducing run-flat durability. is there.

  As a result of intensive studies to achieve the above object, the present inventors have determined that at least one of the bead filler and the side reinforcing rubber layer has a specific weight average low molecular weight conjugated diene polymer instead of a softener or a tackifier. By using a rubber composition blended with a rubber component having a molecular weight and a composition, it was found that a decrease in run-flat durability can be suppressed while maintaining high processability of the rubber composition, and the present invention has been completed. It was.

That is, the first run flat tire of the present invention is a run flat tire including a sidewall portion, a tread, a carcass, a bead core, and a bead filler.
The bead filler was measured by gel permeation chromatography with respect to 100 parts by mass of a rubber component (A) having a polystyrene-converted weight average molecular weight of 150,000 to 2,000,000 and containing at least natural rubber or polyisoprene rubber. A rubber composition comprising 0.1 to 30 parts by mass of a low molecular weight conjugated diene polymer (B) having a polystyrene-equivalent weight average molecular weight of 2,000 to 10,000 and 3 to 10 parts by mass of sulfur is used. .

The second run flat tire of the present invention is a run flat tire provided with a sidewall portion, a tread, a carcass and a side reinforcing rubber layer.
With respect to 100 parts by mass of the rubber component (A) having a polystyrene-reduced weight average molecular weight of 150,000 to 2,000,000 measured by gel permeation chromatography and containing at least natural rubber or polyisoprene rubber, the side reinforcing rubber layer is subjected to gel permeation chromatography. A rubber composition comprising 0.1 to 30 parts by mass of a low molecular weight conjugated diene polymer (B) having a measured polystyrene equivalent weight average molecular weight of 2,000 to 10,000 and 3 to 10 parts by mass of sulfur is used. And

Furthermore, the third run flat tire of the present invention is a run flat tire including a sidewall portion, a tread, a carcass, a bead core, a bead filler, and a side reinforcing rubber layer.
At least one of the bead filler and the side reinforcing rubber layer has a polystyrene-converted weight average molecular weight of 150,000 to 2,000,000 as measured by gel permeation chromatography, and 100 parts by mass of a rubber component (A) containing at least natural rubber or polyisoprene rubber. On the other hand, a rubber composition obtained by blending 0.1 to 30 parts by mass of a low molecular weight conjugated diene polymer (B) having a polystyrene equivalent weight average molecular weight of 2,000 to 10,000 measured by gel permeation chromatography and 3 to 10 parts by mass of sulfur. It is characterized by using things.

  In a preferred embodiment of the run flat tire of the present invention, the rubber component (A) is at least one selected from the group consisting of natural rubber, polyisoprene rubber, styrene-butadiene copolymer rubber, polybutadiene rubber, and isobutylene isoprene rubber. Consists of.

  In another preferred embodiment of the run-flat tire of the present invention, the low molecular weight conjugated diene polymer (B) is polybutadiene.

  In another preferred embodiment of the run flat tire of the present invention, the rubber composition further contains carbon black and / or silica.

  According to the present invention, at least one of the bead filler and the side reinforcing rubber layer is replaced with a low molecular weight conjugated diene polymer instead of a softener or a tackifier, and further a rubber component having a specific weight average molecular weight and composition. By using a rubber composition blended in a specific amount, it is possible to provide a run-flat tire that suppresses a decrease in run-flat durability while maintaining a high workability of the rubber composition.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view of one embodiment of the run-flat tire of the present invention. The tire shown in FIG. 1 has a pair of left and right bead portions 1 and a pair of sidewall portions 2, and a tread 3 connected to both sidewall portions 2, and extends in a toroidal shape between the pair of bead portions 1. A radial carcass 4 that reinforces each of these parts 1, 2, 3, a belt 5 composed of two belt layers arranged on the outer side in the tire radial direction of the crown part of the carcass 4, and the bead part 1, respectively. A bead filler 7 disposed on the outer side in the tire radial direction of the embedded ring-shaped bead core 6 and a pair of side reinforcing rubber layers 8 disposed on the inner side of the carcass 4 of the sidewall portion 2 are provided.

  In the illustrated tire, the radial carcass 4 includes a folded carcass ply 4a having a folded portion wound around the bead core 6 from the inner side in the tire width direction toward the outer side in the radial direction, and the outer side of the folded carcass ply 4a. It consists of the arranged down carcass ply 4b. In the tire of the present invention, the carcass structure and the number of plies are not limited thereto. Further, the bead filler 7 is disposed between the body portion and the folded portion of the folded carcass ply 4 a on the outer side in the tire radial direction of the bead core 6. In addition, although the shape of the side reinforcing rubber layer 8 in the illustrated example has a crescent-shaped cross section, the cross-sectional shape is not particularly limited as long as it has a side reinforcing function.

  In the tire shown in FIG. 1, a belt 5 composed of two belt layers is disposed on the outer side in the tire radial direction of the crown portion of the radial carcass 4. The two belt layers are laminated such that the cords constituting the belt layer intersect with each other across the equator plane, thereby constituting the belt 5. The belt 5 in FIG. 1 is composed of two belt layers, but in the tire of the present invention, the number of belt layers constituting the belt 5 is not limited to this. The run flat tire of the present invention may further include a belt reinforcing layer made of a rubberized layer of cords arranged substantially parallel to the tire circumferential direction on the outer side in the tire radial direction of the belt 5.

  In the run flat tire of the present invention, at least one of the bead filler 7 and the side reinforcing rubber layer 8 has a polystyrene-converted weight average molecular weight of 150,000 to 2,000,000 measured by gel permeation chromatography, and at least natural rubber or polyisoprene rubber. 0.1 to 30 parts by mass of a low molecular weight conjugated diene polymer (B) having a polystyrene-equivalent weight average molecular weight of 2,000 to 10,000 measured by gel permeation chromatography and 100 to 3 parts by mass of the rubber component (A) contained, and sulfur 3 to 10 It is necessary to use a rubber composition formed by blending with parts by mass. Although the illustrated tire includes both the bead filler 7 and the side reinforcing rubber layer 8, the tire of the present invention includes the rubber component (A), the low molecular weight conjugated diene polymer (B), and sulfur. What is necessary is just to provide the bead filler and / or side reinforcement rubber layer in which the rubber composition was used.

  As a result of studies by the present inventors, a low molecular weight conjugated diene having a polystyrene-equivalent weight average molecular weight of 2,000 to 10,000 measured by gel permeation chromatography in place of a softener or tackifier usually added from the viewpoint of improving processability. It was found that the increase in loss tangent (tan δ) of the rubber composition can be suppressed by adding the polymer (B) to the rubber composition while improving the adhesiveness of the rubber composition and reducing the Mooney viscosity. . Therefore, the run-flat tire of the present invention can apply the rubber composition having excellent processability to the bead filler 7 and / or the side reinforcing rubber layer 8 without reducing the run-flat durability.

  The rubber component (A) used in the rubber composition is required to contain at least one of natural rubber (NR) and polyisoprene rubber (IR). If neither the natural rubber nor the polyisoprene rubber is contained in the rubber component (A), run-flat durability is lowered. The rubber component (A) includes conjugated diene high molecular weights such as styrene-butadiene copolymer rubber (SBR), polybutadiene rubber (BR), and isobutylene isoprene rubber (IIR) in addition to natural rubber and polyisoprene rubber. The body is mentioned. In addition, the said rubber component (A) may be used individually by 1 type, and may blend and use 2 or more types. In the case where the rubber component (A) contains a styrene-butadiene copolymer rubber, the ratio of the styrene unit in the entire rubber component (A) is preferably less than 30% by mass, and 20% by mass. % Is more preferable, and it is more preferable that it is less than 15% by mass. When the ratio of the styrene unit to the whole rubber component (A) is less than 30% by mass, the rubber component (A) is excellent in compatibility with the low molecular weight conjugated diene polymer (B).

  The rubber component (A) is required to have a polystyrene-equivalent weight average molecular weight of 150,000 to 2,000,000 as measured by gel permeation chromatography. If the polystyrene-equivalent weight average molecular weight is less than 150,000, the unvulcanized viscosity will be too low, the torque during kneading will not be applied, and the kneading may be insufficient. On the other hand, if it exceeds 2,000,000, the unvulcanized viscosity will remarkably increase, and the workability and molding workability during kneading will be remarkably deteriorated. In addition, there is no restriction | limiting in particular as a method of manufacturing the said rubber component (A), For example, the thing similar to the manufacturing method of the low molecular weight conjugated diene type polymer (B) demonstrated below is mentioned.

  The rubber composition contains 0.1 to 30 mass of low molecular weight conjugated diene polymer (B) having a polystyrene equivalent weight average molecular weight of 2,000 to 10,000 measured by gel permeation chromatography with respect to 100 mass parts of the rubber component (A). Contains. When the content of the low molecular weight conjugated diene polymer (B) is less than 0.1 parts by mass, the effect of imparting processability to the rubber composition is low, and when it exceeds 30 parts by mass, the fracture characteristics of the vulcanized rubber are deteriorated. Tend.

The low molecular weight conjugated diene polymer (B) used in the rubber composition requires a polystyrene-reduced weight average molecular weight of 2,000 to 10,000 as measured by gel permeation chromatography, and preferably 2,000 to 6,000. When the polystyrene-equivalent weight average molecular weight is less than 2,000, the low-loss performance is lowered and the run-flat durability is lowered. On the other hand, when the polystyrene-equivalent weight average molecular weight exceeds 10,000, the processability of the rubber composition decreases.

  In the low molecular weight conjugated diene polymer (B), the ratio of the aromatic vinyl compound unit to the whole of the monomer units constituting is preferably less than 5% by mass. The low molecular weight conjugated diene polymer (B) may contain, for example, a styrene-butadiene copolymer. In this case, the proportion of styrene units in the entire polymer (B) is 5% by mass. If it becomes above, exothermicity falls and there exists a possibility that run flat durability may not fully be secured.

  The low molecular weight conjugated diene polymer (B) is preferably a homopolymer of a conjugated diene compound or a copolymer of an aromatic vinyl compound and a conjugated diene compound. Here, conjugated diene compounds as monomers include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene, 2-phenyl-1,3-butadiene, and 1,3-hexadiene. Among these, 1,3-butadiene is preferable. On the other hand, examples of the aromatic vinyl compound as a monomer include styrene, p-methylstyrene, m-methylstyrene, p-tert-butylstyrene, α-methylstyrene, chloromethylstyrene, vinyltoluene and the like. Therefore, polybutadiene is particularly preferable as the low molecular weight conjugated diene polymer (B). In addition, these monomers may be used independently and may be used in combination of 2 or more type.

  The low molecular weight conjugated diene polymer (B) is not particularly limited, and for example, a conjugated diene compound that is a monomer alone or a monomer in a hydrocarbon solvent inert to the polymerization reaction. It can be obtained by polymerizing a mixture of an aromatic vinyl compound and a conjugated diene compound. In the case of introducing at least one functional group into the molecule of the low molecular weight conjugated diene polymer (B), (1 A method of polymerizing a monomer using a polymerization initiator to form a polymer having a polymerization active site, and then modifying the polymerization active site with various modifiers; It can be obtained by a polymerization method using a polymerization initiator having a group, for example, a polymerization initiator having a Sn—Li, C—Li or N—Li bond.

  As a polymerization initiator used for the synthesis | combination of the said polymer (B), an alkali metal compound is preferable, a lithium compound is still more preferable, and hydrocarbyl lithium and a lithium amide compound are still more preferable. In addition, when a lithium compound is used as the polymerization initiator, the aromatic vinyl compound and the conjugated diene compound are polymerized by anionic polymerization. When hydrocarbyl lithium is used as the polymerization initiator, a polymer having a hydrocarbyl group at the polymerization initiation terminal and the other terminal being a polymerization active site is obtained. On the other hand, when a lithium amide compound is used as a polymerization initiator, a polymer having a nitrogen-containing functional group at the polymerization initiation terminal and a polymerization active site at the other terminal is obtained, and the polymer is modified with a modifier. It can be used as a low molecular weight conjugated diene polymer (B) having at least one functional group. In addition, the usage-amount of a polymerization initiator has the preferable range of 0.2-20 mmol per 100g of monomers.

  Examples of the hydrocarbyl lithium include ethyl lithium, n-propyl lithium, isopropyl lithium, n-butyl lithium, sec-butyl lithium, tert-octyl lithium, n-decyl lithium, phenyl lithium, 2-naphthyl lithium, and 2-butyl-phenyl. Examples include lithium, 4-phenyl-butyllithium, cyclohexyllithium, cyclopentyllithium, reaction products of diisopropenylbenzene and butyllithium, and among these, ethyllithium, n-propyllithium, isopropyllithium, n-butyl Alkyl lithium such as lithium, sec-butyl lithium, tert-octyl lithium and n-decyl lithium is preferable, and n-butyl lithium is particularly preferable.

  The method for producing a conjugated diene polymer using the polymerization initiator is not particularly limited as described above. For example, the monomer is polymerized in a hydrocarbon solvent inert to the polymerization reaction. Thus, the polymer (B) can be produced. Here, hydrocarbon solvents inert to the polymerization reaction include propane, n-butane, isobutane, n-pentane, isopentane, n-hexane, cyclohexane, propene, 1-butene, isobutene, trans-2-butene, cis -2-butene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, benzene, toluene, xylene, ethylbenzene and the like. These may be used alone or in combination of two or more.

  The above polymerization reaction may be carried out in the presence of a randomizer. The randomizer can control the microstructure of the conjugated diene compound portion of the polymer. More specifically, the randomizer can control the vinyl bond amount of the conjugated diene compound portion of the polymer, It has actions such as randomizing diene compound units and aromatic vinyl compound units. Examples of the randomizer include dimethoxybenzene, tetrahydrofuran, dimethoxyethane, diethylene glycol dibutyl ether, diethylene glycol dimethyl ether, bistetrahydrofurylpropane, triethylamine, pyridine, N-methylmorpholine, N, N, N ′, N′-tetramethylethylenediamine, 1 , 2-dipiperidinoethane, potassium-t-amylate, potassium-t-butoxide, sodium-t-amylate and the like. The amount of these randomizers used is preferably in the range of 0.1 to 100 molar equivalents per mole of polymerization initiator.

  The anionic polymerization is preferably carried out by solution polymerization, and the concentration of the monomer in the polymerization reaction solution is preferably in the range of 5 to 50% by mass, more preferably in the range of 10 to 30% by mass. When the conjugated diene compound and the aromatic vinyl compound are used in combination, the content of the aromatic vinyl compound in the monomer mixture may be appropriately selected according to the amount of the aromatic vinyl compound in the target copolymer. it can. Further, the polymerization mode is not particularly limited, and may be batch type or continuous type.

  The polymerization temperature of the anionic polymerization is preferably in the range of 0 to 150 ° C, more preferably in the range of 20 to 130 ° C. The polymerization can be carried out under a generated pressure, but it is usually preferred to carry out the polymerization under a pressure sufficient to keep the monomer used in a substantially liquid phase. Here, when the polymerization reaction is carried out under a pressure higher than the generated pressure, it is preferable to pressurize the reaction system with an inert gas. Moreover, it is preferable to use what removed reaction-inhibiting substances, such as water, oxygen, a carbon dioxide, and a protic compound, as raw materials, such as a monomer used for superposition | polymerization, a polymerization initiator, and a solvent.

  Furthermore, when the polymerization active site of the (co) polymer having the polymerization active site is modified with a modifier, the modifier used is preferably a nitrogen-containing compound, a silicon-containing compound or a tin-containing compound. In this case, a nitrogen-containing functional group, a silicon-containing functional group, or a tin-containing functional group can be introduced by a modification reaction.

  The modification reaction of the polymerization active site by the modifying agent is preferably performed by a solution reaction, and the solution may contain a monomer used at the time of polymerization. The reaction mode of the modification reaction is not particularly limited, and may be a batch type or a continuous type. Furthermore, the reaction temperature of the modification reaction is not particularly limited as long as the reaction proceeds, and the reaction temperature of the polymerization reaction may be employed as it is. The amount of modifier used is preferably in the range of 0.25 to 3.0 mol, and more preferably in the range of 0.5 to 1.5 mol, with respect to 1 mol of the polymerization initiator used for the production of the polymer.

  In the rubber composition used for the run flat tire of the present invention, the reaction solution containing the polymer (B) is dried to separate the polymer (B), and then the obtained polymer (B) is used as the rubber component. The reaction solution containing the polymer (B) may be blended with the rubber cement of the rubber component (A) in a solution state and then dried to obtain the rubber component (A) and the polymer. You may obtain the mixture of (B).

  In the rubber composition, a vulcanizing agent such as sulfur can be used for crosslinking the rubber component (A) and the low molecular weight conjugated diene polymer (B) to form a three-dimensional network structure. However, the low molecular weight conjugated diene polymer (B) is difficult to be cross-linked because of its low molecular weight, and as a result, the flow of the polymer (B) that does not form cross-linkage may increase the tan δ of the rubber composition. is there. Then, the said rubber composition needs to contain 3-10 mass parts of sulfur with respect to 100 mass parts of rubber components (A). If the sulfur content is within the above specified range, even if a conjugated diene polymer (B) having a low molecular weight is used, the conjugated diene portion of the rubber component (A) is incorporated into the three-dimensional network structure without any problem. The unvulcanized viscosity can be effectively lowered without impairing the low loss performance. In addition, when the sulfur content is less than 3 parts by mass, the sulfur cannot be involved in the three-dimensional network structure, loss increases, and run-flat durability tends to decrease. On the other hand, when the sulfur content exceeds 10 parts by mass, re-crosslinking during heat aging is promoted, the heat aging property of the rubber is deteriorated, and the run-flat durability tends to decrease due to running deterioration.

  The rubber composition preferably further contains a filler. Here, examples of the filler include carbon black and silica. As carbon black, those of FEF, SRF, HAF, ISAF, and SAF grade are preferable, and those of HAF, ISAF, and SAF grade are more preferable. On the other hand, as silica, wet silica and dry silica are preferable, and wet silica is more preferable. These fillers may be used alone or in combination of two or more. Moreover, in the said rubber composition, it is preferable that content of a filler is 30-90 mass parts with respect to 100 mass parts of said rubber components (A). When the content of the filler is less than 30 parts by mass, the fracture characteristics and wear resistance of the vulcanized rubber are not sufficient, while when it exceeds 90 parts by mass, the workability tends to deteriorate.

  In the rubber composition, in addition to the rubber component (A), the low molecular weight conjugated diene polymer (B), a vulcanizing agent such as sulfur, a filler, a compounding agent usually used in the rubber industry, for example, , Softeners, tackifiers, anti-aging agents, silane coupling agents, vulcanization accelerators, vulcanization accelerators and the like can be appropriately selected and blended within a range that does not impair the object of the present invention. As these compounding agents, commercially available products can be suitably used. The rubber composition is prepared by blending the rubber component (A) with the low molecular weight conjugated diene polymer (B) and various compounding agents appropriately selected as necessary, kneading, heating, extruding, and the like. Can be manufactured.

  In the run flat tire of the present invention, a rubber composition containing the rubber component (A) and the low molecular weight conjugated diene polymer (B) is applied to at least one of the bead filler 7 and the side reinforcing rubber layer 8. It can be produced by forming a green tire and vulcanizing the green tire according to a conventional method. In the run flat tire of the present invention, the gas filled in the tire may be normal or air with a changed oxygen partial pressure, or an inert gas such as nitrogen.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

<Production Example 1 of Polymer (A-1)>
To a dried and nitrogen-substituted 800 mL pressure-resistant glass container, 300 g of cyclohexane, 40 g of 1,3-butadiene, 13 g of styrene, 0.25 mmol of ditetrahydrofurylpropane, and 0.25 mmol of n-butyllithium (n-BuLi) were added. Thereafter, a polymerization reaction was carried out at 50 ° C. for 1.5 hours. The polymerization conversion rate at this time was almost 100%. Next, 0.06 mmol of tin tetrachloride as a modifier was quickly added to the polymerization reaction system, and a modification reaction was further performed at 50 ° C. for 30 minutes. Thereafter, 0.5 mL of an isopropanol solution (BHT concentration: 5% by mass) of 2,6-di-t-butyl-p-cresol (BHT) was added to the polymerization reaction system to stop the polymerization reaction, and further according to a conventional method. It dried and the polymer (A-1) was obtained.

<Example of production of polymer (B-1)>
Into an 800 mL pressure-resistant glass container dried and purged with nitrogen, 300 g of cyclohexane, 40 g of 1,3-butadiene and 13.2 mmol of ditetrahydrofurylpropane were injected, and further 13.2 mmol of n-butyllithium (n-BuLi) was added. Thereafter, a polymerization reaction was carried out at 50 ° C. for 1.5 hours. The polymerization conversion rate at this time was almost 100%. Thereafter, 0.5 mL of an isopropanol solution (BHT concentration: 5% by mass) of 2,6-di-t-butyl-p-cresol (BHT) was added to the polymerization reaction system to stop the polymerization reaction, and further according to a conventional method. It dried and the polymer (B-1) was obtained.

<Production Examples of Polymers (B-2) to (B-4)>
Polymers (B-2) to (B-4) were synthesized in the same manner as in the production example of the polymer (B-1) except that the amount of n-butyllithium (n-BuLi) used was changed.

<Production example of polymer (B-5)>
Into a dry, nitrogen-substituted 800 mL pressure-resistant glass container, 300 g of cyclohexane, 42.5 g of 1,3-butadiene, 7.5 g of styrene, and 0.80 mmol of ditetrahydrofurylpropane are injected, and n-butyllithium (n-BuLi) is added. After adding 26.4 mmol, a polymerization reaction was carried out at 50 ° C. for 1.5 hours. The polymerization conversion rate at this time was almost 100%. Thereafter, 0.5 mL of an isopropanol solution (BHT concentration: 5% by mass) of 2,6-di-t-butyl-p-cresol (BHT) was added to the polymerization reaction system to stop the polymerization reaction, and further according to a conventional method. It dried and the polymer (B-5) was obtained.

  The weight average molecular weight (Mw) and microstructure of the polymers (A-1) and (B-1) to (B-5) produced as described above were measured by the following methods. The results are shown in Table 1.

(1) Weight average molecular weight (Mw)
Gel permeation chromatography [GPC: Tosoh HLC-8020, column: Tosoh GMH-XL (two in series), detector: differential refractometer (RI)], based on monodisperse polystyrene, The weight average molecular weight (Mw) in terms of polystyrene was determined.

(2) Microstructure The microstructure of the polymer was determined by an infrared method (Morero method).

(Examples 1-4 and Comparative Examples 1-6)
A rubber composition having the formulation shown in Table 2 was prepared, and the rubber composition was used for both the bead filler 7 and the side reinforcing rubber layer 8 to have the structure shown in FIG. A flat tire was manufactured.

<Evaluation>
The rubber composition prepared as described above was evaluated for the viscosity and tackiness of the unvulcanized rubber by the following method, and the tire prepared as described above was evaluated by the following method. The run flat durability was evaluated. The results are shown in Table 2.

(3) Viscosity of unvulcanized rubber According to JIS K6300-1: 2001, the Mooney viscosity [ML _{1 + 4} (130 ° C)] is measured at 130 ° C, and the Mooney viscosity of the compounded rubber of Comparative Example 1 is determined. The index is shown as 100. The smaller the index value, the lower the Mooney viscosity and the better the workability.

(4) Adhesiveness of unvulcanized rubber The test was carried out according to JIS-T9233-3.8.6 (2) Mitsuhashi method (Picuma tack test). One specimen having a width of 15 mm and a length of 100 mm was taken as a test piece of each example and comparative example. The surface of the bonded disk (diameter 50 mm, thickness 14 mm, made of aluminum) was washed with hexane and dried at room temperature for 30 minutes. The sample (test piece) was affixed with a double-sided tape. The start button of the measuring device was pressed, the bonded disk was lowered and brought into contact with the sample. After contact for 30 seconds under a load of 500 gf, the load was raised at 30 mm / second. (Test specimen temperature, bonded part disk temperature, measurement chamber temperature: 23 ° C.) The force when the bonded disk was separated from the sample was measured five times, and the average value was obtained. The value of the rubber composition of Comparative Example 1 was indicated as 100 and indicated as an index. The larger the index value, the higher the tackiness and the better the workability.

(5) Run flat durability Each prototype tire is assembled with a rim at normal pressure, filled with an internal pressure of 230 kPa, allowed to stand at room temperature of 38 ° C for 24 hours, then the valve core is removed and the internal pressure is set to atmospheric pressure, and the load is 5.19 kN. The drum running test was conducted under the conditions of (530 kg), speed 89 km / h, and room temperature 38 ° C. The distance traveled until the failure occurred at this time was measured, and the travel distance until the failure occurred in Comparative Example 1 was taken as 100 and displayed as an index. The larger the index value, the longer the distance traveled until the failure occurs, indicating better run-flat durability. In each example, the rubber composition was used for both the side reinforcing rubber layer and the bead filler.

* 1 Polystyrene equivalent weight average molecular weight = 1,500,000.
* 2 Polymer (A-1).
* 3 JSR, BR01, polystyrene equivalent weight average molecular weight = 550,000.
* 4 Made by BASF, Koresin.
* 5 N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine.
* 6 NS: N-tert-butyl-2-benzothiazyl-sulfenamide.

  From the comparison of Comparative Examples 1 to 3, by adding a softener such as oil or a tackifier in the rubber composition, the viscosity and tackiness of the unvulcanized rubber is improved, but the run-flat durability is greatly reduced. I understand that However, from the results of Examples 1 to 4, a low molecular weight conjugated diene polymer (B) having a polystyrene-reduced weight average molecular weight of 2,000 to 10,000 measured by gel permeation chromatography instead of a softener such as oil or a tackifier. Furthermore, it can be seen that by using a rubber composition containing a specific amount of sulfur, the run-flat durability can be improved while maintaining high processability of the rubber composition. In addition, in Example 4, since the ratio of the styrene unit of a low molecular weight conjugated diene polymer (B) is too high, it turns out that the improvement effect of run flat durability is not fully acquired. Moreover, in the comparative example 6, since the content of sulfur in a rubber composition is low, it turns out that the improvement effect of run flat durability is not fully acquired.

  In Comparative Example 4, the polystyrene equivalent weight average molecular weight of the low molecular weight conjugated diene polymer (B) is out of the range of 2,000 to 10,000, and the effect of improving processability cannot be obtained. Since the component (A) does not contain natural rubber and / or polyisoprene rubber, it can be seen that run-flat durability is deteriorated.

It is sectional drawing of one embodiment of the run flat tire of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bead part 2 Side wall part 3 Tread 4 Radial carcass 4a Folded carcass ply 4b Down carcass ply 5 Belt 6 Bead core 7 Bead filler 8 Side reinforcement rubber layer

Claims (6)

In the run-flat tire with the sidewall portion, tread, carcass, bead core and bead filler,
The bead filler was measured by gel permeation chromatography with respect to 100 parts by mass of a rubber component (A) having a polystyrene-converted weight average molecular weight of 150,000 to 2,000,000 and containing at least natural rubber or polyisoprene rubber. A rubber composition comprising 0.1 to 30 parts by mass of a low molecular weight conjugated diene polymer (B) having a polystyrene-equivalent weight average molecular weight of 2,000 to 10,000 and 3 to 10 parts by mass of sulfur is used. Run flat tire. In the run flat tire provided with the sidewall portion, the tread, the carcass and the side reinforcing rubber layer,
With respect to 100 parts by mass of the rubber component (A) having a polystyrene-reduced weight average molecular weight of 150,000 to 2,000,000 measured by gel permeation chromatography and containing at least natural rubber or polyisoprene rubber, the side reinforcing rubber layer is subjected to gel permeation chromatography. A rubber composition comprising 0.1 to 30 parts by mass of a low molecular weight conjugated diene polymer (B) having a measured polystyrene equivalent weight average molecular weight of 2,000 to 10,000 and 3 to 10 parts by mass of sulfur is used. Run flat tires. In the run flat tire including the sidewall portion, the tread, the carcass, the bead core, the bead filler, and the side reinforcing rubber layer,
At least one of the bead filler and the side reinforcing rubber layer has a polystyrene-converted weight average molecular weight of 150,000 to 2,000,000 as measured by gel permeation chromatography, and 100 parts by mass of a rubber component (A) containing at least natural rubber or polyisoprene rubber. On the other hand, a rubber composition obtained by blending 0.1 to 30 parts by mass of a low molecular weight conjugated diene polymer (B) having a polystyrene equivalent weight average molecular weight of 2,000 to 10,000 measured by gel permeation chromatography and 3 to 10 parts by mass of sulfur. A run-flat tire characterized by using an object.   The rubber component (A) comprises at least one selected from the group consisting of natural rubber, polyisoprene rubber, styrene-butadiene copolymer rubber, polybutadiene rubber and isobutylene isoprene rubber. The run flat tire according to any one of the above.   The run flat tire according to any one of claims 1 to 3, wherein the low molecular weight conjugated diene polymer (B) is polybutadiene.   The run-flat tire according to any one of claims 1 to 3, wherein the rubber composition further contains carbon black and / or silica.

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