JP5204577B2 - Run flat tire - Google Patents

Description

  The present invention relates to a run-flat tire that can continue running at a constant speed even when punctured, and more particularly to a run-flat tire that can improve low heat generation and durability during run-flat running.

  A run-flat tire that can travel at a high speed over a relatively long distance even in a state where air in the tire is removed due to puncture or the like is known. Such a run-flat tire is provided with a side-reinforcing rubber layer having a substantially crescent-shaped cross section inside the carcass of the side wall, and this side-reinforcing rubber layer supports the load during puncture and restricts the vertical deflection of the tire. (See, for example, Patent Document 1). In such run-flat tires, the number of carcass plies is increased and the rubber volume of the side reinforcing rubber layer is increased in order to further increase the load support capability.

JP 2000-351307 A

  However, such an improvement tends to accelerate the tire temperature during run-flat running, particularly the heat generation of the side reinforcing rubber layer, which may lead to a decrease in run-flat durability.

  The present invention has been devised in view of the actual situation as described above, and uses a rubber composition containing carbon black, sulfur or a sulfur compound and lamellar alumina powder or fluorine-containing mica for the side reinforcing rubber layer. Based on the use of a highly elastic aramid fiber cord for the carcass cord, the main object is to provide a run flat tire that can improve low heat generation and durability during run flat running.

The invention according to claim 1 of the present invention includes a carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion, and a side reinforcing rubber layer having a substantially crescent-shaped cross section disposed inside the carcass of the sidewall portion. The side reinforcing rubber layer has a nitrogen adsorption specific surface area of 30 to 100 m ² / g and a dibutyl phthalate oil absorption of 50 ml / 100 g with respect to 100 parts by mass of the diene rubber component. A rubber composition containing 10 to 100 parts by mass of carbon black as described above, 2 parts by mass or more of sulfur or a sulfur compound, and 5 to 120 parts by mass of lamellar alumina powder having an aspect ratio of 3 to 50 or fluorine-containing mica. The carcass is topped with a carcass cord arranged at an angle of 45 to 90 ° with respect to the tire equator. Together consist of a carcass ply coated with arm, the carcass cord, twist coefficient T is represented by the following formula (1) characterized by using the aramid fiber is 0.50 to 0.70.
T = N × √ {(0.125 × D / 2) / ρ} × 10 ⁻³ (1)
However, N is the number of twists (times / 10 cm), D is the total display decitex (fineness) of the cord, and ρ is the specific gravity of the cord material.

The invention according to claim 2 is the run-flat tire according to claim 1, wherein the fluorine-containing mica comprises the following formula (2).
X _{1/3 to 1} Y _{2 to 3} (Z ₄ O ₁₀ ) F _{1.5 to 2} (2)
However, in the above formula (2), X represents ^{Na +, K +, Li +} , Ca 2+, 1 kind of ion selected from the group consisting of ^{Rb 2+} and ^{Sr 2+,} Y is ^{Mg 2+, Fe 2+, Ni 2+} , One ion selected from the group consisting of Mn ²⁺ , Al ³⁺ , Fe ^3+, and Li ⁺ , Z represents one ion selected from the group consisting of Al ³⁺ , Si ⁴⁺ , Ce ⁴⁺ , Fe ^3+, and B ³⁺ , respectively. Represent.

According to a third aspect of the present invention, the fluorine-containing mica is KMg ₃ AlSiO ₃ O ₁₀ F ₂ , KMg _2.5 Si ₄ O ₁₀ F ₂ , NaMG _2.5 Si ₄ O ₁₀ F ₂ , NaMg ₂ LiSi ₄ The run flat tire according to claim _2, which is O ₁₀ F ₂ or LiMg ₂ LiSi ₄ O ₁₀ F ₂ .

  The invention of claim 4 is the run-flat tire according to any one of claims 1 to 3, wherein the carcass cord has the twist coefficient T of 0.60 to 0.70.

The invention according to claim 5 is the run-flat tire according to any one of claims 1 to 4, wherein the topping rubber of the carcass ply has a complex elastic modulus E ^{* of 5} to 13 MPa.

  According to a sixth aspect of the present invention, in the tire meridional section including the tire shaft center in the normal internal pressure state that is mounted on the normal rim and filled with the normal internal pressure, the profile of the tire outer surface is an intersection of the tire outer surface and the tire equatorial plane C. The run-flat tire according to any one of claims 1 to 5, wherein the run-flat tire is formed by a curved surface formed of a plurality of arcs having a radius of curvature that gradually decreases from the tire equator point CP toward the ground contact end side.

In the invention according to claim 7, the tire outer surface profile has a radius of curvature RC of the tire outer surface, where P is a point on the tire outer surface that is separated from the tire equatorial plane C by a distance SP of 45% of the maximum tire cross-sectional width SW. Gradually decreases from the tire equator point CP to the point P, and 60%, 75%, 90% of the half width (SW / 2) of the tire maximum cross-sectional width SW from the tire equator plane C. And Y60, Y75, Y90, and Y100 are the radial distances between the points on the outer surface of the tire and the tire equator point CP, which are separated from each other by the distances X60, X75, X90, and X100 of 100%, respectively. When S is SH
0.05 <Y60 / SH ≦ 0.1
0.1 <Y75 / SH ≦ 0.2
0.2 <Y90 / SH ≦ 0.4
0.4 <Y100 / SH ≦ 0.7
The run-flat tire according to claim 6, wherein the relationship is satisfied.

  The “regular rim” is a rim determined for each tire in the standard system including the standard on which the tire is based. For example, “Standard Rim” for JATMA and “Design Rim” for TRA. Or ETRTO means "Measuring Rim".

  The “regular internal pressure” is the air pressure defined by the standard for each tire. The maximum air pressure described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” is the maximum air pressure for JATMA and TRA for TRA. If the value is ETRTO, it means “INFLATION PRESSURE”, but in the case of passenger car tires, it is 180 kPa.

Further, the viscoelastic properties such as the complex elastic modulus E ^* and the loss elastic modulus E ″ described later are the “viscoelastic spectrometer” manufactured by Iwamoto Seisakusho Co., Ltd. under the following conditions in accordance with JIS-K6394. It is the value measured using "."
Initial strain: 10%
Amplitude: ± 1%
Frequency: 10Hz
Deformation mode: Tensile Measurement temperature: 70 ° C

  In the run flat tire of the present invention, the side reinforcing rubber layer is made of a rubber composition containing a predetermined amount of carbon black, sulfur or a sulfur compound, and lamellar alumina powder having a predetermined aspect ratio or fluorine-containing mica. Each component is dispersed in the rubber composition to increase the rubber hardness and improve the breaking strength. Furthermore, since the thin plate-like alumina powder or fluorine-containing mica has less energy loss than rubber, it helps to reduce the heat generation of the side reinforcing rubber layer. Therefore, a run flat tire using such a rubber composition as a side reinforcing rubber layer can improve the low heat buildup and durability during run flat running.

  In the run flat tire of the present invention, an aramid fiber cord particularly excellent in heat resistance is used as a carcass cord. Therefore, carcass cord damage due to temperature rise during run-flat traveling can be suppressed. Moreover, since an aramid fiber cord is highly elastic, it has an excellent load supporting ability. For this reason, while reducing the number of carcass plies (weight reduction), the amount of vertical deflection of the tire during run-flat running can be reduced, and durability can be further enhanced by a synergistic effect with the improvement in low heat generation described above. In addition, the run flat tire of the present invention can achieve steering stability, high speed, and long distance during run flat running.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a tire meridian cross-sectional view of the run-flat tire 1 of the present embodiment in a normal internal pressure state.

  In FIG. 1, the run-flat tire 1 of the present embodiment includes a carcass 6 that extends from a tread portion 2 through a sidewall portion 3 to a bead core 5 of a bead portion 4, a radially outer side of the carcass 6, and an inner portion of the tread portion 2. A tread reinforcing cord layer 7 disposed on the side, and a side reinforcing rubber layer 11 having a substantially crescent-shaped cross section disposed on the inner side of the carcass 6 of the sidewall portion 3.

  The carcass 6 is formed of one or more carcass plies in which a carcass cord arranged at an angle of 45 to 90 ° with respect to the tire equator C is covered with a topping rubber. The carcass 6 of the present embodiment is composed of one carcass ply 6A in which carcass cords are arranged at an angle of 80 to 90 ° with respect to the tire equator. The carcass ply 6A includes a toroid-shaped main body portion 6a straddling the bead cores 5 and 5 and a pair of folded portions 6b folded around the bead core 5 from the inner side to the outer side in the tire axial direction.

  Between the main body portion 6a and the folded portion 6b, a bead apex rubber 8 for reinforcing the bead is formed of a hard rubber having a rubber hardness of 65 to 98 degrees, for example, and extends in a radially outward direction from the bead core 5. Arranged. In the present specification, “rubber hardness” means hardness according to durometer type A measured at a temperature of 23 ° C. in accordance with JIS-K6253. The height ha of the bead apex rubber 8 from the bead base line BL in the tire radial direction is not particularly limited, but if it is too small, the run-flat durability is insufficient, and conversely if it is too large, the tire mass may increase excessively. There is a risk of deteriorating ride comfort. From such a viewpoint, the height ha of the bead apex rubber 8 is desirably 10 to 60%, more preferably 20 to 50% of the tire cross-section height SH.

  In the present embodiment, the folded portion 6b of the carcass 6 extends beyond the outer end of the bead apex rubber 8 in the radial direction, and the outer end portion 6be of the folded portion 6b is the main body portion 6a of the carcass ply 6A. And a so-called ultra-high turn-up folded structure that is sandwiched between the tread reinforcing cord layer 7 and ends. Thereby, the side wall part 3 is effectively reinforced using one carcass ply 6A.

  Further, since the outer end 6be of the folded portion 6b is separated from the sidewall portion 3 which is greatly bent during run flat travel, it is desirable in that damage from the outer end 6be as a starting point can be suitably suppressed. The tire axial width EW of the overlapping portion between the folded portion 6b and the tread reinforcing cord layer 7 is preferably 5 mm or more, more preferably 10 mm or more, and the upper limit is preferably 40 mm or less from the viewpoint of weight reduction. Preferably it is 30 mm or less. In the case where the carcass 6 is formed of a plurality of carcass plies, it is preferable that at least one carcass ply has this aspect.

  In the present embodiment, the tread reinforcing cord layer 7 is composed of a belt layer 9 placed on the carcass 6 and a band layer 10 stacked on the outer side. The belt layer 9 is formed of two or more belt plies 9A and 9B in the present embodiment, in which a belt cord arranged at an angle of, for example, 10 to 45 ° with respect to the tire equator C is covered with a topping rubber. The Each belt cord 9A, 9B enhances belt rigidity by crossing between plies, and reinforces substantially the entire width of the tread portion 2 with a tagging effect.

  The band layer 10 is composed of one or more band plies in which a band cord spirally wound at an angle of 5 ° or less with respect to the tire equator is covered with a topping rubber, and restrains the belt layer 9; Improve handling stability and high-speed durability. The band ply includes a pair of left and right edge band plies that covers only the outer end of the belt 9 in the tire axial direction, and a full band ply that covers substantially the entire width of the belt 9, and these are used alone or in combination. The In the present embodiment, the band 10 is exemplified by one full band ply. The tread reinforcing cord layer 7 can be formed of only the belt 9 layer.

  The side reinforcing rubber layer 11 has a substantially crescent-shaped cross section extending gradually from the central portion 11a having the maximum thickness toward the inner end 11i and the outer end 11o in the tire radial direction. The inner end 11 i is located on the inner side in the tire radial direction from the outer end of the bead apex rubber 8, and the outer end 11 o is located on the inner side in the tire axial direction from the outer end 7 e of the tread reinforcing cord layer 7. At this time, the overlapping width Wi in the tire radial direction between the side reinforcing rubber layer 11 and the bead apex rubber 8 is 5 to 50 mm, and the overlapping width Wo in the tire axial direction between the side reinforcing rubber layer 11 and the tread reinforcing cord layer 7 is 5. It is preferable to set it to -50 mm or less. Thus, it is possible to suppress the occurrence of a rigidity step at the outer end 11o and the inner end 11i.

  In the present embodiment, the side reinforcing rubber layer 11 is disposed on the inner side (the tire lumen side) of the main body portion 6a of the carcass 6. Therefore, when the sidewall portion 3 is bent and deformed, compressive stress mainly acts on the side reinforcing rubber layer 11, and tensile stress mainly acts on the carcass ply 6A having the cord material. Since the rubber is strong against compression and the cord material is strong against tension, the arrangement structure of the side reinforcing rubber layer 11 as described above efficiently increases the bending rigidity of the side wall portion 3, and the vertical direction of the tire during run-flat running. Deflection can be effectively reduced.

  The rubber hardness of the side reinforcing rubber layer 11 is preferably 60 degrees or more, and more preferably 65 degrees or more. If the rubber hardness is less than 60 degrees, the strain during run-flat running increases, and the durability may decrease. On the other hand, even if the rubber hardness is too high, there is a risk that the longitudinal spring constant of the tire will excessively increase and the ride comfort during normal running will be reduced. From such a viewpoint, the upper limit of the rubber hardness of the side reinforcing rubber layer 11 is preferably 90 degrees or less, more preferably 80 degrees or less. Further, the maximum thickness t of the side reinforcing rubber layer 11 is appropriately set depending on the tire size, the tire category, and the like, but in the case of a passenger car tire, 5 to 20 mm is preferable.

  The side reinforcing rubber layer 11 of the present invention comprises 10 to 100 parts by mass of carbon black, 2 parts by mass or more of sulfur or a sulfur compound, and lamellar alumina powder or fluorine-containing mica with respect to 100 parts by mass of the diene rubber component. It is comprised from the rubber composition containing 5-120 mass parts.

  Examples of the diene rubber component include natural rubber (NR), epoxidized natural rubber (ENR), butadiene rubber (BR), styrene butadiene rubber (SBR), isoprene rubber (IR), butyl rubber (IIR), and acrylonitrile butadiene rubber. (NBR), chloroprene rubber (CR), styrene isoprene butadiene rubber (SIBR), styrene isoprene rubber, or isoprene butadiene rubber may be used, and these may be used alone or in combination of two or more. Of these, natural rubber (NR) and / or butadiene rubber (BR) are preferable because they are excellent in low heat build-up.

  In order to improve the low heat build-up of the side reinforcing rubber layer 11, the diene rubber component preferably contains butadiene rubber, preferably 20 parts by mass or more, more preferably 30 parts by mass or more. In order to increase the rubber strength of the side reinforcing rubber layer 11, the butadiene rubber as the diene rubber component is preferably 80 parts by mass or less, more preferably 70 parts by mass or less. In particular, in order to obtain sufficient rubber hardness as the side reinforcing rubber layer 11, butadiene rubber containing syndiotactic-1,2-polybutadiene crystals (hereinafter simply referred to as “SPB-containing BR”) is used as the butadiene rubber. desirable. The SPB-containing BR is not particularly limited, but VCR 412 and VCR 617 manufactured by Ube Industries, Ltd. are preferable.

  The diene rubber component preferably contains 20-80 parts by mass of natural rubber (NR). When the content of natural rubber (NR) is less than 20 parts by mass, the rubber strength of the side reinforcing rubber layer 11 tends to decrease, and conversely, when the content of natural rubber (NR) exceeds 80 parts by mass, There is a possibility that the low heat buildup of the side reinforcing rubber layer 11 cannot be sufficiently expected. From such a viewpoint, the natural rubber (NR) of the diene rubber component is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, and preferably 70 parts by mass or less, more preferably 60 parts by mass or less. Is desirable.

The carbon black is limited to a nitrogen adsorption specific surface area of 30 to 100 m ² / g. Thereby, the side reinforcement rubber layer 11 can be effectively reinforced and durability during run-flat traveling can be improved. When the nitrogen adsorption specific surface area of carbon black exceeds 100 m ² / g, the side reinforcing rubber layer 11 tends to generate heat. On the other hand, when the nitrogen adsorption specific surface area is less than 30 m ² / g, the reinforcing property of the side reinforcing rubber layer 11 is lowered, and sufficient durability cannot be ensured. From such a viewpoint, the nitrogen adsorption specific surface area of carbon black is preferably 35 m ² / g or more, preferably 80 m ² / g or less, more preferably 60 m ² / g or less.

  Further, the carbon black dibutyl phthalate oil absorption is limited to 50 ml / 100 g or more, preferably 80 ml / 100 g or more. Thereby, the side reinforcing rubber layer 11 can be sufficiently reinforced. In addition, if the dibutyl phthalate oil absorption of carbon black is too large, fatigue resistance characteristics such as elongation at break of the rubber composition may be deteriorated. Therefore, it is preferably 300 ml / 100 g or less, more preferably 200 ml / 100 g or less. .

  Carbon black is blended in an amount of 10 to 100 parts by mass with respect to 100 parts by mass of the diene rubber component. When the blending amount of carbon black is less than 10 parts by mass, the rubber strength of the side reinforcing rubber layer 11 cannot be sufficiently improved. On the other hand, when the content of carbon black exceeds 100 parts by mass, the viscosity at the time of kneading increases and the processability may be significantly deteriorated. From such a viewpoint, the carbon black content is preferably 20 parts by mass or more, preferably 70 parts by mass or less, more preferably 60 parts by mass or less.

  The rubber composition of the side reinforcing rubber layer 11 is mixed with sulfur or a sulfur compound, and insoluble sulfur is particularly preferable in order to suppress surface precipitation. The average molecular weight of the insoluble sulfur is preferably 10,000 or more, more preferably 100,000 or more, from the viewpoint that decomposition does not easily occur even at a low temperature and surface precipitation is difficult. Conversely, the average molecular weight of insoluble sulfur is preferably 500,000 or less, more preferably 300,000 or less, in order to improve the dispersibility in rubber.

  The compounding quantity of sulfur or a sulfur compound needs 2 mass parts or more with respect to 100 mass parts of diene rubber components. When the compounding amount of sulfur or sulfur compound is less than 2 parts by mass, the rubber hardness and breaking strength of the side reinforcing rubber layer 11 cannot be sufficiently improved. Conversely, when the amount of sulfur or sulfur compound is increased, blooming or processability may be deteriorated. From such a viewpoint, the amount of sulfur or sulfur compound is preferably 3 parts by mass or more, more preferably 4 parts by mass or more, and preferably 20 parts by mass or less, more preferably 15 parts by mass or less. It is desirable that

  Further, the rubber composition of the side reinforcing rubber layer 11 is blended with 5 to 120 parts by mass of a lamellar alumina powder or fluorine-containing mica having an aspect ratio of 3 to 50 with respect to 100 parts by mass of the diene rubber component. . Of course, only the lamellar alumina powder or only the fluorine-containing mica may be blended in the rubber composition of the side reinforcing rubber layer 11, or these may be blended together. In addition, as shown in FIGS. 2A and 2B, the aspect ratio is the ratio of the maximum major axis a to the thickness b (a / b) of the thin plate-like alumina powder or fluorine-containing mica particles G. ). As shown in FIG. 2A, when the diameter a of the particle G is not constant, the longest distance is defined as the long diameter a. The aspect ratio of the present embodiment is observed with an electron microscope, the maximum major axis a and the thickness b are measured for any 50 particles G, and the average maximum major axis a ′ and the average thickness b ′ are measured. Suppose that it is calculated | required as ratio (a '/ b').

  Further, when the aspect ratio of the lamellar alumina powder and the fluorine-containing mica is less than 3, the reinforcing effect on the side reinforcing rubber layer 11 is lowered, and sufficient rubber hardness cannot be given. Further, when the aspect ratio exceeds 50, these particles are difficult to disperse in the rubber, and as a result, cracks and the like are easily generated, and the breaking strength of the side reinforcing rubber layer 11 is lowered. From such a viewpoint, the aspect ratio of the lamellar alumina powder and the fluorine-containing mica is preferably 5 or more, more preferably 10 or more, and preferably 40 or less, more preferably 30 or less. .

  The average maximum major axis a ′ of the lamellar alumina powder and the fluorine-containing mica is preferably 2 to 30 μm. When the average maximum long particle diameter is less than 2 μm, the side reinforcing rubber layer 11 cannot be provided with sufficient rubber hardness. On the other hand, when the average maximum major axis exceeds 30 μm, the fatigue resistance of the side reinforcing rubber layer 11 is lowered, and the run-flat durability may be lowered. From such a viewpoint, the average maximum major axis of the lamellar alumina powder and the fluorine-containing mica is preferably 5 μm or more, more preferably 10 μm or more, and preferably 25 μm or less, more preferably 20 μm or less.

  Further, when the amount of lamellar alumina powder or fluorine-containing mica is less than 5 parts by mass with respect to 100 parts by mass of the diene rubber component, the side reinforcing rubber layer The rubber hardness and fracture strength of 11 cannot be sufficiently increased, and as a result, the effect of improving the run-flat durability cannot be expected. Conversely, if the content of the lamellar alumina powder or the fluorine-containing mica exceeds 120 parts by mass, these powders are difficult to disperse in the rubber, and heat generation is likely to occur, and the crack resistance strength may be reduced. is there. From such a viewpoint, the blending amount of the lamellar alumina powder or the fluorine-containing mica is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and preferably 80 parts by mass or less, more preferably 60 parts by mass. The mass part or less is desirable.

Moreover, as a fluorine-containing mica, what is represented by the following Formula (2) is preferable.
X _{1/3 to 1} Y _{2 to 3} (Z ₄ O ₁₀ ) F _{1.5 to 2} (2)
However, in formula (2), X ^{Na +, K +, Li +} , Ca 2+, Rb 2+ and one ion selected from the group consisting of ^{Sr 2+,} Y is ^{Mg 2+, Fe 2+, Ni 2+} , Mn One ion selected from the group consisting of ²⁺ , Al ³⁺ , Fe ³⁺ and Li ⁺ , Z represents one ion selected from the group consisting of Al ³⁺ , Si ⁴⁺ , Ce ⁴⁺ , Fe ³⁺ and B ³⁺ . In particular, among those represented by the above formula (2), KMg ₃ AlSiO ₃ O ₁₀ F ₂ , KMg _2.5 Si ₄ O ₁₀ F ₂ , NaMG _2.5 Si ₄ O ₁₀ F ₂ , NaMg ₂ LiSi ₄ O ₁₀ F ₂ or LiMg ₂ LiSi ₄ O ₁₀ F ₂ is desirable. The fluorine-containing mica is preferably synthesized by a production method such as an internal combustion melting method or an external combustion melting method. As a result, it is possible to obtain fluorine mica having a uniform particle size with reduced variation.

  As described above, the rubber composition contains carbon black, sulfur or a sulfur compound, and a thin plate-like alumina powder or a fluorine-containing mica having a predetermined aspect ratio, so that both excellent strength and low heat generation can be achieved. As a result, run-flat durability can be improved.

  In addition, it is preferable that a silane coupling material is added to the rubber composition in combination with either lamellar alumina powder or fluorine-containing mica. Examples of silane coupling materials include bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylpropyl) tetrasulfide, and 3-mercaptopropyltriethoxysilane. , 2-mercaptoethyltrimethoxysilane, and the like. These may be used alone or in combination of two or more. The amount of the silane coupling material is preferably 2 to 20 parts by mass with respect to 100 parts by mass of lamellar alumina powder or fluorine-containing mica (the total amount when used together).

  Moreover, it is preferable to mix | blend a vulcanization accelerator with the said rubber composition. Examples of the vulcanization accelerator include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N′-dicyclohexyl-2- Examples include benzothiazolylsulfenamide (DZ), mercaptobenzothiazole (MBT), dibenzothiazolyl disulfide (MBTS), diphenylguanidine (DPG) and the like. Sulfur accelerators are desirable. Since these are retarded vulcanization accelerators, they are less likely to burn in the production process and have excellent vulcanization characteristics. In addition, the physical properties of rubber after vulcanization are excellent in low heat generation against deformation caused by external force, and have a great effect on improving the durability of run-flat tires.

  In addition to the above, various compounding agents such as stearic acid, zinc oxide, various anti-aging agents, waxes and / or oils can be appropriately blended with the rubber composition as necessary. Moreover, the said rubber composition can be manufactured in accordance with the conventional method about rubber | gum manufacture. That is, a rubber component or a component is kneaded with a Banbury mixer, a kneader, an open roll, etc., extruded into a predetermined cross-sectional shape, incorporated into a raw tire, and then vulcanized to form the side reinforcing rubber layer 11. sell.

In addition, the rubber composition having the above composition has a breaking strength (T _B ) of preferably 10 MPa or more, more preferably 12 MPa or more, and even more preferably 14 MPa or more in physical properties after vulcanization. desirable. Thereby, the load support capability of the side reinforcing rubber layer 11 can be increased, and the run-flat durability can be further improved. The upper limit of the breaking strength is not particularly set, but is usually preferably 30 MPa or less.

Further, the rubber composition preferably has a loss elastic modulus (E ″) and a complex elastic modulus (E ^* ) satisfying the following formula (3).
E ″ / (E ^* ) ² ≦ 7.0 × 10 ⁻⁹ Pa ⁻¹ (3)

E ″ / (E ^* ) ² is also called loss compliance, but when this value is limited to 7.0 × 10 ⁻⁹ Pa ⁻¹ or less, the side reinforcing rubber layer 11 is repeatedly subjected to compressive stress during run flat running. In particular, the loss compliance is preferable in that the amount of heat generation becomes smaller and the thermal deterioration of the rubber can be suppressed over a long period of time, in particular, the loss compliance is 6.0 × 10 ⁻⁹ Pa ^−1. The lower limit value of the loss compliance is not particularly set, but is usually 1.0 × 10 ⁻⁹ Pa ⁻¹ or more.

  In the run-flat tire 1 of the present embodiment, the rim protect rib 12 is protruded from the bead portion 4. As shown in FIG. 3, the rim protect rib 12 is a rib body that protrudes from the reference contour line j so as to cover the rim flange JF and extends continuously in the tire circumferential direction, and extends beyond the tip of the rim flange JF. The reference surface at the position near the tire maximum width point M from the protruding surface portion 12c, the protruding surface portion 12c that protrudes most outward in the tire axial direction, the radially inwardly inclined surface portion 12i that continues smoothly from the protruding surface portion 12c to the bead outer surface. It forms a trapezoidal cross section surrounded by a radially outer sloped portion 12o that is smoothly connected to the contour line j. The inner inclined surface portion 12i is formed as a concave arc surface having a radius of curvature r larger than the arc portion of the rim flange JF, and protects the rim flange JF from curbs and the like during normal running. Further, during run flat running, the inner inclined surface portion 12i leans against and contacts with the arc portion of the rim flange JF, so that the amount of bead deformation can be reduced, which helps to improve steering stability and run flat durability during run flat.

  In the present invention, an aramid fiber is employed in the carcass cord of the carcass ply 6A in order to improve the handling stability and durability during the run-flat running.

  The aramid fiber is known as a highly elastic fiber, and is used for the carcass cord of the run flat tire 1 to enhance the load supporting ability of the tire. Accordingly, for example, the amount of deformation of the tire during run-flat running can be reduced while reducing the weight of the tire by reducing the number of carcass plies, reducing the diameter of the carcass cord, and / or reducing the cord arrangement density (number of cord ends). . In addition, the aramid fiber has excellent heat resistance in which the decrease in elastic modulus at a high temperature of 100 to 150 ° C. is small compared to other organic fiber cord materials. Therefore, it is possible to prevent the carcass cord from being reduced in strength and damaged by the rise in tire temperature during run-flat running, and from causing an increase in the amount of tire deformation due to a drop in elastic modulus and a further increase in tire temperature associated therewith. As a result, run flat durability can be improved. Further, even when the tire temperature rises, the tire rigidity can be increased while maintaining a high elastic modulus, so that the steering stability at the time of run flat can be improved. This achieves higher speed and longer distance in run flat travel.

  On the other hand, aramid fibers tend to have poor fatigue resistance due to their high elastic modulus. Therefore, as shown in FIG. 4, the carcass cord 20 of the present embodiment has a two-strand structure in which two filament bundles 21 (ie, strands 21) of a twisted aramid fiber are twisted together by further twisting. Is adopted, and twisting at this time is performed with a higher twisting coefficient T than in the past.

Here, the “twist coefficient T” is the number of twists of the cord N (unit: times / 10 cm), the total display decitex (total fineness) of one cord is D (unit: dtex), and the specific gravity of the cord material is When ρ, it is shown by the following formula (1).
T = N × √ {(0.125 × D / 2) / ρ} × 10 ⁻³ (1)

  And by increasing the twist coefficient T to the range of 0.50 to 0.70, the fatigue resistance, which is a defect of the aramid fiber cord, can be improved, and the run-flat durability is higher than that of the conventional rayon cord. Can be greatly improved. If the twist coefficient T of the carcass cord 20 is less than 0.50, the effect of improving fatigue resistance is small, and run-flat durability cannot be sufficiently increased. On the contrary, when the twist coefficient T exceeds 0.70, it becomes difficult to twist the cord, which is disadvantageous for productivity. In particular, the lower limit of the twist coefficient T is preferably 0.60 or more, whereby the fatigue resistance of the cord can be further improved and the run-flat durability can be further improved.

  In the carcass cord 20, a two-strand structure is employed in order to exert an excellent reinforcing effect by utilizing the high elasticity that is an important characteristic of the aramid fiber. At that time, a so-called balance twist in which the number of lower twists and the number of upper twists are equal is preferable, but the ratio of the number of twists (number of lower twists / number of upper twists) is in the range of 0.2 to 2.0, preferably 0.8. Within the range of 5 to 1.5, the number of lower twists and the number of upper twists may be made different.

  The total display decitex D (fineness) is not particularly limited, but in the case of a run flat tire, a range of 1500 to 5000 dtex is preferable. The product of the number n of cord ends (5/5 cm) in the carcass ply 6A and the total display decitex D is preferably in the range of 70000 to 150,000. When the product is less than 70,000, the run-flat durability and steering stability are insufficient even though it is an aramid fiber cord. Conversely, when it exceeds 150,000, the rigidity of the carcass 6 becomes excessive and the riding comfort is impaired. There is a risk of unnecessary increase in tire mass and cost. From such a viewpoint, the lower limit of the product D × n is more preferably 100,000 or more, and the upper limit is more preferably 120,000 or less.

  Further, damage to the carcass cord 20 due to fatigue resistance is likely to occur at a portion that undergoes compressive strain when the tire is deformed, that is, at the bead side portion 6b1 of the folded portion 6b as shown in FIG. However, when the rim protect rib 12 is protrudingly provided as in the present embodiment, bead deformation during run-flat running is reduced, and compression distortion is less likely to act on the carcass cord 20. As a result, the fatigue damage of the carcass cord 20 when an aramid fiber is employed can be further effectively suppressed, and the run-flat durability can be further improved. Thus, in the tire using the carcass cord 20 of the aramid fiber, it is preferable to provide the rim protect rib 12 from the viewpoint of suppressing fatigue damage of the cord.

Further, it is desirable that a high elastic rubber having a complex elastic modulus E ^{* of 5} to 13 MPa is used as the topping rubber of the carcass ply 6A. By adopting the high elastic rubber as the topping rubber in this way, the strain acting on the carcass cord 20 can be reduced when the tire is deformed, and further improvement in run-flat durability is achieved. If the complex elastic modulus E ^* is less than 5 MPa, the above effect cannot be sufficiently expected. Conversely, if the complex elastic modulus E ^* exceeds 13 MPa, the rubber becomes too hard and the ride comfort may be lowered. From such a viewpoint, the lower limit of the complex elastic modulus E ^* is preferably 5.5 MPa or more, more preferably 6 MPa or more, and the upper limit is preferably 11 MPa or less, more preferably 9 MPa or less.

  Further, as shown in FIG. 5, in the tire meridional section in the normal internal pressure state, the profile of the tire outer surface 2 </ b> A is formed by a curved surface including a plurality of arcs having different curvature radii. In particular, in the case of the run flat tire 1, the curved surface composed of a plurality of arcs whose curvature radius R gradually decreases from the tire equator point CP, which is the intersection of the tire outer surface 2A and the tire equator plane C, toward the ground contact end side. It is desirable to form a profile. Thereby, the rubber volume of the said side reinforcement rubber layer 11 can be suppressed to the minimum, and the weight reduction of a tire and the improvement of riding comfort can be aimed at.

  More specifically, when a point on the tire outer surface 2A that separates the distance SP of 45% of the maximum tire cross-sectional width SW from the tire equator plane C is P, the radius of curvature RC of the tire outer surface 2A is determined from the tire equator point CP. It is desirable to set so as to gradually decrease until reaching the point P. The “tire maximum cross-sectional width SW” is the maximum width at the reference contour line j of the tire outer surface 2A. The reference contour line j is locally formed on the tire outer surface 2A, for example, characters, figures, symbols, It means a smooth contour line excluding local uneven portions such as the rim protect rib 12.

Further, points on each tire outer surface 2A that separate distances X60, X75, X90, and X100 of 60%, 75%, 90%, and 100% of the half width (SW / 2) of the tire maximum cross-sectional width SW from the tire equatorial plane C, respectively. Are P60, P75, P90 and P100, and the radial distances between the points P60, P75, P90 and P100 on each tire outer surface 2A and the tire equator point CP are Y60, Y75, Y90 and Y100. When the tire cross-section height is SH, the radial distances Y60, Y75, Y90, and Y100 each satisfy the following relationship.
0.05 <Y60 / SH ≦ 0.1
0.1 <Y75 / SH ≦ 0.2
0.2 <Y90 / SH ≦ 0.4
0.4 <Y100 / SH ≦ 0.7

Here, RY60 = Y60 / SH
RY75 = Y75 / SH
RY90 = Y90 / SH
RY100 = Y100 / SH
A range RYi that satisfies the above relationship is illustrated in FIG. As shown in FIG. 5 and FIG. 6, such a profile has a feature that the region of the sidewall portion is short. Therefore, by adopting the run flat tire, the rubber volume of the side reinforcing rubber layer 11 can be reduced. It is possible to achieve a reduction in mass and an improvement in ride comfort in a flat tire. In addition, the profile that satisfies the above relationship has a tread that is very round, so the footprint becomes a vertically long oval shape with a small ground contact width and a large ground contact length, which helps to improve noise performance and hydroplaning performance. (See, for example, Japanese Patent No. 2999489 for its action). When the values of RY60, RY75, RY90, and RY100 are below the respective lower limit values, the tire outer surface 2A is flattened around the tread portion 2, so that the difference in profile from the conventional tire is reduced. On the contrary, if the upper limit value is exceeded, the tire outer surface 2A has a remarkably convex shape centering on the tread portion 2, so that the ground contact width becomes too small to ensure the required driving performance in normal driving.

  In the tire, by predetermining the tire size, the tire flatness, the maximum tire cross-sectional width, the maximum tire height, etc. can be generally determined from the tire standards such as JATMA and ETRTO. Therefore, the RY60, RY75, RY90 and RY100 Can be easily calculated. Accordingly, the tire outer surface 2A is smooth from the tire equator point CP to the point P so as to satisfy the ranges of RY60, RY75, RY90 and RY100 at the respective positions and so that the radius of curvature RC gradually decreases. It can be determined appropriately by drawing a curve.

  In addition, as shown in FIG. 7, the tire has a tire shaft between outermost ends in the tire axial direction where the tire outer surface 2 </ b> A contacts the ground in a state where a load of 80% of the normal load is applied to the tire in the normal internal pressure state. The ground contact width CW, which is a directional distance, is preferably 50 to 65% of the tire maximum cross-sectional width SW. This is because when the ground contact width CW is less than 50% of the maximum tire cross-sectional width SW, wandering performance is degraded, such as being easily wobbled during normal driving, and uneven wear tends to occur due to uneven ground pressure. . When the ground contact width CW exceeds 65% of the tire maximum cross-sectional width SW, the ground contact width becomes excessively large, and it tends to be difficult to achieve both passing noise and hydroplaning performance.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

  Run-flat tires having the structure shown in FIG. 1 were prototyped according to the specifications shown in Table 1, and various performances were tested. In addition, about the side reinforcement rubber layer, it was set as the mixing | blending 1 thru | or 9 shown in Table 2.

  Moreover, the manufacturing method of a side reinforcement rubber layer is as follows. First, according to the formulation shown in Table 2, chemicals other than sulfur and a vulcanization accelerator were kneaded at 150 ° C. for 4 minutes using a Banbury mixer manufactured by Kobe Steel Co., Ltd. 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 3 minutes at 80 ° C. to extrude the unvulcanized rubber composition. And various tire members containing this rubber composition were bonded together according to a conventional method, a green tire was molded, and this was vulcanized, and a run flat tire was manufactured.

Moreover, the detail of the mixing | blending in Table 2 is as follows.
Natural rubber (NR): RSS # 3
Butadiene rubber (BR): VCR412 manufactured by Ube Industries, Ltd. (SPB average particle size: 250 nm, SPB content: 12 parts by mass)
Carbon Black (FEF): Diamond Black E (N2SA: 41 m ² / g, DBP oil absorption: 115 ml / 100 g) manufactured by Mitsubishi Chemical Corporation
Thin plate-like alumina powder: Seraph YFA10030 manufactured by Kinsei Matec Co., Ltd. (aspect ratio: 30, average particle diameter: 10 μm)
Fluorine-containing mica: PDM-8W (KMg ₃ AlSiO ₃ O ₁₀ F ₂ , aspect ratio 35, average particle size 12 μm) manufactured by Topy Industries, Ltd.
Stearic acid: cocoon manufactured by Nippon Oil & Fats Co., Ltd. Zinc oxide: Two types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Anti-aging agent: Antigen 6C (N- (1,3-dimethylbutyl) manufactured by Sumitomo Chemical Co., Ltd. -N'-phenyl-p-phenylenediamine)
Silane coupling agent: Si-75 manufactured by Degussa Japan Co., Ltd.
Sulfur: Insoluble sulfur (Mucron OT manufactured by Shikoku Kasei Kogyo Co., Ltd.)
Vulcanization accelerator: Noxeller NS (Nt-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

Further, the tires have the same specifications except for the parameters listed in Table 1. The common specifications are as follows.
Tire size: 245 / 40ZR18
Carcass: 1 ply, cord angle 90 ° (to tire equator)
Belt layer: Number of belt plies 2, cord angle ± 24 ° (to tire equator)
Side reinforcing rubber layer: Maximum thickness 10.0mm or 8.0mm

Also, the tread profile for each tire is in the range of RY60 = 0.05 to 0.1, RY75 = 0.1 to 0.2, RY90 = 0.2 to 0.4, RY100 = 0.4 to 0.7. The one with substantially the same profile was used.
The test method is as follows.

<Break strength of side reinforcing rubber layer>
A test piece with a thickness of 2 mm was cut from the side reinforcing rubber layer of the run-flat tire, and a tensile test was conducted using No. 3 dumbbells in accordance with JIS-K6251 “Vulcanized rubber and thermoplastic rubber-Determination of tensile properties”. The breaking strength (T _B ) of each formulation was measured. The larger the value, the better.

<Loss compliance>
Using the test piece, a complex elastic modulus E ^* and a loss elastic modulus E ″ were measured, and E ″ / (E ^* ) ² was calculated. The smaller the value of E ″ / (E ^* ) ² , the better the low heat buildup.

<Runflat durability>
Each test tire is assembled on a rim (18x8.5J) from which the valve core has been removed, and run on the drum tester under the conditions of speed (80km / h) and longitudinal load (4.14kN) in a deflated state. The running distance until the tire broke was measured and evaluated by an index with Comparative Example 1 taken as 100. The larger the value, the better.
The test results are shown in Tables 1 and 2.

  As a result of the test, it was confirmed that the run-flat tires of the examples had improved low heat generation and durability during run-flat running compared to the comparative examples.

It is sectional drawing which shows one Embodiment of the run flat tire of this invention. (A), (b) is the expansion perspective view of the particle | grains explaining an aspect-ratio. It is sectional drawing which expands and shows a bead part. It is a side view explaining a carcass cord. It is a diagram which shows the profile of a tire outer surface. It is a diagram which shows the range of RYi in each position of a tire outer surface. It is sectional drawing which expands and shows the tread part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Run flat tire 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 6A Carcass ply 11 Side reinforcement rubber layer 20 Carcass cord

Claims (7)

A run flat tire comprising a carcass extending from a tread portion to a bead core of a bead portion and a bead core of the bead portion, and a side reinforcing rubber layer having a substantially crescent-shaped cross section disposed inside the carcass of the sidewall portion,
The side reinforcing rubber layer is composed of 10 to 100 parts by mass of carbon black having a nitrogen adsorption specific surface area of 30 to 100 m ² / g and a dibutyl phthalate oil absorption of 50 ml / 100 g or more with respect to 100 parts by mass of the diene rubber component. A rubber composition containing 2 or more parts by mass of sulfur or a sulfur compound and 5 to 120 parts by mass of a lamellar alumina powder having an aspect ratio of 3 to 50 or fluorine-containing mica,
The carcass is composed of a carcass ply in which a carcass cord arranged at an angle of 45 to 90 ° with respect to the tire equator is covered with a topping rubber, and the carcass cord has a twist coefficient T expressed by the following formula (1) of 0. A run flat tire characterized by using aramid fibers of 50 to 0.70.
T = N × √ {(0.125 × D / 2) / ρ} × 10 ⁻³ (1)
However, N is the number of twists (times / 10 cm), D is the total display decitex (fineness) of the cord, and ρ is the specific gravity of the cord material. The run-flat tire according to claim 1, wherein the fluorine-containing mica is composed of the following formula (2).
X _{1/3 to 1} Y _{2 to 3} (Z ₄ O ₁₀ ) F _{1.5 to 2} (2)
(In the formula (2), X is one ion selected from the group consisting of Na ⁺ , K ⁺ , Li ⁺ , Ca ²⁺ , Rb ²⁺ and Sr ²⁺ , Y is Mg ²⁺ , Fe ²⁺ , Ni ²⁺ , One ion selected from the group consisting of Mn ²⁺ , Al ³⁺ , Fe ^3+, and Li ⁺ , Z represents one ion selected from the group consisting of Al ³⁺ , Si ⁴⁺ , Ce ⁴⁺ , Fe ^3+, and B ³⁺ , respectively. Represents.) The fluorine-containing mica is KMg ₃ AlSiO ₃ O ₁₀ F ₂ , KMg _2.5 Si ₄ O ₁₀ F ₂ , NaMG _2.5 Si ₄ O ₁₀ F ₂ , NaMg ₂ LiSi ₄ O ₁₀ F ₂ or LiMg ₂ LiSi _4. The run-flat tire according to claim 2, which is any one of O ₁₀ F ₂ .   The run-flat tire according to any one of claims 1 to 3, wherein the carcass cord has the twist coefficient T of 0.60 to 0.70. The run-flat tire according to any one of claims 1 to 4, wherein the topping rubber of the carcass ply has a complex elastic modulus E ^{* of 5} to 13 MPa.   In the tire meridional section including the tire center in the normal internal pressure state mounted on the normal rim and filled with the normal internal pressure, the profile of the tire outer surface is grounded from the tire equator point CP, which is the intersection of the tire outer surface and the tire equatorial plane C. The run-flat tire according to any one of claims 1 to 5, wherein the run-flat tire is formed by a curved surface composed of a plurality of arcs whose radius of curvature gradually decreases toward an end side. When the tire outer surface profile is P, a point on the tire outer surface separating a distance SP of 45% of the tire maximum cross-sectional width SW from the tire equatorial plane C is
The radius of curvature RC of the outer surface of the tire gradually decreases from the tire equator point CP to the point P, and
Points on the outer surface of the tire separating distances X60, X75, X90 and X100 of 60%, 75%, 90% and 100% of the half width (SW / 2) of the tire maximum cross-sectional width SW from the tire equatorial plane C, respectively , When the radial distance from the tire equator point CP is Y60, Y75, Y90 and Y100, respectively, and the tire cross-section height is SH,
0.05 <Y60 / SH ≦ 0.1
0.1 <Y75 / SH ≦ 0.2
0.2 <Y90 / SH ≦ 0.4
0.4 <Y100 / SH ≦ 0.7
The run flat tire according to claim 6, satisfying the relationship:

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