JP2009137446A - Run flat tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve durability in run flat running while suppressing increase in a tire mass. <P>SOLUTION: In the run flat tire 1 equipped with a sidewall-reinforcing rubber layer 11, as a carcass cord 20, an aramid fiber cord 21 having a cord twisting coefficient T of 0.50-0.70 is used. The sidewall-reinforcing rubber layer 11 is composed of a rubber composition having 30-100 m<SP>2</SP>/g nitrogen adsorption specific surface area, 10-100 parts by mass of carbon black having a dibutyl phthalate oil absorption amount of 50 ml/100 g or more, 5-120 parts by mass of a needle-like natural ore having an aspect ratio of 3-50 and an average diameter of 2-800 μm, and 2 parts by mass or more of sulfur or a sulfur compound. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a run-flat tire that can travel a relatively long distance even in a deflated state in which air in the tire has escaped due to puncture or the like.

  As such a run-flat tire, a side reinforcing rubber layer having a crescent-shaped cross section is provided on the inner side (lumen side) and side wall portion of the carcass forming the skeleton of the tire, and the load of the tire in a deflated state is determined by the side reinforcing rubber. A so-called side-reinforcing type that enables run-flat running by supporting with a layer is known.

  With this type of tire, the tire temperature during run-flat driving is significantly higher than during normal driving in an inflated state, so from the standpoint of ensuring run-flat durability, rayon with excellent heat resistance as a carcass cord Fiber cord is used. On the other hand, since the run flat travel distance largely depends on the side reinforcing rubber layer, in order to improve the run flat running performance and durability, the rubber volume (length and thickness) and / or rubber of the side reinforcing rubber layer. Breaking due to this deformation is suppressed by increasing the elastic modulus and suppressing tire deformation.

  In view of the trend toward higher speed and longer distance in recent run-flat travel, further improvement in run-flat durability is strongly desired.

  However, an increase in the rubber volume leads to an increase in tire mass, and there is a problem that fuel efficiency and riding comfort are deteriorated during normal driving. Also, increasing the rubber elastic modulus by increasing the amount of reinforcing filler such as carbon black will increase the exothermic properties of the rubber, and increase the vulcanization density by using a large amount of vulcanizing agent and vulcanization accelerator. When increasing the rubber elastic modulus, there is a problem that the breaking strength of the rubber is reduced and the breaking strength is lowered. I haven't achieved a satisfactory result.

  Therefore, the present invention basically employs an aramid fiber cord having a specified twist coefficient for the carcass cord and a rubber composition in which acicular natural ore such as wollastonite is blended for the side reinforcing rubber layer. Thus, an object of the present invention is to provide a run-flat tire capable of greatly improving run-flat durability while suppressing an increase in tire mass.

JP 2005-264150 A Japanese Patent No. 2999489

In order to achieve the above object, the invention of claim 1 of the present application includes a carcass extending from a tread portion through a sidewall portion to a bead core of a bead portion, and a central portion disposed on the sidewall portion and having a maximum thickness. A run-flat tire comprising a crescent-shaped side reinforcing rubber layer extending in the radial direction with a reduced thickness,
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 formed by a curved surface composed of a plurality of arcs with different curvature radii,
And the carcass comprises a carcass ply in which aramid fiber cords arranged at an angle of 45 to 90 ° with respect to the tire circumferential direction are covered with a topping rubber,
The aramid fiber cord has a twist coefficient T represented by the following formula (1) in a range of 0.50 to 0.70,
Moreover, the side reinforcing rubber layer is composed of 10 to 10 parts by weight 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 per 100 parts by mass of the diene rubber component. It consists of a rubber composition containing 5 to 120 parts by mass of acicular natural ore with an aspect ratio of 3 to 50 and an average diameter of 2 to 800 μm, and 2 or more parts of sulfur or a sulfur compound. It is characterized by.
T = N × √ {(0.125 × D / 2) / ρ} × 10 ⁻³ −−− (1)
(However, N is the number of upper twists (times / 10 cm), D is the total display decitex (fineness), and ρ is the specific gravity of the cord material.)

  The invention according to claim 2 is characterized in that the acicular natural ore is wollastonite.

  In the invention of claim 3, the rubber composition is characterized in that the diene rubber component contains 20 to 80% by mass of butadiene rubber.

In the invention of claim 4, the side reinforcing rubber layer has a breaking strength of 10 MPa or more, and the loss elastic modulus (E ″) and the complex elastic modulus (E *) satisfy the following formula: Yes.
E ″ / (E *) ² ≦ 7.0 × 10 ⁻⁹ Pa ⁻¹

  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 specified by the standard for each tire. The maximum air pressure described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INPRESSION 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. The “regular load” is the load specified by the standard for each tire. The maximum load capacity listed in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” is the maximum load capacity for JATMA and TRA for TRA. If the value is ETRTO, it is "LOAD CAPACITY".

  The present invention employs an aramid fiber cord that is particularly excellent in heat resistance as the carcass cord. Therefore, the cord damage due to the temperature rise during the run flat traveling can be suppressed. Moreover, since aramid fiber cords are highly elastic and can enhance load carrying capacity, combined with the aforementioned heat resistance improvement, run flat durability can be improved. This makes it possible to reduce the volume of the reinforcing rubber layer.

  Further, a rubber composition in which carbon black, acicular natural ore, and sulfur or a sulfur compound are blended in the side reinforcing rubber layer is employed. Since this rubber composition is excellent in low heat build-up and breaking strength as shown in “Best Mode for Carrying Out the Invention”, an increase in tire mass is achieved by a synergistic effect with the use of the aramid fiber cord. The run-flat durability can be greatly improved while keeping low.

  However, since aramid fibers are inferior in fatigue resistance, when used in carcass cords, there is a risk that run-flat durability will be reduced. Therefore, in the present invention, by limiting the twist coefficient T to a range of 0.50 to 0.70, fatigue resistance is overcome while exhibiting the above effects.

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

  In FIG. 1, a run flat tire 1 according to the present embodiment includes a carcass 6 extending from a tread portion 2 through a sidewall portion 3 to a bead core 5 of a bead portion 4, and arranged on the sidewall portion 3 and having a run flat function. A side reinforcing rubber layer 11 having a crescent-shaped cross section for securing.

  The carcass 6 includes one or more carcass plies in which a carcass cord 20 (shown in FIGS. 4A and 4B) arranged at an angle of 45 to 90 ° with respect to the tire circumferential direction is covered with a topping rubber 25. 6A. In this example, a case is shown in which a carcass ply 6A is formed by arranging carcass cords at an angle of 80 to 90 °. The carcass ply 6A includes a series of ply folding portions 6b that are folded around the bead core 5 from the inner side to the outer side in the tire axial direction on both sides of the ply main body portion 6a straddling the bead cores 5 and 5.

  A bead apex rubber for bead reinforcement made of a hard rubber having a rubber hardness of, for example, 65 to 98 degrees and extending radially outward from the bead core 5 between the ply main body portion 6a and the ply folded portion 6b. 8 is arranged. In the present specification, “rubber hardness” means the hardness by durometer type A measured at a temperature of 23 ° C. 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 is excessively increased. This is disadvantageous for the present invention, such as causing deterioration of 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 this example, the ply turn-up portion 6b of the carcass 6 rolls up over the bead apex rubber 8 radially outward, and its outer end portion 6be is sandwiched between the ply main body portion 6a and the belt layer 7. It has a so-called ultra-high turn-up folding structure that terminates in a short time. Thereby, the side wall part 3 can be effectively reinforced using the one carcass ply 6A. Further, since the outer end portion 6be of the ply turn-up portion 6b is separated from the sidewall portion 3 that is greatly bent during run-flat travel, damage starting from the outer end portion 6be can be suitably suppressed. The tire axial direction width EW of the overlapping portion between the ply turn portion 6b and the belt layer 7 is preferably 5 mm or more, more preferably 10 mm or more, and the upper limit is preferably 40 mm or less, and more preferably 30 mm or less from the viewpoint of weight reduction. 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.

  A belt layer 7 for reinforcing the tread is disposed outside the carcass 6 in the radial direction and inside the tread portion 2. The belt layer 7 is composed of two or more belt plies 7A, 7B in this example, in which steel belt cords arranged at an angle of, for example, 10 to 35 ° with respect to the tire circumferential direction are covered with a topping rubber. It is formed. The belt layer 7 is improved in belt rigidity when the belt cords cross each other between the plies. The width of the belt layer 7 (in this example, the width of the wide belt ply 7A) BW is preferably 0.70 to 0.95 times the maximum tire width SW, so that almost the entire area of the tread portion 2 can be obtained. A tagging effect is applied over the entire range, and a special profile of the tire outer surface described later is maintained. The tire maximum width SW is a tire axial direction distance between the tire maximum width positions M and M in the normal internal pressure state described above. In addition, the tire maximum width position M is determined from a tire cross-sectional contour shape (hereinafter sometimes referred to as a reference contour j) excluding characters, patterns, rim protectors 12 and the like provided on the sidewall portion 3 in a normal internal pressure state. Specifically, the height is substantially the same as the position m of the maximum width of the carcass 6.

  A band layer (not shown) can be provided outside the belt layer 7 mainly for the purpose of improving high-speed running performance. This band layer is composed of one or more band plies in which a band cord wound spirally at an angle of 5 ° or less with respect to the tire circumferential direction is covered with a topping rubber. The band ply includes a pair of left and right edge bands that cover only the outer end portion of the belt layer 7 in the tire axial direction, and a full band that covers substantially the entire width of the belt layer 7, and these are used alone or in combination. .

  Moreover, in this example, the case where the rim protector 12 is protrudingly provided by the said bead part 4 is illustrated. As shown in FIG. 2, the rim protector 12 is a rib body that protrudes from the reference contour j so as to cover the rim flange JF, and protrudes most outward in the tire axial direction beyond the tip of the rim flange JF. Radial direction smoothly connected to the reference contour line j at a position in the vicinity of the tire maximum width position M from the surface portion 12c, a radially inwardly inclined surface portion 12i that continuously extends from the protruding surface portion 12c to the bead outer surface, and the protruding surface portion 12c. It forms a trapezoidal cross section surrounded by the outer slope portion 12o. The inner slope portion 12i is formed of a concave arc surface having a larger radius of curvature r than the arc portion of the rim flange JF, and protects the rim flange JF from curbs and the like during normal running. Also, during run flat running, the inner slope 12i leans against and contacts 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 cord 21 is employed for the carcass cord 20.

  The aramid fiber has a property that the decrease in elastic modulus is small compared to other organic fiber cord materials even at a high temperature of 100 to 150 ° C. and is excellent in heat resistance. Accordingly, it is possible to prevent the carcass cord from being reduced in strength and causing damage due to a rise in tire temperature during run-flat running, or an increase in tire deformation due to a drop in elastic modulus and a further increase in tire temperature associated therewith. . Furthermore, since the aramid fiber cord is highly elastic, the load supporting ability can be enhanced by using it for the carcass 6. Therefore, tire deformation at the time of run-flat can be reduced, and in combination with the above-described improvement in heat resistance, run-flat durability can be further improved. In addition, since the burden of the load supporting capacity in the side reinforcing rubber layer 11 can be reduced by the amount of increase in the load supporting capacity, the maximum thickness t of the side reinforcing rubber layer 11 is reduced as compared with the conventional tire mass. Can be reduced, and the ride comfort can be improved.

  However, since the aramid fiber has a high elastic modulus and is inferior in fatigue resistance, there is a problem that the aramid fiber cord causes fatigue fracture due to large tire deformation during run-flat running. Therefore, in this invention, the aramid fiber cord 21 is formed with the twist coefficient T in the range of 0.50-0.70 higher than before. In this example, as schematically shown in FIG. 4B, two aramid fiber filament bundles 22 (that is, strands 22) twisted together as aramid fiber cord 21 are twisted together with an upper twist. A twisted structure is adopted.

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

  And by increasing the twist coefficient T to a range of 0.50 to 0.70, it exhibits high load supporting ability while overcoming fatigue breakage of the cord during run flat running, and the excellent run flat durability described above. Can be played. If the twist coefficient T is less than 0.50, the effect of improving fatigue resistance is insufficient, fatigue fracture during run-flat running cannot be suppressed, and conversely the run-flat durability is impaired. If the twist coefficient T exceeds 0.70, the twisting process of the cord becomes difficult and disadvantageous to productivity, and the high elasticity that is an important characteristic of the aramid fiber is not fully utilized, and the elastic modulus of the cord is reduced. This is disadvantageous to the effect of improving the run-flat durability, for example, the load carrying capacity is reduced. From such a viewpoint, the lower limit of the twist coefficient T is particularly preferably 0.60 or more.

  Further, the carcass cord 20 employs a two-strand structure in order to exhibit an excellent load supporting ability by utilizing the high elasticity 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. Further, the product (n × D) of the number n of cord ends (5/5 cm) and the total display decitex D in the carcass ply 6A is preferably in the range of 70000 to 150,000. If the strength is insufficient and, on the other hand, exceeds 150,000, the carcass rigidity becomes excessive, resulting in a disadvantage in ride comfort and an unnecessary increase in mass and material 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, the fatigue rupture of the carcass cord 20 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 ply folded portion 6b as shown in FIG. However, in this example, since the rim protector 12 is provided so as to protrude from the bead portion 4 as described above, the bead deformation during the run-flat running is reduced, and the compressive strain hardly acts on the carcass cord 20. As a result, the fatigue fracture of the carcass cord 20 when an aramid fiber is employed can be further suppressed, and the run-flat durability can be further improved. In other words, in the tire using the aramid fiber for the carcass cord 20, it is preferable to use the rim protector 12 from the viewpoint of suppressing fatigue breakage of the cord.

  In this example, as the topping rubber 25 of the carcass ply 6A, a rubber having a complex elastic modulus (E *) of 5 MPa or more and higher elasticity than the conventional carcass topping rubber is used. The complex elastic modulus (E *) of the conventional carcass topping rubber is about 3.8 MPa. By adopting high-elasticity rubber as the topping rubber in this way, the strain applied to the carcass cord 20 when the tire is deformed can be reduced, the fatigue fracture of the carcass cord 20 can be further suppressed, and the run-flat durability can be further improved. Yes. If the complex elastic modulus (E *) is less than 5 MPa, the above effect cannot be expected. Conversely, if the complex elastic modulus (E *) is more than 13 MPa, the rubber becomes too hard and the ride comfort deteriorates at a stretch. From such a viewpoint, the lower limit of the complex elastic modulus (E *) is preferably 5.5 MPa or more, 6 MPa or more, 7 MPa or more, more preferably 8 MPa or more, and the upper limit is preferably 12 MPa or less.

  Next, the side reinforcing rubber layer 11 has a crescent-shaped cross section extending gradually from the central portion 11a having the maximum thickness t 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 belt 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 belt layer 7 is 0 to 50 mm. It is preferable to prevent the occurrence of a rigid step at the outer end 11o and the inner end 11i.

  In the present example, the side reinforcing rubber layer 11 is disposed on the inner side (tire lumen side) of the ply main body portion 6a of the carcass 6. Therefore, when the sidewall portion 3 is bent and deformed, a compressive load is mainly applied to the side reinforcing rubber layer 11, and a tensile load is mainly applied to the carcass ply 6A having the cord material. Since rubber is strong against compressive load and cord material is strong against tensile load, 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 tire during run flat running Can be effectively reduced.

  Reference numeral 13 in the drawing denotes an inner liner rubber, which is arranged in a toroid shape so as to include the inside of the side reinforcing rubber layer 11 and substantially straddle between the bead portions 4 and 4 in order to maintain the tire internal pressure. ing. The inner liner rubber 13 is made of a low air permeability rubber including gas barrier properties such as butyl rubber, halogenated butyl rubber and / or brominated butyl rubber.

  Next, the side reinforcing rubber layer 11 is formed from a rubber composition in which a rubber component is blended with at least carbon black, acicular natural ore, and sulfur or a sulfur compound. In particular, acicular natural ores such as wollastonite have the effect of increasing the breaking strength of rubber while suppressing heat generation, and can greatly contribute to the improvement of run-flat durability.

  Specifically, as the rubber component, natural rubber (NR), butadiene rubber (BR), syndiotactic-1,2-polybutadiene (1,2BR), styrene-butadiene copolymer rubber (SBR), isoprene rubber (IR), acrylonitrile-butadiene copolymer rubber (NBR), chloroprene rubber (CR), styrene-isoprene-butadiene copolymer rubber (SIBR), styrene-isoprene copolymer rubber, isoprene-butadiene copolymer rubber and other diene rubbers These may be used alone or in combination of two or more.

  However, it is preferable to contain 20% by mass or more of BR as the rubber component, and if the BR content is less than 20% by mass, the exothermic property tends to be high. Further, the upper limit of the BR content is preferably 80% by mass or less, more preferably 60% by mass or less. If the content exceeds 80% by mass, the rubber strength tends to decrease.

The carbon black preferably has a nitrogen adsorption specific surface area (N ₂ SA) of 30 m ² / g or more, more preferably 35 m ² / g or more. When N ₂ SA is less than 30 m ² / g, the reinforcing property is insufficient and sufficient durability cannot be obtained. Further, the upper limit of N ₂ SA is preferably 100 m ² / g or less, more preferably 80 m ² / g or less, and further preferably 60 m ² / g or less. When N ₂ SA exceeds 100 m ² / g, the exothermic property is high. Become.

  The carbon black preferably has a dibutyl phthalate oil absorption (DBP oil absorption) of 50 ml / 100 g or more, 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.

  The carbon black content is 10 parts by mass or more, preferably 20 parts by mass or more, and more preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount of carbon black is less than 10 parts by mass, sufficient rubber strength cannot be obtained. The carbon black content is 100 parts by mass or less, preferably 70 parts by mass or less, more preferably 60 parts by mass or less. When the carbon black exceeds 100 parts by mass, the compounding viscosity increases and it becomes difficult to knead and extrude the rubber.

  Next, as the acicular natural ore, wollastonite is particularly preferable from the viewpoint of safety. The aspect ratio of this acicular natural ore (the ratio L / D of the maximum length L to the diameter D) is 3 or more, preferably 5 or more, more preferably 10 or more. If the aspect ratio of the acicular natural ore is less than 3, sufficient rubber hardness cannot be obtained. The aspect ratio of the acicular natural ore is 30 or less, preferably 20 or less. When the aspect ratio is larger than 30, the dispersion in rubber is lowered and the breaking strength is lowered. The aspect ratio is obtained as L / D by observing the needle-like natural ore with an electron microscope, measuring the diameter and length of 50 arbitrary particles, and calculating the average diameter D and the average length L.

  The average diameter of the acicular natural ore is 2 μm or more, preferably 5 μm or more, more preferably 8 μm or more. When the average diameter is less than 2 μm, a sufficient average length cannot be obtained, and a sufficient rubber hardness cannot be obtained. Moreover, the average length of acicular natural ore is 6 micrometers or more, Preferably it is 10 micrometers or more, Furthermore, it is 30 micrometers or more. If it is less than 6 μm, sufficient strength cannot be obtained. The upper limit of the average length is 800 μm or less, preferably 600 μm or less, and further 300 μm or less. When it exceeds 800 μm, the dispersion becomes poor and the bending fatigue resistance is lowered.

  The compounding amount of the acicular natural ore is 5 parts by mass or more, preferably 10 parts by mass or more, and particularly preferably 15 parts by mass or more with respect to 100 parts by mass of the rubber component. When the blending amount is less than 5 parts by mass, the effect obtained by blending acicular natural ore cannot be sufficiently obtained. Moreover, the compounding quantity of acicular natural ore is 120 mass parts or less, Preferably it is 80 mass parts or less, Most preferably, it is 60 mass parts or less. If the blending amount exceeds 120 parts by mass, it will be difficult to disperse into rubber and heat will be generated easily.

  Moreover, it is preferable to add a silane coupling agent to the rubber composition of the side reinforcing rubber layer 11 in combination with the acicular 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 thereof include triethoxysilane and 2-mercaptoethyltrimethoxysilane, and these can be used alone or in any combination.

  The sulfur or sulfur compound used in the rubber composition is preferably insoluble sulfur in terms of suppressing sulfur surface precipitation. As the insoluble sulfur, sulfur having an average molecular weight of 10,000 or more, particularly 100,000 or more and 500,000 or less, particularly 300,000 or less is preferably used. 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 the sulfur or sulfur compound is preferably 2 parts by mass or more, more preferably 3 parts by mass or more with respect to 100 parts by mass of the rubber component, and the upper limit thereof is 10 parts by mass or less, and further 8 parts by mass. The following is preferable. 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.

  Furthermore, the rubber composition of the side reinforcing rubber layer 11 may contain zinc oxide, wax, stearic acid, oil, an anti-aging agent, a vulcanization accelerator, and the like used for normal rubber compounding.

  The compounds used as the vulcanization accelerator are various, but among them, the sulfenamide accelerator is a delayed vulcanization accelerator, and is not easily burned in the production process, and has excellent vulcanization characteristics. Used most often. In addition, rubber compounding using a sulfenamide accelerator has low heat build-up with respect to deformation due to external force even in rubber physical properties after vulcanization, so that the greatest object of the present invention is to improve the durability of run flat tires. Great effect.

  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.

  Such a rubber composition can exhibit excellent low heat buildup and breaking strength (TB) in the rubber physical properties after vulcanization, and therefore, due to a synergistic effect with the adoption of the aramid fiber cord, It is possible to greatly improve the run flat durability while keeping the increase in mass low.

Here, the breaking strength (TB) of the side reinforcing rubber layer 11 is 10 MPa or more, more preferably 12 MPa or more, and further preferably 14 MPa or more, and if it is less than 10 MPa, it is easily broken by bending deformation during run flat running, As a result, run-flat durability is significantly reduced. In the side reinforcing rubber layer 11, the loss elastic modulus (E ″) and complex elastic modulus (E *) preferably satisfy the following formulas.
E ″ / (E *) ² ≦ 7.0 × 10 ⁻⁹ Pa ⁻¹

When E ″ / (E *) ² exceeds 7.0 × 10 ⁻⁹ Pa ⁻¹ , heat generation becomes large due to bending deformation at the time of run-flat running, which promotes thermal deterioration of rubber and results in early destruction. From this point of view, E ″ / (E *) ² is more preferably 6.0 × 10 ⁻⁹ Pa ⁻¹ or less.

And when the said rubber | gum physical property is employ | adopted, the said breaking strength (TB) and E '' / (E *) ² can be easily set to the above-mentioned range.

  Next, in the tire meridional section in the normal internal pressure state, the profile of the tire outer surface 2A is formed by a curved surface including a plurality of arcs having different curvature radii. In particular, in the case of a run-flat tire, the profile is defined by a curved surface including 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 contact end side. Is preferably formed. As a result, the rubber volume of the side reinforcing rubber layer 11 can be further reduced to further reduce the weight of the tire and improve the riding comfort. In particular, by adopting a special profile as proposed in Japanese Patent No. 2999489, the above-described effects can be further enhanced.

  More specifically, as shown in FIG. 4, when a point on the tire outer surface 2A that separates the distance SP of 45% of the maximum tire width SW from the tire equatorial plane C is P, the radius of curvature RC of the tire outer surface 2A is The tire equator point CP is set so as to gradually decrease from the point E to the point P.

  Further, points on each tire outer surface 2A separating the distances X60, X75, X90 and X100 of 60%, 75%, 90% and 100% of the half width (SW / 2) of the tire maximum width SW from the tire equatorial plane C, respectively. Let P60, P75, P90 and P100. The radial distances between the points P60, P75, P90 and P100 on the tire outer surface 2A and the tire equator point CP are Y60, Y75, Y90 and Y100.

When the tire cross-sectional height, which is the radial height from the bead base line BL to the tire equator point CP in the normal internal pressure state, is SH, the radial distances Y60, Y75, Y90, and Y100 are as follows: It is characterized by satisfying the 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
FIG. 4 illustrates a range RYi that satisfies the above relationship. As shown in FIGS. 4 and 5, in the profile satisfying the above relationship, since the tread is very round, the footprint has a shape with a small ground contact width and a large ground contact length, and noise performance and hydroplaning performance. Helps improve.

  In such a special profile, since the region of the sidewall portion 3 is short, the rubber volume of the side reinforcing rubber layer 11 can be reduced by adopting it in the run flat tire 1, and the mass reduction in the run flat tire can be reduced. Further improvement in ride comfort can be achieved. However, in the tread portion 2 having a large rubber volume, the amount of deformation is larger than that of a tire having a normal profile, and heat generation is large. Therefore, an aramid fiber carcass cord with improved heat resistance can be more advantageous from the viewpoint of heat resistance for a tire of this special profile.

  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 a tire size of 245 / 40R18 having the structure shown in FIG. 1 were prototyped according to the specifications shown in Table 1, and the run-flat durability of each sample tire was tested. The results are shown in Table 1. Except as described in Table 1, the specifications are substantially the same.
-Carcass is the number of plies (1), cord angle (90 °),
・ The belt layer consists of the number of plies (2), cord angle (+ 24 ° / -24 °), steel cord (2 + 7 / 0.22), number of cords driven (24 / 5cm),
It is said.

In Table 1, the twist coefficient T is represented by the following formula (1).
T = N × √ {(0.125 × D / 2) / ρ} × 10 ⁻³ −−− (1)
The specific gravity ρ of the rayon fiber cord is 1.51, and the specific gravity ρ of the aramid fiber cord is 1.44.

  As a tread profile, RY60 = 0.06, RY75 = 0.08, RY90 = 0.19, RY100 = 0.57 in the normal profile, and RY60 = 0.09, RY75 = 0.14 in the special profile. RY90 = 0.37 and RY100 = 0.57.

  Further, as a side reinforcing rubber layer, the overlapping length Wo = 15 mm with the belt layer, the overlapping length Wi = 10 mm with the bead apex rubber, the length L = 30 mm in the tire radial direction, and the total length S along the thickness center line S = 35 mm and maximum thickness t = 7 mm.

The compositions of the rubber compositions G1 and G2 used for the side reinforcing rubber layer are shown in Table 2, and the materials in Table 2 are shown below.
NR: RSS # 3,
・ BR: VCR412 manufactured by Ube Industries, Ltd.
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
Needle-like natural ore (wollastonite): Sakai Kogyo Co., Ltd. NYAD-G (L600 μm, D40 μm, aspect ratio 15),
・ Stearic acid: Agate made 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 manufactured by Sumitomo Chemical Co., Ltd.
・ Insoluble sulfur: Shikoku Kasei Kogyo Co., Ltd.'s mucron OT,
-Vulcanization accelerator: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Co., Ltd.

The test method is as follows.
<Break strength (TB)>
A sheet having a thickness of 2 mm was cut out from the side reinforcing rubber layer of the tire, and the breaking strength (TB) was measured according to JIS K6251.

<E ”/ (E *) ² >
In accordance with the provisions of JIS-K6394, using a viscoelasticity spectrometer manufactured by Iwamoto Seisakusho Co., Ltd., E "(loss elastic modulus), E * (complex Elastic modulus) was measured to determine E ″ / (E *) ² .

<Runflat durability>
The tire is mounted on a rim (18 × 8.5 J) from which the valve core has been removed, and in the deflated state, the speed (80 km / h), longitudinal load (65% of normal load), room temperature (38 °) on the drum tester The travel distance until the tire breaks is measured under the condition of ± 2 °), and displayed as an index with Comparative Example 4 as 100. The larger the value, the better the run flat durability.

It is sectional drawing which shows one Example of the run flat tire of this invention. It is the principal part enlarged view. (A) is sectional drawing which shows a carcass ply, (B) is a perspective view which shows 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.

Explanation of symbols

2 Tread portion 3 Side wall portion 4 Bead portion 5 Bead core 6 Carcass 6A Carcass ply 11 Side reinforcing rubber layer 20 Carcass cord 21 Aramid fiber cord 25 Topping rubber

Claims (4)

A carcass that extends from the tread part to the side wall part to the bead core of the bead part, and a crescent-shaped side reinforcement that extends in the radial direction from the central part that is arranged in the side wall part and has the maximum thickness. A run-flat tire comprising a rubber layer,
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 formed by a curved surface composed of a plurality of arcs with different curvature radii,
And the carcass comprises a carcass ply in which aramid fiber cords arranged at an angle of 45 to 90 ° with respect to the tire circumferential direction are covered with a topping rubber,
The aramid fiber cord has a twist coefficient T represented by the following formula (1) in a range of 0.50 to 0.70,
Moreover, the side reinforcing rubber layer is composed of 10 to 10 parts by weight 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 per 100 parts by mass of the diene rubber component. It consists of a rubber composition containing 5 to 120 parts by mass of acicular natural ore with an aspect ratio of 3 to 50 and an average diameter of 2 to 800 μm, and 2 or more parts of sulfur or a sulfur compound. Run-flat tire characterized by.
T = N × √ {(0.125 × D / 2) / ρ} × 10 ⁻³ −−− (1)
(However, N is the number of upper twists (times / 10 cm), D is the total display decitex (fineness), and ρ is the specific gravity of the cord material.)   The run-flat tire according to claim 1, wherein the acicular natural ore is wollastonite.   The run-flat tire according to claim 1 or 2, wherein the rubber composition contains 20 to 80 mass% of butadiene rubber in a diene rubber component. The side reinforcing rubber layer has a breaking strength of 10 MPa or more, and the loss elastic modulus (E ″) and the complex elastic modulus (E *) satisfy the following formulas: Run-flat tire according to crab.
E ″ / (E *) ² ≦ 7.0 × 10 ⁻⁹ Pa ⁻¹

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