JP6227492B2 - Run flat tire - Google Patents

Description

  The present invention relates to a run flat tire.

  There is a pneumatic tire called a run-flat tire that can travel a certain distance even when the air pressure inside the tire is reduced to 0 kPa due to a failure such as puncture. As a technique for enabling run-flat running with such an internal pressure lowered, it is known to reinforce the sidewall portion by providing a side reinforcing rubber portion on the inner surface of the sidewall portion.

  In order to suppress deformation of the tire during run-flat running, a rubber composition with a high hardness is often used for the side-reinforcing rubber, but this is because the temperature of the side reinforcing rubber becomes higher during run-flat running. Runflat durability may be reduced.

  Conventionally, a reinforcing structure in which the side reinforcing rubber part is divided into a plurality of parts has been proposed. For example, in Patent Document 1, a side reinforcing rubber portion is sandwiched between a relatively high hardness first reinforcing rubber layer, a relatively low hardness second reinforcing rubber layer adjacent to the outer side in the tire width direction, and a carcass ply. And a relatively hard third reinforcing rubber layer disposed on the outer side in the tire width direction. In Patent Document 2, the side reinforcing rubber portion is divided into two layers, an inner layer and an outer layer, and the inner layer is composed of a rubber composition containing a co-crosslinking agent and a peroxide, and the outer layer is made of peroxide, sulfur, and a sulfur compound. It is disclosed that it comprises a rubber composition containing it. Patent Document 3 discloses that the side reinforcing layer is divided into two in the tire radial direction, and the inner reinforcing layer is configured using a thermoplastic resin or a thermoplastic elastomer. However, it is not disclosed to use a rubber composition in which the tensile stress at high temperature is equal to or higher than the tensile stress at normal temperature in the inner reinforcing layer of the side reinforcing rubber portion divided into two layers inside and outside in the tire width direction, In terms of run-flat durability, it was not always sufficient.

JP 2004-345385 A JP 2007-32127 A JP 2011-235687 A

  An object of this invention is to provide the run flat tire which can improve run flat durability.

  A run flat tire according to the present invention includes a tread portion, a pair of sidewall portions extending radially inward from both ends of the tread portion, and a pair of bead portions provided radially inward of the sidewall portion. A carcass ply extending from the tread portion through the sidewall portion to the bead portion and locked by the bead portion, and a side provided on the sidewall portion to reinforce the sidewall portion And a reinforced rubber part. The side reinforcing rubber portion includes an outer reinforcing layer disposed on the tire inner surface side of the carcass ply and an inner reinforcing layer disposed on the tire inner surface side of the outer reinforcing layer. The inner reinforcing layer has a ratio (M50H / M50N) of a tensile stress (M50H) at 50% elongation at a measurement temperature of 100 ° C to a tensile stress (M50H) at 50% elongation at a measurement temperature of 23 ° C of 1.0. It consists of the rubber composition which is 1.3 or less. The outer reinforcing layer has a ratio (M50h / M50n) of a tensile stress (M50h) at 50% elongation at a measurement temperature of 100 ° C to a tensile stress (M50n) at 50% elongation at a measurement temperature of 23 ° C is 0.1. It consists of a rubber composition that is less than 1.0. The tensile stress (M50H) at the time of 50% elongation of the inner reinforcing layer at a measurement temperature of 100 ° C. is larger than the tensile stress (M50h) at the time of 50% elongation of the outer reinforcing layer at a measurement temperature of 100 ° C.

  According to the present invention, the inner reinforcing layer and the outer reinforcing layer are provided as the side reinforcing rubber portions, and the outer reinforcing layer on the carcass ply side is made of the low-rigidity rubber composition, and the inner side disposed on the inner side. The reinforcement layer is made of a rubber composition whose tensile stress at high temperature is equal to or higher than that at normal temperature, so that excessive deformation of the sidewall during run-flat running is suppressed and run-flat durability is achieved. Can be improved.

Half sectional view of a run flat tire according to an embodiment Half sectional view of a run flat tire according to another embodiment Cross-sectional view of the test road used to evaluate the passability

  As shown in FIG. 1, a run flat tire according to one embodiment is a pneumatic radial tire for passenger cars, and includes a tread portion (1) and a pair of left and right sidewall portions (2) extending radially inward from both ends thereof. ) And a pair of left and right bead portions (3) provided radially inward of the sidewall portion (2). An annular bead core (4) is embedded in each of the pair of bead portions (3). In the figure, CL indicates the tire equator. In this example, the tire has a symmetrical structure with respect to the tire equator CL.

  In the tire, at least one carcass ply (5) extending in a toroidal shape is embedded between the pair of bead cores (4). In this example, the number of carcass plies (5) is one, but two or more may be provided. The carcass ply (5) extends from the tread portion (1) through the sidewall portion (2) to the bead portion (3), and the end portion of the carcass ply (5) around the bead core (4) in the bead portion (3). It is locked by turning back. The end portion of the carcass ply (5) is folded around the bead core (4) from the inside to the outside in the tire width direction and locked. The carcass ply (5) includes a carcass cord made of an organic fiber cord or the like and a covering rubber that covers the carcass cord. The carcass cords are arranged substantially at right angles to the tire circumferential direction. An inner liner layer (6) for maintaining air pressure is provided on the tire inner surface side of the carcass ply (5).

  Between the main body part (5A) of the carcass ply (5) and the folded part (5B), a bead filler (7) made of hard rubber is provided on the outer periphery (ie, radially outer peripheral side) of the bead core (4). It has been. The bead filler (7) has a triangular cross section in which the width gradually decreases toward the radially outer side.

  A belt (9) comprising at least two belt plies is arranged between the carcass ply (5) and the tread rubber portion (8) on the radially outer peripheral side of the carcass ply (5) in the tread portion (1). Has been. A belt reinforcing layer (10) is provided on the outer peripheral side of the belt (9).

  Each of the pair of sidewall portions (2) is provided with a side reinforcing rubber portion (11) also called a side pad in order to increase the rigidity thereof. The side reinforcing rubber portion (11) is disposed on the tire inner surface side of the carcass ply (5) in the sidewall portion (2), and is sandwiched between the carcass ply (5) and the inner liner layer (6). . The side reinforcing rubber part (11) is thick at the central part in the radial direction of the side wall part (2), and gradually becomes thinner from the central part toward the tread part (1) side and the bead part (3) side. In the tire meridian cross section shown in FIG. 1, a crescent-shaped cross section is formed.

  The side reinforcing rubber portion (11) extends inward in the radial direction beyond the tip (ie, radially outer end) of the bead filler (7), and is closer to the front (ie, radially outward) than the bead core (4). It ends with. Therefore, the side reinforcing rubber part (11) and the bead filler (7) have an overlap in the tire radial direction. In this overlapping portion, the side reinforcing rubber portion (11) and the bead filler (7) are adjacent to each other with the main body portion (5A) of the carcass ply (5) interposed therebetween.

  In the present embodiment, the side reinforcing rubber portion (11) is disposed on the tire inner surface side of the outer reinforcing layer (12) and the outer reinforcing layer (12) disposed on the tire inner surface side of the carcass ply (5). It consists of an inner reinforcing layer (13). The side reinforcing rubber part (11) has an inner and outer two-layer structure divided in the tire width direction over the entire tire radial direction, and the inner reinforcing layer (13) has an inner liner layer (6) and an outer reinforcing layer (12 The outer reinforcing layer (12) is interposed between the inner reinforcing layer (13) and the carcass ply (5).

The inner reinforcing layer (13) has a ratio of M50H / M50N, where the tensile stress at 50% elongation at a measurement temperature of 23 ° C. is M50N and the tensile stress at 50% extension at a measurement temperature of 100 ° C. is M50H. Is formed using a rubber composition satisfying the following relationship. That is, the rubber composition constituting the inner reinforcing layer (13) satisfies the following relationship in physical properties of vulcanized rubber.
1.0 ≦ M50H / M50N ≦ 1.3

  As a result, an inner reinforcing layer (13) having the same physical properties can be obtained, and while maintaining the driving performance during normal driving (for example, overpass performance), the deformation of the side wall during the run-flat driving is suppressed and the run-flat is suppressed. Durability can be improved. More specifically, in a rubber composition with a high hardness generally used for a side reinforcing rubber portion of a run flat tire, the elastic modulus decreases at a high temperature. In this embodiment, this relationship is reversed to correspond to a run flat running time. A rubber composition is used in which the tensile stress at high temperature (100 ° C.) is equal to or higher than the tensile stress at normal temperature (23 ° C.) corresponding to normal running. When M50H / M50N is 1.0 or more, it is possible to suppress run-down durability and improve run-flat durability. More preferably, the tensile stress at high temperature is higher than the tensile stress at normal temperature, that is, M50H / M50N> 1.0, and more preferably, M50H / M50N is 1.1 or more. On the other hand, if M50H / M50N is too large, the run-flat durability is impaired, for example, the rigidity at high temperatures becomes too high, causing failure at the bead portion. M50H / M50N is preferably less than 1.3, more preferably 1.2 or less.

On the other hand, the outer reinforcing layer (12) has a tensile stress at 50% elongation at a measurement temperature of 23 ° C. as M50n, and a tensile stress at 50% extension at a measurement temperature of 100 ° C. as M50h, which is the ratio M50h. / M50n satisfies the following relationship, and M50h is formed using a rubber composition having an inner reinforcing layer (13) that is smaller than the tensile stress M50H at 50% elongation at a measurement temperature of 100 ° C. That is, the rubber composition constituting the outer reinforcing layer (12) has the following relationship in physical properties of vulcanized rubber.
0.1 ≦ M50h / M50n <1.0
M50h <M50H

  Thereby, the outer reinforcing layer (12) having the same physical properties is obtained, and the run-flat durability can be remarkably improved in combination with the above-mentioned physical property specifications of the inner reinforcing layer (13). Specifically, the outer reinforcing layer (12) is made of a rubber composition that has lower rigidity than the inner reinforcing layer (13) and has a reduced tensile stress at high temperatures. Such characteristics are relatively close to those of peripheral rubber such as carcass ply-coated rubber as compared with the inner reinforcing layer (13), so that the inner reinforcing layer (13) exhibits the deformation suppressing effect, The run-flat durability can be further improved by reducing the difference in physical properties with the surrounding rubber. In addition, when M50h / M50n is 0.1 or more, excessive deformation of the outer reinforcing layer (12) can be suppressed and failure can be suppressed. M50h / M50n is preferably 0.8 or less, and more preferably 0.3 or more.

  The tensile stress (M50H) at 50% elongation at a measurement temperature of 100 ° C. of the rubber composition constituting the inner reinforcing layer (13) is 3.5 MPa or more, which increases the rigidity of the sidewall portion at high temperatures. It is preferable in improving run flat durability. M50H is more preferably 3.5 to 5.5 MPa, still more preferably 4.0 to 5.3 MPa. When M50H is 5.5 MPa or less, it is possible to improve run-flat durability by suppressing the rigidity from becoming too high at high temperatures and making the sidewall portion difficult to bend. The tensile stress (M50N) at 50% elongation at a measurement temperature of 23 ° C. is not particularly limited, but is preferably 3.0 to 5.0 MPa in order to maintain good running performance during normal running. Preferably, the lower limit is 3.5 MPa or more, and the upper limit is 4.5 MPa or less.

  The tensile stress (M50h) at 50% elongation at a measurement temperature of 100 ° C. of the rubber composition constituting the outer reinforcing layer (12) is preferably 0.7 to 3.3 MPa, more preferably 0.9 to 3.0 MPa. The tensile stress (M50n) at 50% elongation at a measurement temperature of 23 ° C. is not particularly limited, but is preferably 2.5 to 3.8 MPa, and more preferably 2.9 to 3.4 MPa.

  For the inner reinforcing layer (13), various rubber compositions having physical properties of the above vulcanized rubber can be used by blending a rubber component made of a diene rubber with a filler. In the rubber composition for an inner reinforcing layer according to one embodiment, a phenolic thermosetting resin and a methylene donor as a curing agent thereof are blended with a rubber component including natural rubber (NR) and polybutadiene rubber (BR). The mass ratio of the blend amount of the phenolic thermosetting resin with respect to the methylene donor is 1.5 times or more.

  The natural rubber and polybutadiene rubber as the rubber component are not particularly limited, and those generally used in the rubber industry can be used. The blending ratio of the two in the rubber component is not particularly limited. For example, the natural rubber may be 20 to 70% by mass or 30 to 60% by mass. 30-80 mass% may be sufficient as polybutadiene rubber, and 40-70 mass% may be sufficient as it. The tear resistance can be improved by increasing the content of natural rubber, and the bending fatigue resistance can be improved by increasing the content of polybutadiene rubber.

  The rubber component may be composed only of natural rubber and polybutadiene rubber, but other diene rubbers may be blended. Other rubbers are not particularly limited, and examples thereof include styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), and chloroprene rubber (CR).

  As the phenol-based thermosetting resin, a thermosetting resin obtained by condensing at least one phenol compound selected from the group consisting of phenol, resorcin, and alkyl derivatives thereof with an aldehyde such as formaldehyde is used. , High hardness can be achieved. In addition to methyl group derivatives such as cresol and xylenol, the alkyl derivatives include derivatives of relatively long chain alkyl groups such as nonylphenol and octylphenol. Specific examples of the phenolic thermosetting resin include an unmodified phenolic resin (straight phenolic resin) obtained by condensing phenol and formaldehyde, an alkyl-substituted phenolic resin obtained by condensing alkylphenol such as cresol, xylenol, and octylphenol with formaldehyde, Various novolak type phenol resins such as resorcin-formaldehyde resin obtained by condensing resorcin and formaldehyde, and resorcin-alkylphenol co-condensed formaldehyde resin obtained by condensing resorcin, alkylphenol and formaldehyde are exemplified. Further, for example, an oil-modified novolak phenol resin modified with at least one oil selected from the group consisting of cashew nut oil, tall oil, rosin oil, linole oil, oleic acid and linolenic acid can also be used. Any one of these phenol-based thermosetting resins may be used, or two or more thereof may be used in combination.

  Hexamethylenetetramine and / or melamine derivatives are used as the methylene donor to be blended as a curing agent for the phenol-based thermosetting resin. Examples of the melamine derivative include at least one selected from the group consisting of hexamethoxymethyl melamine, hexamethylol melamine pentamethyl ether, and polyvalent methylol melamine. Among these, as a methylene donor, hexamethoxymethyl melamine and / or hexamethylene tetramine are preferable, and hexamethoxymethyl melamine is more preferable.

  The blending amount (A) of the phenol-based thermosetting resin is A / B ≧ 1.5 in terms of mass ratio with the blending amount (B) of the methylene donor. If the proportion of the methylene donor as the curing agent is too large, the rubber crosslinking system may be adversely affected. By using it at an appropriate ratio, it becomes easy to set the ratio of M50H / M50N within the above range, and the effect of suppressing deformation during run-flat running can be enhanced and the run-flat durability can be improved. A / B is more preferably 2.0 or more, and further preferably 2.5 or more. The upper limit of A / B is preferably 7.0 or less, more preferably 5.0 or less, and still more preferably 4.0 or less.

  Although the compounding quantity of a phenol type thermosetting resin is not specifically limited, It is preferable that it is 1-20 mass parts with respect to 100 mass parts of rubber components, More preferably, it is 1-10 mass parts. Moreover, the compounding quantity of a methylene donor is although it does not specifically limit, It is preferable that it is 0.2-10 mass parts with respect to 100 mass parts of rubber components, More preferably, it is 0.5-5 mass parts.

  The rubber composition for the inner reinforcing layer may contain a quinoline anti-aging agent and at least one anti-aging agent other than the quinoline anti-aging agent. By blending these two or more anti-aging agents, run flat durability can be improved.

  Examples of the quinoline antioxidant include 2,2,4-trimethyl-1,2-dihydroquinoline polymer (TMDQ) and 6-ethoxy-2,2,4-trimethyl-1,2-dihydro- Examples include at least one selected from the group consisting of quinoline (ETMDQ).

  Other anti-aging agents used in combination with quinoline anti-aging agents include, for example, aromatic secondary amine-based anti-aging agents, phenol-based anti-aging agents, sulfur-based anti-aging agents, and phosphite-based anti-aging agents. And at least one antiaging agent selected from the group consisting of:

  Examples of the aromatic secondary amine type antioxidant include N-phenyl-N ′-(1,3-dimethylbutyl) -p-phenylenediamine (6PPD), N-isopropyl-N′-phenyl-p- Phenylenediamine (IPPD), N, N'-diphenyl-p-phenylenediamine (DPPD), N, N'-di-2-naphthyl-p-phenylenediamine (DNPD), N- (3-methacryloyloxy-2- P-phenylenediamine-based antioxidants such as hydroxypropyl) -N′-phenyl-p-phenylenediamine, N-cyclohexyl-N′-phenyl-p-phenylenediamine; p- (p-toluenesulfonylamido) diphenylamine, 4 , 4′-bis (α, α-dimethylbenzyl) diphenylamine (CD), octylated diphenylamine Down (ODPA), diphenylamine-based antiaging agent such as styrenated diphenylamine; N- phenyl-1-naphthylamine (PAN), such as naphthylamine antioxidant such as N- phenyl-2-naphthylamine (PBN), and the like. Any of these may be used alone or in combination of two or more.

  Examples of the phenol-based anti-aging agent include monophenol-based anti-aging agents such as 2,6-di-tert-butyl-4-methylphenol (DTBMP) and styrenated phenol (SP); 2,2′-methylene- Bis (4-methyl-6-tert-butylphenol) (MBMBP), 2,2′-methylene-bis (4-ethyl-6-tert-butylphenol) (MBETB), 4,4′-butylidene-bis (3- Bisphenol-based antioxidants such as methyl-6-tert-butylphenol) (BBMTBP) and 4,4′-thio-bis (3-methyl-6-tert-butylphenol) (TBMTBP); 2,5-di-tert- Butylhydroquinone (DBHQ), 2,5-di-tert-amylhydroquinone (DAHQ), etc. Examples include idroquinone anti-aging agents. Any of these may be used alone or in combination of two or more.

  Examples of the sulfur-based antioxidant include benzimidazole-based antioxidants such as 2-mercaptobenzimidazole, 2-mercaptomethylbenzimidazole, and zinc salt of 2-mercaptobenzimidazole; dithiocarbamate salts such as nickel dibutyldithiocarbamate Anti-aging agents; thiourea-based anti-aging agents such as 1,3-bis (dimethylaminopropyl) -2-thiourea and tributylthiourea; and organic thioacids such as dilauryl thiodipropionate. Examples of the phosphite antioxidant include tris (nonylphenyl) phosphite. Any of these may be used alone or in combination of two or more.

  Among other antiaging agents used in combination with the quinoline type antiaging agent, among them, aromatic secondary amine type antiaging agents are preferable, and p-phenylenediamine type antiaging agents are more preferable.

  The blending amount of the quinoline anti-aging agent is preferably 20% by mass or more with respect to the total blending amount of the anti-aging agent, and the effect of improving the run flat durability can be enhanced. More preferably, it is 25 mass% or more, More preferably, it is 30 mass% or more. The upper limit of this ratio is preferably 80% by mass or less, and more preferably 75% by mass or less. The total blending amount of the anti-aging agent, that is, the total blending amount of the quinoline anti-aging agent and the other anti-aging agent is preferably 1 to 10 parts by mass, more preferably 100 parts by mass of the rubber component. Is 1.5-7 parts by mass, more preferably 2-5 parts by mass. The compounding amount of the quinoline antioxidant is preferably 0.2 to 8 parts by mass, more preferably 0.5 to 4 parts by mass with respect to 100 parts by mass of the rubber component.

  A filler such as carbon black and / or silica can be blended in the rubber composition for the inner reinforcing layer. It is preferable that the compounding quantity of a filler is 20-100 mass parts with respect to 100 mass parts of rubber components, More preferably, it is 30-80 mass parts, More preferably, it is 50-70 mass parts. As the filler, carbon black alone or a blend of carbon black and silica is preferable, and carbon black is more preferable. In addition, the value of the tensile stress of the rubber composition can be adjusted by the type and blending amount of the filler. The carbon black is not particularly limited. For example, ISAF class (N200 series), HAF class (N300 series), FEF class (N500 series), GPF class (N600 series) (both ASTM grade) are used. More preferably, it is FEF grade.

  On the other hand, as the rubber composition constituting the outer reinforcing layer (12), various rubber compositions having physical properties of the vulcanized rubber can be used by blending a filler with a rubber component made of a diene rubber. . The rubber composition for the outer reinforcing layer according to one embodiment is one in which the rubber component includes natural rubber (NR) and polybutadiene rubber (BR), and the blending ratio of both is the same as the rubber composition for the inner reinforcing layer, It is preferable that the natural rubber is 20 to 70% by mass (more preferably 30 to 60% by mass) and the polybutadiene rubber is 30 to 80% by mass (more preferably 40 to 70% by mass).

  Like the rubber composition for the inner reinforcing layer, the rubber composition for the outer reinforcing layer may contain a quinoline-based anti-aging agent and at least one anti-aging agent other than the quinoline-based anti-aging agent. An example, a compounding ratio, and a compounding quantity are the same as the case of the rubber composition for inner side reinforcement layers. The rubber composition for the outer reinforcing layer can also contain a filler such as carbon black and / or silica. Carbon black is preferable as the filler, as in the rubber composition for the inner reinforcing layer. The blending amount of the filler is preferably 20 to 80 parts by mass with respect to 100 parts by mass of the rubber component, more preferably 30 to 60 parts by mass, and a smaller amount than the rubber composition for the inner reinforcing layer. Is preferred.

  The rubber composition for the outer reinforcing layer may contain a phenol-based thermosetting resin and a methylene donor. However, the ratio of M50h / M50n tends to be within the above range if not added. Moreover, it is preferable that the compounding quantity of a phenol type thermosetting resin is a small quantity rather than the rubber composition for inner side reinforcement layers.

  The rubber composition for the inner reinforcing layer and the rubber composition for the outer reinforcing layer include, in addition to the above components, oil, zinc white, stearic acid, wax, vulcanizing agent, vulcanization accelerator, and the like in the tire rubber composition. Various commonly used additives can be blended. Here, examples of the vulcanizing agent include sulfur components such as powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur. Although not particularly limited, the blending amount thereof is 100 parts by mass of the rubber component. It is preferable that it is 0.1-10 mass parts with respect to it, More preferably, it is 0.5-8 mass parts, More preferably, it is 1-5 mass parts. Moreover, as a compounding quantity of a vulcanization accelerator, it is preferable that it is 0.1-7 mass parts with respect to 100 mass parts of rubber components, More preferably, it is 0.5-5 mass parts.

  The rubber composition for the inner reinforcing layer and the rubber composition for the outer reinforcing layer can be prepared by kneading according to a conventional method using a commonly used Banbury mixer, kneader, roll, or other mixer. Moreover, the inner side reinforcement layer (13) and outer side reinforcement layer (12) which consist of this rubber composition can be formed by vulcanization-molding a tire at 140-180 degreeC, for example according to a conventional method.

  In the tire according to the present embodiment, as shown in FIG. 1, the outer reinforcing layer (12) is in contact with the carcass ply (5), and the inner reinforcing layer (13) is provided in non-contact with the carcass ply (5). Yes. That is, the side reinforcing rubber part (11) is in contact with the carcass ply (5) only by the outer reinforcing layer (12), and the inner reinforcing layer (13) is not in contact with the carcass ply (5). Thus, run flat durability can be improved by making the highly rigid inner reinforcing layer (13) non-contact with the relatively low rigidity carcass ply (5).

  The cross-sectional area ratio between the inner reinforcing layer (13) and the outer reinforcing layer (12) is not particularly limited. For example, the cross-sectional area Si in the meridian cross section shown in FIG. And the ratio of the cross-sectional area So of the outer reinforcing layer (12) may be Si / So = 1/3 to 3/1, or 1/2 to 2/1.

  In the embodiment shown in FIG. 1, the side reinforcing rubber portion (11) has a two-layer structure inside and outside in the entire tire radial direction, and the height in the tire radial direction of the inner reinforcing layer (13) and the outer reinforcing layer (12) is the same. Is set. However, it is not always necessary to have a double structure over the entire tire radial direction, and a single-layer structure may be used partially.

  For example, in the embodiment shown in FIG. 2, the inner end (12A) in the tire radial direction of the outer reinforcing layer (12) extends inward in the tire radial direction from the inner end (13A) in the tire radial direction of the inner reinforcing layer (13). doing. Thus, by extending the outer reinforcing layer (12) inward in the tire radial direction, it is possible to more effectively suppress a failure in the bead portion (3) during run-flat running.

  In the example shown in FIG. 2, in detail, the inner reinforcing layer (13) and the outer reinforcing layer (12) have substantially the same tire radial direction outer end position (position in the tire radial direction). The position of the inner end in the direction does not match, and the inner end (12A) of the outer reinforcing layer (12) is positioned inward in the tire radial direction from the inner end (13A) of the inner reinforcing layer (13). Therefore, the height (dimension in the tire radial direction) Ho of the outer reinforcing layer (12) is larger than the height Hi of the inner reinforcing layer (13) (Ho> Hi). The ratio Hi / Ho of the height Hi of the inner reinforcing layer (13) to the height Ho of the outer reinforcing layer (12) is preferably 0.7 or more and less than 1.0, more preferably 0.8 or more and 0.0. 9 or less. Since this ratio Hi / Ho is 0.7 or more, it is possible to reduce the load on the outer reinforcing layer (12) during run-flat travel and to suppress the deformation of the inner reinforcing layer (13). Run-flat durability can be improved.

  2 is the same as that of the embodiment shown in FIG. 1 except that the outer reinforcing layer (12) is extended as described above.

  The above dimensional values are those in a normal state with no load in which a tire is mounted on a regular rim and filled with a regular internal pressure. Here, the regular rim is “standard rim” in the JATMA standard, “Design Rim” in the TRA standard, and “Measuring Rim” in the ETRTO standard. The normal internal pressure is “maximum air pressure” in the JATMA standard, “maximum value” described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the TRA standard, and “INFLATION PRESSURE” in the ETRTO standard.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

[Preparation and evaluation of rubber composition]
Using a Banbury mixer, according to the formulation (parts by mass) shown in Table 1 below, first, in the first step (non-pro mixing step), components other than sulfur, vulcanization accelerator and methylene donor are added and mixed (discharge temperature) = 160 ° C.) Then, in the second step (final mixing step), sulfur, a vulcanization accelerator, and a methylene donor were added and mixed (discharge temperature = 100 ° C.) in the second step (for the side reinforcing rubber part). A rubber composition was prepared.

The details of each component in Table 1 are as follows.
・ NR: Natural rubber, RSS No. 3 ・ BR: “BR01” manufactured by JSR Corporation
・ Carbon black: N550, “Seast SO” manufactured by Tokai Carbon Corporation
・ Stearic acid: “Lunac S-20” manufactured by Kao Corporation
・ Phenolic resin: Oil-modified novolak-type phenolic resin, "Sumilite Resin PR13349" manufactured by Sumitomo Bakelite Co., Ltd.
・ Zinc flower: "Zinc flower No. 1" manufactured by Mitsui Mining & Smelting Co., Ltd.
Anti-aging agent 1: N-phenyl-N ′-(1,3-dimethylbutyl) -p-phenylenediamine, “Antigen 6C” manufactured by Sumitomo Chemical Co., Ltd.
Anti-aging agent 2: 2,2,4-trimethyl-1,2-dihydroquinoline polymer (TMDQ), “ANTAGE RD” manufactured by Kawaguchi Chemical Industry Co., Ltd.
・ Vulcanization accelerator: “Noxeller NS-P” manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
・ Sulfur: Shikoku Chemicals Co., Ltd. “Muclon OT-20”
-Methylene donor: Hexamethoxymethylmelamine, "CYREZ 964RPC" manufactured by Mitsui Cytec Co., Ltd.

  For each rubber composition, using a test piece having a thickness of 2 mm vulcanized at 160 ° C. for 25 minutes, the tensile stress (M50N, M50n) at 50% elongation at 23 ° C. and The tensile stress (M50H, M50h) at 50% elongation was measured, and the ratio between the two (M50H / M50N, M50h / M50n) was determined.

  -Tensile stress at 50% elongation at 23 ° C: Conforms to JIS K6251. About the dumbbell-shaped No. 3 type test piece, the tensile test was implemented at room temperature 23 degreeC, and the tensile stress at the time of 50% elongation was calculated | required.

  -Tensile stress at 50% elongation at 100 ° C: Conforms to JIS K6251. After holding a dumbbell-shaped No. 3 specimen in a thermostatic bath at 100 ° C for 1 hour or longer, a tensile test is carried out in a 100 ° C atmosphere with a tensile tester equipped with a thermostatic bath. Tensile stress at 50% elongation Asked.

  As shown in Table 1, in Formulations 1 to 4, the M50 ratio between room temperature and high temperature was less than 1.0, and the rigidity decreased at high temperatures. In Formulation 5, by increasing the amount of carbon black and adding a phenolic resin and a methylene donor to Formulation 1, there was no decrease in tensile stress at high temperatures, but the increase in rigidity was too large, and the M50 ratio was 1 .3 exceeded. On the other hand, in blends 6 to 10 in which a predetermined amount of a phenolic resin and a methylene donor are blended and two or more aging inhibitors including a quinoline aging inhibitor are blended, the tensile stress at high temperature is increased to normal temperature. And the high temperature M50 ratio could be in the range of 1.0 to 1.3.

[Production and evaluation of tires]
The rubber composition shown in Table 1 is used for the inner reinforcing layer (13) and the outer reinforcing layer (12) as shown in Table 2, and the height ratio between the inner reinforcing layer (13) and the outer reinforcing layer (12). Hi / Ho was changed as shown in Table 2, and a radial tire having a tire size: 245 / 40ZR18 having the structure shown in FIG. 2 was vulcanized in accordance with a conventional method. About each tire, all the structures other than the side reinforcement rubber part were made into the common structure. In addition, the side reinforcement rubber part (11) of Comparative Examples 1 to 3 has a single layer structure.

  Each tire obtained was evaluated for run-flat durability and overriding performance. Each evaluation method is as follows.

  Run-flat durability: A drum testing machine made of steel with a smooth surface and having a diameter of 1700 mm was used. The tire internal pressure was 0 kPa, and the load was 65% of the load capacity corresponding to the load index. After increasing the speed to 80 km / h in 5 minutes from the start of the test, the vehicle was run at 80 km / h until a failure occurred. The distance traveled until the failure occurred was indexed with the tire of Comparative Example 1 as 100. The larger the number, the better the run flat durability.

  ・ Saddle overpassability: A test road having a cross-sectional shape shown in FIG. 3 simulating a saddle on a general road by mounting a test tire incorporated in a standard rim with an internal pressure of 200 kPa on the front wheel of the test vehicle (height difference of the saddle h = 20 mm) Thus, sensory evaluation was carried out on the overpassability of the tire. The items that could easily get over the kite were marked with ○, those that were slightly difficult to get over were marked with △, and those that were very difficult to get over were marked with ×.

  The results are as shown in Table 2. Comparative Examples 1 to 3 are examples in which the side reinforcing rubber portion has a single layer structure. In this case, the M50 ratio is 1.0 to 1.3 in the case of Comparative Example 1 in which the M50 ratio is 1.2. Compared with Comparative Examples 2 and 3 which are not present, the run flat durability was excellent. In Comparative Examples 4 to 10 in which each M50 ratio of the inner reinforcing layer and the outer reinforcing layer does not satisfy the specified range although the side reinforcing rubber portion has a two-layer structure, the improvement effect of the run flat durability with respect to Comparative Example 1 is It was not obtained. On the other hand, in Examples 1 to 9, the run flat durability could be remarkably improved without impairing the saddle riding performance.

DESCRIPTION OF SYMBOLS 1 ... Tread part, 2 ... Side wall part, 3 ... Bead part, 5 ... Carcass ply, 7 ... Bead filler, 11 ... Side reinforcement rubber part, 12 ... Outer reinforcement layer, 13 ... Inner reinforcement layer

Claims (3)

A tread portion, a pair of sidewall portions extending radially inward from both ends of the tread portion, and a pair of bead portions provided radially inward of the sidewall portion,
A carcass ply extending from the tread portion through the sidewall portion to the bead portion and locked by the bead portion, and a side reinforcing rubber portion provided at the sidewall portion to reinforce the sidewall portion; In the run flat tire provided,
The side reinforcing rubber portion includes an outer reinforcing layer disposed on the tire inner surface side of the carcass ply, and an inner reinforcing layer disposed on the tire inner surface side of the outer reinforcing layer,
The inner reinforcing layer has a ratio (M50H / M50N) of a tensile stress (M50H) at 50% elongation at a measurement temperature of 100 ° C to a tensile stress (M50H) at 50% elongation at a measurement temperature of 23 ° C of 1.0. It consists of a rubber composition that is 1.3 or less,
The outer reinforcing layer has a ratio (M50h / M50n) of a tensile stress (M50h) at 50% elongation at a measurement temperature of 100 ° C to a tensile stress (M50n) at 50% elongation at a measurement temperature of 23 ° C is 0.1. A rubber composition that is less than 1.0
The tensile stress (M50H) at 50% elongation of the inner reinforcing layer at a measurement temperature of 100 ° C. is larger than the tensile stress (M50h) at 50% elongation of the outer reinforcing layer at a measurement temperature of 100 ° C.,
Run flat tire.   The run-flat tire according to claim 1, wherein the outer reinforcing layer is in contact with the carcass ply and the inner reinforcing layer is provided in non-contact with the carcass ply.   The run-flat tire according to claim 1 or 2, wherein an inner end in the tire radial direction of the outer reinforcing layer extends further inward in the tire radial direction than an inner end in the tire radial direction of the inner reinforcing layer.

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