JP6177725B2 - 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 (Patent Literature). 1 and 2).

  In such a side reinforcing type run flat tire, a rubber having a high hardness is used for the side reinforcing rubber portion for run flat durability. If a steel cord with low rigidity is applied to the belt ply in order to improve riding comfort, the tread grounding shape is likely to be deformed, and steering stability and wear resistance are reduced.

  In Patent Document 3, in a side-reinforced type run-flat tire, the tread rubber portion has a two-layer structure of a cap rubber layer and a base rubber layer, and the rubber hardness of the cap rubber layer is set larger than the rubber hardness of the base rubber layer. Is disclosed. However, there is no disclosure about increasing the volume ratio of such a hard cap rubber layer in the shoulder region.

  On the other hand, in Patent Document 4, the volume ratio of the cap rubber layer whose rubber hardness is smaller than that of the base rubber layer is set to be small in the shoulder region, and thereby the rigidity of the shoulder region is increased and the wear resistance is improved. Is disclosed. In Patent Document 5, the volume ratio of the cap rubber layer having a rubber hardness larger than that of the base rubber layer is set to be small in the shoulder region, and thereby the rigidity of the shoulder region is lowered, and the rollover is performed while maintaining the steering stability. It is disclosed to improve the properties. However, these documents do not disclose use in run-flat tires, nor do they disclose that an excellent effect is achieved by a combination of a specific side reinforcing rubber portion and a belt cord.

  In Patent Document 6, a steel cord is formed by bundling a plurality of steel core wires arranged in parallel to each other in a plane with a steel wrapping wire and pressing the both sides in the short diameter direction to deform the wrapping wire. Is used for tire belt plies. However, it is not disclosed that it is used for a run-flat tire, and it is not disclosed that an excellent effect is achieved by a combination with a side reinforcing rubber portion made of a specific rubber composition.

JP 2010-042739 A JP 2002-103925 A JP 2009-029277 A Japanese Patent Laid-Open No. 2005-239067 JP 2008-273485 A JP2013-21692A

  An object of the present invention is to provide a run flat tire excellent in wear resistance and steering stability without impairing run flat durability and ride comfort.

  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, 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, a tread rubber portion provided in the tread portion, and the carcass ply and the tread rubber in the tread portion And a side reinforcing rubber portion that is provided on the sidewall portion and reinforces the sidewall portion. The side reinforcing rubber part 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 of 1. It consists of a rubber composition that is 0 or more and 1.3 or less. The belt has an n + 1 structure in which a plurality of steel main filaments are arranged in a line without twisting them together to form a main filament bundle, and one steel wrapping filament is wound around the main filament bundle (however, A belt ply in which a flat steel cord of n = 3 to 6) is arranged so that the major axis direction thereof is parallel to the belt surface is provided. The steel cord is formed by pressing the both sides in the short diameter direction to deform the wrapping filament, and the short diameter (Da) of the steel cord after pressing with respect to the short diameter (Db) of the steel cord before pressing. The ratio (Da / Db) has a relationship of 0.80 or less. The tread rubber portion has a two-layer structure including a cap rubber layer that forms a tread surface that serves as a ground contact surface and a base rubber layer that is disposed radially inward of the cap rubber layer, at a measurement temperature of 60 ° C. The rubber hardness (Hc) of the cap rubber layer is larger than the rubber hardness (Hb) of the base rubber layer, and the difference (Hc−Hb) between them is 5 or more and 15 or less. The tread rubber portion includes a pair of shoulder circumferential grooves that define shoulder land portions at both ends in the width direction, with the width direction outer end at the groove bottom of the shoulder circumferential groove as a boundary, and the shoulder side of the boundary The shoulder region, the tire equator side as the center region, the volume ratio of the cap rubber layer occupying the total amount of the cap rubber layer and the base rubber layer is greater than 50% in the shoulder region, and the shoulder region The volume ratio is larger than the volume ratio in the center region.

  According to the present invention, the side reinforcing rubber portion is configured using a rubber composition having a tensile stress at a high temperature equal to or higher than that at a normal temperature, and a specific flat steel cord is attached to the belt ply with a cord major axis of It was applied to be arranged parallel to the width direction of the belt, and further, the volume ratio of the cap rubber layer having a rubber hardness larger than that of the base rubber layer in the tread rubber portion was arranged to be larger in the shoulder region than in the center region. Thus, the wear resistance and the steering stability can be improved without impairing the run-flat durability and ride comfort.

Half sectional view of a run flat tire according to an embodiment The partially expanded perspective view of the steel cord concerning one embodiment Sectional view of steel cord along line III-III in Fig. 2 Partially enlarged sectional view of a belt ply including the steel cord Cross section of sample for out-of-plane stiffness measurement Cross section of sample for in-plane stiffness measurement The figure for explaining the measuring method of out-of-plane and in-plane rigidity 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 the pair of bead portions (3). In the tire, at least one carcass ply (5) extending between the pair of bead portions (3) is embedded. In the figure, CL indicates the tire equator. In this example, the tire has a symmetrical structure with respect to the tire equator CL.

  The carcass ply (5) extends from the tread portion (1) through the sidewall portion (2) to the bead portion (3), and the bead portion (3) is folded around the bead core (4) from the inner side to the outer side in the tire width direction. Is locked. The carcass ply (5) is formed by arranging carcass cords made of organic fiber cords or the like substantially at right angles to the tire circumferential direction. Between the main body of the carcass ply (5) and its folded portion, a bead filler (6) made of hard rubber having a triangular cross section is disposed on the radially outer peripheral side of the bead core (4).

  An inner liner layer (7) for maintaining air pressure is provided on the tire inner surface side of the carcass ply (5). The inner liner layer (7) is provided over the entire inner surface of the tire.

  Each of the pair of sidewall portions (2) is provided with a side reinforcing rubber portion (8) also called a side pad in order to increase the rigidity thereof. The side reinforcing rubber part (8) is disposed on the tire inner surface side of the carcass ply (5) in the side wall part (2). In this example, the carcass ply (5) and the inner liner layer (7) It is sandwiched. The side reinforcing rubber portion (8) is thick at the central portion in the radial direction of the side wall portion (2), and is gradually thinned from the central portion toward the tread portion (1) side and the bead portion (3) side. In the tire meridian cross section shown in FIG. 1, a crescent-shaped cross section is formed.

  The tread portion (1) is provided with a tread rubber portion (9) that forms a tread surface as a ground contact surface. The tread rubber portion (9) has a two-layer structure including a cap rubber layer (10) that forms a tread surface and a base rubber layer (11) that is disposed on the radially inner side of the cap rubber layer. A groove including a plurality of circumferential grooves (12) extending in the tire circumferential direction is provided on the tread surface which is the surface of the tread rubber portion (9), and a tread pattern is formed by the grooves.

  A belt (13) is disposed between the carcass ply (5) and the tread rubber portion (9) on the outer peripheral side (tire radial direction outer side) of the carcass ply (5) in the tread portion (1). The belt (13) is provided so as to overlap the outer periphery of the crown portion of the carcass ply (5), and is composed of at least two belt plies. In this embodiment, the belt (13) is composed of two belt plies, a first belt ply (13A) on the carcass ply (5) side and a second belt ply (13B) on the tread rubber portion (9) side. It is configured. On the outer peripheral side of the belt (13), a belt reinforcing layer (14) made of an organic fiber cord spirally wound at an angle of 0 ° to 5 ° with respect to the tire circumferential direction is provided in the width direction of the belt (13). It is provided so as to cover the whole.

  The run-flat tire according to the present embodiment is used as a belt cord constituting the rubber composition used for the side reinforcing rubber portion (8) for reinforcing the sidewall portion (2) and the belt ply (13A) (13B). Each of the steel cord and the tread rubber portion (9) has a configuration described in detail below.

The side reinforcing rubber part (8) is formed using a rubber composition having a novel physical property that improves run-flat durability, and the rubber composition is stretched by 50% at a measurement temperature of 23 ° C. The tensile stress at 50% elongation at a measurement temperature of 100 ° C. is defined as M50H, and the ratio M50H / M50N satisfies the following relationship. That is, the rubber composition constituting the side reinforcing rubber portion (8) satisfies the following relationship in physical properties of vulcanized rubber.
1.0 ≦ M50H / M50N ≦ 1.3
As a result, a side reinforcing rubber portion (8) having the same physical properties is obtained, and while maintaining the running performance during normal running (for example, saddle riding performance), the deformation of the side wall during run flat running is suppressed. Flat 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 rigidity at high temperatures becomes too high and runflat durability is impaired. M50H / M50N is preferably less than 1.3, more preferably 1.2 or less.

  When the tensile stress (M50H) at 50% elongation at 100 ° C. of the rubber composition is 3.5 MPa or more, it increases the rigidity of the sidewall portion at high temperature and improves run-flat durability. preferable. The lower limit of M50H is more preferably 4.0 MPa or more. Further, the upper limit of M50H is not particularly limited, but is preferably 5.5 MPa or less, more preferably 5.3 MPa or less. By setting such an upper limit, the rigidity becomes too high at high temperatures. Therefore, it is possible to improve the run-flat durability by suppressing the side wall portion from becoming difficult to bend.

  The tensile stress (M50N) at 50% elongation at 23 ° C. of the rubber composition is not particularly limited, but is 3.0 to 5.0 MPa in order to maintain good running performance during normal running. More preferably, the lower limit is 3.5 MPa or more, and the upper limit is 4.5 MPa or less.

  In the side reinforcing rubber part (8), various rubber compositions having a physical property of the vulcanized rubber, which are obtained by blending a diene rubber as a rubber component with a filler, can be used. A rubber composition according to an embodiment is obtained by blending a diene rubber containing natural rubber and polybutadiene rubber with a phenol thermosetting resin and a methylene donor as a curing agent thereof. The mass ratio of the blending amount of the phenolic thermosetting resin with respect to is 1.5 times or more.

  In the rubber composition, the diene rubber as a rubber component includes natural rubber (NR) and polybutadiene rubber (BR). Natural rubber and polybutadiene rubber 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 5.0 or less, and 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 diene rubbers, 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 diene rubbers, More preferably, it is 0.5-5 mass parts.

  The rubber composition according to the embodiment preferably contains 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-based anti-aging agent and the other anti-aging agent is preferably 1 to 10 parts by mass with respect to 100 parts by mass of the diene rubber. Preferably it is 1.5-7 mass parts, More preferably, it is 2-5 mass parts. The amount of the quinoline-based anti-aging agent 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 diene rubber.

  The rubber composition according to the embodiment may contain a filler such as carbon black and / or silica. It is preferable that the compounding quantity of a filler is 20-100 mass parts with respect to 100 mass parts of diene rubbers, 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.

  In addition to the above components, the rubber composition according to the embodiment includes various additives commonly used in tire rubber compositions such as oil, zinc white, stearic acid, wax, vulcanizing agent, and vulcanization accelerator. 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 masses of diene rubber. It is preferable that it is 0.1-10 mass parts with respect to a part, 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 diene rubbers, More preferably, it is 0.5-5 mass parts.

  The rubber composition can be prepared by kneading according to a conventional method using a commonly used Banbury mixer, kneader, roll, or other mixer. Moreover, the side reinforcement rubber part which consists of this rubber composition can be formed by vulcanization-molding a tire at 140-180 degreeC, for example according to a conventional method. With such a rubber composition, a phenolic thermosetting resin and a methylene donor are blended in the above mass ratio, and two or more antiaging agents including a quinoline antiaging agent are blended. It is easy to set the ratio of M50H / M50N within the above range by increasing the tensile stress at, and the run-flat durability can be remarkably improved.

  Next, the steel cord applied to the belt (13) will be described.

  In this embodiment, as shown in FIG. 2, as a steel cord (20), a plurality of main filaments (21) made of steel are aligned in a line without twisting to form a main filament bundle (22). A flat steel cord having an n + 1 structure (where n = 3 to 6) in which a steel wrapping filament (23) is wound around the main filament bundle (22) is used.

  As the main filament (21), a steel filament having a circular cross section and a diameter, that is, a filament diameter (d) of 0.15 to 0.30 mm can be used. The diameter (d) is more preferably 0.15 to 0.25 mm. In addition, the cross-sectional shape of the main filament may not be a perfect circle, and may be an ellipse, for example.

  The main filament bundle (22) is formed by arranging a plurality of main filaments (21) having the same diameter so as to be arranged in a horizontal row without being twisted. That is, the main filaments (21) are juxtaposed so as to form one layer along one plane. Therefore, the obtained steel cord (20) is flat and has a major axis (Dl) and a minor axis (Da) as shown in FIG. With such a flat steel cord, the bending rigidity in the major axis direction is high and the bending rigidity in the minor axis direction is low, so that the balance between steering stability and ride comfort is improved while maintaining run-flat durability. Can do.

  The number of main filaments (21) constituting the main filament bundle (22) is 3 to 6. By using three or more, the ratio of in-plane rigidity and out-of-plane rigidity described later can be easily set to 10 or more. In addition, since the number is six or less, the main filament bundle (22) can be easily arranged in a line.

  As the wrapping filament (23) wound around the main filament bundle (22), a straight steel filament which is not corrugated or the like is used. The shape of the main filament bundle (22) can be maintained by restraining the main filament (21) with the wrapping filament (23). Therefore, a high in-plane rigidity can be obtained by giving the aligned main filament bundle (22) a sense of unity as a steel cord.

  Note that the winding pitch (p) of the wrapping filament (23) with respect to the main filament bundle (22) is not particularly limited because it varies depending on the number of main filaments (21), the filament diameter, etc. For example, 2.0 to 30.0 mm It may be 3.0 to 10.0 mm. The main filament (21) may be a straight metal filament that is not corrugated, or may be a corrugated metal filament.

  As the steel cord (20) according to the present embodiment, a flat cord formed by wrapping around the main filament bundle (22) with the wrapping filament (23) as described above is pressed from both sides in the minor axis direction. A modified one of the wrapping filament (23) is used. By the pressing, the wrapping filament (23) is deformed along the shape of the space and enters a part of at least a part of the space formed between the adjacent main filaments (21). That is, at least a part of the space is filled with at least a part of the wrapping filament (23). Therefore, the restraining force of the main filament (21) by the wrapping filament (23) can be increased. Further, since a relatively large plastic deformation is applied to the wrapping filament (23), the rotational torque and the repulsive force inherent in the wrapping filament (23) are reduced. Therefore, the main filament bundle (22) can be easily held in a line, and the excellent effect of the flat cord can be easily exhibited.

  As the steel material used for the main filament (21) and the wrapping filament (23), carbon steel made of various piano wires containing carbon can be used. The carbon content of the main filament (21) is not particularly limited, but is preferably 0.70 to 1.20% by mass. As an embodiment, one having a carbon content of 0.85 mass% or more and less than 0.95 mass% can be used. Further, in the present embodiment, the hardness of the wrapping filament (23) is lower than the hardness of the main filament (21). The hardness can be adjusted by the carbon content. As one embodiment, the carbon content (mass%) of the main filament (21) is Cc, and the carbon content (mass%) of the wrapping filament (23) is Cw. It is preferable that it is 05-0.40 (mass%). By setting such a difference, the wrapping filament can be deformed without breaking when the steel cord is pressed. That is, when Cc-Cw is 0.05% by mass or more, the wrapping filament (23) is easily deformed by pressing, and when it is 0.40% by mass or less, the wrapping filament (23) is pressed by pressing. The possibility of disconnection can be reduced. Cc-Cw is more preferably 0.10 to 0.30% by mass.

  The pressing can be performed using a rolling roll (not shown), and the flat cord after the wrapping filament (23) is wound is sandwiched and pressed from the upper and lower surfaces by the rolling roll. Since the wrapping filament (23) is located outside and its hardness is lower than that of the main filament (21), the wrapping filament (23) can be preferentially deformed by pressing. A space having a substantially fan-shaped cross section is formed between adjacent main filaments (21), and when pressed by a rolling roll, the inner peripheral side of the wrapping filament (23) is deformed so as to fill the space, A protrusion (23a) is formed along the shape of the space. At the same time, a recess (23c) is formed between the protrusions (23a), and the outer peripheral side portion (23b) of the wrapping filament (23) is deformed into a flat shape.

  In the steel cord (20) according to the present embodiment, the ratio (Da / Db) of the short diameter (Da) of the steel cord after pressing to the short diameter (Db) of the steel cord before pressing is 0.80 or less. Have. By pressing from both sides as described above, the thickness of the steel cord (20) having the wrapping filament (23) after deformation, that is, the short diameter (Da) after pressing is the steel cord having the wrapping filament before deformation. Is smaller than the minor axis (Db) before pressing. In this way, by pressing with a force of a magnitude that satisfies Da / Db ≦ 0.80, the deformation of the wrapping filament (23) into the space between the main filaments (21) becomes sufficient, and the wrapping filament (23 ) Can be sufficiently secured. Further, the rotational torque and repulsive force inherent in the wrapping filament (23) can be made sufficiently small. Da / Db is more preferably 0.65 to 0.75.

  The diameter before pressing of the wrapping filament (23), that is, the filament diameter (d0) is preferably smaller than the diameter (d) of the main filament (21), and preferably 0.10 to 0.15 mm. By being 0.15 mm or less, the rotational torque and the repulsive force inherent in the wrapping filament (23) can be sufficiently reduced by pressing. Moreover, when it is 0.10 mm or more, the possibility of disconnection during pressing can be reduced. The cross-sectional shape of the wrapping filament does not have to be a perfect circle, and may be, for example, an ellipse.

  In one embodiment, the steel cord (20) preferably has a ratio (R1 / R2) of the in-plane rigidity (R1) to the out-of-plane rigidity (R2) of 10 or more and 30 or less. When R1 / R2 is 10 or more, ride comfort can be improved while maintaining run-flat durability and steering stability. Moreover, when R1 / R2 is 30 or less, it is easy to ensure the rigidity of the tire tread. R1 / R2 is more preferably 15 or more.

  Here, the in-plane rigidity is the bending rigidity when the steel cord (20) is bent in the major axis direction (B) (left and right direction in FIG. 3), and corresponds to the rigidity in the width direction in the tire. Further, the out-of-plane rigidity is the bending rigidity when the steel cord (20) is bent in the minor axis direction (A) (vertical direction in FIG. 3), and corresponds to the radial rigidity in the tire. In order to have such in-plane rigidity and out-of-plane rigidity, the thickness and number of main filaments to be aligned may be set appropriately. For example, by increasing the diameter of the main filament, the in-plane rigidity and Both the out-of-plane rigidity can be increased, and the in-plane rigidity can be increased and the ratio of R1 / R2 can be increased by increasing the number of aligned main filaments.

  The value of the in-plane rigidity (R1) is not particularly limited, and may be 0.5 to 15.5 N / 8 or 1.2 to 15.5 N / 8. The value of the out-of-plane rigidity (R2) is not particularly limited and may be 0.04 to 0.55 N / piece or 0.12 to 0.55 N / 8.

  As shown in FIG. 4, the belt plies (13A) and (13B) have the steel cord (20) arranged such that the major axis direction (B) is parallel to the belt surface (that is, the belt outer peripheral surface). Is formed. That is, in the belt ply, the steel cord (20) is embedded in the coating rubber (30) at a predetermined interval so that the short diameter direction (A) thereof coincides with the thickness direction (K) of the belt ply. Yes. Therefore, the steel cord (20) is arranged so that the major axis direction (B) is parallel to the tread surface. With this configuration, it is possible to reduce the thickness of the belt ply to suppress an increase in tire weight, and to reduce the bending rigidity in the tire radial direction while maintaining the bending rigidity in the tire width direction.

  The steel cord (20) is inclined at an angle of, for example, 10 ° to 35 ° with respect to the tire circumferential direction, and is disposed so as to intersect each other between the two belt plies (13A) (13B). ing. The number of steel cords driven into the belt ply is not particularly limited, and may be, for example, 10 to 30 / 25.4 mm, or 10 to 25 / 25.4 mm.

  Next, the tread rubber portion (9) will be described.

  In this embodiment, the rubber hardness (Hc) of the cap rubber layer (10) at a measurement temperature of 60 ° C. is larger than the rubber hardness (Hb) of the base rubber layer (11) at a measurement temperature of 60 ° C. (Hc> Hb). ). The hardness difference (Hc−Hb) between the two is 5 or more and 15 or less. Further, the volume ratio of the cap rubber layer (10) to the total amount of the cap rubber layer (10) and the base rubber layer (11) ((cap rubber layer volume / (cap rubber layer volume + base rubber layer volume)) × 100%) is Vs in the shoulder region (9S) of the tread rubber portion (9), Vc is in the center region (9C), and Vs> Vc, that is, the volume ratio (Vs) in the shoulder region (9S) is It is set larger than the volume ratio (Vc) in the center region (9C). Furthermore, the volume ratio (Vc) in the shoulder region (9S) is greater than 50%. By forming the tread rubber portion (9) in this way, it is possible to suppress the deformation of the tread grounding shape during traveling and improve the steering stability and the wear resistance without impairing the ride comfort.

  Here, the rubber hardness is a value (durometer hardness) measured with a type A durometer in a 60 ° C. atmosphere in accordance with JIS K6253.

  The rubber hardness (Hc) of the cap rubber layer (10) may be, for example, 55 to 70 or 58 to 65. The rubber hardness (Hb) of the base rubber layer (11) may be 45 to 60 or 50 to 55, for example. When the difference in hardness (Hc−Hb) between the two is 5 or more, it is possible to enhance the effect of improving wear resistance and steering stability during run-flat running. Moreover, when this hardness difference (Hc-Hb) is 15 or less, deterioration of riding comfort can be suppressed. A method for providing such a hardness difference is not particularly limited. For example, in the rubber composition for forming the cap rubber layer (10) and the base rubber layer (11), the type of rubber component used, the amount of filler such as carbon black or silica, What is necessary is just to change the compounding quantity of a sulfurizing agent and / or a vulcanization accelerator.

  The shoulder region (9S) and center region (9C) in the tread rubber portion (9) are set as follows. As shown in FIG. 1, the tread rubber portion (9) is provided with a pair of left and right shoulder circumferential grooves (12A) that define and form shoulder land portions (16) at both ends in the width direction. The shoulder circumferential grooves (12A) are a pair of outermost left and right circumferential grooves among a plurality of (for example, 3 to 5) circumferential grooves (12) provided as main grooves on the tread surface. Then, it is one each of the both ends of the four circumferential grooves. The shoulder land portion (16) may be a rib continuous in the tire circumferential direction, or a block row in which a plurality of blocks are arranged in parallel in the tire circumferential direction.

  The outer edge in the width direction at the groove bottom of the shoulder circumferential groove (12A) is defined as a boundary (15) (that is, the circumferential line passing through the outer edge in the tire width direction of the groove bottom is defined as a boundary line). 15) the shoulder side (that is, the outer side in the tire width direction) is the shoulder region (9S), and the tire equator (CL) side is the center region (9C).

  At this time, in the tread rubber portion (9), the volume ratio (Vs) of the cap rubber layer (10) in the shoulder region (9S) is greater than the volume ratio (Vc) of the cap rubber layer (10) in the center region (9C). Is also set larger. When the above flat steel cord (20) is used for the belt ply, the tread grounding shape is greatly deformed during run-flat running, and the steering stability tends to decrease, but the cap rubber layer (10) with high rubber hardness When the volume ratio is set to Vs> 50% and Vs> Vc, and the rigidity in the shoulder region (9S) is increased, deformation of the tread ground contact shape during traveling can be effectively suppressed. Therefore, steering stability and wear resistance can be improved. The volume ratio (Vs) of the cap rubber layer (10) in the shoulder region (9S) is preferably 60 to 85%, more preferably 65 to 80%. The volume ratio (Vc) of the cap rubber layer (10) in the center region (9C) is not particularly limited, but may be, for example, 30 to 65% or 40 to 60%.

  In order to set the volume ratio as described above, in the embodiment shown in FIG. 1, the thickness of the cap rubber layer (10) is larger in the shoulder region (9S) than in the center region (9C), and the base rubber layer (11) The thickness is thinner in the shoulder region (9S) than in the center region (9C).

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

[Preparation and Evaluation of Side Reinforced Rubber Part 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: Sulfenamide, “Noxeller NS-P” manufactured by Ouchi Shinsei Chemical Co., Ltd.
・ Methylene donor: hexamethoxymethylmelamine, “CYREZ 964RPC” manufactured by Mitsui Cytec Co., Ltd.
Sulfur: Shikoku Kasei Kogyo "Muclon OT-20".

For each rubber composition, using a test piece having a thickness of 2 mm vulcanized at 160 ° C. for 25 minutes, a tensile stress (M50N) at 50% elongation at 23 ° C. and 50% at 100 ° C. was measured according to the following method. The tensile stress (M50H) at the time of extension was measured, and the ratio between the two (M50H / M50N) was obtained.
・ M50: Conforms to JIS K6251. A tensile test was performed on the dumbbell-shaped No. 3 test piece at a room temperature of 23 ° C., and a tensile stress (M50N) at 50% elongation was obtained. Moreover, after holding a test piece in a 100 degreeC thermostat for 1 hour or more, a tensile test is implemented in a 100 degreeC atmosphere with a tensile tester with a thermostat, and tensile stress (M50H) at the time of 50% elongation is implemented. Asked.

  As shown in Table 1, in Formulation 1, which is a control, M50H / M50N, which is a ratio of normal temperature to high temperature tensile stress, was 0.9, and the rigidity decreased at high temperatures. In Formulation 2, the increase in carbon black and the addition of phenolic resin and methylene donor to Formulation 1 resulted in no decrease in tensile stress at high temperatures, but the increase in rigidity was too large, and M50H / M50N was It exceeded 1.3. On the other hand, while blending a predetermined amount of a phenolic resin and a methylene donor and blending two or more anti-aging agents including a quinoline anti-aging agent, the mixing stresses at high temperatures increase M50H. / M50N ratio could be in the range of 1.1 to 1.2.

[Preparation of composition for tread rubber part]
Using a Banbury mixer, according to the formulation (parts by mass) shown in Table 2 below, first, in the first step, components other than sulfur and vulcanization accelerator are added and mixed (discharge temperature = 160 ° C.), and then obtained. In the second step, sulfur and a vulcanization accelerator were added to and mixed with the mixture (discharge temperature = 100 ° C.) to prepare a rubber composition for a cap rubber layer and a rubber composition for a base rubber layer.

Details of each component in Table 2 are as follows.
E-SBR: “SBR0122” manufactured by JSR Corporation
・ NR: Natural rubber, RSS No. 3 ・ BR: “BR150B” manufactured by Ube Industries, Ltd.
・ N339: Carbon black, “Seast KH” manufactured by Tokai Carbon Co., Ltd.
・ N550: Carbon black, “Seast SO” manufactured by Tokai Carbon Co., Ltd.
・ Aroma oil: “Process NC140” manufactured by JX Nippon Oil & Energy Sun Energy Co., Ltd.
・ Silica: “Nip Seal AQ” manufactured by Tosoh Silica Co., Ltd.
Silane coupling agent: “Si69” manufactured by Degussa
・ Stearic acid: “Lunac S-20” manufactured by Kao Corporation
・ Phenolic resin: "Sumilite Resin PR13349" manufactured by Sumitomo Bakelite Co., Ltd.
・ Zinc flower: “Zinc flower 1” manufactured by Mitsui Mining & Smelting Co., Ltd.
Anti-aging agent: “Antigen 6C” manufactured by Sumitomo Chemical Co., Ltd.
NS: Vulcanization accelerator, “Noxeller NS-P” manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
・ CZ: Vulcanization accelerator, “Soccinol CZ” manufactured by Sumitomo Chemical Co., Ltd.
・ Sulfur: “Powder sulfur” manufactured by Tsurumi Chemical Co., Ltd.

  About each rubber composition, rubber hardness was measured with a type A durometer in a 60 ° C. atmosphere in accordance with JIS K6253 using a test piece vulcanized at 160 ° C. for 25 minutes. The rubber hardness is shown in Table 2.

[Production and evaluation of steel cords]
Steel cords having the structure shown in the belt column in Tables 3 and 4 below were produced. Each steel cord consists of a main filament bundle in which a plurality of main filaments made of steel (carbon content = 0.92 mass%) are arranged in a single line without being twisted, and each strand has a diameter d = 0.15 mm. This is an n + 1 structure steel cord that is wrapped with a steel wrapping filament (carbon content = 0.72 mass%) and pressed with a rolling roll. In Table 2, 0.22 of “4 × 0.22 + 1” indicates that the main filament diameter d is 0.22 mm. Comparative Example 7 was not pressed. The winding pitch of the wrapping filament was p = 5.0 mm. The measurement method for filaments and steel cords is as follows.

  -Carbon content of the filament: Infrared absorption method according to JIS G1211 (Annex 3: Quantitative determination of total carbon-high frequency induction furnace combustion). More specifically, steel is melted by high-frequency heating using LECO's "CS-400" apparatus, and quantitative analysis is performed by an infrared absorption method.

  -Filament diameter and cord diameter: Measure the diameter of steel cord and filament with a predetermined thickness meter in accordance with JIS G3510.

  ・ Cord shape: When wrapped with a wrapping filament, ○ (good) indicates that the aligned main filaments are lined up in a row, △ indicates that they are slightly broken, and × (bad) indicates that they are largely broken It was.

  In-plane rigidity / out-of-plane rigidity (R1 / R2): A sample for measuring out-of-plane rigidity having a cross-sectional shape shown in FIG. 5 and a sample for measuring in-plane rigidity having a cross-sectional shape shown in FIG.

  As shown in Fig. 5, the sample for measuring out-of-plane rigidity is driven with steel cords placed in parallel so that the major axis direction is parallel to the surface opposite to the topping. The thickness was set to 0.50 mm, and a topping was manufactured with an opposite width of 300 mm. The obtained topping was vulcanized at 160 ° C. for 20 minutes and cut so that eight steel cords were included to obtain an out-of-plane stiffness measurement sample.

  For the in-plane stiffness measurement sample, eight untopped toppings are stacked so that the major axis directions are parallel to each other, then vulcanized at 160 ° C. for 20 minutes, and cut out as shown in FIG. Thus, a sample for in-plane rigidity measurement including 8 steel cords was obtained.

  As shown in FIG. 7, the in-plane stiffness and the out-of-plane stiffness are measured by placing a sample (40) on a pair of support rolls (42) and (42) and using a pushing jig (44) from above. The sample (40) was pushed 10 times at 30 mm, and the load when it was pushed 5 mm at the time of the 10th push was measured, and these loads were defined as in-plane stiffness and out-of-plane stiffness, respectively. Both of these are the bending stiffness per 8 steel cords. The support roll (42) is a rotatable roll with almost no load (rotational resistance) during rotation, the roll diameter was 20 mm, and the distance between the rolls (distance between the axes) was 100 mm. The sample (40) is arranged so that the longitudinal direction N of the steel cord is perpendicular to the axial direction of the support roll (42), and is pushed in from above each sample shown in FIGS. Arranged. The pushing jig (44) was a roll with a diameter of 15 mm, and the pushing speed was 300 mm / min.

  In addition, the composition of the rubber composition for coating at the time of producing the topping anti is 60 parts by mass of carbon black HAF (“Seast 300” manufactured by Tokai Carbon Co., Ltd.) with respect to 100 parts by mass of natural rubber (RSS # 3). Aging inhibitor ("Santflex 6PPD" manufactured by Flexis) 2.0 parts by mass, 2.0 parts by mass of cobalt stearate, 2.0 parts by mass of phenolic resin ("Sumikanol 620" manufactured by Taoka Chemical Co., Ltd.), hexa Methoxymethylmelamine was 4.0 parts by weight, zinc white No. 3 was 8.0 parts by weight, insoluble sulfur was 6.0 parts by weight, and vulcanization accelerator DZ was 1.0 part by weight.

[Production and evaluation of tires]
Tire sizes according to the configurations shown in Tables 3 and 4 were used using the rubber composition of Table 1 for the side reinforcing rubber part, the rubber composition of Table 2 for the tread rubber part, and using the steel cord as a belt cord. : Radial tire of 245 / 40ZR18 was vulcanized according to a conventional method. About each tire, all the structures other than a belt, a tread rubber part, and a side reinforcement rubber part were made into the common structure. The angle of the steel cord in the belt ply (13A) / (13B) was + 27 ° / −27 ° with respect to the tire circumferential direction. For each tire, the number of steel cords to be driven was set so that the belt strength was almost the same. The belt ply was produced by arranging the steel cords with the number of drivings shown in Tables 3 and 4 so that the major axis direction thereof was parallel to the belt surface, and using a calender device as a topping counter.

  For the carcass layer, rayon cord 1840 dtex / 3 was driven and one ply was applied at 21 wires / 25 mm. The belt reinforcing layer was made of nylon 66 cord 1400 dtex / 2, and was 28 caps / 25 mm to form one cap.

  About each obtained tire, run-flat durability, the steering stability at the time of run-flat driving | running | working, abrasion resistance, and saddle overpassability were evaluated. Each measurement / 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.

  Steering stability: A test tire incorporated in a standard rim with an internal pressure of 200 kPa was mounted on a test vehicle with a displacement of 2500 cc, and three trained test drivers ran the test course for sensory evaluation. The scoring was based on a 10-point evaluation, and relative comparison was performed with the tire of Comparative Example 1 as 6 points, and the average score of 3 people was displayed as an index with the tire of Comparative Example 1 as 100. The larger the number, the better the steering stability.

  Abrasion resistance: A test tire incorporated in a standard rim with an internal pressure of 200 kPa was attached to a 4WD vehicle with a displacement of 2000 cc, and 10000 km was run while rotating left and right every 2500 km, and the depth of the remaining groove after running was measured. The remaining groove is an average value of four. The value of Comparative Example 1 is expressed as an index, and the larger the index, the better the wear resistance.

  ・ Saddle overpassability: A test road having a cross-sectional shape shown in FIG. 8 that imitates a saddle on a general road by attaching a test tire incorporated in a standard rim with an internal pressure of 200 kPa to 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 Tables 3 and 4. In Comparative Example 1, the difference in hardness between the cap rubber layer and the base rubber layer of the tread rubber portion is small. Compared to the comparative example 1, when it was Examples 1 to 10, the steering stability and the wear resistance were improved without impairing the run-flat durability and the overriding ability (riding comfort).

  In Comparative Example 2, the difference in hardness between the cap rubber layer and the base rubber layer in the tread rubber part was too large, so that the overpass performance was poor. In Comparative Example 3, since the rubber hardness of the cap rubber layer was lower than that of the base rubber layer, steering stability and wear resistance were impaired.

  In Comparative Example 4, since the number of the main filaments of the belt cord aligned was 7, the main filaments could not take a shape aligned in a row, and the saddle overpassability and steering stability were inferior to Comparative Example 1, The effect of improving wear resistance was not obtained. In Comparative Example 5, M50H / M50N, which is the ratio between the normal temperature and high temperature tensile stress of the side reinforcing rubber part, was 0.9, and the rigidity was lowered at high temperature. The run flat durability was inferior to that of Comparative Example 1. In Comparative Example 6, M50H / M50N was too large as 1.4, and therefore run-flat durability was deteriorated. In Comparative Example 7, since Da / Db was 1.00 which was not specified, the binding force of the wrapping filament was insufficient, the shape in which the main filaments were arranged in a row was slightly disturbed, and the effect of improving steering stability was also obtained. There wasn't.

  In Comparative Examples 8 to 10, the volume ratio of the cap rubber layer in the shoulder region of the tread rubber portion was small, and the steering stability and wear resistance were poor. In Comparative Example 11, since the volume ratio of the cap rubber layer in the shoulder region and the center region of the tread rubber portion was reversed, the steering stability and wear resistance improvement effects could not be obtained.

DESCRIPTION OF SYMBOLS 1 ... Tread part, 2 ... Side wall part, 3 ... Bead part, 5 ... Carcass ply, 8 ... Side reinforcement rubber part, 9 ... Tread rubber part, 9S ... Shoulder area | region, 9C ... Center area | region, 10 ... Cap rubber layer, 11 ... base rubber layer, 12A ... shoulder circumferential groove, 13 ... belt, 13A, 13B ... belt ply, 15 ... border, 16 ... shoulder land, 20 ... steel cord, 21 ... main filament, 22 ... main filament bundle, 23 ... Wrapping filament

Claims (4)

A tread portion, a pair of sidewall portions extending radially inward from both ends of the tread portion, a pair of bead portions provided radially inward of the sidewall portion, and the tread portion through the sidewall portion A carcass ply extending to the bead portion and locked by the bead portion, a tread rubber portion provided in the tread portion, and a belt disposed between the carcass ply and the tread rubber portion in the tread portion. And a run-flat tire provided with a side reinforcement rubber portion that is provided in the sidewall portion and reinforces the sidewall portion,
The side reinforcing rubber part 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 of 1. A rubber composition that is 0 or more and 1.3 or less,
The belt has an n + 1 structure in which a plurality of steel main filaments are aligned in a single line without twisting to form a main filament bundle, and one steel wrapping filament is wound around the main filament bundle (however, n = 3 to 6) provided with a belt ply in which flat steel cords are arranged so that the major axis direction thereof is parallel to the belt surface, and the steel cords are pressed from both sides in the minor axis direction to wrap the filaments. The ratio (Da / Db) of the short diameter (Da) of the steel cord after pressing to the short diameter (Db) of the steel cord before pressing is 0.80 or less. ,
The tread rubber portion has a two-layer structure including a cap rubber layer that forms a tread surface that serves as a ground contact surface and a base rubber layer that is disposed radially inward of the cap rubber layer. The rubber hardness (Hc) of the cap rubber layer is greater than the rubber hardness (Hb) of the base rubber layer, and the difference (Hc−Hb) between the two is 5 to 15, and the tread rubber portion is A pair of shoulder circumferential grooves that define the shoulder land portions at both ends in the width direction are provided, with the width direction outer end at the groove bottom of the shoulder circumferential groove as a boundary, the shoulder side of the boundary as a shoulder region, and the tire equator side As a center region, the volume ratio of the cap rubber layer in the total amount of the cap rubber layer and the base rubber layer is larger than 50% in the shoulder region, One, the volume ratio of the shoulder region is greater than the volume ratio in the center region,
Run flat tire.   The run-flat tire according to claim 1, wherein the rubber composition has a tensile stress (M50H) at 50% elongation at a measurement temperature of 100 ° C of 3.5 MPa or more. The rubber composition is a diene rubber containing natural rubber and polybutadiene rubber, a phenolic thermosetting resin, a methylene donor as its curing agent, a quinoline antiaging agent, and a quinoline antiaging agent. It is formed by blending at least one anti-aging agent, and the mass ratio of the blended amount of the phenolic thermosetting resin with respect to the methylene donor is 1.5 times or more.
The run flat tire according to claim 1 or 2. The steel cord has a ratio (R1 / R2) of in-plane rigidity (R1) that is bending rigidity in the major axis direction to out-of-plane rigidity (R2) that is bending rigidity in the minor axis direction is 10 or more and 30 or less.
The run flat tire according to any one of claims 1 to 3.

Images