JP4769613B2 - Pneumatic safety tire - Google Patents

Description

  The present invention relates to a pneumatic safety tire, and more particularly to a pneumatic safety tire having improved run-flat performance by suppressing buckling deformation of a tread portion.

Conventionally, as one of so-called run-flat tires that can safely travel a certain distance even when the internal pressure of the tire is reduced due to puncture or the like, the cross-section is approximately crescent on the innermost surface of the carcass of the tire sidewall portion. A run flat tire having a side reinforcing rubber layer in the form of a so-called side reinforcing type run flat tire is known. These side-reinforced run-flat tires reduce the amount of bending deformation at the side wall, thereby causing temperature destruction due to rubber heat generation at the bent part and abrasion damage of the inner liner rubber between the buttress part and the bead part. It is intended to suppress the structural destruction of and improve the durability.
However, in order to sufficiently reduce the amount of bending deformation, a large increase in volume of the rubber reinforcing layer is required, leading to an increase in tire weight and material cost. On the other hand, there is also a problem that the durability cannot be sufficiently improved because rubber heat generation is promoted.

In addition, it is known that when such a side-reinforced run-flat tire travels in a run-flat state, so-called buckling occurs in which the center of the tread surface is lifted from the road surface. In a tire in which buckling occurs, the contact pressure of the tread shoulder portion increases, and as a result, the heat generated by the reinforcing rubber disposed at a position close to the shoulder portion increases, so that the tire may be broken.
For this reason, side-reinforced run-flat tires that have improved durability by suppressing the occurrence of buckling during run-flat running in side-reinforced run-flat tires are desired, and various studies have been made on these. .

  For example, Patent Document 1 discloses a number of cords that are substantially orthogonal to the tire equatorial plane between a belt and a belt reinforcing layer made of an organic fiber cord such as nylon fiber or aramid fiber disposed on the outer periphery of the belt. A tire is described in which at least one reinforcing layer comprising an array is arranged. By arranging the reinforcing layer in this way, it is possible to suppress the occurrence of buckling and improve the run-flat durability, but with the increase in the rigidity of the entire tread portion due to the arrangement of the reinforcing layer, the normal internal pressure is increased. There was a problem that the vibration ride comfort deteriorated when there was a collision input from the road surface during traveling.

  In Patent Document 2, the outermost belt layer of the belt layers constituting the belt is composed of a pair of left and right small belt members, and the deformation of the tread portion is particularly large when buckling occurs. The result of suppressing the occurrence of buckling without overlapping both small belt members in the range of 20 to 50% of the tread installation width and increasing the belt out-of-plane bending rigidity outside the overlapped range. In addition, a tire is described that has improved durability during run-flat running without sacrificing ride comfort. However, such a tire has a problem that the manufacturing process becomes complicated because the structure of the belt layer is complicated.

On the other hand, in Patent Document 3, the bending deformation at the sidewall portion is strongly related to the buckling deformation at the tread portion, and the higher the buckling deformation amount, the larger the bending deformation amount at the sidewall portion. Further, it is disclosed that bending deformation can be suppressed by suppressing buckling deformation low.
Furthermore, in order to effectively suppress buckling deformation in a state where the internal pressure is zero such as during puncture, the tread portion is not reinforced and strengthened by the cord reinforcing layer, but a highly elastic reinforcing rubber layer is used. Is also required to be interposed between the carcass plies in the tread portion or between the plies between the carcass and the belt layer.
In the cord reinforcing layer, or the belt layer and the carcass layer, the stiffness, particularly the circumferential stiffness is exhibited only when a sufficient tension is applied to the cord by the filling internal pressure. It is said that it is difficult to expect an effective increase in the bending stiffness in the axial direction by changing the material of the cord or adding a cord layer.
Further, in Patent Document 3, a highly elastic reinforced rubber layer having a predetermined elastic modulus, thickness, and width is interposed between carcass plies or between plies between a carcass and a belt layer, so that the back of the tread portion is provided. It is disclosed that by effectively suppressing ring deformation, bending deformation at the sidewall portion can be reduced and durability during run-flat running can be improved. However, further improvements are necessary to cope with the recent increase in size and weight of run-flat tires.

JP-A-6-191243 JP 2004-359145 A Japanese Patent No. 3335112

  An object of the present invention is to provide a pneumatic safety tire with improved run-flat performance by suppressing buckling deformation of the tread portion without impairing riding comfort during normal internal pressure driving under such circumstances. It is what.

［式中、Ａは不飽和結合によって重合された不飽和化合物由来の部分であり、繰り返し単位において同一でも異なっていてもよい］で表される繰り返し単位から実質的になる上記（１）〜（１３）の空気入り安全タイヤ、及び
（１５） 前記式（ＩＩ）中のＡがエチレン基である上記（１４）の空気入り安全タイヤ、
を提供するものである。 The inventor of the present invention paid attention to the fact that the tire tread reaches a high temperature of 100 ° C. or higher during run-flat running in order to achieve the above-mentioned object, and as a result of earnestly examining the relationship between the thermal contraction phenomenon of the fiber cord and tire buckling deformation, Even when the internal pressure is zero, there is a strong correlation between the heat shrinkage stress and buckling deformation of the fiber cords that make up the fiber reinforced ply layer. It has been found that the above problem can be solved by disposing a predetermined width between the ply layers of the carcass ply layer on the radially inner side of the ply layer or between the ply layers of the carcass ply layer and the belt ply layer. The present invention has been completed based on this finding.
That is, the present invention
(1) A sidewall having a bead core embedded in the tip is continuous from both ends of the cylindrical crown portion toward the inside in the radial direction, and the space between one of these sidewalls through the crown portion and the other sidewall is the fiber cord. The carcass layer is composed of at least one carcass layer, and both ends thereof are wound around the bead core in the axial direction and fixed, and a plurality of belt layers and a tread portion are sequentially arranged on the outer periphery of the crown portion of the carcass layer. In the pneumatic safety tire provided with a reinforcing rubber layer having a substantially crescent-shaped cross section that reinforces and supports the load on the inner circumferential surface of the carcass layer of the sidewall, the carcass layer on the radially inner side of the belt layer Between the ply layers or between the carcass layer and the belt layer, the proportion of the width of the first belt ply layer in the tire width direction is 5 to 5 00% fiber reinforced ply layer (A) is provided, and at least a part of the fiber cords constituting the fiber reinforced ply layer (A) has a maximum heat shrinkage stress in the range of 0.1 to 1.8 cN / dtex. Pneumatic safety tire characterized by using a certain cord,
(2) The fiber cord constituting the fiber reinforced ply layer (A) includes at least 50% by mass of polyketone fiber, and the polyketone fiber yarn contained in the fiber cord has a tensile strength of 10 cN / dtex or more and elasticity. The pneumatic safety tire according to the above (1), wherein the rate is 200 cN / dtex or more, and the thermal shrinkage rate during dry heat treatment at 150 ° C. for 30 minutes after the adhesive (Dip treatment) is 1% to 5%,
(3) The pneumatic safety tire according to (1) or (2) above, wherein the total fineness of the fiber cord constituting the fiber-reinforced ply layer (A) is 1000 to 7000 dtex,
(4) The upper twist coefficient R of the fiber cord constituting the fiber reinforced ply layer (A) is represented by the following formula (I)
R = N × (0.125 × D / ρ) ^1/2 × 10 ⁻³ (I)
[Where N is the number of twists of the cord (times / 10 cm), D is the total number of decitex of the cord, and ρ is the density of the cord], and the upper twist coefficient R is 0.4 to 0.95 A pneumatic safety tire according to the above (1) to (3),
(5) The pneumatic safety tire according to the above (1) to (4), wherein the fiber cord constituting the fiber reinforced ply layer (A) is disposed at an angle of ± 10 degrees or less with respect to the tire equatorial plane.
(6) The pneumatic safety tire according to (1), wherein the fiber cord constituting the carcass layer includes at least 50% by mass of polyketone fibers and has a maximum heat shrinkage stress of 0.1 to 1.8 cN / dtex.
(7) The polyketone fiber base yarn contained in the fiber cord forming the carcass ply layer has a tensile strength of 10 cN / dtex or more, an elastic modulus of 200 cN / dtex or more, and is dried at 150 ° C. for 30 minutes after the adhesive (Dip treatment). The pneumatic safety tire of (6) above, wherein the heat shrinkage rate during heat treatment is in the range of 1% to 5%,
(8) The pneumatic safety tire according to (6) or (7), wherein at least one winding end portion of the carcass layer is disposed so as to have an overlapping portion with the belt ply layer end portion,
(9) The pneumatic safety tire according to (8), wherein the width of the overlapping portion with the end portion of the belt layer is 10 to 30 mm,
(10) The pneumatic safety tire according to (1), wherein the belt reinforcing layer (B) is disposed at an angle of ± 10 degrees with the tire equatorial plane on the radially outer side of the belt layer.
(11) The pneumatic safety according to (10), wherein the fiber cord constituting the belt reinforcing layer (B) includes at least 50% by mass of polyketone fibers and has a maximum heat shrinkage stress of 0.1 to 1.8 cN / dtex. tire,
(12) The polyketone fiber raw yarn contained in the fiber cord constituting the belt reinforcing layer (B) has a tensile strength of 10 cN / dtex or more, an elastic modulus of 200 cN / dtex or more, and 150 ° C. after the adhesive (Dip treatment). X Pneumatic safety tire according to (10) or (11) above, wherein the heat shrinkage rate during dry heat treatment is in the range of 1% to 5%,
(13) The pneumatic safety tire according to (1) above, wherein at least one of (2) to (12) above is combined,
(14) The polyketone constituting the polyketone fiber is represented by the following general formula (II)

[In the formula, A is a portion derived from an unsaturated compound polymerized by an unsaturated bond, and may be the same or different in the repeating unit]. 13) A pneumatic safety tire according to (15), and (15) the pneumatic safety tire according to (14), wherein A in the formula (II) is an ethylene group,
Is to provide.

  According to the present invention, there is provided a pneumatic safety tire that has improved run-flat performance by suppressing buckling deformation of the tread portion without impairing riding comfort during normal internal pressure traveling, and without particularly changing the process. can do.

  First, the pneumatic safety tire of the present invention occupies the width of the first belt ply layer in the tire width direction between the ply layers of the carcass layer on the radially inner side of the belt layer or between the carcass layer and the belt layer. Is provided with a fiber reinforced ply layer (A) of 5 to 100%, and at least a part of the fiber cord constituting the fiber reinforced ply layer (A) has a maximum heat shrinkage stress of 0.1 to 1.8 cN / dtex. It is necessary to use codes in the range.

In the pneumatic safety tire of the present invention, the width of the fiber-reinforced ply layer (A) provided in the tire width direction between the carcass layers on the radial inner side of the belt layer or between the carcass layer and the belt layer. The ratio of the first belt ply layer to the width needs to be 5 to 100%. More preferably, it is 40 to 90%.
By making the width of the fiber reinforced ply layer (A) within the above range, the effect of suppressing the occurrence of buckling during run-flat running is obtained, and the crack growth from the end of the fiber reinforced ply layer (A) is deteriorated. Suppressing and obtaining excellent tire durability.
The fiber-reinforced ply layer (A) is provided on the outer side in the tire width direction from the tire equator.
Here, the first belt ply layer refers to a belt ply layer adjacent to the carcass layer.
Further, it is necessary to use a cord having a maximum heat shrinkage stress in a range of 0.1 to 1.8 cN / dtex for at least a part of the fiber cord constituting the fiber reinforced ply layer (A). More preferably, it is desirable to use a cord in the range of 0.5 to 1.6 cN / dtex. By making the maximum heat shrinkage stress within the above range, it is possible to suppress the occurrence of buckling during run-flat running, suppress the remarkable shrinkage of the cord due to heating during tire manufacture, stabilize the finished tire shape, and uniformity A tire having excellent characteristics and improved run-flat durability can be obtained.

  Furthermore, it is desirable that the fiber cord constituting the fiber-reinforced ply layer (A) contains at least 50% by mass of polyketone fiber, preferably 70% by mass or more, and more preferably 100% by mass. By setting the content of the polyketone fiber in the above range, a cord excellent in high heat shrinkability, high strength, dimensional stability, heat resistance, and adhesion to rubber can be obtained.

In the pneumatic safety tire of the present invention, the tensile strength of the polyketone fiber yarn contained in the cord constituting the fiber-reinforced ply layer (A) is preferably 10 cN / dtex or more, more preferably 15 cN / dtex or more. . By setting the tensile strength within the above range, sufficient strength as a tire can be ensured. Although there is no restriction | limiting in particular about the upper limit of tensile strength, Usually, it is about 18 cN / dtex.
The elastic modulus of the polyketone fiber yarn is preferably 200 cN / dtex or more, more preferably 250 cN / dtex or more. By setting the elastic modulus within the above range, sufficient shape retention as a tire can be ensured.
Although there is no restriction | limiting in particular about the upper limit of an elasticity modulus, Usually, it is about 350 cN / dtex.
Furthermore, as a cord constituting the fiber-reinforced ply layer (A) after the adhesive treatment (Dip treatment) containing at least 50% by mass of the polyketone fiber, the thermal shrinkage rate during dry heat treatment at 150 ° C. for 30 minutes is 1% to 5%. %, More preferably in the range of 2% to 4%. By setting the heat shrinkage rate in the range, it is possible to secure the alignment efficiency and the tire strength by heating at the time of manufacturing the tire, and to obtain a stable tire shape.

Further, the cord constituting the fiber reinforced ply layer (A) needs to have a total fineness of 1000 to 7000 dtex. More preferably, it is 2200-4200 dtex. By making the total fineness within the above range, it is possible to suppress the deterioration of the riding comfort at the time of normal internal pressure and obtain the effect of suppressing the buckling at the time of run-flat running.
Usually, the cord can be made by twisting filaments, and the number of filament bundles to be twisted is not particularly limited, but twin twist or 3 consisting of twisting 2 to 3 filament bundles having a fineness of 500 to 3000 dtex. This twisted cord is preferred.
For example, it is possible to obtain a twisted yarn cord by applying a lower twist to the filament bundle, then combining two or three of them and applying an upper twist in the opposite direction.
As the cord used for the fiber reinforced ply layer, cords such as 1670 dtex / 2 (total fineness 3340 dtex) and 1100 dtex / 2 (total fineness 2200 dtex) are preferably used.

Further, the fiber cord constituting the fiber-reinforced ply layer (A) has an upper twist coefficient R of the following formula (I)
R = N × (0.125 × D / ρ) ^1/2 × 10 ⁻³ (I)
[Wherein N is the number of twists of the cord (times / 10 cm), D is the total number of decitex of the cord, and ρ is the density of the cord. It is preferable that the range of the upper twist coefficient R is 0.4 to 0.95. More preferably, it is 0.55-0.85. By making the upper twist coefficient within the above range, occurrence of buckling during run-flat running can be suppressed, and disorder of the cord arrangement and deterioration of tire uniformity resulting from the deterioration of the cord performance can be suppressed.

  In the pneumatic safety tire of the present invention, it is preferable that the fiber cords constituting the fiber reinforced ply layer (A) are disposed at an angle of ± 10 degrees or less with respect to the tire equatorial plane. By setting the angle of disposition of the fiber reinforced ply layer (A) within the above range, an excellent buckling suppressing effect can be obtained.

［式中、Ａは不飽和結合によって重合された不飽和化合物由来の部分であり、繰り返し単位において同一でも異なっていてもよい］で表される繰り返し単位から実質的になることが好ましい。
本発明に用いられるポリケトン繊維コードの原料であるポリケトンは、上記式（ＩＩ）で表される繰り返し単位から実質的になるポリケトンが好ましい。また、該ポリケトンの中でも、繰り返し単位の９７モル％以上が１−オキソトリメチレン［−ＣＨ₂−ＣＨ₂−ＣＯ−］であるポリケトンが好ましく、９９モル％以上が１−オキソトリメチレンであるポリケトンがさらに好ましく、１００モル％が１−オキソトリメチレンであるポリケトンが最も好ましい。繰り返し単位中の１−オキソトリメチレンの割合が高いほど分子鎖の規則性が向上し、高結晶性で高配向度の繊維が得られる。 The polyketone constituting the polyketone fiber is represented by the following general formula (II):

[Wherein A is a portion derived from an unsaturated compound polymerized by an unsaturated bond, and may be the same or different in the repeating unit], and preferably substantially consists of a repeating unit.
The polyketone which is a raw material of the polyketone fiber cord used in the present invention is preferably a polyketone substantially consisting of a repeating unit represented by the above formula (II). Among the polyketones, a polyketone in which 97 mol% or more of repeating units is 1-oxotrimethylene [—CH ₂ —CH ₂ —CO—] is preferable, and polyketone in which 99 mol% or more is 1-oxo trimethylene. Is more preferable, and a polyketone in which 100 mol% is 1-oxotrimethylene is most preferable. As the proportion of 1-oxotrimethylene in the repeating unit is higher, the regularity of the molecular chain is improved, and a fiber with high crystallinity and high degree of orientation can be obtained.

  The polyketone, which is the raw material of the polyketone fiber cord, may be partially bonded to each other and from the unsaturated compound, but the portion derived from the unsaturated compound and the ketone group are alternately arranged. The ratio is preferably 90% by mass or more, more preferably 97% by mass or more, and most preferably 100% by mass.

  In the formula (II), the unsaturated compound constituting A is most preferably ethylene, but propylene, butene, pentene, cyclopentene, hexene, cyclohexene, heptene, octene, nonene, decene, dodecene, styrene, acetylene. , Unsaturated hydrocarbons other than ethylene such as allene, methyl acrylate, vinyl acetate, acrylamide, hydroxyethyl methacrylate, undecenoic acid, undecenol, 6-chlorohexene, N-vinylpyrrolidone, diester of sulphonylphosphonic acid, styrene sulfonic acid It may be a compound containing an unsaturated bond such as sodium, sodium allyl sulfonate, vinyl pyrrolidone and vinyl chloride.

  As a method for fiberizing a polyketone obtained by a conventional method, (1) after spinning an undrawn yarn, it is subjected to multistage hot drawing and drawn at a specific temperature and magnification in the final drawing step of the multistage hot drawing. A method and (2) a method of performing unstretched yarn spinning, followed by heat stretching, and rapid cooling while applying high tension to the fiber after completion of the heat stretching are preferred. A desired filament suitable for production of the polyketone fiber cord can be obtained by fiberizing the polyketone by the method (1) or (2).

  Here, the spinning method of the unstretched yarn of the polyketone is not particularly limited, and a conventionally known method can be employed. Specifically, JP-A-2-112413, JP-A-4-228613, Wet spinning method using an organic solvent such as hexafluorooisopropanol and m-cresol as described in JP-T-505344, WO99 / 18143, WO00 / 09611, JP2001-164422, A wet spinning method using an aqueous solution of zinc salt, calcium salt, thiocyanate, iron salt or the like as described in JP-A Nos. 2004-218189 and 2004-285221 is preferable.

Further, as a method for drawing the obtained undrawn yarn, a hot drawing method in which the undrawn yarn is drawn by heating to a temperature higher than the glass transition temperature of the undrawn yarn is preferable. In the above method (2), it may be performed in one stage, but it is preferably performed in multiple stages.
There is no restriction | limiting in particular as this heat drawing method, For example, the method etc. which run a thread | yarn on a heating roll or a superheat plate, etc. are employable. Here, the heat stretching temperature is preferably in the range of 110 ° C. to (melting point of polyketone), and the total stretching ratio is preferably 10 times or more.

When the polyketone fiber is fiberized by the method (1) above, the temperature in the final drawing step of the multistage hot drawing is in the range of 110 ° C. to (the drawing temperature of the drawing step one step before the final drawing step −3 ° C.). Further, the draw ratio in the final drawing step of the multistage hot drawing is such that when the polyketone is fiberized by the method (2), the tension applied to the fiber after completion of the hot drawing is 0.5 to 4 cN / dtex. The range is preferable, and the cooling rate in the rapid cooling is preferably 30 ° C./second or more, and the cooling end temperature in the rapid cooling is preferably 50 ° C. or less.
Here, there is no restriction | limiting in particular as a rapid cooling method of the heat-stretched polyketone fiber, A conventionally well-known method can be employ | adopted, Specifically, the cooling method using a roll is preferable. In addition, since the polyketone fiber obtained in this way has a large residual elastic strain, it is usually preferable to perform relaxation heat treatment so that the fiber length is shorter than the fiber length after hot drawing. Here, the temperature of the relaxation heat treatment is preferably in the range of 50 to 100 ° C., and the relaxation ratio is preferably in the range of 0.980 to 0.999 times.

  The polyketone fiber preferably has a crystal structure with a crystallinity of 50 to 90% and a crystal orientation of 95% or more. When the degree of crystallinity is less than 50%, the fiber structure is not sufficiently formed and sufficient strength cannot be obtained, and the shrinkage property and dimensional stability during heating may be unstable. For this reason, the crystallinity is preferably 50 to 90%, more preferably 60 to 85%.

  The resulting cord can be made by twisting filament bundles. There is no restriction | limiting in particular about the number of filament bundles twisted, The code | cord | chord which twisted two or three filament bundles normally is used.

  By cording the polyketone fiber cord obtained as described above, a cord / rubber composite used for the belt reinforcing layer can be obtained. Here, the coating rubber of the polyketone fiber cord is not particularly limited, and a coating rubber used for a conventional belt or a carcass reinforcing layer can be used, but a belt coating rubber can be used for the belt reinforcing layer. preferable. Prior to rubberizing the polyketone fiber cord, an adhesive treatment may be applied to the polyketone fiber cord to improve the adhesion to the coating rubber.

The heat shrinkage stress of the polyketone fiber cord thus obtained is about 4 times that of a conventional fiber material such as nylon 66 and about 10 times that of polyethylene terephthalate.
Also, in order to make the most effective use of the high heat shrinkage characteristics of polyketone fibers, the processing temperature during processing and the temperature of the molded product during use are the temperature that indicates the maximum heat shrinkage stress (hereinafter referred to as the maximum heat shrinkage temperature). It is desirable that the temperature be close.
When used as a fiber material for reinforcing rubber such as tire cords and belts, the processing temperature such as the RFL treatment temperature and vulcanization temperature is 100 to 250 ° C, and the materials such as tires and belts are repeatedly used and rotated at high speed. The maximum heat shrinkage temperature is in the range of 100 to 250 ° C., more preferably 150 to 240 ° C., because the temperature when heat is generated becomes as high as 100 to 200 ° C.

Examples of the types of carcass cords used in the woven fabric include (a) cords made only of polyketone fibers, and (b) cords in which polyketone fibers and fibers other than polyketone fibers are mixed or twisted. It is preferable that at least 50% by mass of the polyketone fiber is contained in one cord. Polyketone fibers are used in the carcass cord at least 50% by weight, preferably at least 75% by weight, more preferably at least 90% by weight, and most preferably 100% by weight.
By setting the ratio of the polyketone fiber in the cord within the above range, excellent heat shrinkability, strength, dimensional stability, heat resistance, adhesion to rubber, and the like of the cord can be obtained.

  The fiber other than the polyketone fiber is not particularly limited as long as the ratio is less than 50% by mass, and known fibers such as polyamide fiber, polyester fiber, rayon fiber, and aramid fiber are used depending on the application and purpose. When the amount of fibers other than polyketone fibers exceeds 50% by mass, for example, in the case of cords made of polyester fibers or polyamide fibers, the strength and dimensional stability are impaired, and in the case of warp yarns made of rayon fibers, the strength is greatly impaired. In the case of warp made of aramid fibers, the adhesiveness with rubber is greatly impaired.

Next, the fiber cord constituting the carcass layer of the pneumatic safety tire of the present invention is not particularly limited, and for example, nylon, polyester, rayon, polyketone fiber, etc. can be used, but it is used for the belt reinforcing layer. It is particularly preferable to use a fiber cord containing at least 50% by mass of polyketone fiber and having a maximum heat shrinkage stress in the range of 0.1 to 1.8 cN / dtex, like the fiber cord to be produced.
When the cord containing at least 50% by mass of polyketone fiber is applied to both the belt reinforcing layer and the carcass cord, the heat shrinkage stress of both is efficiently utilized, and the cord is applied only to the bell and the reinforcing layer due to their interaction. Further, the buckling deformation of the tread portion can be suppressed and the run flat performance can be improved.

Polyketone fibers are used in the carcass cord at least 50% by weight, preferably at least 75% by weight, more preferably at least 90% by weight, and most preferably 100% by weight.
By setting the ratio of the polyketone fiber in the cord within the above range, excellent heat shrinkability, strength, dimensional stability, heat resistance, adhesion to rubber, and the like of the cord can be obtained.
The maximum heat shrinkage stress of the carcass cord is preferably in the range of 0.1 to 1.8 cN / dtex. More preferably, it is 0.4-1.6 cN / dtex, Most preferably, it is 0.4-1.0 cN / dtex. By setting the maximum heat shrinkage stress within the above range, the tire has a stable shape that suppresses the reduction in carcass cord alignment efficiency due to heating during tire manufacture, ensures sufficient tire strength, and suppresses significant shrinkage of the carcass cord. Can be obtained.

Furthermore, the tensile strength of the polyketone fiber base yarn contained in the fiber cord constituting the carcass layer is 10 cN / dtex or more, the elastic modulus is 200 cN / dtex or more, and 150 ° C. × 30 minutes as a cord after the adhesive treatment (Dip treatment) It is preferable that the heat shrinkage rate during the dry heat treatment is 1% to 5%.
The tensile strength of the polyketone fiber yarn is preferably 10 cN / dtex or more, more preferably 15 cN / dtex or more. By setting the tensile strength within the above range, sufficient strength as a tire can be ensured. Although there is no restriction | limiting in particular about the upper limit of tensile strength, Usually, it is about 18 cN / dtex.
The elastic modulus of the polyketone fiber yarn is preferably 200 cN / dtex or more, more preferably 250 cN / dtex or more. By setting the elastic modulus within the above range, it is possible to secure sufficient shape retention as a tire and to obtain a buckling suppressing effect during run flat running. Although there is no restriction | limiting in particular about the upper limit of an elasticity modulus, Usually, it is about 350 cN / dtex.
Furthermore, as a cord after the adhesive treatment (Dip treatment) containing at least 50% by mass of the polyketone fiber, the thermal shrinkage rate during dry heat treatment at 150 ° C. for 30 minutes is in the range of 1% to 5%, more preferably 2 It is desirable to be in the range of% to 4%. By setting the heat shrinkage rate within the above range, it is possible to secure the alignment efficiency and the tire strength by heating at the time of manufacturing the tire, and to obtain a stable tire shape.

The pneumatic safety tire of the present invention is preferably disposed so as to have an overlapping portion of at least one winding end portion and belt layer end portion of the carcass layer. By having an overlapping portion with the belt layer end portion, when a fiber cord containing at least 50% by mass of polyketone fiber is applied as a carcass cord, the utilization factor of the heat shrinkage stress of the cord can be increased.
Moreover, it is preferable that the width | variety of the overlap part of the said winding edge part and a belt layer edge part is 10-30 mm. By setting the width of the overlapping portion in the above range, deterioration of uniformity can be suppressed and the utilization rate of the heat shrinkage stress of the carcass cord can be efficiently increased.

In the pneumatic safety tire of the present invention, it is preferable that a belt reinforcing layer (B) is further disposed on the outer side in the radial direction of the belt layer at an angle of ± 10 degrees with respect to the tire equatorial plane. By providing this belt reinforcing layer, the effect of suppressing the occurrence of buckling becomes more synergistic.
The fiber cord constituting the belt reinforcing layer (B) is not particularly limited, and for example, nylon, polyester, rayon, polyketone fiber, etc. can be used, but the fiber reinforcing ply layer (A) or carcass layer can be used. It is particularly preferable to use a fiber cord containing at least 50% by mass of polyketone fiber and having a maximum heat shrinkage stress in the range of 0.1 to 1.8 cN / dtex as in the fiber cord constituting. The polyketone fiber is used in the fiber cord constituting the belt reinforcing layer at least 50% by mass, preferably at least 75% by mass, more preferably at least 90% by mass, and most preferably 100% by mass.
By setting the ratio of the polyketone fiber in the cord within the above range, excellent heat shrinkability, strength, dimensional stability, heat resistance, adhesion to rubber, and the like of the cord can be obtained.

Moreover, it is preferable that the maximum heat shrinkage stress of the fiber cord which comprises the said belt reinforcement layer (B) exists in the range of 0.1-1.8 cN / dtex. More preferably, it is 0.4-1.6 cN / dtex, Most preferably, it is 0.4-1.0 cN / dtex. By setting the maximum heat shrinkage stress within the above range, it is possible to suppress a decrease in the efficiency of arranging the cord due to heating at the time of manufacturing the tire, to sufficiently secure the strength of the tire, and to obtain a tire having a stable shape while suppressing a significant contraction of the cord. be able to.
By applying a cord containing at least 50% by mass of polyketone fiber to each of the fiber-reinforced ply layer (A), the carcass layer, and the bell and the reinforcing layer (B), the heat shrinkage stress of the three parties can be efficiently utilized and the interaction between them. Therefore, compared with the case where the cord is applied only to the fiber reinforced ply layer, the buckling deformation of the tread portion can be further suppressed and the run flat performance can be improved.

Further, the tensile strength of the polyketone fiber base yarn included in the fiber cord constituting the belt reinforcing layer (B) is 10 cN / dtex or more, the elastic modulus is 200 cN / dtex or more, and 150 as the cord after the adhesive treatment (Dip treatment). It is preferable that the heat shrinkage rate during dry heat treatment at 1 ° C. for 30 minutes is 1% to 5%.
The polyketone fiber yarn has a tensile strength of 10 cN / dtex or more, more preferably 15 cN / dtex or more. By setting the tensile strength within the above range, sufficient strength as a tire can be ensured. Although there is no restriction | limiting in particular about the upper limit of tensile strength, Usually, it is about 18 cN / dtex.
The elastic modulus of the polyketone fiber yarn is preferably 200 cN / dtex or more, more preferably 250 cN / dtex or more. By setting the elastic modulus within the above range, it is possible to secure sufficient shape retention as a tire and to obtain a buckling suppressing effect during run flat running. Although there is no restriction | limiting in particular about the upper limit of an elasticity modulus, Usually, it is about 350 cN / dtex.
Furthermore, as a cord after the adhesive treatment (Dip treatment) containing at least 50% by mass of the polyketone fiber, the thermal shrinkage rate during dry heat treatment at 150 ° C. for 30 minutes is in the range of 1% to 5%, more preferably 2 % To 4%. By setting the heat shrinkage rate within the above range, it is possible to secure the alignment efficiency and the tire strength by heating at the time of manufacturing the tire, and to obtain a stable tire shape.

In the present invention, the heat shrinkage stress of the cord containing 50 mass% of at least the polyketone fiber constituting the fiber reinforced ply layer (A), the carcass layer, and the belt reinforcing layer (B) is reversibly repeated corresponding to the tire temperature. It is preferable to express.
The heat shrinkage stress of the cord containing 50% by mass of at least the polyketone fiber used in the present invention rapidly increases when it exceeds 110 ° C. That is, the thermal shrinkage stress increases as the tire temperature rises.
When the temperature of the tire rises due to run-flat running, the polyketone fiber in the belt reinforcing layer exerts a large heat shrinkage stress and improves the rigidity of the entire tread part, thereby suppressing the occurrence of the tire buckling phenomenon, As a result, the run flat durability of the tire is improved. The increase in tire temperature due to run-flat running may be 200 ° C. or higher.
On the other hand, at low temperatures, that is, when running at normal internal pressure, the heat shrinkage stress of the polyketone fiber is hardly exerted and the rigidity is hardly improved. The ride comfort during driving is not impaired.
The shrinkage of the polyketone fiber cord returns as the cord reaches room temperature, and reappears when the cord reaches a high temperature. This phenomenon occurs reversibly and is repeated every time the tire is driven.

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view in the width direction showing one embodiment of the pneumatic safety tire of the present invention.
A tire 1 shown in FIG. 1 has a pair of left and right bead portions 2, a pair of sidewall portions 3, and a tread portion 4 connected to both sidewall portions 3, and bead cores embedded in the bead portions 2, respectively. The carcass layer 6 that extends in a toroidal shape between the two and reinforces each of the portions 2, 3, 4 and is disposed inside the carcass layer 6 of the sidewall portion 3. A pair of substantially crescent-shaped reinforcing rubber layers 7, a belt layer 8 including at least two first belt ply layers 9 and a second belt ply layer 10 disposed inside the tread portion 4, and the belt layers 8, at least one belt reinforcing layer 12 disposed on the outer side in the tire radial direction, in the illustrated example, a first belt reinforcing layer 12 disposed so as to cover the entire belt layer 8, and the first belt reinforcing layer 12 Tire radius direction Outside and a second belt reinforcing layer 13 of the deployed pair so as to cover the end portion in the width direction of the belt layer 8. Reference numeral 14 denotes a bead filler, and 15 denotes a rim guard.

  The carcass layer 6 in the illustrated example is composed of a single carcass ply layer, and a main body extending in a toroidal shape between a pair of bead cores 5, and the bead cores 5 around the bead cores 5 from the inside to the outside in the tire width direction. The folded end portion rolled up radially outward has an overlap portion with the end portion of the belt layer 8, but the number of plies and the structure of the carcass layer 6 are set in the pneumatic safety tire of the present invention. However, it is not limited to these.

  Further, the belt layer constituting the belt 8 in the illustrated example is usually composed of a rubberized layer of cords, preferably a rubberized layer of steel cords, extending incline with respect to the tire equatorial plane, and further two belt layers. The cords constituting the belt layer are laminated so as to intersect with each other across the equator plane. In the illustrated example, the belt layer 8 is composed of two first belt ply layers 9 and a second belt ply layer 10, but in the pneumatic safety tire of the present invention, a belt ply layer constituting the belt 8 layer. The number of sheets may be three or more.

In the pneumatic safety tire of the present invention, the fiber reinforced ply layer 11 is composed of a rubberized layer of cords arranged at an angle of ± 10 degrees or less with respect to the tire equator plane. A fiber cord containing 50% by mass of polyketone fiber and having a high maximum heat shrinkage stress is applied. The width of the fiber reinforced ply layer 11 is 5 to 100% of the width of the first belt ply layer 9.
In the illustrated example, the fiber reinforced ply layer 11 is disposed between the belt layer 8 and the carcass layer 6, but when the carcass layer 8 is composed of a plurality of carcass ply layers, the diameter of the belt layer 8. It is also an embodiment of the present invention to dispose the fiber reinforced ply layer 11 between the ply layers of the carcass layer on the inner side in the direction.

Furthermore, in the pneumatic safety tire of the present invention, the first belt reinforcing layer 12 is composed of a rubberized layer of cords arranged at an angle of ± 10 degrees or less with respect to the tire equatorial plane, and the cord includes at least the polyketone described above. A fiber cord containing 50% by mass of fiber and having a high maximum heat shrinkage stress is applied. The width of the first belt reinforcing layer 9 is preferably in the range of 95 to 105% of the width of the belt 8.
In addition, as shown in FIG. 1, the pneumatic safety tire of the present invention is provided with one second belt reinforcement so as to cover the outer end in the width direction of the belt layer 8 outside the belt layer 8 in the tire radial direction. Although the layer 13 is provided, the arrangement of the first belt reinforcing layer 12 and the second belt reinforcing layer 13 is not essential. The second belt reinforcing layer 13 is composed of a rubberized layer of cords arranged at an angle within ± 10 degrees with respect to the tire equator plane, like the first belt reinforcing layer 14. The material of the cord is not limited, and examples thereof include organic fibers such as steel, nylon, polyester, aramid, and polyketone. Since higher run-flat durability can be obtained, it is preferable that the cord constituting the second belt reinforcing layer 13 is a fiber cord having a high maximum heat shrinkage stress and containing at least 50% by mass of the polyketone fiber.

  The width of the second belt reinforcing layer 13 is preferably 20 mm or more as viewed from the belt end in order to ensure the run-flat durability effect. Further, the width of the second belt reinforcing layer 13 may be the same as the width of the first belt reinforcing layer 12.

EXAMPLES Next, although an Example is given and this invention is demonstrated in more detail, this invention is not limited to the following Example at all. Various measurement methods were performed based on the following methods.
<Code property evaluation>
1. Tensile strength and tensile modulus Measured according to JIS-L-1013. As the tensile elastic modulus, an initial elastic modulus value calculated from a load at an elongation of 0.1% and a load at an elongation of 0.2% was adopted.
2. Dry heat shrinkage rate Dry heat treatment was performed in an oven at 150 ° C. for 30 minutes, and the fiber length before and after the heat treatment was measured by applying a load of 1/30 (cN / dtex) and obtained by the following equation. Dry heat shrinkage rate (%) = (Lb−La) / Lb × 100 (where Lb is the fiber length before heat treatment, and La is the fiber length after heat treatment)
3. Maximum heat shrinkage stress Adhesive treatment (Dip treatment), a sample obtained by fixing a polyketone fiber cord before vulcanization to a length of 25 cm, is heated at a heating rate of 5 ° C / min, and the stress generated in the cord is measured. It was measured. It is a value obtained by reading the maximum heat shrinkage stress from the obtained temperature-stress curve.

<Tire performance evaluation>
1. Uniformity measurement In accordance with JASOC607, under the internal pressure of 200 kPa and the load of 4510N, the low speed RFV and the high speed RFV of each of the five test tires were measured. The index is shown as 100. Smaller numbers indicate better uniformity. The low speed is a value at a peripheral speed of 7 km / h, and the high speed is a value at a peripheral speed of 120 km / h.
2. Run-flat durability test A test tire is mounted on the right front wheel of an FR vehicle with a rim (16 × 71 / 2JJ) and an internal pressure of 0 kgf / cm ² and traveled at a speed of 80 km / h until the tire breaks. Comparison was made based on travel distance (km). The load applied to the tire during running was 585 kg. The running distance (km) until the tire broke was measured.

<Manufacture of polyketone fibers>
A polyketone polymer with an intrinsic viscosity of 5.3, which is a completely alternating copolymer of ethylene and carbon monoxide, prepared by a conventional method is added to an aqueous solution containing 65% by weight of zinc chloride / 10% by weight of sodium chloride, and stirred at 80 ° C. for 2 hours. It melt | dissolved and the dope with a polymer concentration of 8 mass% was obtained.
This dope is heated to 80 ° C., filtered through a 20 μm sintered filter, passed through a 10 mm air gap from a 50-hole nozzle with a diameter of 0.10 mmφ kept at 80 ° C., and 5% by weight of zinc chloride. Was extruded at a rate of discharge of 2.5 cc / min into water at 18 ° C. containing a coagulated yarn while being drawn at a speed of 3.2 m / min.
Subsequently, the coagulated yarn was washed with an aqueous sulfuric acid solution having a concentration of 2% by weight and a temperature of 25 ° C., and further washed with water at 30 ° C., and then the coagulated yarn was wound at a speed of 3.2 m / min.
After impregnating IRGANOX 1098 (manufactured by Ciba Specialty Chemicals) and IRGANOX 1076 (manufactured by Ciba Specialty Chemicals) into the coagulated yarn by 0.05% by weight (vs. polyketone polymer), the coagulated yarn was dried at 240 ° C. A finishing agent was applied to obtain an undrawn yarn.
As the finishing agent, oleic acid lauryl ester / bisoxyethyl bisphenol A / polyether (propylene oxide / ethylene oxide = 35/65: molecular weight 20000) / polyethylene oxide 10 mol addition oleyl ether / polyethylene oxide 10 mol addition castor oil ether / The one having a composition of sodium stearyl sulfonate / sodium dioctyl phosphate = 30/30/10/5/23/1/1 (mass% ratio) was used.

The obtained undrawn yarn was drawn at 240 ° C. in the first stage, followed by the second stage at 258 ° C., the third stage at 268 ° C., the fourth stage at 272 ° C., and then the second stage at 200 ° C. The film was stretched five times at 1.08 times (stretching tension 1.8 cN / dtex) and wound with a winder. The total draw ratio from the undrawn yarn to the five-stage drawn yarn was 17.1 times.
This fiber had high physical properties of strength 15.6 cN / dtex, elongation 4.2%, and elastic modulus 347 cN / dtex.

<Manufacture of sample tires>
About the polyketone fiber, what was manufactured above was used. As for the others, trial tires (tire size: 225 / 60R17) were each prototyped with a one-ply structure based on the contents described in Table 1. Note that the widths of the overlapping portions of the carcass ply winding portion and the belt layer end portion were all 20 mm. The run flat durability was measured for each tire. The test results are shown in Table 1.

Conventional Example A rayon fiber cord (1840 dtex / 3) having a maximum heat shrinkage stress of 0 cN / dtex is applied to the carcass, and a 66 nylon fiber cord (1400 dtex / 2) having a maximum heat shrinkage stress of 0.07 cN / dtex is applied to the belt reinforcing layer. Applied.

Examples 1-3
Polyketone fiber cord (1670 dtex / 2) having a maximum heat shrinkage stress of 0.45 cN / dtex (Example 1), 0.91 cN / dtex (Example 2), 0.89 cN / dtex (Example 3) A layer (1840 dtex / 3) with a maximum heat shrinkage stress of 0 cN / dtex is applied to the carcass with a maximum heat shrinkage stress of 0.07 cN / dtex. A 66 nylon fiber cord (1400 dtex / 2) was applied to the belt reinforcement layer.

Examples 4-6
Polyketone fiber cord (1670 dtex / 2) having a maximum heat shrinkage stress of 0.45 cN / dtex (Example 4), 0.91 cN / dtex (Example 5), 0.89 cN / dtex (Example 6) A polyketone fiber cord (1670 dtex / 2) having a maximum heat shrinkage stress of 0.91 cN / dtex is applied to the carcass and applied to the carcass with a maximum heat shrinkage stress of 0.07 cN / dtex. A 66 nylon fiber cord (1400 dtex / 2) having a thickness of 1 was applied to the first belt reinforcing layer.

Examples 7-9
Polyketone fiber cord (1670 dtex / 2) having a maximum heat shrinkage stress of 0.91 cN / dtex is applied to a fiber reinforced ply layer (50% of the belt width), and the polyketone fiber having a maximum heat shrinkage stress of 0.91 cN / dtex 66 nylon fiber cord (1400 dtex / 2) having a maximum heat shrinkage stress of 0.15 cN / dtex as Example 7 and a maximum heat shrinkage stress of 0.25 cN / dtex as Example 8 when the cord (1670 dtex / 2) was applied to the carcass A polyethylene ketone cord (1670 dtex / 2) having a maximum heat shrinkage stress of 0.91 cN / dtex as Example 9 was applied to the first belt reinforcing layer.

Example 10
A polyketone fiber cord (3340 dtex / 3) having a maximum heat shrinkage stress of 0.90 cN / dtex is applied to a fiber-reinforced ply layer (50% ratio to 1 belt width), and a rayon fiber cord having a maximum heat shrinkage stress of 0 cN / dtex ( 1840 dtex / 3) was applied to the carcass, and a 66 nylon fiber cord (1400 dtex / 2) having a maximum heat shrinkage stress of 0.07 cN / dtex was applied to the first belt reinforcement layer.

Comparative Example 1
A polyketone fiber cord (940 dtex / 1) having a maximum heat shrinkage stress of 0.90 cN / dtex is applied to a fiber reinforced ply layer (70% of the belt width), and a rayon fiber cord having a maximum heat shrinkage stress of 0 cN / dtex (1840 dtex / 3) was applied to the carcass and 66 nylon fiber cord (1400 dtex / 2) having a maximum heat shrinkage stress of 0.07 cN / dtex was applied to the first belt reinforcement layer.

Comparative Example 2
Polyketone fiber with a maximum heat shrinkage stress of 0.08 cN / dtex, 66 nylon blended cord (PK1670 dtex / 2, 37%, 66 nylon 1400 dtex / 2, 63%) and fiber reinforced ply layer (70% of the belt width) The rayon fiber cord (1840 dtex / 3) having a maximum heat shrinkage stress of 0 cN / dtex is applied to the carcass, and the 66 nylon fiber cord (1400 dtex / 2) having a maximum heat shrinkage stress of 0.07 cN / dtex is applied to the first. Applied to belt reinforcement layer.

Comparative Example 3
A polyketone fiber cord (1670 dtex / 2) having a maximum heat shrinkage stress of 0.70 cN / dtex is applied to a fiber reinforced ply layer (110% of the belt width), and a rayon fiber cord having a maximum heat shrinkage stress of 0 cN / dtex ( 1840 dtex / 3) was applied to the carcass, and a 66 nylon fiber cord (1400 dtex / 2) having a maximum heat shrinkage stress of 0.07 cN / dtex was applied to the first belt reinforcement layer.

注」
＊１．ＰＫ：ポリケトン繊維
＊２．ＰＫ：１６７０ｄｔｅｘ／１
＊３．６６Ｎ：１４００ｄｔｅｘ／２
＊４．Ｒｗ／１Ｂｗ×１００：第１ベルトプライ層の幅（１Ｂｗ）に対する繊維補強プライ層の幅（Ｒｗ）の割合（％）
＊５．ＰＥＮ：ポリエチレンナフタレート繊維

note"
* 1. PK: Polyketone fiber * 2. PK: 1670 dtex / 1
* 3.66N: 1400 dtex / 2
* 4. Rw / 1Bw × 100: ratio (%) of the width (Rw) of the fiber-reinforced ply layer to the width (1Bw) of the first belt ply layer
* 5. PEN: Polyethylene naphthalate fiber

As is apparent from Table 1, the tires of Examples 1 to 9 of the present invention using polyketone fibers in the fiber reinforced ply layer are the conventional examples and Comparative Example 1 in which the total fineness of the polyketone fibers used in the belt reinforcing layer is small. Compared to the tire of Comparative Example 3 using a mixed twist cord having a small maximum heat shrinkage stress as the fiber reinforced ply layer and the tire of Comparative Example 4 in which the ratio of the width of the fiber reinforced ply layer to the width of the first belt ply layer exceeds 100% Flat durability is improved.
In addition, the run-flat durability of the tires of Examples 4 to 6 using the polyketone fiber cord having a high maximum heat shrinkage stress as the carcass cord is considerably improved by the synergistic effect.
Further, the tires of Examples 7 to 8 using the cord having a high maximum heat shrinkage stress for the belt reinforcing layer (first belt reinforcing layer) further increase the synergistic effect and considerably improve the run flat durability. In particular, in the tire of Example 9 in which the polyketone fiber having high heat shrinkage stress is applied to any of the fiber reinforced ply layer, the carcass cord, and the belt reinforcing layer, the run flat durability test completed 300 km.
Further, as is apparent from Table 1, it can be seen that the tire uniformity characteristics of the pneumatic safety tire of the embodiment of the present invention are equivalent to or improved compared with the conventional tire.

ADVANTAGE OF THE INVENTION According to this invention, the pneumatic safety tire which suppressed the buckling deformation | transformation of the tread part and improved the run flat performance without impairing riding comfort at the time of normal internal pressure traveling can be provided.
In particular, it can be suitably applied to a side-reinforced pneumatic safety tire.

1 is a left sectional view in the width direction showing one embodiment of a pneumatic safety tire of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tire 2 Bead part 3 Side wall part 4 Tread part 5 Bead core 6 Carcass layer 7 Reinforcement rubber layer 8 of a substantially crescent-shaped cross section Belt layer 9 First belt ply layer 10 Second belt ply layer 11 Fiber reinforced ply layer 12 First belt Reinforcing layer 13 Second belt reinforcing layer 14 Bead filler 15 Rim guard 1Bw First belt ply layer width Rw Fiber reinforcing ply layer width

Claims (15)

  From the both ends of the cylindrical crown portion toward the inside in the radial direction, sidewalls with a bead core embedded in the tip portion are connected, and the space between one of these sidewalls through the crown portion and the other sidewall is the carcass layer of the fiber cord. The carcass layer is composed of at least one piece, and both ends thereof are wound around the bead core in the axial direction and fixed, and a plurality of belt layers and a tread portion are sequentially arranged on the outer periphery of the crown portion of the carcass layer to reinforce each of them. In addition, in the pneumatic safety tire provided with a reinforcing rubber layer having a substantially crescent-shaped cross section, which shares and supports a load on the inner circumferential surface of the carcass layer of the sidewall, the ply layer of the carcass layer on the radially inner side of the belt layer Or between the carcass layer and the belt layer, the proportion of the width of the first belt ply layer in the tire width direction is 5 to 100% The fiber reinforced ply layer (A) is provided, and at least a part of the fiber cord constituting the fiber reinforced ply layer (A) has a maximum heat shrinkage stress in the range of 0.1 to 1.8 cN / dtex. Pneumatic safety tire characterized by using.   The fiber cord constituting the fiber-reinforced ply layer (A) contains at least 50% by mass of polyketone fiber, and the polyketone fiber yarn contained in the fiber cord has a tensile strength of 10 cN / dtex or more and an elastic modulus of 200 cN. 2. The pneumatic safety tire according to claim 1, which has a thermal shrinkage ratio of 1% to 5% during dry heat treatment at 150 ° C. for 30 minutes after the adhesive (Dip treatment).   The pneumatic safety tire according to claim 1 or 2, wherein the total fineness of the fiber cord constituting the fiber-reinforced ply layer (A) is 1000 to 7000 dtex. The upper twist coefficient R of the fiber cord constituting the fiber reinforced ply layer (A) is represented by the following formula (I)
R = N × (0.125 × D / ρ) ^1/2 × 10 ⁻³ (I)
[Where N is the number of twists of the cord (times / 10 cm), D is the total number of decitex of the cord, and ρ is the density of the cord], and the upper twist coefficient R is 0.4 to 0.95 The pneumatic safety tire according to any one of claims 1 to 3.   The pneumatic safety tire according to any one of claims 1 to 4, wherein the fiber cord constituting the fiber-reinforced ply layer (A) is disposed at an angle of ± 10 degrees or less with respect to the tire equatorial plane.   The pneumatic safety tire according to claim 1, wherein the fiber cord constituting the carcass layer includes at least 50% by mass of polyketone fibers and has a maximum heat shrinkage stress of 0.1 to 1.8 cN / dtex.   The tensile strength of the polyketone fiber base yarn contained in the fiber cord constituting the carcass layer is 10 cN / dtex or more, the elastic modulus is 200 cN / dtex or more, and 150 ° C. × 30 minutes after the adhesive (Dip treatment) during dry heat treatment The pneumatic safety tire according to claim 6, wherein the thermal shrinkage ratio is in the range of 1% to 5%.   The pneumatic safety tire according to claim 6 or 7, wherein at least one winding end portion of the carcass layer is disposed so as to have an overlapping portion with the belt layer end portion.   The pneumatic safety tire according to claim 8, wherein the width of the overlapping portion with the end portion of the belt layer is 10 to 30 mm.   2. The pneumatic safety tire according to claim 1, wherein a belt reinforcing layer (B) is disposed at an angle of ± 10 degrees with respect to a tire equatorial plane on a radially outer side of the belt layer.   The pneumatic safety tire according to claim 10, wherein the fiber cord constituting the belt reinforcing layer (B) includes at least 50% by mass of polyketone fibers and has a maximum heat shrinkage stress of 0.1 to 1.8 cN / dtex.   The tensile strength of the polyketone fiber base yarn contained in the fiber cord constituting the belt reinforcing layer (B) is 10 cN / dtex or more, the elastic modulus is 200 cN / dtex or more, and 150 ° C. × 30 minutes after the adhesive (Dip treatment) The pneumatic safety tire according to claim 10 or 11, wherein a thermal shrinkage rate during dry heat treatment is in a range of 1% to 5%.   The pneumatic safety tire according to claim 1, wherein at least one of claims 2 to 12 is combined. The polyketone constituting the polyketone fiber is represented by the following general formula (II)

[Wherein A is a portion derived from an unsaturated compound polymerized by an unsaturated bond, and may be the same or different in the repeating unit]. A pneumatic safety tire according to any one of the above.   The pneumatic safety tire according to claim 14, wherein A in the formula (II) is an ethylene group.

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