JPH0659763B2 - Tire with polyester carcass reinforcement layer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a passenger car tire having excellent steering performance, and more specifically, to a carcass ply-reinforcing organic fiber made of a polyester cord having high rigidity and used in a vulcanization process. The present invention relates to a radial tire for passenger cars, which prevents deterioration of the rigidity of polyester cord.

(Prior Art) Generally, a radial tire for passenger cars has a carcass ply (1) composed of a rubber matrix and a reinforcing organic fiber cord embedded therein as shown in FIG. Of the belt plies (12), (12) '... made of a large number of parallel steel cords embedded in a rubber matrix while the steel cords are in contact with the tire equator. It has a structure in which a belt (11) formed by cross-polymerization so as to form an angle of ° is laminated on the top of the carcass ply (1), and the carcass is twisted by the lateral acceleration during operation. Place the high bead filler (8) on the bead core (7) of the tire bead to prevent the response characteristics from deteriorating.
(9), the end of the carcass ply (1) is folded back from the inside to wrap around the bead core assembly (9),
The folded portion (3) is attached to the outside of the carcass ply (1) and terminates.

Radial tires of this type are more widely used in recent years because they are superior in steering stability, braking performance, high-speed durability, wear resistance, and load durability to bias tires. In order to further improve the driving performance of the tire in order to improve the running safety of the tire, use a rubber composition with a large friction coefficient in the tread part, or tire flatness (ratio between tire height and tire width). The flat radial tire has been used habitually by increasing the contact area by reducing the contact angle.

However, even if the road surface gripping force becomes large, the steering response does not become high accordingly, so that the rigidity of the carcass must also be made large in order to improve the driving performance. However, if the rigidity of the carcass becomes excessive, the ride comfort deteriorates.

Polyester cords are generally used in the carcass of flat radial tires, and it is preferable to increase the rigidity of the cord in order to increase the rigidity of the carcass. 15
Many attempts have been made, such as a method for improving the stretching process disclosed in Japanese Patent No. 430 or a method for relatively lowering the degree of polymerization of polyester proposed in Japanese Patent Laid-Open No. 58-8119. In addition, the polyester cord has an intermediate elongation (2.3 g / d) if the material, spinning conditions, and twist structure are determined.
The elongation (when the load is applied, which is different from the breaking elongation) and the dry heat shrinkage (hereinafter referred to as dry heat shrinkage) at a temperature of 150 ° C (hereinafter referred to as the dimensional change coefficient) are constant. The ratio can be arbitrarily selected within a limited range by changing the heat setting conditions. The broken line (I) in FIG. 3 shows the relationship between the intermediate elongation and the dry heat shrinkage of the conventional high polymerization polyester cord. As is clear from this diagram (I), the dimensional change coefficient is about 8.5%, which is a substantially constant value. The Young's modulus of such a cord increases as the intermediate elongation decreases. The dry heat shrinkage is an index that indicates how much the polyester cord shrinks when heated, and when the polyester cord is slightly heated and loosely heated to the extent that there is room for further shrinkage when heated again, dry heat shrinkage The shrinkage rate changes to a small value, and the intermediate elongation increases as the dry heat shrinkage rate decreases. When the cord at any point on the line in Fig. 3 is heated, it moves to the upper left on the line. To do. Therefore, in order to obtain high rigidity, it is sufficient to increase the stretch and heat set in an emergency to reduce the intermediate elongation, but conversely the dry heat shrinkage ratio increases. Therefore, it is necessary to simultaneously reduce the intermediate elongation and the dry heat shrinkage.

The polyester cord thus prepared is embedded in a rubber matrix to form a carcass ply, but in order to improve adhesion with rubber prior to embedding, it is usually
After being dipped in resorcin / formalin / retex and dried, the cord is tensioned and fixed by heat setting by stretching it by 2 to 10% in an atmosphere of 210 to 250 ° C. to reduce the intermediate elongation.

However, the cord set so that the intermediate elongation is small has a large thermal contraction as a result.
In the tire where the carcass ply (1) surrounds the bead core assembly (9) and terminates in the vicinity thereof as shown in the figure, the carcass ply turnback portion (3) is locked only by the adhesive force of the rubber. When the rubber is plasticized by the high temperature treatment in the vulcanization process, the locking force of the rubber cannot withstand the contracting force of the cord, and the cords slide with each other on the adhesive surface to contract, and the broken line (Fig. 3) Instead of moving I) to the upper left of the figure to reduce the dry heat shrinkage, the intermediate elongation increases, so the rigidity of the tire decreases and the maneuverability cannot be improved sufficiently. Moreover, the unevenness of the side wall portion increases, and a uniform shape cannot be obtained.

On the other hand, JP-A-54-25001 and 58-17400.
No. 4, No. 59-2908, No. 59-40903 and No. 59-81208 have already been disclosed, but the end portion (4) of the carcass ply as shown in FIG. The tire terminated so as to be sandwiched between 1) and the belt ply (12) has a bead core assembly (9).
Since it is difficult for deviation to occur around the cord, the cord is heated during vulcanization under the action of tension that counteracts the contraction stress, and the decrease in modulus is small and the steering response is improved, but the conventional dimensions When a polyester cord with a large coefficient of change is used, at the same time as the cord is in tension, the contraction stress becomes large and the tire shape is distorted, so the vibration generated by the unevenness of the road surface is greatly attenuated at the side part. Without being transmitted to the rim, the tire uniformity deteriorates, and vibration increases, resulting in poor riding comfort.

Furthermore, since the lower part of the side of the carcass folded-back portion (3) is repeatedly subjected to compressive stress, the cord in that portion is easily fatigued. Therefore, in order to prevent this, a code with less fatigue has been demanded. Further, a steel cord reinforcing layer (5) made of a steel cord or a high elastic modulus cord is arranged between the bead core assembly (9) and the carcass folded portion (3), and the neutral line of bending deformation is set to the carcass folded portion ( A method of reducing the effect of compressive stress was attempted in the vicinity of 3).

In addition, especially for tires with a low flatness that emphasizes maneuverability, the vertical line component of the vibration transmitted through the cord is large because the angle formed between the neutral line of the lower part of the side and the tire radial direction is small. As a result, not only the riding comfort is deteriorated, but also since the radius of curvature at the maximum width position is small, compressive stress acts strongly on the inner cord, and fatigue causes a decrease in strength.

Moreover, this can also be said from the following points.

That is, the thickness of the tire is reduced at the place where the tire moves from the lower portion to the side portion of the tire, and the belt ends at the end, so that the rigidity usually changes discontinuously at that portion. Therefore, when the tire comes into contact with the ground, stress concentrates on that portion and is greatly deformed. Therefore, a conventional tire with a small flatness has a good road surface gripping property, and accordingly, a structure in which the carcass rigidity of the above part is increased correspondingly is used, and a tire of the neutral line of the carcass is used to increase the rigidity of the lower half part of the side. The angle to the radial direction was made small. As a result, the height of the maximum width of the carcass is 65 to 70% of the carcass height, the radius of curvature in the vicinity is small, the flex zone of the carcass is narrow, and the stress is concentrated to compress the compressive stress on the inner cord. Causes a strong decrease in the strength of the cord.

In view of the fact that it is desired to develop a radial tire having both good riding comfort and good driving performance, the inventors of the present invention have disclosed in Japanese Patent Laid-Open No. 59-91458 that a radial tire with a particularly small flatness is particularly desired. At the same time, the folding end position of the carcass ply is specified, and the height range of the carcass maximum width position is limited, so that both the riding comfort and the driving performance are improved, and the fatigue due to the compression of the cord is reduced. Was successful.

(Problems to be Solved by the Invention) The inventors of the present invention achieved a great improvement in the function of a flat radial tire by the invention proposed in Japanese Patent Laid-Open No. 59-91458. As a result of repeated detailed studies on the characteristics and behaviors in the tire manufacturing process, the loss tangent (t
The polyester cord having a maximum anδ) temperature of 120 to 135 ° C. gives a carcass having high fatigue resistance and high rigidity, and is embedded in a matrix made of a specific rubber composition so that it can be used in the vulcanization process. Even when exposed to high temperatures, a radial tire with excellent steering performance, comfortable ride, and uniform shape can be obtained without causing a decrease in Young's modulus and strength loss, and the above-mentioned already proposed invention is further added. We have found that it can be improved.

That is, an object of the present invention is to provide a radial tire having excellent driving performance and riding comfort. Another object is to provide a flat radial tire which has good driving performance and riding comfort and has a large road surface gripping property. Still another object is to obtain a radial tire in which the quality and shape of the side wall portion are uniform and the fatigue resistance is high.

Thus, the present invention finds out the characteristics of the polyester cords constituting the carcass ply from a comprehensive viewpoint, and the riding comfort,
It is an object of the present invention to provide a radial tire improved through all of driving performance, road gripping property and fatigue resistance.

(Means for Solving Problems) That is, a feature of the present invention is that a carcass ply made of an organic fiber cord embedded in rubber is arranged so that the cord and the tire equator are substantially orthogonal to each other, Both ends of the carcass ply are folded back from the inside so as to wrap each of the pair of cord core assemblies, end along the outside of the carcass ply and terminate, and further made of a plurality of steel cords embedded in rubber and parallel to each other. The steel cord of a plurality of tires is 10-30 with the tire equator.
In a tire having a radial structure in which a belt formed by cross-polymerization forming an angle of ° is laminated on the top of the carcass ply, the organic fiber cord of the carcass ply incorporated in the tire has an intrinsic viscosity of 0.8 to 1.2. Which is a multifilament twisted yarn substantially made of polyethylene terephthalate having a maximum temperature of loss tangent (tan δ) when measured at a frequency of 10 Hz using a dynamic viscoelasticity measuring device in a temperature range of 120 to 135 ° C. And embedded in a rubber consisting of 50 to 80% by weight of natural rubber and 50 to 20% by weight of synthetic rubber, and post-cure inflation after vulcanization to give a tire with 2.3. The intermediate elongation of the cord when a load of g / d is applied is 6.
The tire of the polyester carcass reinforcing layer has a content of 0% or less and a sum of the intermediate elongation and the dry heat shrinkage at a temperature of 150 ° C. of 8.5% or less.

Here, it should be noted that the characteristics of the cord, that is, the intermediate elongation and the heat shrinkage are related to the history of heat and tension,
Although different depending on the respective states of the depping treatment cord and the cord incorporated in the tire, the respective numerical values in the present invention are intended to be the organic fiber cord of the carcass ply incorporated in the tire among them.

The organic fiber cord applied to the present invention is obtained by melt-spinning and stretching a substantial polyethylene terephthalate having an intrinsic viscosity [η] of at least 0.8, preferably 0.8 to 1.2 when measured at a temperature of 25 ° C. using orthochlorophenol as a solvent. It is a twisted yarn of multifilament. Here, the term "substantially polyethylene terephthalate" means that at least 85 mol% is an ethylene terephthalate unit, and the remaining 15 mol% is, for example, an aromatic dicarboxylic acid such as isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, or propylene. This means that it may be a random copolymer, a block copolymer or a blend polymer in which a diol component such as glycol or butylene glycol, an oxy acid such as P-oxybenzoic acid or the like is copolymerized. If the content of ester units other than ethylene terephthalate exceeds 15 mol%, the heat-setting property of the obtained fiber deteriorates, and the dimensional stability of the cord against heat and the initial modulus decrease. In order to secure the thermal stability of the cord, the ethylene terephthalate unit having 100% is most preferable.

When the intrinsic viscosity [η] is less than 0.8, the strength of the cord is insufficient and the fatigue resistance is poor, which is not possible.
Also, if it exceeds 1.2, melt spinning becomes considerably difficult, and therefore it is not recommended.

The above polyester has a temperature of 120 to 135 at which the maximum loss tangent (tan δ) obtained by measuring the spinning and stretching conditions and changing the temperature at a frequency of 10 Hz using a dynamic viscoelasticity measuring instrument is 120 to 135. Use a code that will be in ° C. As a method thereof, for example, the method described in JP-A-58-156017, that is, a filament is formed by extruding from a spinneret equipped with a large number of large-diameter orifices of about 0.75 to 25 mm to form a quenching delay collar immediately below the spinneret. Therefore, the quenching of the filament is delayed, and the spun yarn formed by continuously combining the filaments is 1500 to 35
After being wound on a winder at a speed of 00 m / min, it is continuously or discontinuously stretched at 215 to 230 ° C. to obtain a high-strength polyester yarn. It is also useful for obtaining the cord applied to the present invention that the stretching step is performed according to the method described in JP-A-59-1714.

That is, the spun unstretched yarn is pre-stretched 1.10 times or less between the unstretched yarn first supply roller and the unstretched second supply roller maintained at 100 ° C. or lower, and then until the first stretching roller. High temperature pressurized steam of 200 ° C. or higher is sprayed between them, the stretching point is fixed at that position to perform the first stage stretching of 40% or more of the total stretching ratio, and further the first stretching roller and the second stretching roller are used. By passing through a slit heater with an ambient temperature of 170 to 420 ° C in a non-contact state for 0.3 seconds or more, and then performing a relax treatment of 10% or less at 280 to 165 ° C. The stability is further improved. The filament yarn thus obtained is combined and twisted so that the total number of filaments becomes about 100 to 1000, and it becomes a reinforcing cord of the carcass ply used for the tire of the present invention.

Spinning of the above polyester yarn. The stretching condition is a temperature (hereinafter, referred to as maximum temperature of loss tangent (tan δ) obtained by measuring the dynamic viscoelasticity of the obtained filament at a frequency of 10 Hz using a dynamic viscoelasticity tester. tan δ peak temperature) is appropriately selected to be in the range of 120 to 135 ° C. That is, the tan δ peak temperature correlates with the fine structure of filament, especially the orientation of the molecular chains in the amorphous part,
The higher the orientation, the higher the orientation. Therefore, the spinning and drawing conditions that affect the orientation, such as the spinning draft ratio, the spinning speed, the cooling speed of the spun yarn, the drawing temperature, and the draw ratio, are selected within the range of the above-mentioned process conditions, and the appropriate tan δ is set. It is easy to set the peak temperature. In particular, under the above-mentioned spinning conditions, tension is applied and stretched during the cooling of the yarn, so that the temperature difference between the surface layer and the central portion of the spun filament becomes an obstacle to spinnability and drawability. There is. Therefore, it is desirable to reduce the diameter of the spinning filament in order to minimize the cooling delay in the central portion and eliminate the above-mentioned obstructive factors. Finally, the single yarn fineness of the conventional yarn is 4 to 1.
On the contrary to 0d, the preferable single yarn fineness of the yarn applied to the present invention is about 1 to 6d.

The cord having a tan δ peak temperature of 120 to 135 ° C. has a high Young's modulus, and a typical example of the relationship between the intermediate elongation and the dry heat shrinkage is shown by the solid line (II) in FIG. As can be clearly understood by comparing this with the broken line (I) showing the dimensional change coefficient of the conventional cord, the dimensional change coefficient is about 7 in this example.
It is around 9%, whereas the conventional code is about 9%,
Therefore, even if the cord applied to the present invention is heat-set under the condition that the intermediate elongation is small, the dry heat shrinkage rate is remarkably smaller than that of the conventional cord. Therefore, the cord contracts during vulcanization and the intermediate elongation increases, and as a result, the rigidity of the carcass decreases, and if the expected steering performance cannot be obtained, the conventional phenomenon is almost eliminated.

The cord having a tan δ peak temperature of less than 120 ° C. does not have a sufficient degree of molecular chain orientation and is therefore composed of filament having low strength and Young's modulus. Is low and the steering performance is inferior, and the object of the present invention is not met.

On the other hand, when the tan δ peak temperature is high, the dry heat shrinkage tends to be large, and when the tan δ peak temperature exceeds 135 ° C, the carcass is heated under the condition that the intermediate elongation of the cord is decreased to increase the rigidity. Even if the intermediate elongation before setting and assembling into the tire is small, it shrinks during the vulcanization process of the tire and the dimensional change coefficient does not change significantly before and after vulcanization, but to the right along the curve in Fig. 3 If the carcass ply is moved between the carcass ply and the belt in order to compensate for this, the carcass rigidity becomes insufficient, resulting in a lack of rigidity of the carcass, resulting in reduced fatigue resistance. Not only that, but also the unevenness of the side wall portion becomes conspicuous, and the commercial value of the tire is impaired.

The cord obtained as described above is made into a weave, and then a rubber adhesive typified by, for example, resorcinol, formalin, and latex is applied to extend the cord by 2 to 10%,
Heat set at an ambient temperature of 10 to 250 ° C.,
Furthermore, relaxation treatment is performed at an ambient temperature of 200 to 240 ° C.,
Shrink about 0-2%. The cord subjected to such a treatment has a small thermal contraction even when it is set in a tensioned state, and its dimensional change coefficient is still maintained in the state of the solid line (II) in FIG.

Also, after the tire vulcanization process is over, the cord of the high temperature tire taken out from the vulcanizer is filled with air pressure higher than the internal pressure when the tire is used so that the cord does not contract heat during cooling. It is preferable to perform so-called post cure inflation (PI) for cooling while tensioning.

Next, a cord having a tan δ peak temperature of 120 to 135 ° C has a fatigue resistance of about 10% better under the same strain amount condition as a cord having a higher tan δ peak temperature, but since the degree of molecular chain orientation is low, it undergoes hydrolysis. Tends to be easy. Since the cord of the present invention has a lower tan δ peak temperature than conventional cords, the heat generated by the rotation of the tire accelerates the hydrolysis of the polyester filament and causes a problem in aging resistance. Since the concentration of free carboxyl end groups of polyester is greatly involved in this hydrolysis reaction, in order to reduce it, for example, an end capping agent such as an epoxy compound, a carbodiimide compound, or a cyclic carbonate compound typified by ethylene carbonate is added. It is desirable to give resistance to hydrolysis.

However, the resistance imparted by the above cannot be said to be sufficient, and the vulcanization accelerator compounded in the rubber matrix which burys the impurities and the cord in the natural rubber generally shows a catalytic action for hydrolysis. Consideration should be given to the rubber composition and the choice of vulcanization accelerators.

That is, the smaller the natural rubber content in the rubber matrix, the smaller the hydrolysis action of the cord, but on the other hand, the green strength of the tire is reduced, which makes it difficult to manufacture the tire. Therefore, the content of natural rubber that maintains an appropriate green strength and suppresses the hydrolysis promoting action of the cord to an allowable range is 50 to 80% by weight, preferably 60.
˜70 wt%, the remaining 50 to 20 wt%, preferably 40 to 30 wt%, is styrene-butadiene rubber,
It is at least one synthetic rubber selected from the group consisting of putadiene rubber and isoprene rubber. Above all, solution-polymerized styrene-butadiene rubber in which the styrene content is 10 to 20% by weight, 35 to 50% by weight of the butadiene component is 1.2 bonds, and the rest is 1.4 bonds It is particularly preferable because it has high properties and the filling in the cord gap is good.

The vulcanization accelerator compounded in the rubber matrix is preferably one having a small catalytic action for the hydrolysis of the polyester cord and having the property of enhancing the initial modulus of the synthetic rubber. A compound in which all of the hydrogens bonded to the nitrogen atom of the sulfenamide group have been replaced, for example N-oxydiethylene-2-benzothiazolylsulfen-amide,
N, N-dicyclohexylbenzothiazol-sulfonamide and the like are preferable, and Ncyclohexyl-2benzothiazolsulfonamide is not preferable because it has a property of promoting hydrolysis.

(Example) Hereinafter, the tire of the present invention will be described with reference to Examples and Comparative Examples.

FIG. 1 is a view showing the left half of the cross section of the tire. In the figure, the end of the carcass ply (1) has an annular bead core (7).
And a bead core assembly (9) consisting of a bead filler (8) made of high hardness rubber arranged along the outer peripheral surface of the carcass ply turn-back portion.
(3) extends along the outer surface of the carcass ply (1), and terminates overlapping with the belt ply (12). A steel cord (5) biased to a known cord angle (5) is sandwiched between the carcass ply turnback portion (3) and the bead core assembly (9).

FIG. 2 is a diagram showing a left half of a cross section of a conventional tire having a structure having two carcass plies. In the figure, the end portion of the inner carcass ply (1) includes an annular bead core (7) and a bead filler made of high hardness rubber arranged along the outer peripheral surface thereof.
(8) is folded back around the bead core assembly (9) from the inside to the outside, the carcass ply turnback portion (3) extends along the outer surface of the bead core assembly (9), and the bead filler (8) It ends in the middle of the height. The outer carcass ply (1) is arranged along the outer surfaces of the bead filler (8) and the carcass ply folded-back portion (3) and terminates near the hide core.

The size of the tire manufactured here was 195 / 60R15, and the respective measuring methods and testing methods were based on the following.

(1) Loss tangent (tan δ) Made by Iwamoto Manufacturing. Using a viscoelasticity tester, dynamic viscoelasticity was measured at a frequency of 10 Hz and a load of 0.5 g / d.

(2) Intermediate elongation The elongation when a load of 2.3 g / d is applied according to JIS-L-1017.

(3) Dry heat shrinkage Shrinkage when left for 30 minutes at a temperature of 150 ° C. according to JIS-L-1017.

(4) Strength retention after running The tire was run for 10,000 km, then disassembled, the strength of the cord was measured, and compared with the strength of the cord before molding, the retention is shown.

(5) Steering response Established by Japan Society of Automotive Engineers, automobile standard JASO / Z / 110 test vehicle speed 100Km / h The steering force is input periodically, and in response, a periodic change in the traveling direction of the vehicle is generated. The phase lag and the magnitude of the change are detected, and the control tire is set to 100, and the index is displayed so that the better one becomes larger.

(6) Ride comfort 50 Kg / h on a road surface with a triangular prism attached at a right angle to the traveling direction of the vehicle
Measure the amplitude of vertical vibration when passing at the speed of
The ratio of the reciprocal of the index is displayed with the conventional tire (Comparative Example 2) as 100.

(7) Side unevenness Average value of 10 to 100 tires of recess depth. The second
Table 1 shows the cord-embedded rubber compounds used in the examples and comparative examples shown in the table.

However, in Table 2 above, "1u1d" at the upper end position of the winding
Means "1 up 1 down", one of the two carcass plies is wound up from the inside to the outside of the bead core, and the other one is reversed from the outside of the tire to the inside of the bead core. It means wrapping around.

The "super HTU" is an abbreviation for high turn up, as shown in FIG. 1, in which one carcass ply is rolled up from the inside to the outside of the bead core to bring its end to the shoulder part.

The following is clear from the above test results.

(1) Tire Nos. 2 to 5 (Examples of the present invention) had a small dimensional change coefficient of 8.5% or less, and had a tan δ peak temperature of 122 to 13
At 3 ℃, using a polyester cord with an intermediate elongation of 5.6 or less,
In addition, 60/40 or 70 / of natural rubber and synthetic rubber is embedded rubber.
All of the tires using the blended ratio of 30 showed high strength retention after running, steering response and riding comfort index, and the side unevenness was extremely small compared to other tires. .

(2) Tire number 6 uses the same code as tire number 2,
In the case where post cure inflation (PI) was not performed, the dimensional change coefficient of the cord when it became a tire was not much different from the tire number 2, but the cord of the tire that was taken out of the vulcanizer and had a high temperature was Heat shrinkage during cooling, intermediate elongation exceeds 6%, poor steering response, and large side irregularities.

(3) Tire No. 7 is an example in which a cord having a small intermediate elongation is embedded in a rubber matrix of 100% natural rubber, and shows a low strength retention rate.

(4) Tire No. 8 has a too low tan δ peak temperature and a low degree of orientation, so the intermediate elongation is large and the steering response is extremely poor.

(5) Tire No. 9 is an example in which the intrinsic viscosity of polyester is low, and the strength retention is extremely low.

(Effects of the Invention) As described in detail above, the tire of the present invention uses a cord made of a polyester multifilament twisted yarn having an intrinsic viscosity of 0.8 to 1.2 to secure the strength of the cord, facilitate spinning, and further, provide a loss tangent. The maximum temperature is 12
Since it has a temperature of 0 to 135 ° C, it has high rigidity with a cord intermediate elongation of 6.0 or less and a dimensional change coefficient of 8.5% or less when it is used as a tire, and it prevents both lowering of steering performance and fatigue resistance and both performances. The resistance of the polyester cord to hydrolysis by mixing the natural rubber with the embedded rubber in a predetermined range, and as a whole they are composed of a carcass with high rigidity, so that operation such as maneuvering response is performed. The carcass ply has excellent performance and the dry heat shrinkage rate is extremely small in spite of its high rigidity, so both ends of the carcass ply wrap around the bead core assembly and are folded back from the inside to the end of the carcass attached to the outside. ,
Even if the tire has a structure that is not held by the belt,
The rigidity of the carcass ply is well maintained without the folding back portion shifting and the intermediate elongation increasing during the rubber vulcanization process.
Therefore, the carcass where the folded end of the carcass ply does not extend to the belt part and the side wall part is relatively thin,
A tire having excellent driving performance and comfortable riding comfort due to its high rigidity and moderate elasticity is provided.

A flat radial tire having a folded end portion of the carcass ply extending along the outside of the carcass and sandwiched between the carcass ply and the belt, wherein the height of the maximum width of the carcass is 55-55 of the carcass height. The composition is set to be in the range of 65%, that is, the present inventors have filed a patent application No. 59-91.
When the present invention is applied to the tire proposed in No. 458, road surface graspability is increased, and driving performance and riding comfort are excellent,
Moreover, a tire having good fatigue resistance can be obtained. Further, since the tire of the present invention has been carefully devised in rubber composition and selected an appropriate vulcanization accelerator, it suppresses hydrolysis of the polyester cord, prevents its strength loss and decrease in adhesive strength, and increases tire durability. At the same time, the tire has a uniform shape quality with less unevenness on the side wall.

Thus, the tire of the present invention combines excellent driving performance, comfortable riding comfort, and great fatigue resistance and durability,
It has the effects of improving the running safety of the vehicle and reducing the fatigue of passengers, and is expected to be put to practical use in the future.

[Brief description of drawings]

FIG. 1 is a left half sectional view showing an example of a tire according to the present invention,
FIG. 2 is a left half sectional view showing an example of a conventional tire, and FIG. 3 is a diagram showing a relationship between intermediate elongation and dry heat shrinkage of a carcass ply reinforcing polyester cord.
(I) shows the dimensional change coefficient of the conventional polyester cord, and (II) shows the dimensional change coefficient of the polyester cord applied to the present invention. (1) ... Carcass ply, (3) ... Carcass ply turnback, (4) ... Carcass ply end, (5) ... Steel cord reinforcing layer, (9) ... Bead core assembly, (11) ... Belt, (12) ), (12 ′)… Belt ply,

Continuation of the front page (56) Reference JP-A-59-2908 (JP, A) JP-A-57-212240 (JP, A) JP-A-54-25001 (JP, A) JP-A-57-144106 (JP , A)

Claims (2)

[Claims] 1. A carcass ply made of an organic fiber cord embedded in rubber is arranged so that the cord and the tire equator are substantially orthogonal to each other, and both ends of the carcass ply surround each of a pair of bead core assemblies. A plurality of belt plies consisting of a large number of steel cords parallel to each other that are folded back from the inside to the outside and terminate along the outside of the carcass ply. In a tire having a radial structure in which a belt formed by cross-polymerizing to form an angle is laminated on the crown of the carcass ply, the organic fiber cord of the carcass ply incorporated in the tire is
A multifilament twisted yarn made of substantially polyethylene terephthalate having an intrinsic viscosity of at least 0.8, wherein a temperature showing a maximum loss tangent (tan δ) when measured with a dynamic viscoelasticity measuring instrument at a frequency of 10 Hz is 120.
To 135 ° C., embedded in a rubber composed of 50 to 80% by weight of natural rubber and 50 to 20% by weight of synthetic rubber. A tire having a polyester carcass reinforcing layer, which has an intermediate elongation of 6.0% or less when a load of 2.3 g / d is applied and a sum of the intermediate elongation and the dry heat shrinkage at a temperature of 150 ° C. of 8.5% or less. 2. Both ends of the carcass ply wrap around a pair of bead core assemblies and a steel cord reinforcing layer superposed on each of the bead core assemblies, and further extend along the outside of the carcass ply, the ends of which are a belt and a carcass ply. The tire of the polyester carcass reinforcing layer according to claim 1, which is sandwiched between the two.