JPS621602A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To prevent separation of carcass plies to enhance the durability of a pneumatic tire, by utilizing cords which are arranged at specific angles and formed of aromatic group polyamide fibers in carcass plies, and by setting the twist angles and 100% modulus thereof in specific ranges, respectively. CONSTITUTION:A pneumatic tire is formed in an ultraflat shape structure having a ratio of cross-sectioned height to maximum cross-sectioned width within a range of 0.25-0.75. Further, the angle of cords 6 constituting carcass plies 4 with respect to the circumferential direction E of the tire are set to be within a ranged from 70-90 deg.. With the above-mentioned condition, the cords 6 are formed of aromatic polyamide fibers as raw material yarns which are subjected to a yarn twist process. Further, the twist angle of the yarns after the yarn twist process are set within a range of 31.3-39.3 deg.. when it is measured with respect to the axis L of each cord 6 at the acute angle side thereof. Further, the 100% modulus of a cord rubber 7 into which the cords 6 are embedded is set in a range of 30-70kg/cm<2>.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a pneumatic radial tire, and more particularly to a pneumatic radial tire for competition having an ultra-flat cross-sectional structure.

[Prior art]

BACKGROUND ART Ultra-flat radial tires with a ratio of cross-sectional height to maximum cross-sectional width of 0.25 to 0.75 are used as tires for competitions that run at ultra-high speeds. It is said that such a radial tire for competition needs to have the following characteristics.

(1) The ground contact area during load transfer during high-speed driving is as large as possible. (2) When a lateral external force is applied to the tire, the tire must have sufficient lateral rigidity to withstand it. (3) When driving These include deformation of the ground-contacting part and small bulge.

In order to satisfy these required characteristics, the tire carcass ply has become a very important structural part. In order to further improve the performance of this carcass ply, attempts have been made to use aromatic polyamide fibers, which have significantly greater strength and modulus, in the carcass ply cord instead of conventional nylon fibers.

However, due to its molecular structure, aromatic polyamide fibers are highly crystalline and have poor adhesion to coated rubber, so they have the disadvantage of being susceptible to separation phenomena (separation phenomenon between the cord and rubber), especially at the ends of carcass cords. be. For this reason, attempts have been made to overcome these drawbacks, such as using two dips for surface adhesion treatment and using special coated rubber, but they are still lacking in sufficient durability. At present, it has not yet been achieved, and it is hardly put into practical use.

[Purpose of the invention]

An object of the present invention is to provide a pneumatic radial tire that uses aromatic polyamide fibers as the carcass cord of an ultra-flat radial tire, prevents separation of the carcass cord terminals, and has improved durability.

[Structure of the invention]

The present invention achieves the above object, and the cords of the carcass ply are arranged in a range of 70° to 90° with respect to the circumferential direction of the tire, and the ratio of the tire cross-sectional height to the maximum cross-sectional width is 0.25.
An ultra-flat radial tire having an angle of 0.75 to 0.75, wherein the cord of the carcass ply is made of aromatic polyamide fiber, and the twist angle measured from the acute angle side with respect to the axis of the cord is 31.3 to 39. .30 range,
Moreover, the coated rubber in which the cord is embedded has a 100% modulus of 30 to 70 kg/cm2.

〔Example〕

Hereinafter, the present invention will be specifically described with reference to embodiments shown in the drawings.

FIG. 1 is a sectional view of a pneumatic radial tire for competitions according to an embodiment of the present invention.

This pneumatic radial tire has a pair of left and right bead parts 1
．． 1, a sidewall part 2.2 that continues to this bead part 1.1, and a trend part 3 that straddles between this sidewall part 2.2, and has a cross-sectional height H and a maximum cross-sectional width W.
It has an ultra-flat structure with a ratio of 0.25 to 0.75.

4 is a carcass ply consisting of two plies, each of which has left and right bead portions 1. 1 beads la, l
The tire is wrapped around a from the inside to the outside so that the middle part straddles the sidewall part 2 and the tread part 3. This carcass ply 4 does not necessarily have to be two plies, and it is sufficient to provide at least one ply or more. At a portion of the carcass ply 4 corresponding to the tread portion 3, a reinforcing belt layer 5 composed of a plurality of layers is provided on the outside thereof.

As shown in FIG. 3, the carcass ply 4 is composed of a cord 6 and a coat rubber 7 in which the cord 6 is embedded. As shown in FIG. 2, the cord 6 is arranged so that the angle α with respect to the tire circumferential direction E is in the range of 70° to 90′.

The cord 6 is twisted using aromatic polyamide fibers as yarns. The aromatic polyamide fiber is preferably a yarn having a tensile strength of 150 kg/m or more and a tensile modulus of 3000 kg/Tsuru2 or more.The aromatic polyamide fiber is twisted into a cord, and its surface In the cord 6 of the present invention, the twist angle θ after the twisting process is
As shown in FIG. 4, the angle is set to be in the range of 31.3'' to 39.3' when measured from the acute angle side with respect to the axis of the cord 6.

If the twist angle θ of the cord 6 is smaller than 31.3', the effect of improving the adhesion between the cord 6 and the coat rubber 7 will not be improved, and separation will easily occur at the folded end 4e during competition use or the like. In addition, the twist angle θ is 39.
If it is larger than 3', the effect of improving the adhesion between the cord 6 and the coated rubber 7 will not increase, and the folded end 4e
Separation is likely to occur, and the process of twisting the aromatic polyamide fibers becomes difficult, causing flaws and deteriorating the physical properties of the cord.

Further, in the carcass ply 4, the coat rubber 7 in which the cord 6 is embedded has a 100% modulus of 30 to 70.
kg/-. This means that the modulus of the aromatic polyamide fiber Cord 6 is
Since it is significantly larger than general nylon fibers, if the 100% modulus of the coated rubber 7 is less than 30 kg/cat, the twist angle θ of 31.3° to 39.3'
This is because the effect of improving adhesion by the cord 6, which has been changed to 6, will not be utilized. Moreover, if it exceeds 70 kg/cd, the coat rubber becomes too hard, which impedes productivity during tire manufacturing and causes an increase in costs.

In any case, the effect of preventing separation in the carcass cord terminal according to the present invention cannot be obtained simply by setting the twist angle θ of the cord 6 in the range of 31.3° to 39°3''; Coat rubber 7 of 10
The 0% modulus can only be obtained by setting it in the range of 30 to 70 m/-.

Further, in the pneumatic radial tire of the present invention, it is preferable that the density of the cords 6 embedded in the coated rubber 7 as described above is 30 to 60 cords per 50 m+m when measured in a direction perpendicular to the cords. If the density is less than 30 150 am, the strength as a carcass ply will be insufficient, and if the density is less than 60 1b, the distance between adjacent cords 6.6 will become too narrow, so the cord 6 This is because it becomes difficult to allow the coat rubber to enter the space between the cords 6 and the coat rubber 7, which tends to cause a decrease in the adhesive force between the cord 6 and the coat rubber 7. Also,
If the number of cords 6 becomes too large, this is not preferable because it causes an increase in cost.

〔Effect of the invention〕

As described above, the present invention comprises a carcass ply cord of an ultra-flat radial tire having a ratio of cross-sectional height to maximum cross-sectional width of 0.25 to 0.75 from aromatic polyamide fibers, The twist angle measured from the acute angle side should be in the range of 31.3 to 39.3 degrees, and the 100% modulus of the coated rubber should be in the range of 30 to 70k.
g/cJ range, the above cord twist angle and the modulus of the coated rubber work synergistically to prevent separation at the carcass cord terminals while using aromatic polyamide fibers with high strength and modulus, greatly increasing durability. can be improved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a pneumatic radial tire according to an embodiment of the present invention, FIG. 2 is a plan view of a carcass ply in the same radial tire, FIG. 3 is a longitudinal cross-sectional view of the carcass ply, and FIG. 4 is a cross-sectional view of the same radial tire. It is a top view of the carcass cord in a tire. 4.-carcass ply, 4e...terminal section, 6..
-Cord, 7-・-Coat rubber, θ・−・Twisting angle, α−・Angle of car force cord with respect to tire circumferential direction.

Claims (3)

[Claims] (1) The cords of the carcass ply are arranged in the range of 70° to 90° with respect to the circumferential direction of the tire, and the ratio of the tire cross-sectional height to the maximum cross-sectional width is in the range of 0.25 to 0.75. A flat radial tire, wherein the cord of the carcass ply is made of aromatic polyamide fiber, and the twist angle measured from the acute angle side with respect to the axis of the cord is 31.3.
° to 39.3°, and the 100% modulus of the coated rubber in which this cord is buried is 30 to 70 kg/
A pneumatic radial tire characterized by cm^2. (2) Tensile strength of aromatic polyamide fiber is 150 kg
The pneumatic radial tire according to claim 1, which has a tensile modulus of elasticity of at least 3000 kg/mm^2 and a tensile modulus of at least 3000 kg/mm. (3) Carcass ply cord 30~ per 50mm
The pneumatic radial tire according to claim 1, wherein the pneumatic radial tire is embedded in the coated rubber at a density of 60.