GB2041843A

GB2041843A - Pneumatic radial tire

Info

Publication number: GB2041843A
Application number: GB8003664A
Authority: GB
Original assignee: Bridgestone Corp
Current assignee: Bridgestone Corp
Priority date: 1979-02-05
Filing date: 1980-02-04
Publication date: 1980-09-17
Also published as: JPS55113605U; GB2041843B; JPS5827842Y2

Abstract

A pneumatic radial tire (1) comprises a carcass (7) composed of cords arranged in a radial plane of the tire or in a plane inclined at a small angle with respect to the radial plane and a reinforcing belt (10) composed of cords inclined at an angle of 10 DEG -25 DEG with respect to the circumferential direction of the tire, wherein the reinforcing belt comprises a plurality of layers (13) formed by folding at least one sheet (11) composed of cords of a polyethylene terephthalate low polymer having an intrinsic viscosity of 0.3-0.8 and an elastic modulus of at least 6x10<4> kg/cm<2>, and a coating rubber (12) applied on the surface of the cords and having a modulus at 300% elongation of 11x10<-4> to 33x10<-4> times the elastic modulus. <IMAGE>

Description

SPECIFICATION Pneumatic radial tire This invention relates to a pneumatic radial tire, and more particularly to a pneumatic radial tire reinforced with a belt composed of cords of a polyethylene terephthalate low polymer and suitable for use on passenger cars.

Hitherto, rayon cords and steel cords have preferably been used as the belt material for radial tires.

However, since rayon cords are susceptible to moisture, it is unavoidable that the elastic modulus and tenacity of the rayon cord are adversely affected by the moisture inevitably absorbed during the production of tire or by water penetrating through external damage sustained during the running of the tire.On the other hand, steel cords are apt to separate out from the adjoining rubber coating because they are subjected to corrosion by penetrated water as mentioned above and further the end portions thereof have poor adhesion to the rubbers The present invention provides a pneumatic radial tire comprising a carcass composed of a number of cords arranged in a radial plane of the tire or in a plane inclined at a small angle with respect to the said radial plane and toroidally extending between a pair of bead portions, and a reinforcing belt superimposed about the crown portion of the said carcass and composed of a number of cords inclined at a small angle with respect to the circumferential direction of the tire, wherein the said belt comprises a plurality of layers formed by folding at least one sheet composed of cords of a polyethylene terephthalate low polymer having an intrinsic viscosity of 0.3-0.8 as measured at 250C in orthochlorophenol and an elastic modulus of at least 6x 104 kg/cm2, and a coating rubber applied on the surface of the said cords and having a modulus at 300% elongation of 11 x10-4 to 33 X10-4 times the said elastic modulus and closely bonding the adjoining opposite rubbers with each other.

The term "intrinsic viscosity" used herein means the viscosity when extrapolating from the relative value between the practically measured concentration and viscosity to the value at zero concentration.

The higher the extrapolated value, the higher the viscosity and also the higher the heat shrinkability of the cord. Acco;ding to the invention, it has been found that the intrinsic viscosity as defined above should be within a range of 0.3-0.8. On the other hand, when the elastic modulus of the cord is less than 6 x 104 kg/cm2, the suitability thereof as a belt reinforcement is lacking and as a result the improved cornering stability and wear resistance of the radial tire cannot be obtained. Moreover, the elastic modulus of the cord has an inherent maximum of about 1 3x 104 kg/cm2.

The polyethylene terephthalate cords conventionally known as carcass cords for radial tires have an intrinsic viscosity of about 0.93 and an elastic modulus of about 4.3 x 104 kg/cm2. Therefore, they are considerably different from the cords utilized in the tire according to the invention in respect of the properties required for the belt reinforcement.

According to the invention, it is further essential that the coating rubber in the belt has a modulus at 300% elongation corresponding to a range of 11 x 10-433 xl 0-4 times the elastic modulus of the cord, which develops a higher buffering action on an interlaminar shearing stress caused by external force when the belt is disposed in the usually used structure, i.e. the cord layers of the belt are crossed with each other and the cords of each cord layer are inclined at an angle of 100--250 with respect to the circumferential direction of the tire.

The invention will be further described, by way of example only, with reference to the accompanying drawing, which is a cross-sectional view of an embodiment of a pneumatic radial tire according to the invention.

The drawing shows a radial tire 1 comprising a pair of bead portions 2, a pair of side portions 3 and a tread portion 4, wherein the side portions and the tread portion extend toroidally between the bead portions in a conventional manner.

At the end of each bead portion 2 is disposed an annular bead wire 5. A carcass 7 toroidally extends from one of the bead wires 5 through a crown portion 6 to the other bead wire 5. The carcass 7 is composed of one or a few rubberized ply layers each containing a number of textile cords formed of rayon, nylon and polyethylene terephthalate high polymer, which are preferably used in conventional tires, as well as the same polyethylene terephthalate low polymer as used in the reinforcing belt in accordance with the invention, and which are arranged in a radial plane of the tire or in a plane inclined at a small angle with respect to a radial plane.Both ends of the carcass 7 are outwardly turned over the bead wires 5 and may be terminated at a distance h corresponding to about 1/2 of the tire sectional height H expressed as the distance from the base of the beads to the top of the tread to form turn-up portions 8.

In the illustrated embodiment, a rubber filler 9 is disposed in each space defined by the carcass 7 and a turn-up portion 8 so as to extend from the upper surface of the bead wire 5 toward the tread portion 4 over a range corresponding to 20-47% of the tire sectional height H. The rubber filler has a modulus at 20% elongation of 25-75 kg/cm2 and a Shore A hardness of 80 96 and is very hard.

In this way, the rigidity at a lower region A of the tire extending from the bead portion 2 to the side portion 3 is increased, whereby the usual relatively large deforming region of the tire is reduced to a relatively narrow upper part of the side portion 3. However, the influence of such deformation on both ends of a belt 10 can advantageously be mitigated by the particular belt structure as described below.

The belt 10 is superimposed about a crown portion of the carcass 7 in a tread 14 of the tire. In this case, the belt 10 consists of a plurality of layers formed by folding at least one sheet composed of polyethylene terephthalate cords having a low polymerization degree and a considerably high elastic modulus of at least 6x 104 kg/cm2, which cords are inclined at an angle of 100--250 with respect to the circumferential direction of the tire or the equatorial line C-C of the tire, and a coating rubber applied on the surface of the cords and having a modulus at 300% elongation of 1 x x10-4--33x10-4 times the elastic modulus of the cord and closely bonding the adjoining opposite rubbers with each other.In the illustrated embodiment, the belt 10 is composed of four laminated layers 13~" 13-2, 133and 134by folding each of two sheets 11-1 1~, and 1 1-2 in two. In the folding of the sheet, the adjoining opposite rubbers are directly bonded with each other. The coating rubber after bonding is illustrated by reference numeral 12.

In the illustrated embodiment, the folded parts 15~, and 15-2 of the two sheets 1 1~, and 1 1, are positioned at both edges of the tread 4, and further the cords of the layers 1 3~r to 1 34 are crossed with each other toward the opposite direction in the coating rubber 12. Of course, it is possible to fold a single sheet into three or four layers in a manner similar to that described above.

Moreover, the term "elastic modulus" of the cord used herein means the relation between the tensile strength of the cord and the elongation thereof and is expressed by a numerical value (kg/cm2) calculated from the ratio a/s wherein a is the tenacity of the cord when extrapolating from the linear portion of the tensile strength after the stretching to a value at 100% elongation of the cord and s is the cross-sectional area of the cord. The cross-sectional area s of the cord is calculated from the cord diameter defined according to JIS L-1 017.

The results of the high-speed durability, wear resistance and cornering performance will be described below with respect to the tires of the present invention and of the prior art.

The test tire had a size of 1 65 SR 13, and comprised a radial carcass of one ply composed of polyethylene terephthalate high polymer cord of 1,500 d/2, and had fundamentally the structure and shape as shown in the drawing.

In the following Table 1 are shown details of conventional tires A and B and of a tire C according to the invention, respectively.

Table 1

Kind of tire A B C Kind of cord Rayon PET HMPET (1,650 d/2) (1,500 d/2) (1,500 d/2) Belt Elastic modulus of cord (kg/cm2) 9.2 x104 4.25x104 10.5x104 Modulus of coating rubber (kg/cm2) (109410-4) (229410-4) (17181 0-4) (109x410-4) (229x410-4) (171x890-4 20% modulus (kg/cm2) 12 12 53 Rubber filler Shore A hardness (0) 7,0 70 94 (Note) (1) PET is polyethylene terephthalate high polymer.

(2) HMPET is polyethylene terephthalate low polymer.

(3) Numerical value in the parenthesis of the column "modulus of coating rubber" is a ratio of the modulus of the coating rubber to the elastic modulus of the cord.

The test tire was mounted on a rim of 4 > J and inflated to an internal pressure of 2.1 kg/cm2. The measured results are shown in the following Table 2.

The high speed durability was measured as follows. First, the test tire was trained by running on a steel drum having a diameter of 1.7 m and a smooth surface at a speed of 80 km/hr under a load of 420 kg for 1 20 minutes. After the training, the tire was left to stand at room temperature (380C) for 3 hours and then run at a speed of 1 21 km/hr for 30 minutes. After the complete running under the above conditions, the running speed was increased by steps of 8 km/hr (129, 137, 145 km/hr) every 30 minutes until failure occurred. In Table 2 are shown the speed and running time at the occurrence of the failure as the high speed durability.

The wear resistance is indicated by an index based on the tire A after the tire was practically run over a distance of 40,000 km, and the cornering performance is also indicated by an index based on the tire A when measuring the cornering power (riser portion of cornering force in a curve between the slipping angle and the cornering force). In both cases, the larger the numerical value, the more the property is improved.

Table 2

Kind of tire | A | B | C High speed durabil- 177 km/hr 153 km/hr 185 km/hr ity (25') (9') (21') Wear resistance 100 -70 99 Cornering perform- 100 71 102 ance As is apparent from Table 2, the properties of the tire B using the polyethylene terephthalate high polymer as a reinforcing belt are considerably inferior to those of the tire C using the polyethylene terephthalate low polymer. Further, the wear resistance and cornering performance of the tire C are substantially equal to those of the tire A using rayon cord as the reinforcing beit. Regarding the high speed durability, the tires A and B were obliged to stop running due to interlaminar separation failure by heat generation, while the tire C was very stable against thermal fatigue up to a considerably higher speed.

Claims

1. A pneumatic radial tire comprising a carcass composed of a number of cords arranged in a radial plane of the tire or in a plane inclined at a small angle with respect to the said radia! plane and toroidally extending between a pair of bead portions, and a reinforcing belt superimposed about the crown portion of the said carcass and composed of a number of cords inclined at a small angle with respect to the circumferential direction of the tire, wherein the said belt comprises a plurality of layers formed by folding at least one sheet composed of cords of a polyethylene terephthalate low polymer having an intrinsic viscosity of 0.3-0.8 as measured at 250C in orthochlorophenol and an elastic modulus of at least 6x 104 kg/cm2, and a coating rubber applied on the surface of the said cords and having a modulus at 300% elongation of 11 x 10-4 to 33 x 10-4 times the said elastic modulus and closely bonding the adjoining opposite rubbers with each other.

2. A pneumatic radial tire as claimed in claim 1, wherein the said cords of the belt are inclined at an angle of 100--250 with respect to the circumferential direction of the tire.

3. A pneumatic radial tire according to claim 1, substantially as herein described with reference to, and as shown in, the accompanying drawing.