GB2030525A - Tubeless pneumatic tire - Google Patents

Abstract

A tubeless pneumatic tire comprises an inner rubberized carcass ply (1) which is composed of cords impregnated with a material which fills the gaps between filaments or strands of the cords so as to prevent passage of air along the cords via the gaps. The preferred material is resorcin-formalin- latex resin, and the cords are firstly dipped into the material under a given tension and dried, secondly pressed between rollers, and thirdly dipped into the material. The ply 1 is stated to be capable of efficiently eliminating air leak failure without increasing the thickness of an inner liner (5) and without inducing air trap failure during the manufacture of the tire. <IMAGE>

Description

SPECIFICATION Tubeless pneumatic tire This invention relates to a tubeless pneumatic tire and more particularly to an improved carcass construction thereof.

Pneumatic tires are mainly divided into tubeless tires and tires including a tube. The tubeless tire is provided at its innermost side in the radial direction with an inner liner composed of a rubber layer impermeable to air. This construction of the tubeless tire is different from that of a tire including a tube.

In the course of manufacturing the tubeless pneumatic tire, the rubber layer of the inner liner becomes fluidized, and as a result the rubber layer becomes locally thin and tends to easily expose the cords of the carcass ply to the inner cavity of the tire and hence involves the following problems.

That is, the above-mentioned exposure of the cords of the carcass ply causes the air filled in the inner cavity of the tire to penetrate from the exposed surface of the cords of the carcass ply to inside the cords. A cord is usually composed of about 200 to 300 multifilaments, so that gaps formed between adjacent filaments and between adjacent turns of a stranded filament communicate with each other in the lengthwise direction of the cord. As a result, the air filled in the inner cavity of the tire and penetrated into the inside of the cords flows through the above-mentioned communicating gaps, the upper end of a turn-up portion of the carcass ply formed by winding the carcass ply around a bead core and that portion of the outer cover rubber layer which is thinnest and which corresponds to the upper end of a rim flange and is radiated into the outside air.The radiation of the air filled in the inner cavity of the tire to the outside air adversely affects the pneumatic tire. Even if the air filled in the inner cavity of the tire is not radiated to the outside air, the air accumulated in the gaps formed inside the cords expands due to heat generated inside the tire when it is used, thereby inducing a tire failure such as a separation failure of the inside carcass ply.

The use of cords which are permeable in their lengthwise direction to air provides the important advantage that it is possible to eliminate the drawback which has been encountered when the tire is manufactured by superimposing layers one upon the other. That is, an unvulcanized green case is manufactured as follows. First, a plurality of carcass plies are superimposed one upon the other. Then, a side wall rubber, breaker layer and tread portion rubber layer are superimposed one upon the other in the order as mentioned. In this case, a greater or lesser amount of air is confined in gaps formed between these superimposed layers.If all of the cords of the carcass ply are made impermeable to air, innumerable minute bubbles confined inside the rubber when it is kneaded and the air confined in the gaps formed between the superimposed layers have no means of escape therefrom and are trapped, thereby significantly reducing the durability of the tire and adversely affecting the quality of the tire.

Heretofore, it has been proposed to make the rubber layer of the inner liner thick for the purpose of preventing the air filled in the inner cavity of the tire from penetrating into the inside of the carcass. In this case, the thickness of the cord layer of the inner liner must be made thicker than the thickness which is required for preventing the cords from becoming exposed. However, the use of an inner liner of such large thickness has a number of disadvantages. In the first place, the tire becomes undesirable heavy. Secondly, the generation of heat in the tire and the fuel cost would be undesirably great. Thirdly, the manufacturing cost of the tire is excessively increased. Finally, it is impossible to use the carcass for both tubeless tires and tires including a tube.

The present invention provides a tubeless pneumatic tire comprising a toroidal carcass composed of a plurality of rubberized plies having cords symmetrically arranged across a pair of bead cores in a sectional plane containing the rotational axis of the tire, wherein the rubberized ply of the toroidal carcass which faces the inner cavity of the tire is composed of air impermeable cords which substantially interrupt communication between gaps formed in the said cords along the lengthwise direction thereof.

In the present invention, it is preferable to use air impermeable cords including gaps hermetically sealed by a liquid cord treating agent impregnated into the cord under pressure.

The cords are treated twice by means of a resorcin-formalin-latex resin (hereinafter referred to as RFL resin), for example, which are well known as liquid cord treating agents. In the first treatment, the cord is immersed into the RFL resin under a given tension in the usual manner and then the cord is dried. Under this condition, the RFL resin does not penetrate into the inner portion of the cord, but the relatively outer surface only ofthe cord is soaked with the RFL resin and becomes hardened. Then, the hardened cord is passed between rollers and pressed. Then, the cord is subjected to the second RFL resin treatment; if necessary, the cord is subjected to the RFL resin treatment more than twice.

When the compressed cord is subjected to the second RFL resin treatment, the RFL resin formed by the first RFL resin treatment is crushed to form gaps for guiding the treating liquid into the centre portion of the cord. The second treatment serves to interrupt the communication between the gaps in the cord thus formed, thereby obtaining an air impermeable cord.

The air impermeable cords may be made of mono-filaments or of stranded cords composed of a plurality of relatively large filaments or of any other cord in which the construction, twisting condition and/or material of the cord are selected such that the treating liquid agent can penetrate into the inner portion of the cord by means of the usual cord treatment.

In the present invention, the air impermeable property of the cord is defined as follows.

Five cords each having a length of 3.8 cm are embedded side by side in a rubber block. Both ends or each cord are exposed from the end surface of the rubber block. To the exposed end of the cord is applied air under pressure of 2 kg/cm2. The amount of air which flows from the exposed end of the cord to the other end thereof, that is the amount of air which flows along the lengthwise direction of the cord through the gaps in the cord, for 30 minutes is measured.

If the value thus measured is substantially equal to 0 cc per unit sectional area with respect to the sectional area of the cord, the cord satisfies the necessary requirements and can be used as the air impermeable cord of a tire according to the invention.

In the tubeless pneumatic tire according to the invention, the above-mentioned air im permeable cord is arranged at the innermost side of the toroidal carcass in the radial direction of the tire and faces the inner cavity of the tire. If the rubberized layer extending from the upper portion of the sidewall where the cord becomes exposed most frequently through the crown portion to the upper portion of the sidewall at the opposed side is composed of the air impermeable cord, it is possible to prevent air leakage due to the exposure of the cord without producing any air traps. It is preferable to wind the air impermeable cord layer together with the remaining rubberized layers around one of the bead cores and extend these rubberized layers to the other bead core and wind them therearound.Alternatively, these rubberized layers may be terminated near the bead cores.

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

The drawing shows a tubeless tire having a carcass construction which is the same as that of a conventional tubeless tire and having a tire size of 6.45-14 6 Ply Rating. The carcass is composed of four rubberized plies, each ply including nylon cords having a bias construction. These four rubberized plies are composed of a first ply 1, a second ply 2, a third ply 3 and a fourth ply 4 in that order from the inner ply in the radial direction. In the drawing, reference numeral 5 designates an inner liner and numeral 6 a bead core. In the present embodiment, each of the plies 1 to 4 is wound around the bead cord 6 from the inside toward the outside thereof.

In each of the plies 1 to 4, the parallel cords are inclined at an angle of about 35" with respect to the circumferential direction of the tire at the centre of its tread portion 7, the cords of one ply extending in an opposite direction with respect to the cords of another ply.

Each cord is composed of 840 d/2 formed of nylon 6 and subjected to a bonding agent treatment with the aid of a resorcin-formalin-latex resin(RFL resin) as usual. If each cord is composed of a multifilament including a bundle of 200 to 300 filaments, the bonding agent or fluid rubber could not penetrate into the centre portion of the multifilament, there thereby remaining a centre cavity.

In the tire shown in the drawing, the first ply 1 shown by a thick full line is composed of cords substantially impermeable to air. That is, in order to eliminate the above-mentioned centre cavity, the RFL resin used for the conventional RFL resin treatment is of low concentration andthe tension applied to the cords when the cords are subjected to the RFL resin treatment is made low. The cords are immersed in the RFL resin and then passed through press rolls and drawn therethrough under pressure. Subsequently, the cords are subjected to a secondary RFL resin treatment with the aid of the same RFL resin bath. In this case, a slightly strong tension which is substantially the same as that used in conventional RFL resin treatment is applied.If necessary, the cords are subjected to a third RFL resin treatment in which the cords are repeatedly immersed in the RFL resin bath under the same conditions as for the secondary treatment. In this way, cords are formed which are substantially impervious to air.

The above-mentioned test result applied to the cords subjected to the secondary treatment was 0 cc/mm3.

The air impervious cords thus obtained were used to form the first innermost ply 1 and the remaining plies 2 to 4 were formed of conventional cords. A tire A constructed as above described according to the invention and a comparative tire B in which all the plies 1 to 4 were composed of conventional plies were manufactured for trial. These tires A and B were mounted on rims and inflated by air under a given internal pressure.

Experimental tests have demonstrated the result that the tires A and B induced no air trap failure, that the tire A was subject to substantially no air leakage and that the comparative tire B was subject to air leakage.

In the tire A embodying the present invention, if all the plies 1 to 4 are composed of air impermeable cords, it was confirmed that air leakage was not produced, but airtrappage was locally produced.

Experimental tests on the internal pressure holding ability of the above-mentioned tires A and B in which provision was made of an inner liner adapted to be used for the conventional tubeless tire have given the results listed in the following Table.

Tire B A Measuring Cords Cords Cords Cords condition are not are are not are exposed exposed exposed exposed Leave tire as 2.95 2.85 2.92 2.95 it is for (100) (96.6) (99.0) (100) 30 days Internal pressure Leave holding tire as 2.80 2.65 2.81 2.81 ability it is for (100) (94.6) (100.4) (100.4) kg/cm2 90 days Leave tire as 2.95 2.40 2.73 2.72 it is for (100) (87.2) (99.3) (98.9) 165 days The experimental tests were carried out under an initial internal pressure of 3.0 kg/cm2. The internal pressure holding ability of the comparative tire B in which the cords are not exposed is shown by an index of 100 in parenthesis ().

As can be seen from the above Table, the internal pressure holding ability of the carcass construction of the conventional tire in which the cords are not exposed becomes significantly different from that of the carcass construction in which the cords are exposed. On the contrary, the internal pressure holding ability of the carcass construction of the tire according to the invention in which the cords are not exposed is substantially the same as that of the carcass construction in which the cords are exposed. As a result, the carcass construction of the tire according to the invention can not only be manufactured efficiently but can also be used efficiently since the performance of the tire is improved, in particular it is possible to prevent generation of heat and to reduce the weight and hence the fuel cost.

As stated hereinbefore, the tubeless pneumatic tire according to the invention is capable of efficiently eliminating air leak failure without increasing the thickness of the inner liner and hence without increasing the weight of the tire and without inducing air trap failure during the manufacture of the tire.

Claims (3)

1. A tubeless pneumatic tire comprising a toroidal carcass composed of a plurality of rubberized plies having cords symmetrically arranged across a pair of bead cores in a sectional plane containing the rotational axis of the tire, wherein the rubberized ply of the toroidal carcass which faces the inner cavity of the tire is composed of air impermeable cords which substantially interrupt communication between gaps formed in the said cords along the lengthwise direction thereof.

2. A tubeless pneumatic tire as claimed in Claim 1, wherein each said air impermeable cord is composed of a bundle of multifilaments impregnated with a liquid cord treating agent under conditions wherein the cord is compressed.

3. A tubeless pneumatic tire substantially as herein described with reference to, and as shown in, the accompanying drawing.