JP2000343913A - Pneumatic radial tire and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the weight of a tire while insuring burst limit inner pressure equal to or more than the case of using steel wire by providing a bead core constituted by winding rubber coated polybenzazole fiber cord, and specifying thickness of coated rubber filling the adjoining gap of fiber cords. SOLUTION: A bead core 3 is formed with a thin rubber coated layer 6 on the outer circumferential face of a polybenzazole fiber cord 5, and the polybenzazole fiber cord with rubber coated layer 7 is wound into required step number and row number so as to be an inner diameter size meeted with the diameter of an applied rim utilizing adhesiveness of the rubber coated layer 6 to be formed. In the bead core 5 of a product tire, thickness of coated rubber filling the adjoining gap of the mutual polybenzazole fiber cords 5 is favorably set to be at least 0.001 mm and under 0.2 mm. Hereby the weight of a tire can be effectively reduced, the burst limit pressure of the bead part can be effectively improved, and the durability of the bead part can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire which achieves low fuel consumption while maintaining a burst limit internal pressure, although the weight of a tire, especially the weight of a bead core, is greatly reduced. And a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, steel wire has been widely and generally used as a constituent material of a bead core. When this steel wire is wound into a bead core by winding it in accordance with the diameter of the applicable rim, the cord is formed to a certain thickness (0.3 mm).
2.02.0 mm) of insulation rubber. This insulation rubber is caused by the rubbing that occurs when the wound steel wires come into contact with each other,
Prevent lowering of the critical internal pressure for tire burst. Insulation rubber also prevents excessive rigidity of the entire bead core, allows deformation when the rim is assembled or released, and also prevents plastic deformation of the steel wire. Further, when the bead core is formed by utilizing rubber tackiness at the time of winding the steel wire, the bead core has a function of facilitating production of an appropriate bead core without deforming.

On the other hand, under recent strong demands for lowering fuel consumption of vehicles, weight reduction of tires is strongly demanded, and many examples of applying organic fiber cords, which are much lighter than steel wires, to bead cores have been seen. Can be For example, Japanese Patent Application Laid-Open No. Sho 4
Japanese Patent Application Laid-Open No. 9-85705 discloses a steel wire bead core from the rubber material, a bead coming off a rim when a steel wire bead core is used, and the like, and a purpose of solving the problems related thereto. Have been.
However, since the organic fiber cord is applied in the same manner as in the case of the steel wire to form the bead core, a decrease in the burst limit internal pressure of the bead portion is inevitable.

[0004] The first cause is due to a difference in tensile properties existing between the steel wire and the organic fiber cord. For example, when a bead core is formed by winding cords in three rows and three rows, when filling the rim-assembled tire with internal pressure, the innermost first cord located in the tire radial direction receives the largest stress. The stress applied to the third-stage cord located on the outermost side in the radial direction is minimized. In this case, when the bead cord is a steel wire, when the stress acting on the first-stage steel wire reaches its elastic limit stress, the steel wire undergoes plastic deformation under the elastic limit stress. Since the second-stage steel wire reaches the elastic limit stress during the plastic deformation, not only the first-stage steel wire but also the All of the steel wires in the second stage can also sufficiently exhibit tensile strength. On the other hand, when the bead is composed of the organic fiber cord, the organic fiber cord does not have a region corresponding to the plastic deformation area of the steel wire, and therefore, the first-stage organic fiber cord has the limit elongation. By reaching and breaking, the second-stage organic fiber cord can not sufficiently exhibit its inherent tensile strength,
The bead portion bursts.

[0005] Therefore, when the cord usage is compared by the value of (number of turns) x (cord strength), when the organic fiber cord is used as a bead cord, it is necessary to use a larger amount of cord than when using a steel wire. Become.

The second cause is that the thickness of the insulation rubber applied to the organic fiber cord is set to be the same as that of the steel wire, so that the organic fiber cord located on the radially inner peripheral side of the bead core is formed. Elongation deformation of
Since the insulation rubber having a large thickness is relatively freely allowed under the elastic deformation, the expansion deformation cannot be effectively restrained by the organic fiber cord located on the outer peripheral side. Therefore, as mentioned above,
This is because the organic fiber cord on the inner peripheral side reaches its elongation limit and breaks before the organic fiber cord on the outer peripheral side exhibits sufficient tensile strength.

Therefore, when the insulation rubber thickness is taken into consideration in addition to the above-described difference in the tensile properties of the cords, a further increase in the amount of the organic fiber cords is required. It was indispensable to secure the critical internal pressure.

As described above, in the prior art using the organic fiber cord as the bead cord, the burst limit internal pressure of the bead portion is not taken into consideration. A large amount of insulation rubber must be used,
The volume of the bead portion had to be increased, and the weight of the bead portion, and eventually the weight of the tire, could hardly be reduced, so that it was almost impossible to satisfy the demand for lighter tires.

On the other hand, when the bead core is formed without applying any insulation rubber to the organic fiber cord, the extension deformation of the cord located on the inner peripheral side is effectively restrained by the cord located on the outer peripheral side. Therefore, with the cooperation of the internal and external codes, the required burst limit internal pressure can be achieved while the code usage is much reduced as compared with the case described above. Therefore, it is possible to satisfy the demand for reducing the weight of the tire. However, in this case, when the organic fiber cord is wound to form the bead core, the adhesiveness between the insulation rubbers cannot be used at all. It is extremely difficult to make the cross-sectional shape exactly as expected.
Even if that is possible, the organic fiber cords located in the central part of the bead core will come into direct contact with each other under the buried state in the bead part,
There has been a problem that the durability and the like caused by the rubbing must be reduced.

[0010]

Therefore, the inventor of the present invention disclosed in Japanese Patent Application Laid-Open No. Hei 10-52871 to solve the above problems by reducing the thickness of the coating rubber layer of the organic fiber cord. An effective means was proposed. With this technology, it has become possible to achieve a large amount of rotation with respect to a bead made of steel wire, and also to ensure durability at the same time.

However, in order to equalize the burst limit internal pressure, it is necessary to secure a sufficient number of windings. Therefore, it is inevitable that the cross-sectional area of the bead becomes relatively large. In some cases, in order to maintain a cross-sectional shape and impart a certain level of durability, production under strict control is necessary, and there is room for improvement.

The present invention provides a method for solving the above-mentioned problems, and achieves a reduction in tire weight while ensuring a burst limit internal pressure equal to or higher than that in the case of using a steel wire. Pneumatic radial tires that can easily and easily mold a bead core having the expected cross-sectional shape and maintain the desired bead core shape even when embedded in the tire and have no variation in durability. The purpose is to propose at the same time.

[0013]

The gist of the present invention is as follows.
It is as follows. (1) A bead core formed by winding a rubber-coated polybenzazole fiber cord, and the thickness of the coated rubber filling the adjacent gap of the polybenzazole fiber cord is 0.001.
A pneumatic radial tire characterized in that the thickness is not less than 0.2 mm and less than 0.2 mm.

(2) The pneumatic radial tire according to the above (1), wherein the polybenzazole fiber cord is made of polyparaphenylene benzobisoxazole.

(3) The pneumatic radial tire according to (1) or (2), wherein the thickness of the covering rubber is less than 0.1 mm.

(4) A solution obtained by dissolving rubber in a volatile organic solvent is adhered to the outer periphery of the polybenzazole fiber cord to form a thin rubber coating layer, and the polybenzazole fiber with a rubber coating layer is formed. Wrap the cord and play
A method for manufacturing a pneumatic radial tire, comprising: a core; and burying the bead core in a tire bead portion.

In this radial tire, in the bead core buried in the bead portion, the adjacent gap between the organic fiber cords is filled with the covering rubber, so that the cords are rubbed due to the organic fiber cords coming into direct contact with each other, It is possible to sufficiently remove the possibility that bead core durability and the like are reduced.

Further, by setting the thickness of the covering rubber layer that fills the cord gap to be 0.001 mm or more and less than 0.2 mm, the above-mentioned effects are maintained, and the tire internal pressure of the organic fiber cord located on the inner peripheral side in the radial direction is maintained. The elongation deformation at the time of filling can be sufficiently constrained by the cords on the outer peripheral side located close to the cord, thereby ensuring effective exertion of the tensile strength of each cord in the radially inner and outer parts. Therefore, the burst limit internal pressure of the bead portion can be made necessary without increasing the cord usage, the bead core volume, and the like, and as a result, the tire weight is effectively reduced. Since the burst limit internal pressure can be improved, the tire weight is effectively reduced.

Here, the thickness of the coated rubber means the average value of the thickness of the coated rubber between the cords adjacent to each other in the up, down, left, right, diagonal directions in the cross section of the bead core. If the thickness is less than 0.001 mm, the workability at the time of forming the bead core becomes poor, while the thickness is reduced.
When the diameter is 0.2 mm or more, it is extremely difficult to sufficiently restrain the bead cord located on the radially inner side with the bead cord located on the outer peripheral side in the tire radial direction.

In the present invention, the number of turns is increased by applying a polybenzazole fiber cord, particularly a polyparaphenylene benzobisoxazole (PBO) fiber cord, as compared with the aramid fiber used in JP-A-10-52871. Can be destroyed,
In addition to being able to further reduce the weight, it is extremely easy to maintain the cross-sectional shape when the tire is buried in the tire, and it is possible to easily reduce variation in durability.

That is, since the PBO fiber cord has a tensile strength almost twice that of the conventional aramid fiber, the number of turns of the cord can be reduced by the amount that the breaking internal pressure becomes almost double. is there. In addition, since the number of windings is small, the deformation of the cross-sectional shape of the bead core can be suppressed in the steps from tire molding to vulcanization, so that it is also possible to suppress variations in durability occurring between tires.

In the method for manufacturing a pneumatic radial tire according to the present invention described above, the polybenzazole fiber cord wound in forming the bead core has a rubber coating layer formed in advance. The bead core having the expected cross-sectional shape can be easily and easily formed by utilizing the adhesiveness of the above-described adhesive, and can be accurately arranged at a required position.

In this case, a solution obtained by dissolving rubber is attached to the outer periphery of the polybenzazole fiber cord by dipping or the like, and the solvent of the attached solution is vaporized to form a rubber coating layer. It is possible to adjust the coating layer to the required thickness. For example, the thickness can be increased by increasing the rubber concentration or the like in the solution.

According to the pneumatic radial tire in which the bead core thus configured is embedded in the goad portion,
The operation and effect as described above can be obtained.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view in the width direction showing an embodiment of a main part of a tire according to the present invention,
Here, the end portion of the radial carcass 1 is
The bead core 4 is wound up from the inside to the outside around the bead core 3 embedded therein, and a bead filler 4 is disposed between the wound end portion 1 a and the main body portion 1 b of the radial carcass 1 on the radially outer peripheral side of the bead core 3.

The bead core 3 has a thin rubber coating layer 6 formed on the outer peripheral surface of a polybenzazole fiber cord 5 as shown in a cross sectional view in FIG. The sol fiber cord 7 is formed by winding the sol fiber cord 7 into a required number of steps and rows as shown in FIG. 3 using an adhesive property of the rubber coating layer 6 with an inner diameter corresponding to the diameter of the applicable rim. . That is, as shown in FIG. 3, one polybenzazole fiber cord 7 with a rubber coating layer may be spirally reciprocally wound up to the required number of stages and rows.

The polybenzazole fiber cord 5
The thin rubber coating layer 6 may be formed on the outer peripheral surface of the cord 5 by, for example, subjecting the outer peripheral face of the cord 5 to a dipping treatment in advance, and then applying a rubber such as a double bond to a volatile organic solvent such as toluene. A solution obtained by dissolving a rubber in which 50 to 120 parts by weight of carbon, 2 to 6 parts by weight of sulfur, and 5 to 20 parts by weight of other oil are blended in 100 parts by weight of a diene rubber having By spraying, brushing or the like, and then uniformly vaporizing the volatile organic solvent, preferably by forcibly vaporizing, leaving only the rubbery substance on the outer peripheral surface of the cord 5. It can be carried out. Here, the “dip treatment” means that the cord 5 is immersed in a mixed solution of resorcin, formalin, latex or the like, and then subjected to a heating treatment and a tensile treatment. Here, as described above, the thickness of the rubber coating layer 6 can be adjusted simply, easily, and as intended by changing the rubber concentration in the solution.

Incidentally, the formation of the conventional rubber coating layer on the outer peripheral surface of the cord is generally performed as shown in a schematic diagram in FIG.
With respect to the kneaded rubber R extruded from the extruder EX through the die MP, the cord C is caused to travel in the die through a cord guide CG attached to the die MP, in a direction perpendicular to the flow direction of the kneaded rubber R. The adhesion of the kneaded rubber R is performed by adhering the kneaded rubber R to the outer peripheral surface of the cord C. Here, the adjustment of the amount of the kneaded rubber R attached is performed by changing the traveling speed of the cord C. In case, code C
The kneaded rubber R is directly attached to the outer peripheral surface of the cord guide CG. From the viewpoint of workability, the guide hole diameter of the cord guide CG cannot be completely matched with the cord diameter. It is practically impossible to make it less than 0.1mm.

The arrangement of the bead core 3 configured as described above on the tire bead portion 2 can be performed in the tire molding process in exactly the same manner as in the prior art.
The vulcanization molding of the green tire including the bead core 3 can also be performed in the same manner as in the related art.

Here, in the bead core 3 of the product tire, the thickness of the covering rubber filling the adjacent gap between the polybenzazole fiber cords is preferably 0.001 mm or more and 0.2 mm or more.
Less than The thickness here is within the cross section of the bead core 3 irrespective of its cross-sectional location.
As schematically shown in FIG. 5, the thickness of each covering rubber t that fills the gap between the cords adjacent in the respective directions such as up, down, left, right, and oblique is measured, and the average value thereof is obtained. . It is essential that 0 is not present in any of the measurements.

That is, the thickness of the coated rubber is preferably at least 0.001 mm in order to ensure reliable prevention of mutual contact between the polybenzazole fiber cords 5, while the maximum thickness thereof is in the radial direction. In order to sufficiently reduce the difference in tensile stress acting on each of the polybenzazole fiber cord 5 located on the inner peripheral side and the polybenzazole fiber cord 5 located on the outer peripheral side, the distance is preferably 0.2 mm, more preferably 0.1 mm. Is advantageous.

Here, the rim assembling work of the product tire having the bead core 3 in which the above-mentioned thin covering rubber is interposed between the polybenzazole fiber cords 5 requires the bending rigidity of the polybenzazole fiber cord itself. Therefore, it can be performed extremely smoothly despite the thinness of the covering rubber.

Incidentally, when the bead core is constituted by a rubber-coated steel wire, a coating rubber thickness sufficient to allow bending deformation of each cord is given to a bending external force acting on the bead core at the time of rim assembly or the like. Without this, the entire bead core has a rigid structure, so that rim assembly and the like are substantially impossible.

Thus, in this pneumatic radial tire, by using the benz cord as the polybenzazole fiber cord 5 itself, the tire weight can be effectively reduced, and the polybenzazole fiber cord in the bead core 3 can be effectively reduced. By making the thickness of the rubber covering the gap 0.001 mm or more and less than 0.2 mm, the beads 5 are sufficiently restrained from extending and deforming the cord 5 located on the radially inner peripheral side of the tire by the cord 5 located on the radially outer peripheral side. The burst limit internal pressure of the portion 2 can be effectively increased, and the danger of a decrease in the bead portion durability and a decrease in the burst limit internal pressure due to direct contact between the polybenzazole fiber cords can be eliminated.

Further, in the manufacturing method, the thickness of the rubber coating layer 6 can be made sufficiently thin by adhering a solution of rubber to the polybenzazole fiber cord 5, and the thickness can be reduced based on the selection of the solution concentration. The bead core 3 can be easily and easily adjusted as required and adjusted as desired. Further, when the bead core 3 is formed by winding the polybenzazole fiber cord 7 with the rubber coating layer, the rubber coating layer 6 Since the polybenzazole fiber cord 7 can be accurately positioned at a required position by fully utilizing the adhesiveness of the bead core 3, the bead core 3 having the expected cross-sectional shape can be easily, easily, and efficiently manufactured. Can be manufactured well.

[0036]

EXAMPLES Examples of the tire according to the present invention relating to the weight of the bead core and the burst limit internal pressure of the bead portion will be described below. Here, the size is 175 / 70R13
Tire, a radial carcass is composed of two carcass plies, and the end portion is formed around a bead core as shown in FIG.
Winded up as shown.

Here, the constitution of the bead core was as shown in Table 1, and the bead core weight and the burst limit internal pressure of the bead portion were measured for each of them. Here, the burst limit internal pressure is obtained by a hydraulic pressure burst test, and the coating rubber thickness between the bead cords is obtained by measuring the coating rubber thickness by cutting a bead core at a portion other than the burst portion, for example, with a knife. Was.

Table 1 shows not only the structure of the bead core of the example, but also the structure of the bead core of the comparative example. The rubber coating method (A) in which the rubber dissolving solution is applied to the outer surface of the cord is shown. Means a method of forming a rubber coating layer,
The method (a) refers to the method described in FIG. 4 in which the cord is passed through a cord guide having a hole diameter 0.3 mm larger than the diameter of the cord to form a rubber coating layer.

Further, PBO in the table is a polyparaphenylene benzobisoxazole fiber cord, and the structure of the cord is adjusted to match the diameter of one cord with a steel wire.
6670 dtex / 2, the number of twists was 10 × 10. The cord configuration may be one single twist or three or more twists.
The number of dtex can be changed and used. The number of twists and the ratio between the number of twists and the number of twists can be arbitrarily changed and used.

The steel wire bead cores of Comparative Example 2 in the table are those widely used in the past, and the thickness of the rubber coating layer of Comparative Examples 2 and 3 is as thin as the thickness of the rubber coating by insulation. It is a value close to the limit of.
When the rubber is covered with the insulation shown in FIG. 4, the thickness can be adjusted by the passage speed of the cord, the diameter of the guide for passing the cord, and the like. Therefore, virtually 0.
It is not possible to make one with a thickness of less than 3 mm.

In the case of a steel wire bead core, even if a bead core is formed by attaching a thin rubber coating layer with a rubber dissolving solution and embedded in a tire bead portion, the bending rigidity and the like become extremely high, and the rim is assembled. In addition, the steel wire is plastically deformed, and the riding comfort and durability of the tire are extremely deteriorated. In Comparative Example 2, the diameter of the rubber-coated cord can be minimized. Of 1.36 mm.

[0042]

[Table 1]

According to Table 1, comparison between Inventive Examples 4 and 5 and Comparative Examples shows that the burst limit internal pressure of the tire having the bead core using the PBO fiber cord is remarkably improved. Further, according to a comparison between Inventive Examples 4 and 5 and Comparative Example 3, in the inventive example, the weight of the rubber coating layer was reduced, and in the bead structure in which cords were densely arranged in the cross-sectional radial direction, It can be seen that the burst limit internal pressures of 4 and 5 are high.

Further, in Invention Examples 1 to 3, the number of turns of the cord is reduced. However, as compared with the tire having a steel wire bead core of Comparative Example 2, the tire is lighter in weight while maintaining a burst limit internal pressure equal to or higher than that. It can be seen that the conversion has been achieved. Further, it is also possible to apply the present invention to a bead having a cross-sectional shape in which the beads are arranged more densely than a quadrangular one as in the second embodiment.

The performance of each of the cores has been described above. The workability of assembling and releasing the rims of the tires having the respective bead cores is described in Examples 1 to 3.
4. While there was almost no difference between Comparative Examples 1 and 2, the bead core using a steel wire whose rubber coating layer was thinned to the limit by the insulation of Comparative Example 3 had a high bead rigidity and was deformed. It was confirmed that it was difficult to work because it was difficult. This is due to the fact that the polybenzazole fiber cord is twisted, and has a low elasticity at a low load in the tensile direction elastic modulus and a low flexural rigidity as compared with the steel wire. It was also confirmed that the cross-sectional shape of the bead core embedded in the tire also maintained the required shape.

The performance of each bead core that can be read from Table 1 has been described above. The workability of the rim assembling and the rim releasing work of the tire having each bead core was compared with Example 1. 4 and Comparative Examples 1 and 2, there was almost no difference in workability, and each of the tires had better workability than the tire of Comparative Example 3. This is due to the fact that the polybenzazole fiber cord is twisted, so that the elastic modulus in the tensile direction is lower at low loads and the bending stiffness is lower than that of steel wire. Further, it was confirmed that the cross-sectional shape of the bead core embedded in the tire also maintained the required shape.

[0047]

Thus, according to the tire of the present invention,
The tire weight can be reduced while securing a sufficiently high burst limit internal pressure.At the same time, the durability and burst limit internal pressure caused by the direct contact between the polybenzazole fiber cords are sufficiently reduced. Can be prevented.

Further, according to the method of the present invention, the thickness of the rubber coating layer can be made sufficiently thin, and
It can be easily and easily changed as expected, and furthermore, it is possible to easily and quickly construct a bead core having an intended cross-sectional shape by utilizing the adhesiveness of the rubber coating layer. Can be.

[Brief description of the drawings]

FIG. 1 is a tire width direction sectional view showing an embodiment of a main part of a tire according to the present invention.

FIG. 2 is a cross-sectional view showing a polybenzazole fiber cord with a rubber coating layer.

FIG. 3 is a perspective view showing a configuration of a bead core.

FIG. 4 is a schematic diagram illustrating a conventional form of forming a rubber coating layer.

FIG. 5 is a view showing a measurement mode of a coating rubber thickness.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Radial carcass 2 Bead part 3 Bead core 4 Bead filler 5 Polybenzazole fiber cord 6 Rubber coating layer 7 Polybenzazole fiber cord with rubber coating layer

Claims (4)

[Claims] A bead core formed by winding a rubber-coated polybenzazole fiber cord, wherein the thickness of the coating rubber filling an adjacent gap between the polybenzazole fiber cord is 0.001 mm or more and less than 0.2 mm. A pneumatic radial tire characterized by: 2. The pneumatic radial tire according to claim 1, wherein the polybenzazole fiber cord is made of polyparaphenylene benzobisoxazole. 3. The pneumatic radial tire according to claim 1, wherein the thickness of the covering rubber is less than 0.1 mm. 4. An outer periphery of a polybenzazole fiber cord,
A solution obtained by dissolving rubber in a volatile organic solvent is applied to form a thin rubber coating layer, and the polybenzazole fiber cord with the rubber coating layer is wound to form a bead core, and the bead core is used as a tire bead. A method for manufacturing a pneumatic radial tire, wherein the tire is embedded in a part.