JPH0616013A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To improve the joint precision of a tread joint part and improve riding comfort, by forming the joint line of the tread joint part as having a bent line or a curved line which is projected toward the tread ground contact face, side and as one end of the joint line is positioned on the tread ground contact face, in a section which crosses a tire rotation shaft at right angles. CONSTITUTION:A polygonal joint line Lj is formed as being extended from a point Pa on the ground contact face of a tread 4 to a point Pi on the other end face through points Pb, Pc as folding points, and being projected toward the tread round contact face side in the section Pa-Pb-Pc and recessed in the section Pb-Pc-Pi. With this structure, high joint precision and high adhesive strength of the tread joint part can be realized at the same time, vibration comfortableness of a vehicle is improved by improving and keeping the uniformity and open-splice resistivity of the tread 4 can be raised.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to automobile tires, in particular truck / bus tires, industrial vehicle tires and construction vehicle tires, and more particularly to a tread by suppressing peeling failure at the circumferential joint portion of the tread. The present invention relates to a pneumatic tire in which the durability (open splicing resistance) of the vehicle is improved, and further, the vibration of the vehicle caused by the joint portion is remarkably improved to further improve the vibration riding comfort performance.

[0002]

2. Description of the Related Art A perspective explanatory view of a butt joint portion of a tread in an unvulcanized state according to the prior art is shown in FIG. 5 (a), and after vulcanization molding having the tread joint portion of FIG. 5 (a). Part (a) of the tire is cut along the tire equatorial plane, and an explanatory view seen from the tire rotation axis direction is shown in FIG. 5 (b). FIG. 5A is a view showing only the tread joint and omitting other members, and a butt joint to a plane U (indicated by a chain double-dashed line in the figure) orthogonal to the rotation axis of the unvulcanized tire. The joint surface Sb is inclined at an inclination angle of about 60 ° to 70 °, and the joint surface Sb is a substantially flat plane. In addition, J indicates a line on the outside of the joint.

The tire shown in FIG. 5 (b) has a radial carcass 2 as an example of a carcass, and its reinforcing steel cord is shown exposed. In this tire, a belt 3 shown by a dotted line is arranged on the outer peripheral side of the radial carcass 2, and a tread 4 is arranged further on the outer peripheral side of the belt 3. The joining line of the joining portion of the tread is shown by S, and this line is a substantially straight line. The angle of inclination of the joining line S with respect to the line Z passing through the rotation axis A of the tire and orthogonal to this rotation axis is indicated by Φ.

Conventionally, the tread joint portion of a pneumatic tire is formed by the following method. That is, a tread rubber member extruded in a predetermined shape by an extruder is tilted at a predetermined angle in the length direction of the member, and a rotating disk cutter is traversed in the width direction of the member to cut it into a predetermined length. Or, it is cut into a predetermined length with a predetermined inclination angle by a push cutter. At that time, generally, FIG.
As shown in (a) of Fig. 3, when the tread rubber member of this predetermined length is wound around the outer peripheral side of the belt or breaker molded in the unvulcanized state and attached, the tread rubber member is cut as described above. The joint surface portions on both ends are butt-joined and adhesively molded.

After that, vulcanization molding is performed in the mold.
The product tire shown in (b) is obtained. The inclination angle of the joint surface of the joint portion of the product tire generally changes from the unvulcanized state, but the joint surface keeps a substantially flat surface, and the pattern groove portion of FIG. (B)
As shown in, the joining line S of the joining portion appearing in the cross section is substantially the straight line described above.

[0006]

In the conventional tread joint of a product tire, as described above, the joint surfaces of both end portions are inclined to each other. Firstly, the joint area is as small as possible. This is to secure a large adhesive force between the rubbers, and secondly, to apply as much pressure as possible to the joint surface during vulcanization molding. In this way, the tread joint in the product tire is guaranteed to have sufficient adhesiveness.

However, when the unvulcanized tread rubber is wound and stretched and formed, if the joining area is increased as much as possible, the circumferential length of the joining surfaces to be joined to each other becomes long. , The joining surface area becomes large, and the tread is easily deformed because it is unvulcanized rubber, so the amount of circumferential deviation between the joining surfaces tends to become large, making positioning difficult and the joining accuracy greatly deteriorates. There was a problem to do.

Particularly in recent years, it is extremely soft in the unvulcanized state,
Therefore, there is an increasing tendency to require a tread rubber that is easily deformed or an extremely hard tread rubber that is not easily deformed, and this has been highlighted as a problem that further impairs the joining accuracy. This reduction in joining accuracy causes a non-uniform portion of the tread thickness on the tread circumference of the product tire, and this non-uniformity increases uniformity values, especially the value of radial force variation (RFV), which becomes the excitation force for the vehicle, There was a problem that vibration riding comfort was greatly impaired.

If the circumferential length of the joint surface is shortened in order to solve the above problems, the joint accuracy can be improved, but as described above, the mutual joint area is insufficient and the joint surface is perpendicular. This causes a decrease in the pressure component that can be applied in the direction, resulting in a decrease in the adhesive strength of the tread joint, and there is a problem that a peeling failure of this portion during running, a so-called open splice failure occurs. Therefore, it can be said that the accuracy and adhesive strength of the tread joint are a trade-off. Although the above describes the extruded tread rubber,
The same applies to the mold pressing tread rubber.

Therefore, an object of the present invention is to solve the above-mentioned trade-off problem of high joining accuracy and high adhesive strength of the tread joint, and in particular, the joint portion of the extruded tread rubber or the die-pressed tread rubber. To improve the vibration ride comfort of the vehicle by highly improving the joining accuracy of the tread joint portion of the pneumatic tires that it has, and to propose a pneumatic tire that further improves the open splice resistance of the tread. .

[0011]

In order to solve the above problems, a pneumatic tire of the present invention has a carcass of 1 ply or more, a belt or breaker arranged on the outer peripheral side of the carcass, and a belt or breaker of the belt or breaker. Further, with a tread arranged on the outer peripheral side, in a tire having a joint portion in which the tread is joined to each other at an abutting surface inclined with respect to the circumferential direction, when the tread is cut in a plane orthogonal to the tire rotation axis. The joining line of the joining portion that appears has a bent line portion or a curved portion that is convex toward the tread tread side, so that one end of this bent line portion or the curved portion is located on the tread tread surface. It is characterized in that the joint portion is formed.

In a preferred embodiment of the present invention, the joining portion is formed so that the joining line has a bent line portion or a curved portion that is concave toward the tread tread side in an inner region in the thickness direction of the tread. be able to.

As a further preferred embodiment of the present invention, the bent line portion of the joining line may be formed by a substantially straight line, and the curved portion may be formed by a substantially arc.

In another embodiment of the present invention, the bent line portion of the joining line can be formed by a curved line and a substantially straight line forming a substantially arc.

Hereinafter, the present invention will be described more specifically with reference to the illustrated embodiments. FIG. 4 is a widthwise sectional view of the left half of the tire equatorial plane E of the pneumatic tire 1 according to one embodiment of the present invention. The pneumatic tire of this embodiment has a radial carcass 2 of one ply or more (one ply in the example shown) straddling a pair of bead cores 6 in a toroidal shape, and two or more layers arranged on the outer peripheral side of the radial carcass 2. (The example shown is 2
Layer 3), a tread 4 disposed further on the outer peripheral side of the belt 3, and sidewalls 5 extending from both side ends of the tread 4 to the bead portion 7.

Although not shown, a pneumatic tire according to another embodiment of the present invention is provided with a bias carcass of two or more plies that straddles a pair of bead cores 6 in a toroidal shape, and is arranged on the outer peripheral side of the carcass. Breaker with one or more layers,
The breaker further comprises a tread disposed further on the outer peripheral side and a sidewall extending from both side ends of the tread to the bead portion.

Each of the treads 4 of the pneumatic tire according to the present invention uses an extruded or die-pressed tread, and as shown in FIG. 5 (b), this tread has a tendency in the circumferential direction of the tread. It has a joint part in which the joint surfaces inclined to each other are butted against each other.

1 (a) and 1 (b), the tread joint of the pneumatic tire of the embodiment according to the present invention is cut along the tire equatorial plane E or a plane parallel to this, and the cut portion is made horizontal. It is a figure which shows the joining line Lj of the joining part at the time of unfolding. In FIGS. 4A and 4B, 4t indicates a cutting line on the tread surface side of the tread 4, and 4i indicates a cutting line on the tire inner surface side of the tread 4 which is in contact with the belt or breaker. T shown in both figures is the tread thickness. 1A and 1B are views of the tread land portion where the tread 4 has no groove. The same applies to the other examples.

In FIG. 1A, the joining line Lj
On the tread of the tread 4 at a point Pa at one end thereof,
That is, in the figure, a line segment Pb-Pa connecting the bending point Pb inside the tread 4 and the point Pa inside the tread 4 and a point P further inside the tread than the point Pb are located on the cutting line 4t.
c and the line segment Pb-Pc connecting the point Pb and the point P
A line segment Pc- that connects the point Pc and the point Pi located on the cutting line 4i on the inner surface of the tread with c as a bending point
It consists of Pi and. A bending line portion Pa-Pb in which the point Pb is a bending point and the point Pa is located on the tread surface.
As is clear from the figure, -Pc has a convex shape toward the tread tread side.

Further, in FIG. 1A, the bending line portion Pb-Pc-Pi, where the point Pc is a bending point and the point Pi is located on the inner surface of the tread, is directed toward the tread tread side as apparent from the figure. Takes a concave shape. In other words, the bending point P on the tread tread side with respect to the virtual line Pa-Pi that connects the point Pa and the point Pi at the shortest distance
b is located closer to the tread surface than the virtual line Pa-Pi,
The bending point Pc on the inner surface side of the tread is a virtual line Pa-Pi.
Located closer to the inside of the tread.

Further, in FIG. 1 (a), Z₁And Z
₂To the tire rotation axis passing through points Pa and Pb.
It is a vertical line. Illustrated Φ₁Is the vertical line Z₁The line segment P to
a-Pb inclination angle, Φ₂Is the vertical line Z₂Before
It is the inclination angle of the line segment Pb-Pc. Φ is the vertical line Z₁Against
The inclination angle of the virtual line Pa-Pi that
As is clear, Φ₁> Φ, Φ₂<Φ. The line segment
The same applies to Pc-Pi as the line segment Pa-Pb. This
Here, 80 ° ≧ Φ₁≧ 60 °, 45 ° ≧ Φ ₂≧ 10
It is preferable that the angle is °.

The depth To in the tread thickness direction from the cutting line 4t on the tread surface to the point Pb is 15 of the tread thickness T.
% To 40% is preferable. The same depth Ti from the point Pb to the point Pc is 20% of the tread thickness T.
It is preferably not less than 70% and not more than 70%. In addition, depth T here
“I” refers to the total depth of line segments having an inclination angle equal to or less than the inclination angle Φ of the virtual line Pa-Pi, and FIG.
Then, the line segment Pa-Pc corresponds to this. The same applies to the other examples below.

Although the line segment shown in the figure has been described as a straight line, it is not limited to a straight line in the above embodiment, and may be a substantially straight line.

FIG. 1B shows another embodiment in which the joining line Lj is mainly composed of a curved portion. This example
The line segment Pa-Pb and the line segment Pc- described in FIG.
A portion corresponding to Pi is a curve Qa-Qb portion and a curve Qc-
It is a joining line Lj that is a Qi portion and has points Qb and Qc as substantially straight line segments. In the illustrated example, these curved portions are arcs, but each curved portion does not necessarily have to be an arc having a single curvature center, and may be a curved portion having a plurality of curvature centers.

In FIG. 1 (b), curved portions Qa-Qb
Has a substantially circular arc shape centered inward of the tire from the tread surface and having a radius of curvature of R ₁ , and the point Qa at one end thereof is located on the cutting line 4t of the tread surface. In this embodiment, the curve portion Qa parallel to the imaginary line Qa-Qi connecting the points Qa and Qi in the shortest, although it does not have a relatively clear bending point as shown in FIG.
The contact point Ta of the tangent line la of -Qb is located closer to the tread surface than the virtual line Qa-Qb. That is, the curved portion Qa-
Qb has a convex shape toward the tread side.

Further, in FIG. 1B, a curved portion Qc-Qi having a center on the tread tread side and having a radius of curvature of R ₂ has a point Qi at a cutting line 4 on the inner surface of the tread.
i above. The curved line portion Qc-Qi is a virtual line Qa-
The contact point Td of the tangent line ld of the curved portion Qc-Qi parallel to Qi is located closer to the inner surface of the tread with respect to the virtual line Qa-Qb.
That is, the curved portions Qc-Qi have a concave shape toward the tread tread side.

Therefore, although not shown, the inclination angle of each tangent line at each point on the curved portion Qa-Ta with respect to the perpendicular line Z ₁ passing through the point Qa is equal to or larger than the inclination angle Φ of the virtual line Qa-Qi. Becomes In addition, this is the curved portion Td-Q
The same is true for i. Furthermore, the same inclination angle at each point of the line portion from the curved portion Ta-Qb to the curved portion Td-Qi via the line segment Qb-Qc is the imaginary line Qa-Qi.
Is less than the tilt angle at the same point. Where point Qa
The perpendicular line Z _{1 of the} shortest line Qa-Ta connecting the contact point Ta with the contact point Ta.
The inclination angle Φ _{10 with} respect to is in the relationship of Φ ₁₀ > Φ with respect to the inclination angle Φ of the imaginary line, and preferably 80 ° ≧ Φ ₁₀ ≧ 60 °.

In this embodiment, the depth To in the tread thickness direction from the cutting line 4t of the tread surface to the contact Ta is 15% or more and 40% or less of the tread thickness T, and the distance from the contact Ta to the contact Td is The depth Ti is preferably 20% or more and 70% or less of the tread thickness T. Here, the depth Ti means the total depth of line segments having an inclination angle equal to or smaller than the inclination angle Φ of the virtual line Qa-Qi, and in FIG. 1B, the line segment Ta-Td is this. Equivalent to. still,
The same applies to the other embodiments described below.

Although one embodiment of the present invention has been described above with reference to FIGS. 1A and 1B, the present invention is based on another embodiment shown in FIGS. 2A and 2B described below. It can be based on the joining line. 2A and 2B
Shows the joining line Lj of the tread joining portion when the cut portion of the tread 4 is horizontally developed as in the above-described embodiment.

The joining line Lj shown in FIG. 2 (a) has one bending point Pb, and is a substantially straight line segment Pa-Pb and line segment Pb- which is convex toward the tread surface. P
It is composed of one bent line portion having i, and the relationship between the respective inclination angles is the same as that of the embodiment shown in FIG. Also, the relationship between the depth To to the point Pb and the depth Ti from the point Pb to the point Pi to the tread thickness T is shown in FIG.
It is similar to the embodiment of.

The joining line Lj shown in FIG. 2 (b) is composed of one curved portion which is convex toward the tread tread side, and this curved portion may be a circular arc having one radius of curvature.
Further, it can be a complex arc having a plurality of radii of curvature. Further, a joining line L parallel to the virtual line Qa-Qi
The relationship between the depth To of the tangent of j to the contact Ta and the depth Ti from the contact Ta to the point Qi with respect to the tread thickness T is similar to that of the embodiment of FIG. However, Ti in this embodiment has a value corresponding to Qi at the contact point Td in FIG.

FIGS. 3A, 3B and 3C are sectional development views similar to the above, showing the joining line Lj in still another modification of the present invention. Joining line L shown in FIG.
j is a substantially straight line segment Pa-Pb, Pb-Pc, Pc- whose bending points are four points Pb, Pc, Pd and Pe.
Pd, Pd-Pe and Pe-Pi, and line segment Pa-
Pb-Pc forms a bent line portion that is convex toward the tread tread side.

The joining line Lj shown in FIG. 3B is composed of two curved portions which are convex toward the tread tread side and two curved portions which are concave toward the tread tread side.
The contact points of each curved line portion are indicated by Ta, Td, Te, and Tf, and the depth corresponding to the depth Ti shown in FIG. 1B in this example is the depth of the line segment Ta-Td and the line It is the sum of the depth Te and Tf.

The joining line Lj shown in FIG. 3C is the point Ta.
Is a bending line which has a substantially straight line segment Pa-Ta and a substantially arc line segment Ta-Qi and which is convex on the tread surface side. The relationship between each of the tilt angles and the tilt angle Φ in the embodiments of FIGS. 3A, 3B, and 3C is the same as in the other embodiments.

The tread joint of each of the embodiments of the present invention described above is, for example, an ultrasonic cutter utilizing high frequency vibration,
Alternatively, it can be obtained by cutting an unvulcanized tread rubber member into a desired joint surface shape using an ultra-high pressure linear jet water jet cutter. In this case, in a tire in which the shape of the tread joint changes between the unvulcanized state and the state after vulcanization, the shape of the desired joining line after vulcanization depends on the amount of change or the change form. It is sufficient to use an unvulcanized joining line in which the variation is folded in advance so as to be obtained.

The ultrasonic cutter emits ultrasonic waves from a thin nozzle having a slot shape which is substantially aligned with the unvulcanized joining line, and cuts the unvulcanized tread rubber laterally in the width direction. . The jet water jet cutter cuts the unvulcanized tread rubber in the width direction while moving the cutter nozzle from the side of the unvulcanized tread rubber along the unvulcanized joining line. Thus, the unvulcanized tread joint, which is bonded at a predetermined position and the joint surfaces are butt-joined to each other, forms a desired tread joint shape after vulcanization.

[0037]

The operation of the present invention will be described with reference to FIGS. 1A and 1B by using these embodiments as representative examples. In (a) and (b) of FIG. 1, the conventional pneumatic tire having a tread joint having a joining line that is a line that connects the point Pa and the point Pi with a substantially straight line has the above-mentioned problems. However, in the tread joint portion of the present invention, first, as is clear from the figure, the length of the line segment of the joining line Lj is longer than that of the conventional substantially straight line segment Pa-Pi, and therefore, the tread. The area of the joint surfaces of the joint portions can be greatly increased as compared with the conventional tread, and as a result, the adhesive force can be further improved and the open splice resistance can be remarkably improved.

Secondly, the joint portion of the present invention has a line segment Pb-Pc or Φ having an inclination angle greatly falling below the inclination angle Φ of the conventional joint line Pa-Pi, for example, Φ _2. A line segment T having an inclination angle that tends to fall
By providing the respective line portions of a-Td, in other words, by providing the joining surface that is closer to the tire radial direction side, when joining the unvulcanized tread rubber, first, a part of the joining line Lj is provided. The joining surfaces forming the line segment Pb-Pc or the line segment Ta-Td, respectively, can be butt-joined to each other, and then the remaining portion can be joined, and the joining work of the tread rubber when unvulcanized is further improved. This will be easy and the joining accuracy will be further improved. As a result, it is possible to suppress deterioration of uniformity (RFV) due to the tread joint.

Thirdly, the joint angle of the present invention is the inclination angle Φ ₁ or Φ ₁₀ of the joint line Lj of the joint portion on the outer side in the tire radial direction of the tread.
By setting a large value, in other words, by further inclining the joint surface of the joint portion toward the tread tread side, the component force of the pressing force applied perpendicularly to the joint surface during tire vulcanization is increased. As a result, the adhesive strength of the joint surface is further improved, and the peeling failure of this portion can be suppressed. This brings about a remarkable improvement effect particularly against the open splice failure of the tread joint, which frequently occurs from the start of running the tire to the early stage of tread wear.

Fourthly, according to the joint portion of the present invention, fourthly, the above-mentioned various embodiments or their modified examples are appropriately selected depending on the physical properties such as the hardness of the tread rubber or the hardness of the unvulcanized rubber, modulus, tackiness and the like. By applying it, it is possible to sufficiently secure open splice resistance and also maintain good uniformity. There is no fear of sacrificing the other by adopting one like the conventional technology. .

[0041]

[Example] A pneumatic tire for a construction vehicle, which uses an ultra-heavy load, is likely to cause an open splice failure, and has a demand for improving vibration riding comfort due to uniformity (RFV), is taken as the tire of the example. The size is 18.00R25 and tread class E3. The basic structure of the tire is shown in FIG.

The carcass 2 is a one-ply radial carcass having steel cords as reinforcing cords, and the belt 3 is a tire in which four belt layers having reinforcing steel cords are laminated. The thickness T of the tread 4 was 30 mm on the tire equatorial plane E, and this thickness was made uniform in the tread width direction.

With the above-mentioned common structure, FIGS. 1 (a) and 1 (b) are Examples 1 and 2, FIGS. 2 (a) and 2 (b) are Examples 3 and 4, and FIG. 3 (a). And (b) are Examples 5 and 6, and the tread joining line Lj corresponding to each figure is used.
And a tire having Conventional Examples 1 and 2 are tires having a tread joint having a joint line S of the virtual line segment Pa-Pi in FIG. In addition, the circumferential length along the tread surface of the tread joint of the six examples of the example and the conventional example 1 is about 65 mm.
And the conventional example 2 was set to 80 mm. Also, the compounding of the tread rubber used was common to all tires.

Table 1 shows the specifications of the joining lines Lj and S of the above tires. In the table, Φ ₁ , Φ ₁₀ , and Φ are the inclination angles (degrees), To is the depth to the point Pb or Ta in the figure, and Ti is a line having an inclination angle equal to or less than the inclination angle Φ. The depths of the minutes are indicated respectively. Also, R ₁
Is the radius of curvature when the curved portion of the joining line is approximated by one arc, and the position of Ta is a point on this arc.

In order to verify the effect of the present invention, each of the above tires was used as a test tire, and first, the uniformity M was indoors.
Radial force variation (RF
V) was measured and the variation value of the reaction force at the tread joint was determined. The evaluation is represented by an index value with the tire of Conventional Example being 100, and is shown in Table 1. The larger the index value, the better.

Next, in order to evaluate the resistance to open splicing, an actual construction vehicle (32-ton dump truck)
A market evaluation was conducted in which 20 tires of each example were mounted and actually run. For the evaluation, the peeling condition of the tread joint was examined at the time when the tread wear rate was about 10%, and the peeling resistance rate was shown as an index of peeling resistance by indexing the number of tires that caused this peeling as 100 of the conventional tire. Shown in. The larger the index value, the better.

[0047]

[Table 1]

As is apparent from Table 1, the tires of the examples according to the present invention, except for the tires of Examples 3 and 4, have improved uniformity (RFV) level, and in addition,
The number of peeled tread joints has been reduced from approximately 1/3 of the conventional example to 1 /
It can be seen that it has been lowered to about 5. In addition, Example 3
Tires 4 and 4 are at least uniform (RF
It is understood that the level of V) is maintained and the number of peeled strips at the tread joint is reduced to about 2/3 of the conventional example.

[0049]

According to the present invention, a high degree of joint accuracy and a high adhesive force of a tread joint using an extruded tread rubber or a pressed tread rubber, which cannot be simultaneously achieved by the conventional technique, are simultaneously realized. Yes, this allows for uniformity (RF) due to the tread joint.
V) can be improved or maintained to improve the vibration riding comfort of the vehicle, and at the same time, a pneumatic tire having significantly improved open splice resistance of the tread can be provided.

[Brief description of drawings]

1A and 1B are explanatory views showing a joining line in a cross section of a tread joining portion according to an embodiment of the present invention.

2A and 2B are explanatory views showing a joining line in a cross section of a tread joining portion according to another embodiment of the present invention.

3 (a), (b) and (c) are explanatory views showing a joining line in a cross section of a tread joining portion according to still another embodiment of the present invention.

FIG. 4 is a widthwise sectional view of a pneumatic tire according to an embodiment of the present invention in a left half from a tire equatorial plane.

5A and 5B are explanatory views of a tread joint portion in a conventional tire.

[Explanation of symbols]

2 Carcass 3 Belt or breaker 4 Tread Lj Joining line of tread joint Pa Pa Point on tread of bent line at joining line Pi Point of bend line at joining line on tread inner surface Qa On tread of curved part at joining line Point Qi Point on the inner surface of the tread of the curved line at the joining line T Tread thickness

Claims (4)

[Claims] 1. A carcass having one or more plies, a belt or breaker disposed on the outer peripheral side of the carcass, and a tread disposed further on the outer peripheral side of the belt or breaker, the tread having a circumferential direction. In a tire having joints that are joined to each other at a sloping butt surface with respect to each other, the joining line of the joints that appears when cutting at a plane orthogonal to the tire rotation axis is convex toward the tread tread side A pneumatic tire having a bent line portion or a curved portion, wherein the joint portion is formed such that one end of the bent line portion or the curved portion is located on the tread tread surface. 2. The pneumatic tire according to claim 1, wherein the joining line has a bent line portion or a curved portion that is concave toward the tread tread side in an inner region in the thickness direction of the tread. 3. The pneumatic tire according to claim 1, wherein the bent line portion of the joining line is formed by a substantially straight line and the curved portion is formed by a substantially arc. 4. The pneumatic tire according to claim 1, wherein the bent line portion of the joining line is formed by a curved line and a substantially straight line which form a substantially arc.