JPH0811233A - Pneumatic flat radial tire - Google Patents

Abstract

PURPOSE:To obtain an excellently durable, pneumatic ultra flat radial tire without decreasing the molding efficiency by specifying its compression in the turn-up end of a carcass extending to both the ends of a belt and overlapping the belt. CONSTITUTION:The pneumatic radial tire, so called, for 50 series passenger car is of the kind where the tire size is 205/50VR16 and the compression is 60 or lower, and spread over between the bead cores 3 is a carcass consisting of a polyester code arranged at almost 90 deg. with respect to the tire peripheral direction of a pair of bead cores 3, and both the ends are wrapped around and engage to the bead cores. Across belt 5 having codes being crossed each other in its interlayer is arranged, consisting of two layers of steel codes being inclined about at 18 degrees with respect to the tire peripheral direction in the radially directional outside of the crown part 9 of a radial carcass.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a super flat pneumatic radial tire which is excellent in durability without lowering molding efficiency.

[0002]

2. Description of the Related Art A pneumatic radial tire generally has the following common basic structure as shown in FIGS. 6, 8 and 10. That is, the pair of bead cores 3
A radial carcass 2 extends between (only the left half is shown), and the radial carcass includes cords arranged in a direction substantially 90 degrees with respect to the tire circumferential direction. A belt 5 is arranged radially outside the crown portion 9 of the carcass 2, and a tread rubber 6 is arranged further radially outside the belt 5. A side rubber 4 is arranged on the outer side in the radial direction of the side portion 8 of the radial carcass 2. The tread rubber 6 is mainly required to have abrasion resistance because it comes into contact with the road surface, while the side rubber 4 is mainly required to be flexed because it is used in a flex zone which is easily bent and deformed. Since the wear resistance and the flex resistance are in a trade-off relationship in the rubber compounding technique, the tread rubber and the side rubber are each formed by an optimum rubber composition and prepared.

Such a pneumatic radial tire is generally two-stage molded, that is, a first tire component such as a radial carcass is attached on a cylindrical former.
Finally, the molding process is performed through a molding process and a second molding process in which the remaining tire constituent members such as a belt are attached in a state where the diameter is expanded in a toroidal shape. This conventional molding method is roughly classified into the following three types.

The first type (hereinafter referred to as type 1) is
The first molding step (see the figure) of attaching some tire constituent members (inner liner, bead core, stiffener, chefah, other bead reinforcing member, etc.) including the side rubber 4 after attaching the radial carcass 2 on the cylindrical former. The raw case 22 is molded by (No.). Here, the side rubber 4 is attached to the raw case 22. The raw case 22 is expanded in a toroidal shape as shown in FIG. 7, the remaining tire components such as a belt are attached in this state, and the tread 6 is attached to the raw case 22 by a stitching roller (not shown) in the direction of arrow B. Crimping and final molding.

Since the type 1 has the side rubber 4 attached before the tread rubber 6, it is called a side tip type. In the side pretensioning method, as described above, the side rubber 4 is first attached in the first molding step, and the tread rubber 6 is attached in the second molding step. Therefore, as shown in FIG. The joint surface P is exposed in the flex zone of the tire, and the joint surface P has a different rubber layer between a wear-resistant tread rubber having a relatively high hardness and a flexible sidewall rubber having a relatively low hardness. Since it is formed by the above method, cracks are generated from the joint surface P at an early stage, resulting in poor durability. The tire produced by the type 1 molding method had excellent productivity, but had such a structural defect.

The second type (hereinafter referred to as type 2) is
Unlike the type 1 molding method, the side rubber 4 that is pasted in the first molding step is modified so that the side rubber 4 is not substantially stuck in the first molding step. That is, the raw case 32 is molded by sticking the side rubber 4 prepared by sticking the polyethylene sheet 15 in the first molding step (not shown) except the area stuck to the bead core surrounding portion 7 of the tire. Then, in the second molding step, as shown in FIG. 9, the side rubber 4 is caused together with the polyethylene sheet 15, and the belt 5 and the tread rubber 6 are pressure-bonded in the direction of arrow C by a stitching roller (not shown) and attached to the raw case 32. After that, the polyethylene sheet is peeled off and the side rubber 4 is attached to the case 32. Therefore, in the type 2, as shown in FIG. 8, an ideal structure in which the side of the tread rubber end is completely covered by the side rubber 4 is provided, and the joint surface P between the two is the tire side part like the type 1 tire. Avoiding exposure in the flex zone.

Type 2 is referred to as side backing because side rubber is attached later. This type 2 was able to fundamentally eliminate the defect which the type 1 had, which was called the early generation of cracks, which was structurally present, but was obviously inferior in terms of productivity.

The third type (hereinafter referred to as type 3) is
The molding method proposed by Japanese Examined Patent Publication No. 9-18790 is the side-pitch method like Type 1, but differs from the molding method of Type 1 in that the tread rubber used is devised. That is, as shown in FIG. 11, a side edge rubber 4a made of a rubber equivalent to the side rubber is integrally formed on both sides of the tread rubber 6 in advance by a dual tuber or the like to form a tread rubber with a side edge rubber. The belt and the tread rubber with the side edge rubber are pressure-bonded to the pre-tensioned raw case 42 with a stitching roller (not shown) in the direction of arrow D, and these are attached to the raw case 42 to complete the molding. As shown in FIG. 10, the type 3 can have a side rubber 4 similar to that of a type 2 tire in which the side of the end of the tread rubber 6 is covered. The joint surface P with the flexible side rubber is not exposed to the tire side portion,
The wear-resistant tread rubber 6 has a structure in which both ends thereof are held in a wedge shape K by the bend-resistant side rubber 4 and the side edge rubber 4a. The joint surface Q exposed on the side portion is a joint surface between the side rubber 4 and the side edge rubber 4A, which are the same rubber, and is firmly integrated after vulcanization and the like, and cracks generally occur under normal use conditions. There was no problem. Also, it is superior in productivity to the type 2. Type 3 is sometimes referred to as the top D / T method because it uses tread (top) rubber extruded by dual tubers (D / T).

[0009]

Although this type 3 is a general-purpose molding method for pneumatic radial tires,
However, the flat pneumatic radial tire, in particular, the ratio H / S × 1 of the tire sectional height H to the tire maximum width S
It has been found that, in the case of a super flat pneumatic radial tire that is used for high-speed running and has a flatness ratio of 60 (%) of 60 or less, a phenomenon that was not found in a normal tire was observed. That is, a tread rubber 6 with side edge rubbers having side edge rubbers 4a is extruded integrally with a dual tuber or the like, and is attached to the side rubber 4 of the first molded raw case by the side pre-attachment method. However, there is a problem that cracks occur early on the joint surface Q between the side edge rubber 4a and the side rubber 4 which has not caused a problem in the past and the durability is reduced. Since this side edge rubber 4a is a rubber equivalent to the side rubber 4, such a phenomenon was not observed in a normal tire, but it was a phenomenon that occurred in a flat pneumatic radial tire having an aspect ratio of 60 or less.

In such a radial tire having a significantly low flatness, the flex zone at the tire side portion becomes narrow, and the joint surface Q between the side edge rubber 4a and the side rubber 4 is formed.
It was found that the strain generated in the area exposed to the side of the tire became extremely large and cracks were generated early from the joint surface Q. The tire (tire A) shown in FIG. 5 (b)
Is a high-speed passenger car tire of size 205 / 50VR16, a super flat pneumatic radial tire having an aspect ratio of 50, and is manufactured by adopting the tire basic structure and molding method belonging to the above-mentioned type 3. This tire A is a carcass 2
It is the same as the embodiment tire B of FIG. 1 described later except that the end 2e of the turn-up portion 2t ends in the substantially central region of the tire side portion. The solid line A in the graph shown in FIG. 5 (a) indicates that this tire A has an internal pressure of 1.0 kgf / cm.
² shows the results of measuring the amount of strain (%) generated on the side surface of the tire under the condition of a load of 540 kg (JATOMA maximum load), showing a large tensile strain in the area where the joint surface Q is exposed on the side. (%) Is working, and it has been found that this strain causes early cracking from the joint surface Q. An object of the present invention is to provide a super flat pneumatic radial tire having an aspect ratio of 60 or less, which is excellent in durability without causing early cracking without lowering molding efficiency.

[0011]

According to a first aspect of the present invention, there is provided a pair of bead cores, a radial carcass extending between the bead cores, both ends of which are wound around the bead core and locked, and a crown of the carcass. Of the belt, which is arranged on the outer side in the radial direction of the car part, the tread rubber, which is arranged on the outer side of the belt in the radial direction and which is mainly rich in wear resistance, and the both side parts of the tread rubber, which are located on the outer side of the carcass in the radial direction. Side rubber that extends from the to the bead portion and is highly flexible, and at least the carcass, the bead core and the side rubber are attached in the first molding step, and the side edges made of rubber equivalent to the side rubber in both sides in the second molding step. It is a pneumatic radial tire made by attaching a dual structure tread rubber with integrated rubber from above the belt, wrapped around the bead core. Aspect ratio is 60 or less flat pneumatic radial tire turn-up end of the carcass turnup end portion extends to both ends of the belt formed by belt overlap.

The invention according to claim 2 is characterized in that the overlap amount is 5 to 20% of the maximum width of the belt.

[0013]

According to the first aspect of the invention, the turn-up end of the carcass is extended to the belt and overlaps with the belt end so as to end the carcass. Therefore, the side rubber 4 and the side edge rubber 4a of the type 3 tire are terminated. Joint surface Q with
Can reduce the tensile strain (%) in the area exposed to the side portion, and suppress the occurrence of cracks from the Q surface of the junction. The turn-up end 2E of the carcass is extended to the end area of the belt as shown by the dotted line in Fig. 5 (b), and is overlapped with the end portion of the belt, and the only overlap point is 11% of the maximum belt width. For the tire B having the same configuration as the tire A except for the above (the tire B is the same as the example tire of FIG. 1 to be described later), the result of similarly measuring the strain generated on the side surface of the tire is shown in FIG. In the graph of), it is shown by a dotted line B. In the tire B, the tensile strain amount (%) in the portion S where the joint surface Q between the side rubber 4 and the side edge rubber 4a is exposed to the side portion is halved with respect to the tire A, and this contributes to suppressing the occurrence of cracks. There was found. In the graph of FIG. 5A, R represents the reduction amount of the surface strain of the tire B in the exposed portion S with respect to the tire A. According to the invention of claim 2, the crack suppressing function can be reliably achieved by setting the overlap amount to 5 to 20% of the maximum width of the belt,
If it is less than 5%, the tensile strain applied to the turn-up portion of the carcass cannot be sufficiently supported, a sufficient effect cannot be obtained, and the turn-up end portion is peeled off. Also, 2
If it exceeds 0%, the effect of reducing the tensile strain will remain substantially the same, and no further effect can be expected, and only the amount of the carcass material used will increase, which is not preferable in terms of cost.

[0014]

Embodiments of the present invention will be described below with reference to FIGS. In Figure 1, the tire size is 205 / 50V
R16 indicates a so-called 50-series pneumatic radial tire (tire B) for passenger cars having an aspect ratio of about 50. A carcass consisting of a pair of bead cores 3 and polyester cords arranged between the bead cores 3 at about 90 degrees with respect to the tire circumferential direction is spanned between the bead cores 3, and both ends thereof are wound around and locked by the bead cores. ing. On the outer side of the crown portion 9 of the radial carcass in the radial direction, there is arranged a cross belt 5 which is composed of two layers of steel cords which are inclined at an angle of about 18 degrees with respect to the tire circumferential direction, and the cords intersect each other between the layers. A tread rubber 6 having a high wear resistance is arranged on the outer side of the belt 5 in the radial direction. On the outer side in the radial direction of the side portion of the radial carcass 2, there are arranged side rubbers 4 having a high bending resistance, which extend from both sides of the tread rubber to the bead portions, and the side rubbers 4 are pretensioned in the first molding step. A pneumatic radial tire prepared by sticking a dual structure tread rubber in which side edge rubber 4a made of rubber equivalent to side rubber is integrated on both sides in the second molding step from the belt. The turn-up portion 2t of the carcass 2 wound around the bead core passes through the stiffener 19 and the turn-up ends 2E extend to both ends of the belt, and the turn-up end portion overlaps the belt between the belt and the carcass. In the example of the tire of FIG. 1 (the same applies to tire B of FIG. 5), the overlap amount G of the turn-up end portion with the belt end portion is 1 of the maximum belt width L.
1%. Here, the maximum belt width is a tire axial direction distance between both ends of a belt layer having the maximum belt width, and the overlap amount is a vertical line extending from the belt end portion f to the tire axis to indicate a carcass turn-up portion. It is the distance in the tire axial direction between the point h that intersects with the turn-up end 2E.

Next, the molding of the present invention will be described with reference to FIGS. As shown in FIG. 2, at least the radial carcass 2, the bead core 3 and the side rubber 4 are attached on the cylindrical former 20 in the first molding step and the raw case 12 is attached.
Is molded. In addition to this in the raw case, the inner liner on the lower side of the carcass, the stiffener around the bead core,
Flippers and chafers are attached. Side rubber 4 is attached to the raw case 12,
It is molded by the so-called side-heading method. Then
The raw case 11 is transported to the second molding step.

The tread rubber 6 and the side edge rubber 4a are
The tread rubber 6 and the side edge rubber 4a are arranged on the outer side in the radial direction of the belt 5, and the belt tread molding drum BT (FIG. 4) is preliminarily integrally assembled as an annular body 14 on the belt / tread molding drum BT (FIG. 4). Be used for. FIG.
The side edge rubber 4a is integrally extruded by a dual tuber so that the side edge rubber 4a is on the outside of the tread rubber 6 at the joining portion to both end portions 6b of the tread rubber 6,
The example prepared as a tread rubber with a side edge rubber is shown. The belt 5 is first attached on the BT drum, and the tread rubber with the side edge rubber is attached to the outer side in the radial direction thereof to form the annular body 14. Note that the tread rubber 6 and the side edge rubber 4a are separately prepared, these are doubled on the BT drum, and the tread rubber is attached to the raw case expanded in a toroidal shape in the second molding step before being attached to the side. You may make it form in the tread rubber with edge rubber.

As shown in FIG. 3, the bladder 24 is securely held over the holding units 23. The raw case 12 molded in the first molding step is set by hanging it over the raw case holding unit 21, and when high-pressure air is injected into the bladder 24, the raw case 12 expands in a toroidal shape. The annular body 14 is set on the outer side in the half direction of the crown portion 9 of the toroidal raw case 12, and the inner diameter of the annular body 14 is affixed to the outer side in the radial direction of the carcass. In this way, the belt, the tread rubber and the side edge rubber are retained in the crown portion 9 of the raw case 12, and then the tread rubber and the side edge rubber are applied to the raw case 12 from the outside in the arrow A direction by the stitching roll SR. Then, the tread rubber 6 and the side edge rubber 4a are pressed onto the raw case 12 up to the tip end thereof.

In order to confirm the effect of the present invention, an evaluation test for crack resistance and productivity was performed on the above tires A and B, and the results are shown in Table 1. The crack resistance is a result of comparison of crack lengths after traveling a certain distance on an outdoor drum tester. The tire A is shown as an index with 100 as the index, and the smaller the index, the better the result.

[0019]

[Table 1]

[0020]

According to the present invention, since the turn-up end of the carcass is extended to the belt and overlaps with the end portion of the belt to end the carcass, the flatness ratio of the type 3 is less than 60.
In the area where the joint surface Q is exposed to the side portion, a crack is generated in the joint surface Q between the side rubber 4 and the side edge rubber 4a, which is a defect that the flat pneumatic tire of FIG. It was possible to solve the problem by reducing the tensile strain (%). In addition, the types 1 and 2 above
Since the structure and the molding method of the type 3 can be adopted regardless of the structure and the molding method of 3, the flat pneumatic radial tire of high quality can be provided without lowering the molding efficiency.

[0021]

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a tire according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the molding of the present invention, particularly the first molding step.

FIG. 3 is a cross-sectional view showing the molding of the present invention, particularly the second molding step.

FIG. 4 is a cross-sectional view showing an example of molding of the present invention, in particular, molding of a tread and a belt.

FIG. 5 is an explanatory view illustrating the operation of the comparative tire and the tire of the present invention.

FIG. 6 is a cross-sectional view showing the structure of a conventional pneumatic radial tire (type 1).

FIG. 7 is a cross-sectional view showing a conventional side-clad molding method (type 1).

FIG. 8 is a cross-sectional view showing the structure of a conventional pneumatic radial tire (type 2).

FIG. 9 is a cross-sectional view showing a conventional side backing forming method (type 2).

FIG. 10 Conventional pneumatic radial tire (type 3)
FIG. 3 is a cross-sectional view showing the structure of FIG.

FIG. 11 is a cross-sectional view showing a molding method (type 3) using a conventional D / T type tread rubber.

[Explanation of symbols]

2 Carcass 2E Turn-up end of carcass 2t Turn-up part 3 Bead core 4 Side rubber 4a Side edge rubber 5 Belt 6 Tread rubber 6b End of tread rubber 10 Pneumatic radial tire 12 Raw case 14 Annular body 20 Cylindrical former BT belt tread Molding drum G Amount of overlap of the turn-up part with the belt end (width in the axial direction) L Maximum width of the belt Q Joint surface of side edge rubber 4a and side rubber 4

Claims (2)

[Claims] 1. A pair of bead cores, a radial carcass extending between the bead cores and having both ends wound around the bead core and locked, and a belt arranged radially outside a crown portion of the carcass. A tread rubber having a high wear resistance, which is arranged on the outer side in the radial direction of the belt, and a side rubber having a high bending resistance, which extends from the both ends of the tread rubber to the bead portion on the outer side in the radial direction of the side portion of the carcass. A belt having a dual structure in which at least a carcass, a bead core and side rubber are attached in the first molding step, and side edge rubbers made of the same rubber as the side rubber are integrated on both sides in the second molding step. It is a pneumatic radial tire stuck from above, and the turn-up end of the carcass wrapped around the bead core is the belt. A flat pneumatic radial tire having a flatness ratio of 60 or less, which extends to both ends and has a turn-up end portion overlapping a belt. 2. A flat pneumatic radial tire characterized in that the amount of overlap is 5 to 20% of the maximum width of the belt.