JPH07329208A - Formation of unvulcanized tire for flat pneumatic radial tire - Google Patents

Abstract

PURPOSE:To prevent the cracking of a sidewall part free from other deterioration while maintaining the productivity for forming an unvulcanized tire by sticking the previously united outer sidewall rubber members to a green case and laminating them on an inner sidewall rubber member to form an integral sidewall rubber member. CONSTITUTION:A cylindrical green case 11G is obtained by sticking a pair of inner sidewall rubber members 17L to a specific position. On one side, outer sidewall rubber members 17U are previously united on the surfaces of both sides of a tread rubber member 16 and prepared for a second formation as a composite rubber member. The case 11G treated through a first forming process is supplied to a second forming process. The case 11G is toroidally expanded and deformed by narrowing the interval of bead core members 13 in a bead part. A composite member 18 to be formed into a part of an unvulcanized tire 11 is vertically pressed and tucked by a switching roll SR and stuck to the case 11G. At that time, rubber members 17L, 17U form a laminating face Qa and are formed into an integral sidewall rubber 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention has a flatness ratio of 55.
% Of flat pneumatic radial tire unvulcanized tire molding method, especially while maintaining high productivity of unvulcanized tire molding step, the sidewall rubber which is peculiar to the conventional tire type is prominent. The present invention relates to a method for forming an unvulcanized tire for a flat pneumatic radial tire, which is capable of advantageously solving the problem of insufficient durability and exhibiting a highly excellent durability.

[0002]

2. Description of the Related Art First, the outline of the construction of a pneumatic radial tire will be described below by taking a tire 20 shown in FIG. 7 as an example.
FIG. 7 is an explanatory diagram schematically illustrating a main part of a left half cross section from the equatorial plane E of the pneumatic radial tire 20.
A tire 20 shown in FIG. 7 has a radial carcass 4 of 1 ply or more (one ply in the illustrated example) extending in a toroidal shape across a bead core 3 embedded in a pair of bead portions 2 (only one side is shown), and a carcass 4 Belt 5 arranged on the outer periphery and tread rubber 2 arranged on the outer periphery of belt 5
6 and a pair of sidewall rubbers 27 (only one side is shown) that are located outside the carcass 4 from both sides of the tread rubber 26 (only one side is shown) and extend to positions above the bead portions 2.
Have and.

The ply of the carcass 4 has a tire equatorial plane E.
The radial carcass 4 comprises a bead portion 2 and a sidewall portion 8 on which a sidewall rubber 27 is arranged.
And the tread portion 9 in which the tread rubber 26 is arranged is reinforced. The belt 5 includes two or more layers (two layers in the illustrated example) of cord intersecting layers, and strengthens the tread portion 9.

Another example of pneumatic radial tires 40 and 60 shown in FIGS. 8 and 9 as an explanatory view similar to FIG. 7 is a joint surface P (in each drawing) of tread rubbers 46 and 66 and sidewall rubbers 47 and 67. The shape of (shown by the joining line) is shown in FIG.
The tire 20 is the same as the tire 20 shown in FIG. 6 except that it is the same. Therefore, the reference numerals of these same constituent elements are shown in FIG. Regarding the form of the joint surface P, in the example of FIG. 7, the upper end portion of the sidewall rubber 27 is located on the inner side surface of the end portion in the width direction of the tread 26, whereas in the tire 40 shown in FIG. The tire 60 shown in FIG. 9 is located on the outer surface of the end surface, and the tread rubber 66 has the sidewall rubber 6
Rubber with the same composition as the upper end of 7 and this rubber 67-
A wedge shape is difficult to insert between 1 and 1, so to speak, the eclectic arrangement of the two examples described above. The side wall rubber 67 in the case of FIG.
Is the sidewall upper rubber 67-1 and tread rubber 6
6 has joint surfaces P and P ₁ between them.

Regardless of the form of the joint surface, the tread rubbers 26, 46, 66 are portions which directly contact the road surface to generate a driving force and a braking force under the load rolling of the radial tire. Since it is a portion that is subjected to the force, it is required to be a material that exhibits excellent wear resistance as a basic characteristic, while it is also called a flex zone, and the sidewall portion 8 that repeats flexural deformation a very large number of times. Sidewall rubber 2 to be placed
For 7, 47 and 67, it is necessary to apply a material having excellent bending fatigue resistance as a basic characteristic. However, these two characteristics have a trade-off relationship with each other in terms of rubber compounding technology,
Therefore, it is general to apply a completely different kind of rubber composition having a composition so that the required properties can be sufficiently exhibited to the tread rubber and the sidewall rubber of the pneumatic radial tire.

Next, the pneumatic radial tire 20,
Fig. 1 shows three types of unvulcanized tire forming methods immediately before vulcanization to obtain 40 and 60, which correspond to each tire.
A description will be given below using 0, 11, and 12. 10 to 12 are explanatory views schematically illustrating a cross section immediately before finishing of an unvulcanized tire in a second molding step described below, together with a partial cross section of a molding machine.

A molding method common to these three types is to supply the radial carcass ply member 14 to a cylindrical drum (not shown) and wind the ply member a predetermined number of times, and to form a pair of bead core members on the wound drum upper ply member 14. The first molding step (see the reference numerals in FIGS. 10 to 12 above) in which the ply member 14 is folded back around each bead core member 13 to form a tubular green case after the bead core members 13 of the green case are fixed. And a second molding step in which the belt member 15 and the tread rubber members 36, 56, and 76 are attached to the outer circumference by expanding and deforming the green case and expanding the green case. The term "member" as used herein means an unvulcanized member, and the term "gluing" and "gluing" mean that one member is tightly united with the other member by the adhesive force of each member. The same applies hereinafter.

One type of molding method is a molding method for obtaining the tire shown in FIG. 7, and in this case, a rubber member 37 corresponding to the sidewall rubber 27 of FIG. 7 was attached in the first molding step. The green case 31G is supplied to the next second molding step, and the supplied green case 31G is shown in FIG.
As shown in 0, the belt member 15 and the tread rubber member 36 are attached to the outer circumference of the expanded and deformed green case 31G. At that time, the tread rubber member 36 is set to have a total width dimension so as to sufficiently cover the upper end portion of the sidewall rubber member 37. After that, both sides of the tread rubber member 36 are folded in the direction of arrow B in the drawing by a stitching roller (not shown) and pressure-bonded to the sidewall rubber member 37, and sometimes the carcass ply member 1
4 is also pressure-bonded to obtain an unvulcanized tire. This molding method is called a side-pile method because the necessary whole sidewall rubber member 37 is preliminarily adhered to the green case 31G in the first molding step.

The second type is a molding method for obtaining the tire 40 shown in FIG. 8, in which a rubber member 57 corresponding to the sidewall rubber 47 of FIG. 8 is attached to the green case 51G in the first molding step. Is a method similar to the side-pile method, but the major difference is that, as shown in FIG. 11, the mutual attachment areas are stopped in an area 12 corresponding to the bead portion 2 shown in FIG. 8 and this area 12 is excluded. The inner surface of the sidewall rubber member 47 in the remaining area and the green case 51
A point is that a synthetic resin sheet shown by a broken line, for example, a polyethylene sheet 80 is interposed between G and G so as to prevent mutual adhesion and coalescence.

The green case 51G in this state is expanded and deformed as shown in FIG. 11 in the second molding step, and the pair of sidewall rubber members 57 are respectively sunk outward so that the belt member 15 and the belt member 15 are provided on the outer periphery of the green case 51G. Applying the tread rubber member 56 and folding the both sides of the tread rubber member 56 in the direction of the arrow C shown by a stitching roller in the same manner as described above, and adhering them, and subsequently removing the polyethylene sheet 80, and then each side wall rubber member 57 part Then, the green case 51G and the both side surfaces of the tread rubber member 56 are attached to each other to obtain an unvulcanized tire. In this respect, it is called the side back-lining method as opposed to the side-heading method.

The third type is Japanese Patent Publication No. 49-18790.
It is a molding method for obtaining the tire 60 shown in FIG. 9 disclosed in Japanese Patent Laid-Open Publication No. JP-A-2003-163, and the first molding step can be said to be a modified example in which the disadvantage of the side-pitch method is improved. In this modification, in addition to the sidewall rubber member 77 attached to the green case 71G, a pair of strip rubber members 77-1 made of the same compounded rubber composition as this member are attached to the tread rubber member 76 in advance as shown in FIG. The point is to apply the composite rubber member 78 attached to both side surfaces in the second molding step. Other than that, the second molding is performed in the same manner as in Type 1 to obtain an unvulcanized tire.

[0012]

A tire 20 obtained by molding an unvulcanized tire by a side pre-tensioning method according to the first type and then vulcanizing and molding the tire has excellent productivity in the molding process. On the other hand, it has the following disadvantages.

That is, it is unavoidable that the outer position of the joint surface P between the tread rubber 26 and the sidewall rubber 27 appears on the surface of the flex zone, and the tread rubber 26 is indispensable for exhibiting high abrasion resistance. As a characteristic, a material having a relatively high hardness (Shore A hardness or JIS hardness), for example, Shore A hardness 55 ° to 75 ° is applied, while the sidewall rubber 27 is inevitable in order to exhibit excellent bending fatigue resistance. Relatively low hardness,
For example, since it is necessary to apply a material having a Shore A hardness of 40 ° to 60 ° to a tread rubber having a higher hardness than a sidewall rubber, rubber having a large hardness difference should be arranged on both sides of the joint surface P as a boundary. Both of these joints cause cracks to occur at the joint surface P position existing on the surface of the flex zone immediately after the start of tire running, and these cracks gradually propagate to the inside along the joint surface P as the traveling distance increases. It leads to a breakdown, and eventually the durability is insufficient.

A tire 40 obtained by molding an unvulcanized tire by a side backing method according to type 2 and then vulcanizing and molding the tire 40 has a joining surface P appearing on the tire surface above the flex zone (the tire). Since it is located on the outer side in the radial direction, it has an excellent configuration in that it is possible to avoid the occurrence of the crack failure. On the other hand, when forming an unvulcanized tire, the work of attaching and removing the polyethylene sheet and the sidewall rubber member 57 are performed. Since the attachment work is required twice, there is a disadvantage that productivity is obviously impaired in that extra man-hours are added.

The tire 60 obtained by the molding method of the type 3 is the same as the tire 20 and the tire 40.
While having the advantages of each of 0 and 40, it is possible to eliminate the disadvantages of both, and in this respect tires obtained by a molding method superior to the molding methods of type 1 and type 2 I can say. Because the position where the joint surface P ₁ between the upper sidewall rubber strip 67-1 and the tread rubber 60 appears on the tire surface is the same position as the tire 20, it is possible to avoid the above-mentioned crack failure. This is because it is possible to ensure a highly high productivity without requiring the addition of the extra man-hours. Therefore, this type 3 is widely practiced as a method for forming an unvulcanized tire for a pneumatic radial tire.

However, in recent years, flattening of flat tires that exhibit excellent durability and steering stability during high-speed running has been further flattened, and the degree of flattening is determined by the tire cross-section height SH and the cross-section width SW. Percentage ratio (SH / SW) x 100
(%), And this value is called the flatness ratio (JIS Y
When expressed as EAR BOOK), flat pneumatic radial tires of 55 or less tend to be generalized, and in the flattening tendency of the aspect ratio of 55 or less, there is a new type of crack failure that was rarely seen in the past. It came to be found.

The crack failure of this new type occurs at an early stage at the position where the joint surface P between the sidewall rubber 67 and the upper sidewall thin rubber 67-1 shown in FIG. It was found that the failure progresses inward along the joint surface P as the traveling progresses, and that the smaller the nominal value of the aspect ratio is, the more likely the failure is to occur. Up to now, this kind of failure has never occurred in the joint surface of at least the sidewall portion 8 at the time of molding the same compounded rubber composition.

Therefore, an object of the present invention is to maintain the productivity of unvulcanized tire molding at a high level and to provide the sidewall portion with excellent crack resistance without deterioration of other tire performance. It is an object of the present invention to provide an unvulcanized tire forming method for a flat pneumatic radial tire capable of achieving the above, particularly a flat pneumatic radial tire having a flatness ratio of 55 or less.

[0019]

[Means for solving the problem] Focusing on the fact that as the nominal value of the aspect ratio becomes smaller, cracks tend to occur at the joint surface position of the same rubber composition appearing in the sidewall part, the cause is actually investigated and investigated. As a result, the inventors have found that there is a strong correlation between the degree of strain on the surface of the sidewall portion and the nominal value of the aspect ratio, and have completed the present invention. That is, the method for forming an unvulcanized tire for a flat pneumatic radial tire according to the present invention is directed to a radial carcass having one or more plies extending toroidally between bead cores embedded in a pair of bead portions, and a belt arranged on the outer periphery of the carcass. And a pair of sidewall rubbers extending from the both sides of the tread rubber to positions above each bead outside the carcass from both sides of the tread rubber. When molding an unvulcanized tire of a radial tire, each sidewall rubber of the tire obtained after vulcanization is distributed over the entire circumference into an inner portion and an outer portion in the tire radial direction, and the end on the outer surface of the sidewall rubber of the distribution surface. Inner portions corresponding to the inner portion and outer portion whose position is equal to or less than 1/2 of the tire cross-sectional height Each of the sidewall rubber member and the outside sidewall rubber member is separately prepared in advance, and the inside sidewall rubber member of these separately prepared members is assembled into a tubular green case by assembling the carcass ply member and each bead core member. The green case that has been subjected to the first molding step is expanded, and the green case that has undergone the first molding step is expanded and deformed into a toroidal shape by narrowing the mutual intervals of the bead core members, and the belt member and the tread rubber member are expanded around the expanded and deformed green case. In the second molding step, the outer sidewall rubber members that have been previously combined on both side surfaces of the tread rubber member are attached to the green case and are attached to the inner sidewall rubber member to form an integral sidewall rubber member. It is characterized by

In carrying out the present invention, an annular protruding rib located at a height equal to or less than 1/2 of the tire cross-sectional height is provided on the outside of the sidewall rubber, and near the outer edge in the tire radial direction of the rib of the vulcanized tire. And the extruding unit integrally extruding a pair of outer sidewall rubber members as a composite rubber member with a tread rubber member by means of an extruder having a plurality of extrusion heads. Or a belt member and a tread rubber member are bonded together in advance on a molding drum having a predetermined outer diameter and a pair of outer sidewall rubber members are bonded to both side surfaces of the tread rubber member. It is desirable to apply the hybrid member in the second molding step.

[0021]

First, the tire radial direction strain distribution curve generated on the surface of the sidewall portion 8 of the tire under a predetermined load will be described with reference to FIGS. 13 and 14. The right side of FIGS. 13 and 14 shows mainly the cross section of the sidewall portion 8 and the bead portion 2 in the left half section of the tire, and the strain (%) indicates tension (+ sign) and compression (−) on the left side of each drawing.
It is shown separately for each symbol. The tire used for strain measurement had a pneumatic radial tire size for passenger cars of 205/6.
5R15 (Nominal aspect ratio 65) and size 225/4
There are two types of tires, 5ZR17 (nominal flatness ratio 45), and these two types of tires are shown in the same sectional shape for convenience of strain distribution comparison.

The test condition is a broken cord (Co
rd Breaking-Up, CBU) to generate the CBU drum condition that the tire is pressed against the indoor drum with a low internal pressure and a high load, and the normal vehicle condition under the normal JATMA YEAR BOOK and internal load. FIG. 13 shows the test results under the conditions, and FIG. 14 shows the test results under the actual vehicle conditions. The CBU drum condition was diverted because it is a condition that can occur in actual use and is a suitable condition that allows subsequent comparative evaluation to be advantageously carried out within a short time.

Of the strain distribution curves shown in FIGS. 13 and 14, the broken line S ₁ is the strain distribution curve of the nominal 65 of the flatness ratio,
The solid line S ₂ is the strain distribution curve of the aspect ratio nominal 45.
These distribution curves are the same for the right half section and are not shown. Comparing the strain distributions of both types of tires,
Regarding the peak value of the tension strain that affects the occurrence of cracks and its development, the tire with a nominal aspect ratio of 45 does not only show a significantly higher value than the tire with a nominal aspect ratio of 65 under all conditions, but also A new fact has been found that the sectional height position showing the peak value of the tension strain in the tire with the nominal ratio of 45 shifts to a position higher than the position similar to the above in the tire with the nominal ratio of 65.

The tendency for the peak value of the tension strain to increase remarkably and the tendency for the position showing the same peak value to shift to a higher position (a position on the outer side in the radial direction of the tire) tends to decrease as the aspect ratio is reduced. We have found that it is an unavoidable fact that appears more prominently.

Further, as shown in FIGS. 13 and 14, regarding the tension strain at the position where the joint surface P of the sidewall rubbers 67 and 67-1 (see also FIG. 9) appears on the tire surface, the tire having a nominal aspect ratio of 65 is used. Is a relatively small value on the distribution curve S ₁ , while the tire having a flatness ratio of nominal 45 has a remarkably high value in agreement with the vicinity of the peak value on the distribution curve S ₂ . This tension strain occurs every time a large number of repeated flexural deformations occur during load rolling. Therefore, crack failure at the joint surface P, which was rarely seen in the tire with a flatness ratio of 65, was flattened in this experimental example. It can be said that a tire having a nominal ratio of 45, actually a tire having a nominal aspect ratio of 55 or less, appeared only after being put into practical use. Therefore, it is appropriate to call this failure a new type of crack failure.

The reason why a crack failure occurs at the joint surface P of the sidewall rubbers 67 and 67-1 made of the same compounded rubber composition is that the surface condition at the stage of these rubber members is an internal condition to some extent during extrusion. Unlike the above, it is more susceptible to changes during the time from extrusion to molding, and as a result, the bond strength at the joint surface P obtained after vulcanization is weaker than that at the other parts, and eventually, This is because if a large tension strain is repeatedly applied to this weaker bonded state portion, surface cracks tend to occur, and once cracks occur, the strain will concentrate and progress thereafter.

On the other hand, each sidewall rubber is distributed over the entire circumference into an inner portion and an outer portion in the tire radial direction, and the end position on the outer surface of the sidewall rubber of the distribution surface is 1/2 height of the tire section height. The inside sidewall rubber member and the outside sidewall rubber member corresponding to the inside portion and outside portion described below are separately prepared in advance, and the inside sidewall rubber member is attached to the green case in the first molding step. Supplying this to the second molding step, in the second molding step, each outer sidewall rubber member that was previously united on both side surfaces of the tread rubber member was expanded and deformed into a toroid shape into a green case. On the other hand, the belt member and the tread rubber member are attached together, and the inner side wall rubber member is also attached. The above-mentioned distribution surface Q of each sidewall rubber of the tire to be obtained later (see FIGS. 13 and 14), that is, the end position on the outer surface of the sidewall rubber in the joint surface Q after vulcanization of both the inner and outer sidewall rubber members is cross-sectioned. It can be positioned below 1/2 height of the height SH, and this end position corresponds to a strain near 0% region on the strain distribution curve shown in FIGS. 13 and 14, or a strain region closer to the compression side. Therefore, it becomes possible to effectively prevent the occurrence of a new-type crack failure due to a large tension strain.

Further, in the above-mentioned unvulcanized tire molding method, there is no step to be newly added in comparison with the above-mentioned molding method No. 3, so that the productivity can be enhanced through the first and second molding steps. Can be held. Further, since there is nothing to touch the tire structure, it is possible to maintain the performance including the abrasion resistance and durability of the tread rubber at a desired level.

Further, in the case of a tire having an annular protrusion rib on the outside of the sidewall rubber at a position not more than 1/2 height of the tire cross-section height SH, the above-mentioned distribution is made near the outer edge of the protrusion rib top surface in the tire radial direction. Positioning the edge is effective in suppressing new-type crack failures.

Further, a composite rubber member obtained by integrally extruding a pair of outer sidewall rubber members and a tread rubber member using an extruder having a plurality of extrusion heads is applied in the second molding step, or Alternatively, when pasting the belt member and the tread rubber member on the forming drum in advance, if a hybrid member in which a pair of outer sidewall rubber members are attached to the tread rubber member is applied in the second forming step, the number of forming steps can be increased. Contribute to avoiding the increase of.

[0031]

Embodiments of the present invention will be described in detail below with reference to FIGS. First, FIG. 1 shows a left half section from an equatorial plane E of a flat pneumatic radial tire 1 having a nominal aspect ratio of 55 or less. The left half section and the right half section of the tire 1 are symmetrical sections with respect to the equatorial plane E. With. Illustration of the groove provided in the tread portion is omitted.

The basic construction of the tire is the tire 2 described above.
The two-ply radial carcass 4, which is the same as 0, 40, 60 and extends in a toroidal shape between a pair of bead cores 3 (only one side is shown), is folded back around the bead core 3 from the tire inner side to the outer side, and the bead portion 2 is formed. The side wall portion 8 and the tread portion 9 are reinforced, and the belt 5 is made up of four layers of two inner steel cord intersecting layers and two outer circumferentially arranged cord layers to strengthen the tread portion 9. .

The sidewall rubbers 7 extend from both sides of the tread rubber 6 through the joint surface P to the region above the bead portion 2. In this example, a rubber chafer 2M that is arranged along the outer side of the folded portion of the carcass 4 in the bead portion and that engages with the flange of the applicable rim is provided, and the portion between the carcass 4 main body and the folded portion is tapered on the outer periphery of the bead core 3. By providing a rubber stiffener 2N extending to, the bead portion is strengthened.
Therefore, the sidewall rubber 7 of this illustrated example forms a joint surface R with the rubber chafer 2M on the inner side in the tire radial direction. An inner liner impermeable to air is applied to the inner surface of the carcass 4.

The sidewall portion 8 has an annular protruding rib 8
An example in which M is provided is illustrated, and the case of the tire in which the protruding rib 8M is not provided is indicated by a two-dot chain line. The protruding rib 8M is called a rim guard and serves to protect the sidewall portion 8 from being significantly damaged by the rim flange when the tire is largely bent. Therefore, the protruding rib 8M is provided below the sidewall portion 8, more accurately, at a tire cross-section height SH of 1 mm or less.
Position it at less than 1/2 height. Tire cross section height SH
Is the height measured from the rim diameter line RL. The cross-sectional height SH used for the aspect ratio described above is the same as the height SH.

Along the entire circumference of the sidewall rubber 7, the tire radial inner side portion 7L and the tire radial outer side portion 7U are shown by the line segment Q shown in the sectional view, and by the distribution surface Q including the line segment Q as well as the tire. Shall be allocated to. Preferably, this dividing line segment Q is a height bisector line H.
Tilt with respect to L. At that time, it is desirable that the upper portion of the inner portion 7L of the sidewall rubber 7 and the lower portion of the outer portion 7U overlap each other in the tire radial direction, and the outer portion 7U is positioned outside at this overlapping portion.

Either the end Y or the end Z of the dividing line segment Q appearing on the outer surface of the sidewall rubber 7 is located at a height equal to or lower than the height bisector line HL which shows 1/2 of the sectional height SH. It is important to. Here, the former end Y is the protruding rib 8
This is the case of the sidewall portion 8 provided with M, and the latter end Z is the case of the sidewall portion 8 not provided with the protruding rib 8M and shown by the chain double-dashed line. Further, the top surface of the protrusion rib 8M is positioned at a height equal to or lower than the height bisector HL, and the end Y is positioned near the outer edge of the protrusion top surface in the tire radial direction.

Next, the tire 1 described above with reference to FIGS.
The method for forming an unvulcanized tire will be described. FIG. 2 shows the green case 11G and the molding machine 8 for which the first molding process has been completed.
Fig. 3 is an explanatory view schematically showing a cross section with a part of 0 as a diagram, and Fig. 3 is an explanatory view showing a cross section of an unvulcanized tire in the middle of the second molding step and its molding machine in the same manner as Fig. 2. , Fig. 4
FIG. 4 is an explanatory view showing a state in which the unvulcanized tire shown in FIG. 3 has completed the second molding step, similarly to FIG. 3. 5 and 6 are explanatory views similar to FIGS. 2 to 4 in which the belt member 15 and the tread rubber member 16 are assembled in advance as a composite member.

The inner side wall rubber member 1 having a cross-sectional shape corresponding to the contour shapes of the inner side portion 7L and the outer side portion 7U of the side wall rubber 7 determined as described above.
7L and the outside sidewall rubber member 17U are separately prepared by extrusion molding using an extruder or the like. Here, the above-mentioned "corresponding cross-sectional shape" refers to a cross-sectional shape that allows for the amount of deformation that occurs after extrusion molding, through the first and second molding steps, and before the end of the vulcanization step.

First, as shown in FIG. 2, after assembling the radial carcass ply 14 and the pair of bead cores 13 in the first molding step, a pair of inner side and outer side rubber members separately prepared in advance are paired inside. The sidewall rubber member 17L is attached to a predetermined position to obtain the tubular green case 11G. On the other hand, the outer sidewall rubber member 17
U is a composite rubber member that has been previously united on both side surfaces of the tread rubber member 16 and is prepared for the next second molding. At this time, the rubber chafer 2M and the rubber stiffener 2 not shown are shown.
The N and inner liner members shall also be assembled together. In addition, the inside sidewall rubber member 17
It is desirable that L and the rubber chafer 2M member are integrally extruded as a composite rubber member by a dual tuba or the like.

The green case 11G which has undergone the first molding process is supplied to the second molding process described above. Figures 3 and 4
The second molding machine 90 used in this step
Is a toroidally expandable cylindrical bladder 92, a pair of holding members 94 that hermetically holds the bladder 92, and a pair of bead portions of the green case 11G are reliably carried and carried in cooperation with this. And a pair of bead portion carriers 96 that can move toward each other so as to narrow the mutual distance between the pair of bead portions to a predetermined distance (the above is the same as the conventional molding method types 1 to 3). Further, the second molding machine 90 supplies a pressurized fluid (for example, pressurized air) having a predetermined pressure to the bladder 92 so that the bladder 92 can be expanded (expanded) and deformed, and the bladder 92 is restored to the original state by discharging the pressurized fluid. It is provided with a means capable of being restored to a cylindrical shape.

Therefore, as shown in FIG. 3, the green case 11G supplied to the second molding step has a bead core embedded in the bead portion as the pair of bead portion carriers 96 approach each other and the bladder 92 expands in diameter. The space between the members 13 is reduced and the members 13 expand and deform in a toroidal shape. A belt member 15, a tread rubber member 16, and outer sidewall rubber members 17U that are preliminarily united on both side surfaces of the member 16 are applied to the outer periphery of the green case 11G expanded to a predetermined outer diameter.

Prior to this application, as shown separately in FIGS. 5 and 6, three kinds of members 15, 16 and 17U are prepared in advance as a hybrid member 18 which is integrated. The example shown in FIG. 5 is a composite rubber member obtained by integrally extruding a tread rubber member 16 and a pair of outer sidewall rubber members 17U using an extruder having a plurality of extrusion heads, a so-called dual tuba or triple tuba. 18 is prepared, and then the composite rubber member is formed on the molding drum 85 (abbreviated as BT drum) having a predetermined outer diameter so as to prepare the second molding as an integrated hybrid member of the belt member 15 and the tread rubber member 16. This is a type in which 18 is supplied and the belt member 15 and the composite rubber member 18, which have been bonded to the BT drum 85 before that, are bonded to each other to obtain a hybrid member.

In the example shown in FIG. 6, according to the original function of the BT drum 85, the belt member 15 and the tread rubber member 16 are bonded to each other on the BT drum 85, and a pair of outer sidewall rubber members 17U is attached to the composite member. This is a type in which a composite member is obtained by sticking from a position shown by a solid line to a position 16s shown by a broken line. This type is advantageous when the tread rubber member 16 itself is a composite rubber member composed of different rubber compositions. Whichever type is used, such a hybrid member 18 is applied and then applied to the green case 11G in the second molding step shown in FIG. It should be noted that illustration of means for carrying the hybrid member 18 and accurately stopping it at a desired position of the green case 11G is omitted.

Stitching roll SR in the state shown in FIG.
The mixed member 18 is sequentially directed from the outer side in the radial direction to the inner side in the radial direction by pressing in a direction as vertical as possible to the mixed member 18 which should also be a part of the unvulcanized tire 11, and is folded into the green case 11G. wear. At this time, the inner and outer side wall rubber members 17L and 17U form a bonding surface (a line in the figure) Qa to each other to become the integral side wall rubber 17. The line Pa represents the surface where the tread rubber member 16 is attached to both side surfaces and the outer sidewall rubber member 17U.

The unvulcanized tire 11 of the flat pneumatic radial tire 1 completed by the above-mentioned molding method is bladder 92.
The unpressurized tire 11 is taken out from the second molding machine 90 by discharging the pressurized fluid inside, and the unvulcanized tire 11 taken out is conveyed to the next vulcanization step, where vulcanization molding is performed to complete the product tire 1.

The tires used in this example were radial ply tires for passenger cars and had a size of 285 / 30ZR18.
And its configuration complies with FIG. The tire of Example 1 has a sidewall portion 8 indicated by a two-dot chain line in FIG.
The tire of Example 2 is a tire including the annular protrusion rib 8M. The height measured from the rim diameter line RL of the front surface side end Z of the joining surface Q was set to 0.4 SH, and the height of the end Y measured similarly was set to 0.36 SH. The latter end Y has a protruding rib 8
It substantially coincides with the tire radial outer edge of the top surface of M.
When each member was prepared so as to satisfy these set values, and the unvulcanized tire 11 obtained by assembling and molding these members was vulcanized, a joint surface Q substantially in accordance with the set values was obtained. The outer sidewall rubber member 17U was prepared as a composite rubber member with the tread rubber member 16 by an extruder, and the composite member 18 was molded according to FIG.

Therefore, in order to evaluate the effects of Examples 1 and 2, tires of Conventional Examples 1 to 3 produced by the molding method according to Types 1 to 3 were prepared. In each of Conventional Examples 1 to 3, except for the joint surface of the sidewall rubber, all other parts were matched with the examples. All tires were evaluated for productivity in the first and second molding steps, and the result was 100 for Conventional Example 1 (Type 1).
The smaller the value, the better.

Regarding the crack resistance of the sidewall rubber, an outdoor drum tester according to the actual situation is used, and after running for a certain distance under the CBU drum test condition, the length of cracks generated on the surface of the sidewall rubber is measured. A comparative evaluation test was conducted. The test results of both are 100 in Conventional Example 1.
The smaller the number, the better. Table 1 shows the index values of crack resistance and productivity.

[0049]

[Table 1]

As is clear from Table 1, the conventional example 2 (type 2) certainly exhibits excellent durability with practically no problem with respect to crack resistance, but practically decreases productivity. Since the conventional example 3 (type 3) can maintain high productivity,
Again, the deterioration of the crack resistance due to the early occurrence of the new form crack failure remains at a low level which is a quality problem in practical use, while in each of Examples 1 and 2, the productivity is maintained at a high level. Thus, it can be seen that a new type of crack failure can be prevented and excellent crack resistance can be exhibited.

[0051]

According to the present invention, both the inside and outside sidewall rubber members are separately provided so that the outside of the joining surface of the sidewall rubber is located at a height of ½ or less of the sectional height of the vulcanized tire. By preparing and applying a molding method in which the inner side wall rubber member is attached in the first forming step and the outer side wall rubber member is attached in the second forming step,
Both side wall rubber joint surfaces are located in the minimum tension strain area under the load rolling of the tire, and as a result, a new type of sidewall was inevitably generated in the flat pneumatic radial tire with the nominal aspect ratio of 55 or less. Provided is a method for forming an unvulcanized tire for a flat pneumatic radial tire, which can advantageously prevent a partial crack failure and can maintain desired high productivity without impairing other performances and durability. be able to.

[Brief description of drawings]

FIG. 1 is a left half sectional view for explaining a sidewall rubber joining surface of a tire obtained by a molding method according to the present invention.

FIG. 2 is an explanatory view of a cross section of the green case in the first molding step of the molding method according to the present invention.

FIG. 3 is an explanatory view of an unvulcanized tire cross section in the middle of the second molding step in the molding method according to the present invention.

FIG. 4 is an explanatory view of an unvulcanized tire cross section in a second molding step of the molding method according to the present invention.

FIG. 5 is an explanatory view of a cross section of a hybrid member of one example of supplying to the second molding step in the molding method according to the present invention.

FIG. 6 is an explanatory view of a cross section of a hybrid member of another embodiment which is supplied to the second molding step in the molding method according to the present invention.

FIG. 7 is a left half cross-sectional view illustrating a joint surface between a sidewall rubber and a tread rubber of a tire obtained by a molding method of the conventional type one.

FIG. 8 is a left half cross-sectional view illustrating a joint surface between a sidewall rubber and a tread rubber of a tire obtained by a conventional type 2 molding method.

FIG. 9 is a left half cross-sectional view illustrating a joint surface between sidewall rubbers of a tire obtained by a molding method of a conventional type part 3.

10 is an explanatory view of a cross section of an unvulcanized tire in the middle of the second molding step for obtaining the tire shown in FIG.

11 is an explanatory view of a cross section of an unvulcanized tire in the middle of the second molding step for obtaining the tire shown in FIG.

12 is an explanatory view of a cross section of an unvulcanized tire in the middle of the second molding step for obtaining the tire shown in FIG.

FIG. 13 is a strain diagram generated on the tire sidewall surface when a load is applied.

FIG. 14 is a strain diagram generated on the surface of the tire sidewall portion when a load is applied.

[Explanation of symbols]

 1 Flat pneumatic radial tire 2 Bead part 2M Rubber chafer 2N Rubber stiffener 3 Bead core 4 Radial carcass 5 Belt 6 Tread rubber 7 Sidewall rubber 7L Inner sidewall rubber 7U Outer sidewall rubber 8 Sidewall part 8M Annular protrusion rib 9 Tread part 11 Unvulcanized tire 11G Green case 13 Bead core member 14 Radial carcass member 15 Belt member 16 Tread rubber member 17 Side wall rubber member 17L Inner side wall rubber member 17U Outer side wall rubber member 18 Mixed member P Tread rubber and side wall rubber Joint surface Q Inner and outer sidewall rubber joint surface SH Tire cross-section height HL height bisector RL Rim diameter line Y, Z Side wall surface of joint surface Q Location

Claims (4)

[Claims] 1. A radial carcass having one or more plies extending toroidally between bead cores embedded in a pair of bead portions, a belt disposed on the outer periphery of the carcass, and a tread rubber disposed on the outer periphery of the belt. In forming an unvulcanized tire of a flat pneumatic radial tire having a flatness ratio of 55 or less, having a pair of sidewall rubbers extending from both sides of the tread rubber to the position above each bead portion outside the carcass, Each side wall rubber of the tire obtained after vulcanization is distributed over the entire circumference into an inner part and an outer part in the tire radial direction, and the end position on the outer surface of the side wall rubber of the allocating surface is 1/2 height or less of the tire cross section height. The inner sidewall rubber member and the outer sidewall rubber member corresponding to the inner portion and outer portion, respectively. In advance, the inner side wall rubber member of these separately prepared members is attached in a first molding step of assembling the carcass ply member and each bead core member into a tubular green case, and In the second molding step, the green case that has undergone the molding process is expanded and deformed into a toroidal shape by narrowing the mutual interval of the bead core members, and the belt member and the tread rubber member are attached to the outer circumference of the expanded and deformed green case. A flat pneumatic radial tire characterized in that the outside sidewall rubber members combined on both side surfaces of the member are attached to the green case and also attached to the inside sidewall rubber member to form an integral sidewall rubber member. Unvulcanized tire molding method. 2. A vulcanized tire having an annular protruding rib located at a height equal to or less than ½ of the tire cross-sectional height on the outside of the sidewall rubber. The molding method according to claim 1, wherein the molding is performed. 3. A pair of outer sidewall rubber members are extruded integrally as an integrated rubber member with a tread rubber member by an extruder having a plurality of extrusion heads, and the composite member is applied to the second forming step. The molding method according to claim 1 or 2. 4. A hybrid member comprising a belt member and a tread rubber member, which are previously bonded together on a molding drum having a predetermined outer diameter, and a pair of outer sidewall rubber members are bonded to both side surfaces of the tread rubber member. The molding method according to claim 1, wherein the molding method is applied in the second molding step.