JP5276647B2 - Pneumatic tire manufacturing method - Google Patents

Abstract

The invention discloses a method for manufacturing a pneumatic tire. Concave and convex portions on the external surface of the side portion of a tire are prevented from deformation, so that the appearance quality of the tire is improved. The method includes a tire forming process. A plurality of long curtain cloth sheets are successively bonded on a rigid core body along the circumference of the tire so that an annular tire body is formed, wherein the long curtain cloth sheets are formed through covering by sticking glue along the array body of a tire body cord aligned with the tire axially. The side edges of every adjacent long curtain cloth sheet are close to each other or mutually connected on the surface of the tire body without being overlapped, and the side portions of the tire body are equipped with overlapping portions for overlapping of the above side edges. The modulus of an external tire body cord arranged on the outside is set by the array body of the tire body cord to be smaller than the modulus of an internal tire body cord arranged on the inner side of the external tire body cord.

Description

  The present invention relates to a method for manufacturing a pneumatic tire including a carcass forming step of forming a toroidal carcass by sequentially attaching strip-like ply pieces on a rigid core body in the tire circumferential direction.

  In recent years, in order to improve tire uniformity, for example, a rigid core body having an outer shape close to the tire lumen shape of a finished tire is used, and various types including an inner liner rubber, a carcass ply, and the like are provided on the rigid core body. The tire component members are sequentially affixed to form an unvulcanized tire, and the uncured tire is put together with the rigid core body into a vulcanization mold so that the rigid core body that is the inner mold and the outer A manufacturing method for vulcanizing and molding a tire with a vulcanizing mold as a mold has been proposed.

In the case of this manufacturing method, the carcass D that forms the skeleton of the unvulcanized tire is, for example, as shown in FIGS. 6A and 6B, an array A of carcass cords A1 aligned in the tire axial direction is a topping rubber. A plurality of strip ply pieces B in the form of a strip sheet with a small width L1 in the circumferential direction of the tire, and the strip ply pieces B are sequentially stuck on the rigid core C in the circumferential direction of the tire. (See Patent Document 1). At this time, in order to increase the uniformity of the tire, the strip ply pieces B are arranged so that the side edge portions Be and Be of the strip ply pieces B adjacent to each other in the tire circumferential direction are close to or in contact with each other without overlapping in the tread portion Ta. It is arranged in. Therefore, in the sidewall portion Tb, a triangular overlapping portion J where the side edge portions Be and Be overlap each other is inevitably formed, and in the overlapping portion J, as shown in FIG. since overlapping also outside of the carcass cord A1a, A1 a mutually located outermost in the array a, code density is increased. In addition, the code | symbol E in a figure is the inner liner rubber distribute | arranged inside the carcass D. FIG.

  On the other hand, when the vulcanized tire is vulcanized and molded, heat shrinkage occurs in the carcass cord due to the vulcanization heat, and particularly in the overlapping portion J where the cord density increases, the shrinkage force locally increases. For this reason, as shown in FIG. 7B, a part of the overlapping portion J pushes away the inner liner rubber E and is exposed to the tire cavity surface, thereby causing a problem of reducing the airtightness of the tire.

JP-A-11-254906

  Therefore, the present invention is based on the fact that the thermal contraction rate of the outer carcass cord arranged on the outermost side in the carcass cord array is smaller than the thermal contraction rate of the inner carcass cord arranged on the inner side. An object of the present invention is to provide a method for manufacturing a pneumatic tire capable of suppressing the overlapping portion of the strip ply pieces from being pushed out of the inner liner rubber and exposed to the tire inner surface.

In order to solve the above-mentioned problem, the invention of claim 1 of the present application is a method for manufacturing a pneumatic tire including a carcass extending from a tread portion to a bead portion on both sides through a sidewall portion,
Using a rigid core body, a plurality of strip ply pieces in the form of a strip sheet in which an array of carcass cords aligned in the tire axial direction is covered with a topping rubber and the width in the tire circumferential direction is small, the rigid core Including a carcass forming step of forming a toroidal carcass by sequentially pasting in the tire circumferential direction on the body,
In addition, the carcass is arranged in the tread portion so that the side edges of the strip ply pieces adjacent in the tire circumferential direction do not overlap with each other without being overlapped with each other, and in the sidewall portion, the overlapping portion where the side edges overlap. And having
The array of carcass cords comprises an outer carcass cord disposed on the outermost side and an inner carcass cord disposed on the inner side thereof, and the thermal contraction rate Ka at a temperature of 180 ° C. of the outer carcass cord. Is characterized by being smaller than the thermal contraction rate Kb of the inner carcass cord at a temperature of 180 ° C.

  According to a second aspect of the present invention, the heat shrinkage ratio Ka of the outer carcass cord is not more than 0.9 times the heat shrinkage ratio Kb of the inner carcass cord.

  According to a third aspect of the present invention, the carcass cord has a heat shrinkage rate Kb of 3.0 to 6.0%.

  The "heat shrinkage rate" is in accordance with JIS-L1017 item 8.10 (b) "heat-dry shrinkage rate after heating (method B)" and the cord is unloaded for 30 minutes at a temperature of 180 ° C. It means the dry heat shrinkage after heating after heating.

  In the present invention, as described above, the thermal contraction rate of the outer carcass cord arranged on the outermost side in the carcass cord array is set smaller than the thermal contraction rate of the inner carcass cord. Accordingly, it is possible to suppress a local increase in contraction force at the overlapping portion between the strip ply pieces where the cord density increases, and a part of the overlapping portion pushes the inner liner rubber and is exposed to the tire inner surface. It can be suppressed that the airtightness of the tire is impaired.

It is sectional drawing which shows one Example of the pneumatic tire formed by the manufacturing method of this invention. It is sectional drawing which shows an unvulcanized tire formation process. It is sectional drawing which shows a vulcanization | cure process. It is a perspective view which shows a strip ply piece. (A), (B) is explanatory drawing which shows a carcass shaping | molding process. (A), (B) is explanatory drawing which shows the manufacturing method of the conventional pneumatic tire which used the rigid core body. (A), (B) is sectional drawing which shows the overlap part between the strip ply pieces explaining the problem.

Hereinafter, embodiments of the present invention will be described in detail.
FIG. 1 is a cross-sectional view showing an example of a pneumatic tire 1 formed by the manufacturing method of the present invention. The pneumatic tire 1 has bead portions 4 on both sides through a sidewall portion 3 from a tread portion 2. 4, and a belt layer 7 disposed radially outside the carcass 6 and inside the tread portion 2.

  The carcass 6 is formed of one or more layers, in this example, one layer of carcass ply body 6A in which organic fiber carcass cords are radially arranged. The carcass ply body 6A has a toroid shape straddling the bead portions 4 and 4, and both ends of the carcass ply body 6A are not folded around the bead cores 5 arranged in each bead portion 4 in this example. 5 to be sandwiched and locked. Specifically, the bead core 5 is composed of inner and outer core pieces 5i and 5o in the tire axial direction, and both ends of the carcass ply body 6A are sandwiched between the inner and outer core pieces 5i and 5o.

  The inner and outer core pieces 5i, 5o are formed by winding the non-extensible bead wire 5a a plurality of times in the tire circumferential direction. At this time, in the outer core piece 5o, the number of turns of the bead wire 5a is, for example, about 1.2 to 2.0 times larger than that of the inner core piece 5i, and the rigidity is larger than that of the inner core piece 5i. Is preferred. As a result, the bending rigidity of the bead portion 4 can be relatively increased while restricting the total number of turns of the bead wire 5a, which is useful for improving the steering stability. In addition, the code | symbol 8 in a figure is a bead apex which consists of hard rubber | gum whose rubber hardness is 80-100 degree | times, for example, rises from each core piece 5i, 5o in a taper shape, and raises bead rigidity. In addition, in this specification, rubber hardness means the durometer A hardness measured in a 23 degreeC environment by durometer type A based on JIS-K6253.

  The belt layer 7 is formed of two or more belt plies 7A and 7B, in this example, two or more in which high-elasticity belt cords such as steel cords are arranged at, for example, about 10 to 35 ° with respect to the tire circumferential direction. The In the belt layer 7, the belt cords cross each other between the plies, thereby increasing the belt rigidity, and substantially reinforcing the entire width of the tread portion 2 with a tagging effect. In this example, a band layer in which a band cord such as a nylon cord is spirally wound at an angle of 5 degrees or less with respect to the circumferential direction for the purpose of enhancing high-speed durability on the outer side in the radial direction of the belt layer 7. 9 is provided. As the band layer 9, a pair of left and right edge band plies that covers only the outer end of the belt layer 7 in the tire axial direction, and a full band ply that covers substantially the entire width of the belt layer 7 are used alone or in appropriate combination. Can be used. In the present example, the band layer 9 is composed of one full band ply.

  Further, a thin inner liner 10 that forms a tire cavity surface is disposed inside the carcass 6. The inner liner 10 is made of a non-air permeable rubber such as butyl rubber or halogenated butyl rubber, for example, and holds the air filled in the tire lumen in an airtight manner. A side wall rubber 11 forming the outer surface of the side wall portion 3 is disposed outside the carcass 6, and a tread rubber 12 forming the outer surface of the tread portion 2 is disposed outside the band layer 9 in the radial direction.

  Next, a method for manufacturing the pneumatic tire 1 will be described. As shown schematically in FIG. 2, this manufacturing method uses a toroid-shaped rigid core body 20 having an outer shape substantially matching the tire lumen shape of the pneumatic tire 1, and uses the rigid core body 20. The unvulcanized tire forming step S1 for forming the unvulcanized tire 1N by sequentially affixing unvulcanized tire constituent members to the outer surface of the tire, and the unvulcanized tire 1N as schematically shown in FIG. And a vulcanization step S2 in which the rigid core body 20 is put into a vulcanization mold 21 and vulcanized.

The unvulcanized tire forming step S1 includes an inner liner forming step of attaching a member for forming the inner liner 10 to the rigid core body 20, a carcass forming step of attaching a member for forming the carcass 6 , and a member for forming the bead core 5. A bead core forming step for affixing a member, a bead core forming step for affixing a member for forming a bead apex 8, a belt forming step for adhering a member for forming a belt layer 7, a band forming step for adhering a member for forming a band layer 9, a side It includes a sidewall molding process for attaching a member for forming the wall rubber 11, a tread molding process for attaching a member for forming the tread rubber 12, and the like.

  Among these, in the steps other than the carcass forming step in the unvulcanized tire forming step S1 and the vulcanizing step S2, various well-known ones using the rigid core body 20 can be appropriately employed. Only the carcass molding process will be described below.

  In the carcass forming step, as shown in FIG. 4, a plurality of strip sheet-like sheets in which an array 31 of carcass cords 30 aligned in the tire axial direction is covered with a topping rubber 32 and the tire circumferential width L1 is small. The strip ply pieces 13 and the plurality of strip ply pieces 13 are sequentially attached in the tire circumferential direction on the rigid core body 20 as shown in FIGS. A toroidal carcass 6 is formed. At this time, the side edge portions 13e and 13e of the strip ply pieces 13 and 13 adjacent in the tire circumferential direction are arranged in the tread portion 2 so as to be close to or in contact with each other without overlapping each other. Therefore, in the tread portion 2, the cord density of the carcass cord 30 becomes substantially uniform, and a high tire uniformity can be secured. On the other hand, in the side wall part 3, the triangular overlapping part J where the said side edge parts 13e and 13e mutually overlap is inevitably formed. Accordingly, since the cord density of the carcass cord 30 increases in the overlapping portion J, the shrinkage force due to the carcass cord is locally increased during vulcanization molding, and a part of the overlapping portion J pushes the inner liner 10 away. It tends to be exposed on the tire inner surface.

  Accordingly, in the present invention, among the carcass cords 30 arranged on the strip ply piece 13, the outer carcass cord 30a arranged on the outermost side is expressed by the thermal contraction rate Ka at a temperature of 180 ° C. of the inner carcass cord 30b. The heat shrinkage rate Kb at a temperature of 180 ° C. is set smaller. Thereby, it is possible to suppress a local increase in contraction force at the overlapping portion J during vulcanization molding. In this example, the carcass cords 30 are arranged at substantially equal pitch intervals P in the strip ply piece 13.

  In this example, the heat shrinkage rates Ka and Kb are made different by changing the cord material of the outer carcass cord 30a and the inner carcass cord 30b. For example, the thermal shrinkage rate of aromatic polyamide fiber is about 0%, the heat shrinkage rate of rayon fiber is about 1.5 to 2.5%, the heat shrinkage rate of nylon fiber is about 2.3 to 3.3%, high The heat shrinkage rate of the modulus polyester fiber is about 3.5 to 4.5%, and the heat shrinkage rate of the regular polyester fiber is about 4.0 to 5.0%. Accordingly, an organic fiber material having a relatively low heat shrinkage rate is employed for the outer carcass cord 30a, and an organic fiber material having a relatively high heat shrinkage rate is employed for the inner carcass cord 30b.

  As another means for differentiating the thermal shrinkage rate, for example, before the strip ply piece 13 is formed, the outer carcass cord 30a is preliminarily heat-treated to generate a certain amount of thermal shrinkage, or By reducing the tension when dipping the cord and increasing the cord shrinkage during the dipping treatment, the thermal shrinkage rate during vulcanization can be reduced.

  Here, when the unvulcanized tire 1N is put into the vulcanization mold 21 together with the rigid core body 20 and vulcanized and molded, the unvulcanized tire is contained in the vulcanization mold as in the conventional manufacturing method. The so-called vulcanizing stretch that does not expand is not performed. For this reason, if the thermal contraction rate Kb of the inner carcass cord 30b is too small, the inner carcass cord 30b becomes meandering during vulcanization, causing a meandering arrangement, which may impair the tire uniformity. Therefore, the thermal shrinkage ratio Kb of the carcass cord 30b is preferably 3.0% or more, more preferably 4.0% or more. On the other hand, since the ratio of the outer carcass cord 30a to the entire carcass cord 30 is very low, even when the heat shrinkage ratio Ka is small, the influence on the uniformity is small, and therefore the uniformity is maintained. Thus, it is possible to suppress an increase in contraction force at the overlapping portion J, and to prevent a part of the overlapping portion J from being pushed away from the inner liner 10 and exposed to the tire cavity surface.

  For that purpose, the thermal contraction rate Ka of the outer carcass cord 30a is 0.9 times or less, further 0.8 times or less, and further 0.7 times or less of the heat shrinkage rate Kb of the inner carcass cord 30b. Is preferred. Further, the lower limit value of the heat shrinkage ratio Ka is allowable to 0%, that is, 0.0 times the heat shrinkage ratio Kb, but is preferably 0.1 times or more from the viewpoint of uniformity. If the thermal contraction rate Kb of the inner carcass cord 30b is too large, the carcass cord 30b enters or approaches the inner liner 10, and cord looseness is likely to occur. Therefore, the upper limit of the heat shrinkage ratio Kb is preferably 6.0% or less.

  Further, in the inner and outer carcass cords 30a and 30b, the modulus Mo per cord of the outer carcass cord 30a is preferably equal to or less than the modulus Mi per cord of the inner carcass cord 30b, and particularly from the viewpoint of uniformity. /Mi<1.0, more preferably 0 <2 <Mo / Mi <0.8. The modulus is the initial tensile resistance per cord determined in accordance with the chemical fiber tire cord test method of JISL1017. In the “load-elongation” curve of the cord determined in accordance with the test method, Means the slope of the tangent of the “load-extension” curve at the maximum point where the load change with respect to the extension change becomes maximum near the origin.

  If the width L1 of the strip ply piece 13 in the tire circumferential direction is too large, when the strip ply piece 13 is bent from the tread portion 2 to the sidewall portion 3 inward in the tire radial direction, wrinkles are generated and cord disturbance occurs. It becomes easy. In addition, since the overlap width Wj in the circumferential direction at the overlap portion J is also widened, the number of carcass cords that overlap at the overlap portion J is also increased, and the effects of the present invention are not fully exhibited. On the contrary, if the width L1 in the tire circumferential direction is too small, the number of man-hours for affixing the strip ply piece 13 increases and the affixing efficiency is reduced. Therefore, the width L1 is preferably in the range of 10 to 30 mm, and the number of carcass cords 30 in the array 31 is preferably 10 to 30.

In addition, the number N of overlapping carcass cords 30 in the overlapping portion J is preferably 1 to 2, particularly 1 in the tire maximum width position Qm. Therefore, the width L1 of the strip ply pieces 13 and the interval between the side edge portions 13e of the strip ply pieces 13 adjacent to each other in the tire circumferential direction in the tread portion 2 are set in advance so that the overlapping number N is within the above range. Is done.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

  The passenger car tire (tire size 175 / 65R14) having the structure shown in FIG. 1 is manufactured using a rigid core body and based on the specifications in Table 1, and the occurrence rate of exposure of the overlapping portion to the tire lumen surface, And the tire uniformity was tested.

  In the conventional example, a cylindrical carcass ply is formed by winding one carcass ply in the circumferential direction on a cylindrical forming drum without using a rigid core, and this cylindrical carcass ply is connected between bead cores. It is formed by the conventional general manufacturing method which has the expansion | swelling process which expands by and shapes in toroid form. In each of the comparative example and the example, a rigid core was used.

Except as described in Table 1, the specifications are substantially the same.
Strip ply piece ・ Circumferential width L1 --- 20mm,
・ Number of cords --- 20

(1) Exposure rate:
Each of the 20 test tires was formed, and the number of exposed tires in which a part of the overlapping portion was exposed on the inner surface of the tire was measured. The smaller the number, the fewer the number of occurrences and the better.

(2) Uniformity:
Using a tire uniformity tester, RFV was measured in accordance with JASO C607: 2000 “Uniformity test method for automobile tires” and displayed as an index with a conventional example of 100. The smaller the value, the better. The measurement conditions were a rim (5.5 J × 14), internal pressure (200 kPa), tire rotation speed (60 rpm), and longitudinal load (3.54 kPa).

  As shown in the table, it can be confirmed that the tires of the examples can reduce defects in which a part of the overlapping portion is exposed to the tire inner surface while ensuring excellent uniformity.

2 Tread portion 3 Side wall portion 4 Bead portion 6 Carcass 13 Strip ply piece 13e Side edge portion 20 Rigid core body 30 Carcass cord 30a Carcass cord 31 in the outer carcass cord 30b Array 32 Topping rubber J Overlap portion

Claims (3)

A pneumatic tire manufacturing method comprising a carcass extending from a tread portion to a side wall portion to bead portions on both sides,
Using a rigid core body, a plurality of strip ply pieces in the form of a strip sheet in which an array of carcass cords aligned in the tire axial direction is covered with a topping rubber and the width in the tire circumferential direction is small, the rigid core Including a carcass forming step of forming a toroidal carcass by sequentially pasting in the tire circumferential direction on the body,
In addition, the carcass is arranged in the tread portion so that the side edges of the strip ply pieces adjacent in the tire circumferential direction do not overlap with each other without being overlapped with each other, and in the sidewall portion, the overlapping portion where the side edges overlap. And having
The array of carcass cords comprises an outer carcass cord disposed on the outermost side and an inner carcass cord disposed on the inner side thereof, and the thermal contraction rate Ka at a temperature of 180 ° C. of the outer carcass cord. Is made smaller than the thermal shrinkage rate Kb of the carcass cord at a temperature of 180 ° C.   2. The method for manufacturing a pneumatic tire according to claim 1, wherein the outer carcass cord has a heat shrinkage ratio Ka of 0.9 times or less of the heat shrinkage ratio Kb of the inner carcass cord.   The method of manufacturing a pneumatic tire according to claim 1 or 2, wherein the heat shrinkage ratio Kb of the carcass cord is 3.0 to 6.0%.

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