JP5066220B2 - Pneumatic tire and manufacturing method thereof - Google Patents

Description

  The present invention relates to a pneumatic tire having a tread rubber formed by spirally winding a rubber strip and a method for manufacturing the same, and more particularly to a technique capable of effectively preventing molding defects such as bears generated on the outer surface of the tread rubber. .

  In recent years, various strip wind methods for forming tread rubber by spirally winding a small ribbon-like unvulcanized rubber strip in the tire circumferential direction have been proposed in order to eliminate intermediate stock and increase productivity. . Such a strip wind method has a merit of improving the uniformity of the tire because the splice portion is eliminated as compared with the conventional integrally extruded tread rubber.

  FIG. 13 shows a cross-sectional view of a state before vulcanization of the tread rubber a made by the strip wind method. As is apparent from FIG. 13, since this type of tread rubber a has the rubber strip s wound spirally, irregularities remain on the outer surface. For this reason, when it molds with a vulcanization mold, air remains in crevice b and it is easy to produce molding defects, such as a bear.

  In order to solve such a problem, it is conceivable to provide a large number of vent holes on the tread rubber molding surface of the vulcanization mold and to evacuate the remaining air to suppress the bear. However, in such a method, many spews sucked up by the vent hole are formed on the outer surface of the tread, and the appearance is impaired. In addition, many steps are required to remove the spew.

  The present applicant has proposed the following Patent Documents 1 to 5, for example. These techniques describe a vulcanization mold in which segment plates divided in the width direction of the tread rubber are aligned to form a tread rubber molding surface. Such a tread rubber molding surface suppresses the generation of bears by discharging air from a minute mating surface between the segment plates.

JP 2009-023231 A JP 2009-148992 A JP 2007-144997 A JP 2008-087428 A JP 2008-114475 A

  However, the inventors have found that the techniques of Patent Documents 1 to 5 described above have room for further improvement in the suppression of bears for tread rubber made by the strip wind method.

  As a result of intensive research, the inventors have found that the tread rubber made by the strip wind method in which the recesses formed on the outer surface are continuous in the tire circumferential direction is due to the mating surface of the segment plate extending in the tire axial direction. The inventors have found that it is effective to cross the formed dividing lines at a specific pitch, and have completed the present invention.

  As described above, the main object of the present invention is to provide a pneumatic tire that can effectively prevent molding defects such as bears generated on the outer surface of the tread rubber, and a method for manufacturing the same.

  The invention according to claim 1 of the present invention is a method for producing a pneumatic tire comprising a molding step of molding a green cover having a tread rubber, and a vulcanization step of vulcanizing and molding the green cover, The molding step includes a step of spirally winding a ribbon-like unvulcanized rubber strip in the tire circumferential direction to mold the tread rubber, and the vulcanization step includes a plurality of steps extending in the width direction of the tread rubber. The tread rubber molding surface having a plurality of dividing lines extending in the tire axial direction by the mating surfaces of the adjacent segment plates is continuous by connecting the segment plates in the tire circumferential direction. A pitch L of the dividing line of the tread rubber molding surface and a helical pitch W of a rubber strip wound around the outermost side of the tread rubber. L / W is characterized by large and more than 3 than 0.

  The invention according to claim 2 is the method for producing a pneumatic tire according to claim 1, wherein the ratio L / W is 0.5 or more and 2.5 or less.

  The invention according to claim 3 is the method for producing a pneumatic tire according to claim 1, wherein the ratio L / W is 0.7 or more and 2.0 or less.

The invention according to claim 4 is a pneumatic tire molded by a vulcanization mold having a split surface formed by a mating surface extending in the tire axial direction on a tread rubber molding surface for molding the tread rubber, The tread rubber consists of a rubber strip wound body formed by spirally winding a ribbon-like uncured rubber strip in the tire circumferential direction, and the pitch of burrs extending in the tire axial direction sucked up by the dividing surface And a pitch of a linear pattern drawn by an edge of the rubber strip wound around the outermost side of the tread rubber is a pneumatic tire characterized by being greater than 0 and 3 or less .

According to a fifth aspect of the present invention, the tread rubber is divided into a plurality of blocks, and the tread rubber has a linear pattern drawn by an edge of the rubber strip on the tread surface of the block and an intersection of the burr. The pneumatic tire according to claim 4, wherein at least one is included .

The invention according to claim 6 is the pneumatic tire according to claim 5 , wherein the intersecting portion is provided in a tread outer peripheral region within 7 mm from an edge of the tread of the block.

The invention according to claim 7 is the pneumatic tire according to claim 5 , wherein the intersecting portion is provided in a tread outer peripheral region within 5 mm from an edge of the tread of the block.
The invention according to claim 8 is the pneumatic tire according to claim 7 , wherein a plurality of the intersecting portions are provided in the outer peripheral region of the tread surface.

  The method for producing a pneumatic tire of the present invention includes a molding step of molding a green cover having tread rubber, and a vulcanization step of vulcanizing and molding the green cover. The forming step includes a step of forming a tread rubber by winding a ribbon-like unvulcanized rubber strip spirally in the tire circumferential direction. Further, in the vulcanization process, a plurality of dividing lines extending in the tire circumferential direction by connecting a plurality of segments extending in the width direction of the tread rubber in the tire circumferential direction and extending in the tire axial direction by a mating surface of adjacent segments. This is performed with a vulcanization mold having a tread rubber molding surface on which is formed.

  Thus, in the method for producing a pneumatic tire according to the present invention, the segment dividing line extending in the tire axial direction of the vulcanization mold intersects the recess extending in the tire circumferential direction on the outer surface of the raw cover. it can. Therefore, the air remaining between the vulcanization mold and the recess can be discharged from the mating surfaces, and the generation of bears can be suppressed.

  Moreover, the ratio L / W between the pitch L of the dividing line on the molding surface of the tread rubber and the helical pitch W of the rubber strip wound around the outermost side of the tread rubber is limited to a certain range, thereby remaining in the recess. Air can be exhausted uniformly and reliably over the tire circumferential direction.

It is sectional drawing of the pneumatic tire obtained by the manufacturing method of this embodiment. FIG. 2 is a development view of the tread portion of FIG. 1. It is a partial top view of the raw cover of FIG. It is a perspective view of a rubber strip. It is sectional drawing of a vulcanization mold. It is a perspective view of a segment block. FIG. 7 is a front view of FIG. 6. It is AA sectional drawing of FIG. It is an expanded view of the tread part of the raw cover which showed the dividing line of the segment. It is sectional drawing which shows the burr | flash formed in tread rubber. It is an expanded view which expands and shows the block in which a burr | flash is formed. (A), (b), (c), and (d) are the tread expansion | deployment views of the raw cover of a comparative example. It is a fragmentary sectional view of the raw cover made by the strip wind method.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the pneumatic tire 1 obtained by the manufacturing method of the present embodiment includes a toroidal carcass 6 that extends from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and the carcass. 6 and a belt layer 7 arranged on the outer side in the radial direction, and a case of a radial tire for a passenger car is shown.

  The carcass 6 includes a main body portion 6 a that extends from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and a folded portion 6 b that is connected to the main body portion 6 a and wound up around the bead core 5. It is formed from at least one carcass ply 6A. Further, a bead apex 8 extending from the bead core 5 to the outer side in the tire radial direction is disposed between the main body portion 6a and the folded portion 6b of the carcass ply 6A, and the bead portion 4 is appropriately reinforced. The belt layer 7 is formed of two belt plies 7A and 7B in which belt cords made of, for example, steel are arranged at an angle of, for example, 10 to 35 degrees with respect to the tire equator C.

  The pneumatic tire 1 includes a tread rubber 2G disposed on the outer side of the belt layer 7, a sidewall rubber 3G disposed on the outer side in the tire axial direction of the carcass 6 in the sidewall portion 3, and an inner side of the carcass 6. It includes an inner liner rubber 9G made of an air impermeable rubber and a clinch rubber 4G having an excellent wear resistance that is disposed on the outer side in the tire axial direction of the carcass 6 in the bead portion 4 and can contact a rim (not shown).

  As shown in FIG. 2, the tread rubber 2 </ b> G of the present embodiment is formed to include a longitudinal main groove 11 extending in the tire circumferential direction and a lateral groove 12 intersecting the longitudinal main groove 11. By the vertical main grooves 11 and the horizontal grooves 12, the tread rubber 2G is divided into a plurality of blocks B.

  In the present embodiment, the longitudinal main groove 11 is a pair of inner longitudinal main grooves 11A disposed on both sides of the tire equator C, and a pair of outer longitudinal main grooves 11A disposed in the tire axial direction. The outer vertical main groove 11B is included. The horizontal groove 12 includes a plurality of inner horizontal grooves 12A that cross between the inner and outer vertical main grooves 11A and 11B, and a plurality of outer horizontal grooves 12B extending from the outer vertical main grooves 11B to the tread end 2t. Composed. Thus, the tread rubber 2G has a central rib R extending on the tire equator C, an inner block B1 disposed on both sides of the central rib R, and an outer side of the inner block B1 in the tire axial direction. A block-rib type tread pattern including the arranged outer block B2 is formed.

  Next, in the method for manufacturing the pneumatic tire 1 of the present embodiment, as shown in FIG. 3, a molding step for molding the raw cover 1M having the tread rubber 2G, and a vulcanization for vulcanizing the raw cover 1M. Process.

  In the molding step, the raw cover 1M is molded using a molding drum (not shown) according to the custom. The raw cover 1M includes the bead core 5, the carcass ply 6A, the belt layer 7, the clinch rubber 4G, the inner liner rubber 9G, the sidewall rubber 3G, and the tread rubber 2G, and is formed in a toroidal shape.

  Further, in the molding process of this embodiment, as shown in FIGS. 3 and 4, a tread rubber 2G is molded by spirally winding a ribbon-shaped unvulcanized rubber strip S in the tire circumferential direction. The process of carrying out. In this step, for example, a rubber strip S having a thickness t of about 0.3 to 3.0 mm and a width W1 of about 5.0 to 30.0 mm is directly wound around, for example, the outer surface of the belt layer 7 of the raw cover 1M. By tapping, the tread rubber 2G is formed. Such a tread rubber 2G is useful for improving tire uniformity because there is no splice portion (seam) formed in the conventional integrally extruded tread rubber. On the other hand, since the rubber strip S is spirally wound on the tread rubber 2G, a plurality of concave portions 15A and convex portions 15B extending in the tire circumferential direction are formed on the outer surface thereof.

  In the present specification, “unvulcanized” means all embodiments that have not reached complete vulcanization. Accordingly, the rubber member partially or partially vulcanized is included in the concept of “unvulcanized”.

  In the vulcanization step, as shown in FIG. 5, the raw cover 1M is vulcanized using a vulcanizing mold 16 having a cavity 23 that forms the outer surface of the raw cover 1M. The vulcanization mold 16 of the present embodiment includes, for example, a lower mold 17 having one sidewall molding surface 21a, an upper mold 18 having the other sidewall molding surface 21b, and a tread molding having a tread rubber molding surface 22. It comprises a mold 19 and a pair of bead rings 20 that can hold the bead portion 4 of the raw cover 1M.

  In the vulcanization mold 16, the lower mold 17, the upper mold 18, the tread mold 19, and the bead ring 20 are fitted to form the cavity 23. The raw cover 1M disposed in the cavity 23 is pressed against the cavity 23 and vulcanized by expansion of the bladder 24 to which a high-pressure fluid is supplied in accordance with a customary practice.

  The tread mold 19 according to the present embodiment is configured to be continuous in an annular shape by connecting a plurality of segment blocks 26 equally divided in the tire circumferential direction, in this embodiment, nine segment blocks 26 in the tire circumferential direction. .

  As shown in FIGS. 6, 7, and 8, each segment block 26 includes a holder 27 having a substantially U-shaped cross section with a groove 29 recessed in the radially inner side surface, and a groove 29 of the holder 27. And a plurality of segment plates 28 to be held.

  As shown in FIG. 7, the groove 29 has a bottom surface 29a that is a plane perpendicular to the tire equator plane passing through the tire equator C and extends in the tangential direction of the tread rubber molding surface 22, and from both ends of the bottom surface 29a in the width direction. And an inner wall surface 29b extending radially inward.

  The bottom surface 29a is provided with a plurality of ridges 30 protruding inward in the radial direction and having a bulging portion 30a having a larger width on the inner end side thereof at a distance in the tire axial direction. The ridges 30 are formed so as to extend linearly along the bottom surface 29a from one end side S1 in the circumferential direction of the holder 27 toward the other end side S2.

  As shown in FIGS. 6 and 7, the segment plate 28 is formed in a thin plate shape extending in the width direction of the tread rubber 2G (shown in FIG. 5), and has a radially inner inner periphery forming the tread rubber molding surface 22. An inner surface 28a, an outer surface 28b that is located on the opposite side of the inner peripheral surface 28a and that contacts the bottom surface 29a of the holder 27, a first side surface 28c that contacts a segment plate 28 adjacent in the circumferential direction, A second side surface 28d that abuts against the wall surface 29b is formed.

  Further, as shown in FIGS. 6 and 8, the outer surface 28 b of each segment plate 28 has a flat surface and is disposed in contact with the bottom surface 29 a of the holder 27. Such a segment plate 28 can suppress the manufacturing cost as compared with the case where the outer surface 28b is formed in an arc shape.

  Further, the outer surface 28 b of the segment plate 28 is provided with a recess 37 that is recessed inward in the radial direction and that can be inserted into the protrusion 30 of the holder 27. As a result, the plurality of segment plates 28 are held by the holder 27.

  Further, the outer surface 28b of the segment plate 28 is provided with a plurality of cutout grooves 33 that are recessed inward in the radial direction. As shown in FIG. 6, the cutout grooves 33 of the plurality of segment plates 28 arranged in one segment block 26 communicate linearly. As shown in FIGS. 6 and 8, screw shafts 34 are inserted into these cutout grooves 33, and nuts 35 are screwed to both ends thereof, for example, via washers 31. As a result, the plurality of segment plates 28 are united together. The plurality of segment plates 28 are positioned and fixed to the holder 27 by, for example, a fixing tool (not shown) such as a pin inserted toward the holder 27. The fixing of the holder 27 and the segment plate 28 is not limited to such an embodiment. For example, after the plurality of segment plates 28 are bundled together, they are set in a state where they are floated on the mold of the holder 27. The segment plate 28 may be fixed simultaneously with the forming of the holder 27 by pouring a molten metal such as an aluminum alloy.

  Further, an arc-shaped tread rubber molding surface 22 extending in the circumferential direction is formed on the inner peripheral surface 28a of the bundled segment plates 28, and a plurality of protrusions protruding toward the tread rubber 2G as shown in FIG. A piece 32 is provided. The projecting piece 32 forms a reverse pattern of the vertical main groove 11 and the horizontal groove 12 of the tread rubber 2G, and the vertical main groove 11 and the horizontal groove are formed by pressing the raw cover 1M (shown in FIG. 5) in vulcanization molding. 12 is formed.

  In the present embodiment, the plurality of segment plates 28 are held by the holder 27 and then bound by the screw shaft 34. For example, after being bound by the screw shaft 34, the segment plate 28 is held by the holder 27. Also good. In this case, since the notch 33 is recessed from the outer surface 28b of the segment plate 28, the screw shaft 34 can be easily inserted from the outer surface 28b of the segment plate 28, and a plurality of segment plates 28 can be easily positioned. Can be combined.

  Further, the tread rubber molding surface 22 formed by the inner peripheral surface 28a has a mating surface 38 formed by facing the first side surfaces 28c, 28c of the adjacent segment plates 28, as shown in FIG. A plurality of dividing lines 39 extending in the tire axial direction are formed. The dividing line 39 appears on the tread rubber molding surface 22 as a minute gap of 0.01 to 0.1 mm, for example.

  FIG. 9 is a development view of the tread portion of the raw cover 1M showing the dividing line 39 of the segment plate 28. FIG. The ratio L / W between the circumferential pitch L of the dividing line 39 of this embodiment and the helical pitch W of the rubber strip S wound around the outermost side of the tread rubber 2G is limited to greater than 0 and 3 or less. Is done. Here, the helical pitch W is a distance in the tire axial direction between the edges Se of the adjacent rubber strips S. Further, when the pitch L of the dividing line 39 and / or the spiral pitch W of the rubber strip S is not constant, the average value thereof is used.

  As shown in FIG. 5, the tread mold 19 having the above-described configuration is such that the tread rubber 2 </ b> G is pressed against the tread rubber molding surface 22 in the vulcanization process, and the tread rubber molding surface 22 and the tread rubber 2 </ b> G are The air remaining between them is discharged from the dividing line 39 (shown in FIGS. 8 and 9) of the segment plate 28 which is a minute gap.

  Moreover, since the dividing line 39 of the present embodiment extends in the tire axial direction, it can intersect with the recess 15A (shown in FIG. 3) of the tread rubber 2G extending in the tire circumferential direction. Thereby, the dividing line 39 can discharge | emit the air which tends to remain | survive in the recessed part 15A to the exterior more reliably, and can suppress molding defects, such as a bear.

  Further, as shown in FIG. 9, the ratio L / W between the pitch L of the dividing line 39 and the helical pitch W of the rubber strip S is limited to be greater than 0 and 3 or less. In this way, by limiting the pitch L of the dividing line 39 to a certain range with respect to the spiral pitch W, the air remaining in the recess 15A of the tread rubber 2G can be discharged uniformly over the tire circumferential direction. . That is, when the ratio L / W exceeds 3, air may not be sufficiently discharged at the intermediate portion between the dividing lines 39 and 39 adjacent in the circumferential direction, and a bear may be generated.

  In the present embodiment, since the remaining air can be sufficiently discharged without providing a vent hole (not shown) for sucking air, the vulcanized tire has a tread rubber 2G in the vent hole. Spews (not shown) formed by sucking the parts do not occur.

  In order to effectively exhibit the above action, the ratio L / W is preferably 0.5 or more, more preferably 0.7 or more, still more preferably 1.0 or more, and preferably 2. 5 or less, more preferably 2.0 or less, and still more preferably 1.8 or less.

  Since the dividing line 39 forms a minute gap, as shown in FIG. 10, due to the pressure from the bladder 24 (shown in FIG. 5) at the time of external suction and / or vulcanization molding, A part of the tread rubber 2G enters the mating surface 38. As a result, burrs 41 extending in the tire axial direction are formed on the tread rubber 2G of the pneumatic tire 1 after vulcanization molding.

  FIG. 11 shows an enlarged view of the inner block B1. It is preferable that at least one intersection 43 of the burr 41 and the linear pattern 42 drawn by the edge Se of the rubber strip S is included in the tread Bs of the block B. As a result, air that tends to remain on the tread Bs of the block B is reliably discharged from the dividing line 39, so that molding defects such as bearings are effectively suppressed.

  The crossing portion 43 is an outer region of the tread surface that is separated from the edge Be side of the tread Bs of the block B, more specifically, a distance L1 within 7 mm, more preferably within 5 mm from the edge Be of the tread Bs of the block B. It is preferably formed at T1. Generally, in the vulcanization process, the vicinity of the edge Be of the block B is strongly pressed by the protruding piece 32, so that the rubber flow is relatively large and air is easily trapped. However, by providing at least one intersection 43 in the tread outer peripheral region T1, air can be prevented from being trapped and the occurrence of bears can be more reliably suppressed.

  It is preferable that a plurality of the intersecting portions 43 are provided in the outer surface T1 of the tread surface. As a result, air that tends to remain on the tread Bs side of the block B can be more reliably discharged.

  In addition, as shown in FIG. 2, when the rib R is provided in the vicinity of the tire equator C as in the pneumatic tire 1 of the present embodiment, the segment plate 28 may be divided into two in the vicinity of the tire equator C. Good. Such a segment plate 28 is preferable in that air that tends to remain on the tread surface of the rib R in the tire circumferential direction can be efficiently discharged.

  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.

  Pneumatic tires having the basic structure shown in FIG. 1 and vulcanized with a vulcanization mold having the specifications shown in Table 1 were manufactured, and their performance was tested. For comparison, a pneumatic tire vulcanized with a vulcanization mold having the integrally extruded tread rubber shown in FIG. 12A and having no segment plate, and FIG. A pneumatic tire formed by vulcanization molding with a vulcanization mold having no segment plate on the tread rubber comprising the rubber strip wound body shown in (b) was also tested in the same manner.

Also, a pneumatic tire formed of a vulcanization mold having the integrally extruded tread rubber shown in FIG. 12 (c) and having a plurality of segment plates extending in the tire axial direction, and FIG. 12 (d). A pneumatic tire formed by a vulcanization mold having a plurality of segment plates extending in the tire circumferential direction on a tread rubber comprising a rubber strip wound body shown in FIG.
Tire size: 245 / 40R18
Rim size: 18 × 8.5J
Rubber strip thickness t: 1.0 mm
Rubber strip width W1: 10mm

<Uniformity (RFV)>
Based on JASO C607: 2000 uniformity test conditions, radial force variation (RFV), which is a fluctuation component of force in the tire radial direction at the time of rotation, is measured under the following conditions for each of 100 test tires, and the average The value was expressed as an index with Comparative Example 1 as 100. The smaller the value, the better.
Internal pressure: 200 kPa
Load: 4.88kN
Rotation speed: 60rpm

<Finished state after vulcanization>
The surface of the tread rubber of 100 test tires was observed with the naked eye, and the number of tires in which molding defects such as bears occurred was examined. The results are displayed as an index with Comparative Example 1 as 100. The smaller the value, the better.
The test results are shown in Table 1.

  As a result of the test, it was confirmed that the pneumatic tire of the example can effectively prevent molding defects such as bears generated on the outer surface of the tread rubber while improving the uniformity of the tire.

1M raw cover 2G tread rubber 16 vulcanization mold 22 tread rubber molding surface 28 segment plate 38 mating surface 39 dividing line

Claims (8)

A method for producing a pneumatic tire comprising a molding step of molding a green cover having a tread rubber, and a vulcanization step of vulcanizing and molding the green cover,
The forming step includes a step of forming the tread rubber by spirally winding a ribbon-like unvulcanized rubber strip in the tire circumferential direction,
The vulcanization step includes a plurality of segment plates extending in the tire circumferential direction by connecting a plurality of segment plates extending in the width direction of the tread rubber, and extending in the tire axial direction by a mating surface of the adjacent segment plates. While performed with a vulcanization mold having a tread rubber molding surface on which a dividing line of books is formed,
The ratio L / W between the pitch L of the dividing line of the tread rubber molding surface and the helical pitch W of the rubber strip wound around the outermost side of the tread rubber is greater than 0 and 3 or less. A method for manufacturing a pneumatic tire.   The method for manufacturing a pneumatic tire according to claim 1, wherein the ratio L / W is 0.5 or more and 2.5 or less.   The method for manufacturing a pneumatic tire according to claim 1, wherein the ratio L / W is 0.7 or more and 2.0 or less. A pneumatic tire molded with a vulcanization mold having a split surface formed by a mating surface extending in the tire axial direction on a tread rubber molding surface for molding a tread rubber,
The tread rubber is composed of a rubber strip wound body formed by spirally winding a ribbon-like unvulcanized rubber strip in the tire circumferential direction ,
The ratio between the pitch of burrs sucked up by the dividing surface in the tire axial direction and the pitch of the linear pattern drawn by the edge of the rubber strip wound around the outermost side of the tread rubber is greater than 0 and 3 a pneumatic tire, wherein the or less. The tread rubber is divided into a plurality of blocks,
5. The pneumatic tire according to claim 4 , wherein the tread surface of the block includes at least one intersection between a linear pattern drawn by an edge of the rubber strip and the burr . The pneumatic tire according to claim 5 , wherein the crossing portion is provided in a tread surface outer peripheral region within 7 mm from an edge of the tread surface of the block. The pneumatic tire according to claim 5, wherein the intersecting portion is provided in a tread surface outer peripheral region within 5 mm from an edge of the tread surface of the block . The pneumatic tire according to claim 7, wherein a plurality of the intersecting portions are provided in the outer peripheral area of the tread surface.

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