Tire vulcanization mold and tire manufacturing method using the same

Abstract

To provide a tire vulcanization mold that can effectively suppress clogging of vent hole due to spew, and to provide a tire manufacturing method using the same.SOLUTION: In a tire vulcanization mold 10 having a molding surface 31 for molding tire outer surface and a vent hole 32 opened in the molding surface 31, a damming member 33 for damming the rubber while allowing the passage of air is arranged in the vent hole 32, and the distance from the molding surface 31 to the damming member 33 is in the range of 6 mm to 18 mm. An unvulcanized-state tire T is placed inside the tire vulcanization mold 10, and vulcanization is performed while pressurizing the tire T from the inside.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a tire vulcanizing mold equipped with vent holes and a tire manufacturing method using the same, and more specifically to a tire vulcanizing mold that makes it possible to effectively suppress clogging of the vent holes due to spew, and a tire manufacturing method using the same. [Background technology]

[0002] In the manufacturing process of pneumatic tires, an unvulcanized tire is placed inside a tire curing mold and heated while being pressurized from the inside by a bladder to vulcanize the tire. If air remains between the molding surface of the tire curing mold and the unvulcanized tire, this residual air can cause tire surface damage. To prevent such tire surface damage, tire curing molds are provided with multiple vent holes that open to the molding surface for air release.

[0003] However, if at least a portion of the spews (beard-like rubber pieces) formed in the vent holes during vulcanization remain in the vent holes when the tire is demolded and clog the vent holes, air cannot be bled through the vent holes during the next vulcanization, resulting in damage to the tire surface in that area. Furthermore, if the vent holes become clogged with spews, tire production must be temporarily stopped to clean the vent holes, which significantly reduces tire productivity.

[0004] Therefore, in order to prevent clogging of the vent holes, it has been proposed to provide non-through vent holes that do not communicate with the outside of the mold (see, for example, Patent Documents 1 and 2). However, because non-through vent holes do not inherently have the function of discharging air, they have the disadvantage of not being able to fully prevent tire surface damage caused by residual air.

[0005] Another proposed structure involves installing a vent piece with an air hole inside the vent hole and an elastic member that elastically closes the air hole, allowing air to escape through the gap between the vent piece and the elastic member while blocking the rubber with the elastic member (see, for example, Patent Document 3). Similarly, another proposed structure involves installing a valve member near the entrance of the vent hole to prevent the rubber from leaking out (see, for example, Patent Document 4). However, in both cases, the elastic member or valve member must be installed near the entrance of the vent hole to shorten the spew. In such locations, the pressure of the rubber flowing into the vent hole during vulcanization is high, making it easy for the rubber to flow into the gap between the elastic member or valve member, which can result in a deterioration of the valve function. This has the disadvantage of requiring frequent cleaning and replacement of the elastic member or valve member.

[0006] Furthermore, it has been proposed to prevent breakage in the middle of the spew by adopting a structure in which the inner diameter of the vent hole is smaller at the back (see, for example, Patent Document 5). However, in this case, rubber also flows into the small diameter part at the back of the vent hole, which may cause breakage at the tip of the spew, and if the tip of the spew breaks, it will be unable to maintain its exhaust function. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 9-94830 [Patent Document 2] Patent No. 6495239 [Patent Document 3] Patent No. 5227266 [Patent Document 4] Patent No. 6880817 [Patent Document 5] Japanese Patent Application Publication No. 2019-81260 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a tire vulcanization mold that can effectively prevent clogging of vent holes due to spew, and a tire manufacturing method using the same. [Means for solving the problem]

[0009] In order to achieve the above object, the tire vulcanizing mold of the present invention is provided with a molding surface for molding the outer surface of a tire and vent holes opening to the molding surface, and a blocking member is disposed in the vent holes to allow air to pass through while blocking rubber, and the distance from the molding surface to the blocking member is 10mm~14mm It is characterized in that the range is

[0010] The tire manufacturing method of the present invention is characterized in that an unvulcanized tire is placed inside the tire vulcanization mold described above, and the tire is vulcanized while being pressed against the molding surface. [Effects of the Invention]

[0011] As a result of extensive research into tire curing molds equipped with vent holes, the present inventors discovered that when vulcanization is repeatedly performed using such a tire curing mold, dirt gradually accumulates near the tip of the spew formed in the vent hole, causing the tip of the spew to break due to the accumulation of dirt. Furthermore, upon investigating the physical properties of the spew, they found that the pressure in the vent hole gradually decreases from the base to the tip, and that the tip of the spew is heated at a pressure close to atmospheric pressure, causing significant foaming. They also found that the density of the rubber at the tip of the spew decreases, and that its breaking strength also decreases, making it more susceptible to the accumulation of dirt and spew breakage. In light of this situation, the present inventors discovered that vent hole clogging can be effectively prevented by suppressing rubber foaming at the tip of the spew, leading to the present invention.

[0012] Specifically, in the present invention, a tire vulcanization mold is provided with a molding surface for molding the tire outer surface and vent holes opening to the molding surface. A damming member is provided that allows air to pass through the vent holes while blocking the rubber. By blocking the rubber in the vent holes during vulcanization, pressure is generated at the tip of the spew, suppressing rubber foaming. This prevents dirt from accumulating near the tip of the spew formed in the vent holes and prevents breakage of the tip of the spew due to such deposits. This effectively prevents clogging of the vent holes by the spew. As a result, tire surface damage caused by residual air is prevented, and tire productivity is improved by reducing the frequency of vent hole cleaning.

[0013] According to the present invention, the damming member allows air to pass through, so that the residual air can be sufficiently discharged. 10mm~14mm Since the damming member is located within this range and is far enough away from the molding surface that excessive pressure is not generated in the rubber that is blocked by the damming member during vulcanization, rubber does not flow into the gaps in the damming member, and the frequency of replacement and cleaning of the damming member can be reduced.

[0014] In the present invention, it is preferable to provide a vent piece that encompasses at least a portion of the vent hole and is separable from the mold body. By employing a vent piece that is separable from the mold body, it is possible to easily arrange a blocking member for the vent hole.

[0015] The blocking member can be made up of a plurality of plates stacked in a direction perpendicular to the axial direction of the vent hole, in which case the gaps formed between the plates serve as air passages.

[0016] The damming member can be made of a porous material having open cells, in which case the open cells of the porous material serve as air flow paths.

[0017] The blocking member may be formed of a member having a plurality of vent holes penetrating in the axial direction of the vent hole. In this case, the plurality of vent holes serve as air flow paths.

[0018] It is preferable that the blocking member is subjected to a release treatment, which prevents the rubber from adhering to the blocking member and effectively suppresses clogging of the vent hole. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a meridian cross-sectional view showing a tire vulcanizing apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing a vent hole portion of the tire vulcanizing mold according to the present invention. [Figure 3] 1A and 1B are cross-sectional views showing the state of the spew formed in the vent hole of the tire vulcanizing mold according to the present invention, and FIG. [Figure 4] FIG. 10 is a cross-sectional view showing a modified example of the vent hole portion of the tire vulcanizing mold according to the present invention. [Figure 5] FIG. 10 is a cross-sectional view showing another modified example of the vent hole portion of the tire vulcanizing mold according to the present invention. [Figure 6] FIG. 10 is a cross-sectional view showing yet another modified example of the vent hole portion of the tire vulcanizing mold according to the present invention. [Figure 7] FIG. 1 is a cross-sectional view showing a spew formed in a conventional vent hole. [Figure 8] 1A to 1C show the mechanism by which clogging occurs in a conventional vent hole, with (a) to (c) being cross-sectional views showing the state of the vent hole at each stage. DETAILED DESCRIPTION OF THE INVENTION

[0020] The configuration of the present invention will be described in detail below with reference to the accompanying drawings. Fig. 1 shows a tire vulcanizing apparatus according to an embodiment of the present invention, Fig. 2 shows a vent hole portion of a tire vulcanizing mold according to the present invention, and Fig. 3 shows the vent hole portion together with a spew.

[0021] 1, this tire vulcanizing apparatus includes a tire vulcanizing mold (hereinafter referred to as "mold") 10 that molds the outer surface of a pneumatic tire T, and a cylindrical bladder 20 that is inserted inside the pneumatic tire T. In addition, this tire vulcanizing apparatus includes a heating and pressurizing medium supply means (not shown) for supplying a heating and pressurizing medium such as steam to the inside of the bladder 20, and a heating means (not shown) for heating the mold 10.

[0022] The mold 10 is composed of a lower side plate 11 and an upper side plate 12 for molding the sidewall portions of the pneumatic tire T, a lower bead ring 13 and an upper bead ring 14 for molding the bead portions of the pneumatic tire T, and a plurality of sectors 15 for molding the tread portion of the pneumatic tire T, and the pneumatic tire T is vulcanized and molded inside the mold 10. Note that the structure of the mold 10 is not particularly limited, and in addition to a sectional type mold as shown in the figure, a two-split type mold can also be used.

[0023] The lower end of the bladder 20 is held between the lower bead ring 13 and the lower clamp ring 21, and the upper end of the bladder 20 is held between the upper clamp ring 22 and the auxiliary ring 23. In the vulcanized state shown in Fig. 1, the bladder 20 is in a state of expanding radially outward of the pneumatic tire T, but when the pneumatic tire T is removed from the mold 10 after vulcanization, the upper clamp ring 22 moves upward, and the bladder 20 is removed from the inside of the pneumatic tire T.

[0024] In the tire vulcanization apparatus described above, as shown in FIGS. 1 and 2 , the mold 10 has a molding surface 31 that molds the outer surface of the tire and vent holes 32 that open to the molding surface 31. One end of the vent holes 32 opens to the molding surface 31, while the other end communicates with the outside of the mold 10. While FIG. 1 depicts a structure in which the vent holes 32 are formed in the sectors 15 that constitute the mold 10, the vent holes 32 can also be formed in the lower side plate 11, the upper side plate 12, the lower bead ring 13, or the upper bead ring 14, and multiple vent holes 32 can be disposed throughout the mold 10. The mold 10 has a main body 10A and a vent piece 10B that encompasses at least a portion of the vent holes 32 and is separable from the main body 10A of the mold 10. The vent piece 10B is configured to be detachable from the main body 10A of the mold 10.

[0025] In the mold 10, as shown in Fig. 2, a damming member 33 is disposed within the vent hole 32, which allows air to pass through while blocking the rubber. More specifically, the damming member 33 extends along the axial direction of the vent hole 32 and is composed of multiple plates 34 stacked in a direction perpendicular to the axial direction of the vent hole 32. Fine gaps exist between the plates 34 due to their surface roughness, and these gaps serve as air passages. The distance Y from the molding surface 31 to the damming member 33 is set to a range of 6 mm to 18 mm.

[0026] When vulcanizing a pneumatic tire T using the above-mentioned tire vulcanizing apparatus, an unvulcanized pneumatic tire T is placed inside the mold 10, a bladder 20 is inserted inside the pneumatic tire T, and a heating and pressurizing medium is introduced into the bladder 20 while the mold 10 is heated from the outside, thereby vulcanizing the pneumatic tire T while pressurizing the pneumatic tire T toward the molding surface 31.

[0027] During this vulcanization process, air remaining between the molding surface 31 of the mold 10 and the unvulcanized pneumatic tire T is discharged to the outside of the mold 10 through the vent holes 32. Then, as shown in FIGS. 3(a) and 3(b), the unvulcanized rubber G that constitutes the pneumatic tire T enters the vent holes 32, and spews S are formed in the vent holes 32. When the vulcanized pneumatic tire T is removed from the mold 10, the spews S are pulled out through the vent holes 32. Then, the spews S are cut off as necessary.

[0028] Here, the mechanism by which clogging occurs in conventional vent holes will be explained in detail using Figure 7 and Figures 8(a) to 8(c). According to the findings of the present inventors, as shown in Figure 7, in a conventional vent hole 32, the pressure gradually decreases from the base of the spew S toward the tip, and the tip of the spew S is heated under conditions close to atmospheric pressure, causing significant foaming. This foaming is caused not only by the foaming agent contained in the rubber but also by moisture, etc. As a result, the density of the rubber at the tip of the spew S decreases, and the breaking strength also decreases, which makes it more susceptible to the accumulation of dirt and the spew S breaking.

[0029] If the vulcanization process is repeated under these conditions, as shown in Fig. 8(a), dirt accumulates near the tip of the spew S formed in the vent hole 32 of the mold 10, and deposit X gradually grows. Then, as shown in Fig. 8(b), unvulcanized rubber G enters the vent hole 32 during vulcanization and reaches a position beyond the deposit X. Then, as shown in Fig. 8(c), when the spew S is pulled out after vulcanization, the tip of the spew S, which has become integrated with the deposit X, breaks off and blocks the vent hole 32.

[0030] In contrast, the mold 10 described above is provided with a damming member 33 that allows air to pass through the vent holes 32 while blocking the rubber G. As shown in FIG. 3( a), when the rubber G flows into the vent holes 32 during vulcanization, the remaining air is expelled through the damming member 33. Then, as shown in FIG. 3( b), the rubber G is blocked in the vent holes 32, generating pressure at the tips of the spew S and suppressing foaming of the rubber G. Suppressing foaming of the rubber G at the tips of the spew S in this way prevents dirt from accumulating near the tips of the spew S formed in the vent holes 32 and preventing breakage of the tips of the spew S due to the deposits X. This effectively suppresses clogging of the vent holes 32 by the spew S. As a result, tire surface damage caused by residual air is prevented, and the frequency of cleaning the vent holes 32 is reduced, improving the productivity of pneumatic tires T.

[0031] Furthermore, with the above-described mold 10, the damming member 33 allows air to pass through, thereby ensuring sufficient discharge performance of residual air. Furthermore, since the damming member 33 is located sufficiently far from the molding surface 31, excessive pressure is not generated in the rubber G blocked by the damming member 33 during vulcanization, so the rubber G does not flow into the gaps in the damming member 33, reducing the frequency of replacement and cleaning.

[0032] Here, the distance Y from the molding surface 31 to the damming member 33 needs to be in the range of 6 mm to 18 mm. If the distance Y is less than 6 mm, excessive pressure is generated in the rubber G blocked by the damming member 33 during vulcanization, making it easier for the rubber G to flow into the gaps in the damming member 33. Conversely, if the distance Y is greater than 18 mm, the rubber G is less likely to come into contact with the damming member 33, making it impossible to suppress foaming of the rubber G. In particular, the distance Y from the molding surface 31 to the damming member 33 is preferably in the range of 10 mm to 14 mm. Furthermore, since the damming member 33 is intended to block the rubber G flowing into the vent hole 32 during vulcanization, it is positioned so that the rubber G flowing into the vent hole 32 during vulcanization will come into contact with the damming member 33. When determining the distance Y from the molding surface 31 to the damming member 33, the average length of the spew S formed with the damming member 33 removed is determined, and the damming member 33 is disposed at a position, for example, 70% to 90% of the average length of the spew S. The average length of the spew S may be determined through a preliminary vulcanization test, or may be estimated from the rubber properties (viscosity and vulcanization rate).

[0033] The above-described mold 10 includes the vent piece 10B that encompasses at least a portion of the vent hole 32 and is separable from the main body 10A of the mold 10, so that the damming member 33 can be easily disposed in the vent hole 32. That is, because the damming member 33 is disposed in a position on the far side of the vent hole 32, the damming member 33 can be inserted into the vent hole 32 while the vent piece 10B is in a standalone state, and the vent piece 10B equipped with the damming member 33 can be attached to the main body 10A. Alternatively, with the vent piece 10B removed, the damming member 33 may be inserted into the vent hole 32 in the main body 10A of the mold 10, and the vent piece 10B equipped with the damming member 33 may be attached to the main body 10A.

[0034] Fig. 4 shows a modified example of the vent hole portion of the tire vulcanizing mold according to the present invention. In Fig. 4, the damming member 33 is made of a porous material 35 having open cells 35A. In this case, the open cells 35A of the porous material 35 serve as air passages.

[0035] Figure 5 shows another modified example of the vent hole portion of the tire vulcanizing mold according to the present invention. In Figure 5, the blocking member 33 is composed of a member 36 having multiple vent holes 36A penetrating in the axial direction of the vent hole 32. In this case, the multiple vent holes 36A serve as air flow paths. To prevent the inflow of rubber G, the diameter of the vent holes 36A is preferably 0.1 mm or less.

[0036] FIG. 6 shows yet another modified example of the vent hole portion of the tire vulcanization mold according to the present invention. In FIG. 6, the damming member 33 is composed of a valve 37 inserted into the vent hole 32. The valve 37 is composed of an outer cylindrical body 37A fitted into the vent hole 32 and having a valve seat facing the molding surface 31, a valve element 37B inserted inside the outer cylindrical body 37A, and a spring member 37C (e.g., a coil spring) that biases the valve element 37B in a direction away from the valve seat of the outer cylindrical body 37A. The valve 37 is composed of a member 36 having multiple air holes 36A penetrating in the axial direction. The valve 37 closes when the rubber G comes into contact with it, but allows air to pass through until then. Even with this type of valve 37, it is possible to prevent the rubber G from entering the gaps in the valve 37 by positioning it sufficiently away from the molding surface 31.

[0037] In the above-described mold 10, it is preferable that a release treatment is applied to the damming member 33. This prevents the rubber G from adhering to the damming member 33 and effectively suppresses clogging of the vent hole 32. Examples of the release treatment include fluororesin processing and plating. [Example]

[0038] When vulcanizing pneumatic tires, tire vulcanization molds were used that differed only in the structure of the vent holes.

[0039] In the conventional example, a tire vulcanizing mold was used that had many vent holes opening onto the molding surface. In the comparative example, a tire vulcanizing mold was used that had many vent holes opening onto the molding surface, with a damming member disposed near the entrance of each vent hole that allowed air to pass while blocking the rubber. In examples 1 to 3, a tire vulcanizing mold was used that had many vent holes opening onto the molding surface, with a damming member (Figs. 2, 4, and 5) disposed on the far side of each vent hole that allowed air to pass while blocking the rubber. In the comparative example and examples 1 to 3, the distances from the molding surface to the damming members were set as shown in Table 1.

[0040] Using the tire curing mold described above, pneumatic tires were repeatedly cured, and the number of curing cycles required before cleaning work was required due to clogging of the vent holes or valves was investigated, and the results are shown in Table 1. The number of curing cycles is expressed as an index, with the conventional example being set at 100. A higher index value means less clogging of the vent holes and valves.

[0041] [Table 1]

[0042] As can be seen from Table 1, when the tire vulcanization molds of Examples 1 to 3 were used, clogging of the vent holes due to spews was effectively suppressed compared to the conventional example, and the number of vulcanizations before cleaning work was increased. On the other hand, when the tire vulcanization mold of the comparative example was used, rubber flowed into the gaps in the damming members, causing clogging of the damming members and necessitating cleaning work. [Explanation of symbols]

[0043] 10 Tire curing mold 10A main unit 10B Vent Piece 20 Bladder 31 Molding surface 32 Vent Hole 33 Damming member T Pneumatic tire S Spew

Claims

1. A tire vulcanizing mold is provided with a molding surface that molds the outer surface of a tire and vent holes that open to the molding surface, wherein a damming member that allows air to pass through the vent hole while damming up rubber is disposed within the vent hole, and the distance from the molding surface to the damming member is within a range of 10 mm to 14 mm.

2. 2. The tire vulcanization mold according to claim 1, further comprising a vent piece that includes at least a portion of the vent hole and is separable from the main body of the mold.

3. 3. The tire vulcanization mold according to claim 1, wherein the blocking member is made up of a plurality of plates stacked in a direction perpendicular to the axial direction of the vent hole.

4. 3. The tire vulcanizing mold according to claim 1, wherein the damming member is made of a porous material having open cells.

5. 3. The tire vulcanizing mold according to claim 1, wherein the blocking member is formed of a member having a plurality of vent holes passing through in the axial direction of the vent hole.

6. 6. The tire vulcanizing mold according to claim 1, wherein the damming member is subjected to a release treatment.

7. A method for manufacturing a tire, comprising: placing an unvulcanized tire inside the tire vulcanization mold according to any one of claims 1 to 6; and vulcanizing the tire while pressing the tire against the molding surface.

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