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 release layer 33 made of a material having a rubber release property is locally arranged in a region away from the molding surface 31 of the vent hole 32. 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] To resolve the above-mentioned problems, it has been proposed to perform a surface treatment on the entire inner surface of the vent hole to reduce surface friction (see, for example, Patent Document 1). However, when the entire inner surface of the vent hole is surface treated, the reduction in frictional resistance causes the spew formed in the vent hole to become relatively long, which increases the resistance when the spew is pulled out, and the spew may break off at its base and remain inside the vent hose. Therefore, this method is not necessarily effective enough in preventing clogging of the vent hole.

[0005] It has also been proposed to form a release film inside the vent hole by applying a release agent to the surface of an unvulcanized tire before vulcanization (see, for example, Patent Document 2). However, even in this case, the spew formed inside the vent hole becomes relatively long, which increases the resistance when pulled out, and the spew may break off at its base and remain inside the vent hose. Therefore, this method is not necessarily effective enough in preventing clogging of the vent hole. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6317599 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-105360 Summary of the Invention [Problem to be solved by the invention]

[0007] 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]

[0008] In order to achieve the above object, the tire vulcanizing mold of the present invention is a tire vulcanizing mold having a molding surface for molding the outer surface of a tire and vent holes opening to the molding surface, a vent piece that includes at least a portion of the vent hole and is separable from the body of the mold; A release layer made of a material having releasability to rubber is locally disposed in an area of ​​the vent hole away from the molding surface. The release layer is a cylindrical body incorporated in the vent hole, the vent piece has a housing portion that houses the cylindrical body, and the cylindrical body is inserted into the housing portion. It is characterized by the following.

[0009] 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]

[0010] As a result of extensive research into tire vulcanizing molds equipped with vent holes, the inventors recognized the phenomenon that when vulcanization is repeatedly performed using such tire vulcanizing molds, dirt gradually accumulates near the tip of the spew formed in the vent hole, causing the tip of the spew to break due to this deposit. They discovered that clogging of the vent hole can be effectively prevented by suppressing the growth of such deposits, and arrived at the present invention.

[0011] Specifically, in a tire vulcanization mold having a molding surface for molding the tire outer surface and vent holes opening onto the molding surface, a release layer made of a material with releasability for rubber is locally disposed in an area of ​​the vent hole away from the molding surface. This prevents dirt from accumulating near the tip of the spew formed in the vent hole and prevents breakage of the tip of the spew due to such deposits. Furthermore, because the release layer is locally disposed in an area of ​​the vent hole away from the molding surface, the length of the spew is not excessively increased, preventing breakage of the spew from its base due to increased resistance during extraction. This effectively prevents clogging of the vent hole due to the spew. As a result, tire surface damage caused by residual air is prevented, and tire productivity is improved by reducing the frequency of cleaning the vent hole.

[0012] In the present invention, the release layer is preferably disposed in an area that is 50% to 150% of the average length of the spew formed in the vent hole from the molding surface. Alternatively, the release layer is preferably disposed in an area that is 8 mm to 24 mm from the molding surface along the axial direction of the vent hole. By disposing the release layer in an area that is appropriately spaced from the molding surface of the vent hole in this way, clogging of the vent hole by the spew can be effectively suppressed.

[0013] 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, a release layer can be easily formed on the vent hole.

[0015] release layer The release layer may be a cylindrical body embedded in the vent hole. More specifically, the cylindrical body is preferably made primarily of a fluororesin or silicone resin. A release layer made of such a cylindrical body can effectively prevent clogging of the vent hole due to spew.

[0016] Furthermore, it is preferable that the cross-sectional area of ​​the hole formed by the release layer is smaller than the cross-sectional area of ​​the portion of the vent hole on the molding surface side of the release layer. By reducing the cross-sectional area of ​​the hole formed by the release layer in this way, the spew formed in the vent hole can be shortened, and clogging of the vent hole can be more effectively suppressed. [Brief explanation of the drawings]

[0017] [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] FIG. 2 is a cross-sectional view showing a vent hole portion of a tire vulcanizing mold according to the present invention together with a spew formed in the vent hole. [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 (reference example) of the vent hole portion of the tire vulcanizing mold according to the present invention. [Figure 6] 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

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] In the mold 10, as shown in Fig. 2, in an area of ​​the vent hole 32 away from the molding surface 31, a release layer 33 made of a material that has releasability against rubber is locally disposed along the inner circumferential surface of the vent hole 32. The material that makes up the release layer 33 can be one that has lower friction resistance against rubber than the material that makes up the mold 10. In Fig. 2, the release layer 33 is a cylindrical body 34 incorporated into the vent hole 32. The cylindrical body 34 is made primarily of, for example, a fluororesin or a silicone resin.

[0024] 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.

[0025] 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 FIG. 3, the unvulcanized rubber 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.

[0026] According to the above-described mold 10, the release layer 33 made of a material that has releasability for rubber is locally disposed in an area of ​​the vent hole 32 away from the molding surface 31. This prevents dirt from accumulating near the tip of the spew S formed in the vent hole 32 and prevents breakage of the tip of the spew S due to such deposits. Furthermore, because the release layer 33 is locally disposed in an area of ​​the vent hole 32 away from the molding surface 31, the length of the spew S is not excessively increased, and breakage of the spew S from its base due to increased resistance during extraction is suppressed. This effectively suppresses clogging of the vent hole 32 by the spew S. As a result, tire surface damage caused by residual air is prevented, and the productivity of the pneumatic tire T can be improved by reducing the frequency of cleaning the vent hole 32.

[0027] Here, the mechanism by which clogging occurs in conventional vent holes will be described in detail using Figures 6(a) to 6(c). First, as shown in Figure 6(a), when the vulcanization process is repeated, dirt accumulates near the tip of the spew S formed in the vent hole 32 of the mold 10, and deposit X gradually grows. Next, as shown in Figure 6(b), unvulcanized rubber G enters the vent hole 32 during vulcanization and reaches a position beyond the deposit X. Then, as shown in Figure 6(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.

[0028] In the present invention, by locally disposing the release layer 33 in an area of ​​the vent hole 32 away from the molding surface 31, it is possible to prevent dirt from accumulating near the tip of the spew S formed in the vent hole 32, thereby effectively suppressing clogging of the vent hole 32.

[0029] 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 release layer 33 can be easily formed on the vent hole 32. That is, since the release layer 33 is disposed at a location on the back side of the vent hole 32, the release layer 33 can be formed on the vent hole 32 while the vent piece 10B is in a standalone state, and the vent piece 10B with the release layer 33 can be attached to the main body 10A. Alternatively, with the vent piece 10B removed, the release layer 33 can be formed on the vent hole 32 in the main body 10A of the mold 10, and the vent piece 10B can be attached to the main body 10A with the release layer 33.

[0030] In the mold 10, the release layer 33 is preferably disposed in an area that is 50% to 150% of the average length L of the spew S formed within the vent hole 32 from the molding surface 31. More preferably, one end of the release layer 33 is disposed at a position that is 50% to 70% of the average length L of the spew S from the molding surface 31, and the other end of the release layer 33 is disposed at a position that is 130% to 150% of the average length L of the spew S from the molding surface 31. The average length L of the spew S may be determined through a preliminary vulcanization test, or may be estimated from rubber properties (viscosity and vulcanization rate). For example, the release layer 33 is preferably disposed in an area that is 8 mm to 24 mm from the molding surface 31 along the axial direction of the vent hole 32. More preferably, one end of the release layer 33 is positioned 8 mm to 12 mm from the molding surface 31 along the axial direction of the vent hole 32, and the other end of the release layer 33 is positioned 20 mm to 24 mm from the molding surface 31 along the axial direction of the vent hole 32.

[0031] In this way, by arranging the release layer 33 in an area of ​​the vent hole 32 that is a suitable distance from the molding surface 31, clogging of the vent hole 32 by the spew S can be effectively suppressed. If the release layer 33 is too close to the molding surface 31, the length of the spew S increases, making the spew S more likely to break at its base. Conversely, arranging the release layer 33 too far from the molding surface is futile as no further effect can be expected.

[0032] Figure 4 shows a modified example of the vent hole portion of the tire vulcanization mold according to the present invention. In Figure 4, the cross-sectional area of ​​the hole formed by the release layer 33 is smaller than the cross-sectional area of ​​the portion of the vent hole 32 on the molding surface 31 side of the release layer 33. By making the cross-sectional area of ​​the hole formed by the release layer 33 relatively smaller in this way, the spew S formed in the vent hole 32 can be shortened, thereby more effectively suppressing clogging of the vent hole 32.

[0033] Fig. 5 shows another modified example of the vent hole portion of the tire vulcanizing mold according to the present invention. In Fig. 5, a release layer 33 is formed by surface treatment of the vent hole 32. For example, the surface treatment is a fluororesin treatment or a plating treatment. The release layer 33 formed by such surface treatment can effectively prevent clogging of the vent hole 32 by the spew S. [Example]

[0034] When vulcanizing pneumatic tires, tire vulcanization molds were used that differed only in the structure of the vent holes.

[0035] In the conventional example, a tire vulcanizing mold was used that had a large number of vent holes opening onto the molding surface. In the comparative example, a tire vulcanizing mold was used that had a large number of vent holes opening onto the molding surface, with a release layer disposed over the entire area of ​​each vent hole. In Examples 1 to 3, a tire vulcanizing mold was used that had a large number of vent holes opening onto the molding surface, with a release layer (FIGS. 2, 4, and 5) locally disposed in an area of ​​each vent hole away from the molding surface. In Examples 1 to 3, the release layer was disposed in an area 8 mm to 24 mm from the molding surface along the axial direction of the vent hole. In this specification, Example 3 is a reference example.

[0036] Pneumatic tires were repeatedly vulcanized using the tire vulcanization mold described above, and the average length of the spews formed in the resulting pneumatic tires was determined. The occurrence of clogging of the vent holes was also investigated, and the results are shown in Table 1.

[0037] The occurrence of clogging of the vent holes was determined by the number of vulcanizations required until clogging due to breakage at the tip of the spew or clogging due to breakage at the base of the spew occurred. The evaluation results were indicated by an "X" if clogging occurred after 1,000 or fewer vulcanizations, a "△" if clogging occurred after 2,000 or fewer vulcanizations, and an "O" if no clogging occurred even after more than 2,000 vulcanizations.

[0038] [Table 1]

[0039] As can be seen from Table 1, when the tire vulcanizing molds of Examples 1 to 3 were used, clogging of vent holes due to spews was effectively suppressed compared to the conventional example. On the other hand, when the tire vulcanizing mold of the comparative example was used, clogging of vent holes due to breakage of the tip of the spew was suppressed, but as a result of the average length of the spews increasing, clogging of vent holes due to breakage of the base of the spew increased. [Explanation of symbols]

[0040] 10 Tire curing mold 10A main unit 10B Vent Piece 20 Bladder 31 Molding surface 32 Vent Hole 33 Release layer 34 Cylindrical body T Pneumatic tire S Spew

Claims

1. A tire vulcanizing mold having a molding surface that molds the outer surface of a tire and vent holes that open to the molding surface, characterized in that the tire vulcanizing mold is further provided with a vent piece that encompasses at least a portion of the vent hole and is separable from the main body of the mold, and a release layer made of a material that has releasability to rubber is locally disposed in an area of ​​the vent hole away from the molding surface, the release layer being a cylindrical body incorporated in the vent hole, the vent piece having a storage section that stores the cylindrical body, and the cylindrical body being inserted into the storage section.

2. 2. The tire vulcanization mold according to claim 1, wherein the release layer is disposed in an area from the molding surface to 50% to 150% of the average length of the spew formed within the vent hole.

3. 2. The tire vulcanization mold according to claim 1, wherein the release layer is disposed in an area of ​​8 mm to 24 mm from the molding surface along the axial direction of the vent hole.

4. 4. The tire vulcanizing mold according to claim 1, wherein the cylindrical body is made of a fluororesin or a silicone resin as a main raw material.

5. The tire vulcanization mold according to any one of claims 1 to 4, characterized in that the cross-sectional area of ​​the hole formed by the release layer is smaller than the cross-sectional area of ​​the portion of the vent hole that is closer to the molding surface than the release layer.

6. A method for manufacturing a tire, comprising: placing an unvulcanized tire inside the tire vulcanization mold according to any one of claims 1 to 5; and vulcanizing the tire while pressing the tire against the molding surface.

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