Vulcanizing mold and manufacturing method for solid tire

Abstract

To provide a vulcanizing mold and manufacturing method for a solid tire that can reduce defects in an appearance of the solid tire.SOLUTION: A vulcanizing mold for a solid tire of the present invention is the vulcanizing mold that has a molding surface S that molds an outer surface of the solid tire 10 and protrusions 111 arranged on the molding surface S so as to mold grooves in a tread part T of the solid tire 10, and has a plurality of slit parts 141 formed to cross the protrusions 111.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a mold for vulcanizing solid tires, such as pneumatic cushion tires for industrial vehicles, as defined in Chapter F of the Japan Automobile Tire Manufacturers Association (JATMA) Yearbook, and a method for manufacturing solid tires. More specifically, the present invention relates to a mold for vulcanizing solid tires and a method for manufacturing solid tires, which make it possible to reduce defects in the appearance of solid tires. [Background technology]

[0002] Pneumatic cushion tires for industrial vehicles are solid tires for forklifts that have a similar appearance to pneumatic tires. These solid tires are used under low-speed, high-load conditions, and in some cases, under severe conditions such as steering while stationary.

[0003] A solid tire generally has a tread rubber layer on the tread side and a base rubber layer on the rim side, with the base rubber layer being made of a hard rubber composition, and the tread rubber layer being made of a rubber composition that prioritizes grip, abrasion resistance, chipping resistance, heat generation, and rolling resistance. The tread portion is provided with various tread patterns depending on the application. For example, there are rib patterns, lug patterns, rib-lug patterns, and various block patterns.

[0004] When manufacturing a solid tire as described above, an unvulcanized solid tire (green tire) is molded, placed in a mold, and vulcanized in the mold (see, for example, Patent Documents 1 to 3). When vulcanizing a solid tire in a mold, it is necessary for the volume of the green tire to be equal to or larger than the volume of the mold in order to maintain pressure within the mold, but ultimately, weight adjustment is achieved by excess rubber squeezing out from vent holes and the like as vulcanization progresses.

[0005] However, due to the fluidity of the rubber composition constituting the tread rubber layer, for example, the rubber composition may not sufficiently reach the corners of the blocks defined in the tread portion, resulting in air remaining in the mold and creating air marks (depressions) on the outer surface of the tire. This type of appearance defect is called a "bare." This type of appearance defect tends to occur frequently, particularly in block patterns with complex shapes. In addition, although vent holes are provided as a means for venting the mold, the current situation is that such vent holes alone are not sufficient to sufficiently reduce the above-mentioned appearance defect. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 5-200753 [Patent Document 2] Japanese Patent Application Publication No. 7-132516 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-62234 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a vulcanizing mold and a manufacturing method for a solid tire that can reduce defects in the appearance of the solid tire. [Means for solving the problem]

[0008] In order to achieve the above object, the vulcanizing mold for a solid tire of the present invention is characterized in that the vulcanizing mold has a molding surface that molds the outer surface of the solid tire and protrusions arranged on the molding surface so as to mold grooves in the tread portion of the solid tire, and has a plurality of slits formed so as to cross the protrusions.

[0009] In addition, the method for manufacturing a solid tire of the present invention is a method for manufacturing a solid tire using the above-mentioned vulcanization mold, and is characterized in that an unvulcanized solid tire is molded, the solid tire is placed in the vulcanization mold, and the solid tire is vulcanized in the vulcanization mold. [Effects of the Invention]

[0010] In the present invention, in a vulcanizing mold having a molding surface that molds the outer surface of a solid tire and ridges that are arranged on the molding surface so as to mold grooves in the tread portion of the solid tire, by providing a plurality of slits that are formed so as to cross the ridges, the movement of air and rubber is permitted on both sides of the ridges, thereby promoting the flow of the rubber composition that makes up the tread rubber layer, suppressing air from remaining inside the vulcanizing mold, and reducing poor appearance of the solid tire.

[0011] In the present invention, the slit portions are preferably arranged at 30 to 60 locations on the molding surface. By optimizing the number of slit portions, it is possible to effectively reduce defects in the appearance of the solid tire.

[0012] In the present invention, when the protrusions are arranged so as to divide the tread portion into a plurality of blocks, the slits are preferably arranged adjacent to the corners and / or flat portions of the blocks. Since the protrusions surrounding the blocks form closed spaces, the blocks are prone to have poor appearance, but by arranging the slits adjacent to the corners and / or flat portions of the blocks, it is possible to effectively reduce the occurrence of poor appearance in the blocks.

[0013] In the present invention, the depth of the slits is preferably 50% or more of the height of the ridges. The width of the slits is preferably in the range of 0.5 mm to 5.0 mm. By optimizing the depth or width of the slits, it is possible to effectively reduce defects in the appearance of the solid tire.

[0014] In the present invention, the length of the slit portion is preferably 40.0 mm or less. If the slit portion is too long, the rubber composition that flows into the slit portion during vulcanization is likely to remain when the mold is demolded, requiring the removal of residual rubber pieces. However, by optimizing the length of the slit portion, the removal of residual rubber pieces can be reduced.

[0015] In the present invention, the angle that the slit portion forms with respect to the width direction of the protrusion is preferably 45° or less. If the angle of the slit portion is too large, the flow resistance of the rubber composition flowing inside the slit portion increases, but by optimizing the angle, it is possible to effectively reduce defects in the appearance of the solid tire.

[0016] In the present invention, the slits are preferably provided on the ridges extending in the tire circumferential direction. When the mold is closed in the vulcanization process, the rubber composition constituting the tread rubber layer tends to flow in the tire width direction, and the ridges extending in the tire circumferential direction are a major factor in hindering the flow of the rubber composition. Therefore, by providing the slits on the ridges extending in the tire circumferential direction, it is possible to effectively reduce poor appearance of the solid tire.

[0017] According to the method for manufacturing a solid tire of the present invention, an unvulcanized solid tire is molded, the solid tire is placed in the vulcanization mold described above, and the solid tire is vulcanized in the vulcanization mold, thereby reducing defects in the appearance of the solid tire as described above.

[0018] In the present invention, the inner diameter of the solid tire is preferably 8 inches or more. In a solid tire with a small inner diameter, the amount of movement of the rubber composition during vulcanization is small, so that poor appearance hardly occurs, but in a solid tire with a large inner diameter, poor appearance is likely to occur, so that the provision of slit portions has a significant effect.

[0019] In the present invention, the rubber composition constituting the tread rubber layer of the solid tire preferably contains, as a polymer, styrene-butadiene rubber and / or butadiene rubber in addition to natural rubber, and carbon black and / or silica as a reinforcing material. A rubber composition containing only natural rubber as a polymer has poor fluidity, but the addition of styrene-butadiene rubber and / or butadiene rubber can improve the fluidity. Furthermore, adding carbon black and / or silica as a reinforcing material also contributes to improving the fluidity of the rubber composition. Therefore, the above combination can effectively reduce poor appearance of the solid tire.

[0020] In particular, the rubber composition constituting the tread rubber layer of a solid tire preferably contains, as a polymer, styrene-butadiene rubber and / or butadiene rubber in addition to natural rubber, with the blending amount of natural rubber in the polymer being 30 to 70 wt %, and further preferably contains, as a reinforcing material, 30 to 70 phr of carbon black having a DBP absorption of 85 to 160 ml / 100 g in the HAF class. This effectively reduces poor appearance of the solid tire. Furthermore, the above blending can exhibit suitable physical properties as a tread rubber layer of a solid tire.

[0021] In the present invention, the rubber composition constituting the tread rubber layer of a solid tire preferably contains, as a polymer, styrene-butadiene rubber and / or butadiene rubber in addition to natural rubber, with the blending amount of natural rubber in the polymer being 30 to 70% by weight, and further preferably contains, as a reinforcing material, 35 to 55 phr of silica having a VN3 class particle size of 28 to 37 nm and a DBP absorption of 150 to 210 ml / 100 g, and 6 to 13% by weight of a silane coupling agent. This effectively reduces poor appearance of the solid tire. Furthermore, the above blending can exhibit physical properties suitable for the tread rubber layer of a solid tire. [Brief explanation of the drawings]

[0022] [Figure 1]1 is a meridian cross-sectional view showing an example of a solid tire obtained by the present invention. [Figure 2] FIG. 2 is a development view showing a tread portion of the solid tire of FIG. 1. [Figure 3] 1 is a meridian cross-sectional view showing a vulcanization mold for a solid tire according to an embodiment of the present invention. [Figure 4] FIG. 4 is a development view showing the tread molding surface of the vulcanization mold of FIG. 3. [Figure 5] FIG. 5 is an enlarged plan view showing a main part of FIG. 4. [Figure 6] FIG. 6 is a cross-sectional view taken along the line VI-VI in FIG. 5. [Figure 7] FIG. 10 is a meridian cross-sectional view showing a modified example of a vulcanizing mold for a solid tire according to the present invention. [Figure 8] FIG. 10 is a development view showing a modified example of the tread molding surface of the vulcanization mold for the solid tire according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] The configuration of the present invention will be described in detail below with reference to the accompanying drawings, in which Figures 1 and 2 show an example of a solid tire (pneumatic cushion tire for industrial vehicles) obtained by the present invention.

[0024] 1, the solid tire 10 has a toroidal shape and includes a tread rubber layer 1 located on the tread side (the outer side in the tire radial direction) and a base rubber layer 2 located on the rim side (the inner side in the tire radial direction). The solid tire 10 includes at least the tread rubber layer 1 and the base rubber layer 2, but may also include an intermediate rubber layer between the tread rubber layer 1 and the base rubber layer 2.

[0025] The tread rubber layer 1 is composed of a rubber composition primarily composed of a diene rubber such as natural rubber, styrene-butadiene rubber, or butadiene rubber. Carbon black or silica may be added as a reinforcing agent to the rubber composition that constitutes the tread rubber layer 1. In the case of silica, an organic silane coupling agent may also be added. An example of an organic silane coupling agent is bis(triethoxy-silylpropyl)tetrasulfide (TESPT). The rubber composition that constitutes the tread rubber layer 1 may also contain other commonly used compounding agents, antioxidants, tackifiers, resins, oils, plasticizers, waxes, polymer homogenizers, and the like.

[0026] The JIS-A hardness of the tread rubber layer 1 is set, for example, in the range of 50 to 75. When the JIS-A hardness of the tread rubber layer 1 is within the above range, for example, with a pattern such as that shown in Figure 2, starting acceleration, braking, and cornering performance on icy and snowy road surfaces can be improved. Here, if the JIS-A hardness of the tread rubber layer 1 is less than 50, the block rigidity of the tread portion T decreases, causing greater deformation of the tread portion T and reducing the edge effect on icy and snowy roads. This is also undesirable because the vertical rigidity and lateral rigidity of the solid tire 10 decrease, making the solid tire 10 prone to excessive flex. Conversely, if the JIS-A hardness of the tread rubber layer exceeds 75, the tread portion T becomes excessively hard, reducing the adhesive friction force on icy and snowy roads. Furthermore, the vertical rigidity and lateral rigidity of the solid tire 10 become excessively large, resulting in a deterioration in ride comfort. The JIS-A hardness is a durometer hardness measured in accordance with JIS-K6253-3 using an A-type durometer at a temperature of 23°C. The JIS-A hardness of the tread rubber layer 1 described above is merely an example and is not limited thereto.

[0027] The base rubber layer 2 is composed of a rubber composition primarily composed of diene rubbers such as natural rubber, styrene-butadiene rubber, and butadiene rubber. High-styrene SBR may also be used to increase hardness. The rubber composition constituting the base rubber layer 2 may contain carbon black as a reinforcing agent, as well as phenolic resin, oil-modified phenolic resin, etc., and may also contain hexamethylenetetramine or the like as a curing agent for the phenolic resin. The rubber composition constituting the base rubber layer 2 may also contain other commonly used compounding agents, resins, oils, plasticizers, fibers, etc.

[0028] The base rubber layer 2 may have a JIS-A hardness of, for example, 80 or more, and a modulus at 10% elongation of, for example, 1.0 MPa or more. This can suppress wear of the base rubber layer 2 due to rim slippage. This is because making the base rubber layer 2 harder reduces the vertical, lateral, and circumferential movement of the base rubber layer 2 within the rim during running, making it less likely to rub against the rim flange. If the JIS-A hardness of the base rubber layer 2 is below 80, or the modulus at 10% elongation is below 1.0 MPa, the effect of suppressing wear of the base rubber layer 2 decreases. The modulus at 10% elongation is the tensile stress at a predetermined elongation measured at a temperature of 23°C using a dumbbell-shaped No. 1 test piece in accordance with JIS-K6251. The JIS-A hardness and modulus at 10% elongation of the tread rubber layer 1 described above are merely examples and are not limited thereto.

[0029] Two or more bead cores 3 are disposed within the base rubber layer 2, arranged in a continuous ring shape along the tire circumferential direction. Typically, these bead cores 3 are arranged symmetrically with respect to the tire equatorial plane. The bead cores 3 may be formed by winding multiple bead wires around the tire (so-called strand bead wires), by winding a single bead wire around the tire, or by a single steel ring. To ensure adhesion to the base rubber layer 2, when a bead wire is used, its surface is generally plated with zinc or brass (tin and copper). When a steel ring is used, its surface is generally coated with various vulcanization adhesives. Instead of providing the bead cores 3, short fibers may be blended into the rubber composition constituting the base rubber layer 2. If necessary, short fibers may be blended into the rubber composition constituting the base rubber layer 2 simultaneously with the formation of the bead cores 3. As such short fibers, organic fibers such as nylon, polyester, rayon, aramid, vinylon, and cellulose nanofibers, and short fibers made of carbon nanotubes can be used.

[0030] 2, two circumferential grooves 11 extending in the tire circumferential direction are formed in the tread portion T of the solid tire 10. These circumferential grooves 11 define the tread portion T into a center block row 20 located on the tire equator position CL and side block rows 30 located on both sides of the center block row 20.

[0031] The center block row 20 is composed of a plurality of center blocks 21 arranged along the tire circumferential direction. The center block row 20 has a plurality of center lug grooves 22 extending in the tire axial direction and dividing the center blocks 21, and a plurality of center lug grooves 23 extending in the tire axial direction within each center block 21 and having a non-penetrating structure.

[0032] Each side block row 30 is made up of a plurality of side blocks 31 arranged along the tire circumferential direction. Each side block row 30 has a plurality of side lug grooves 32 extending in the tire axial direction to define the side blocks 31, and a plurality of side lug grooves 33 extending in the tire axial direction within each side block 31 and having a non-penetrating structure.

[0033] Fig. 3 shows a vulcanizing mold for a solid tire according to an embodiment of the present invention, and Figs. 4 to 6 show its main parts. As shown in Fig. 3, the vulcanizing mold of this embodiment is composed of a lower mold 101 that molds one side surface of the solid tire 10, an upper mold 102 that molds the other side surface of the solid tire 10, and a plurality of segments 103 that are arranged in an annular shape so as to mold the tread portion T of the solid tire 10. The segments 103 are disposed on the lower mold 101. The inner surfaces of the lower mold 101, upper mold 102, and segments 103 form a molding surface S that molds the outer surface of the solid tire 10. In addition, vent holes 104 are provided on the surface of the upper mold 102 that comes into contact with the segments 103.

[0034] As shown in FIG. 4 , ribs 111, 122, 123, 132, and 133 for forming grooves in the tread portion T of a solid tire 10 are formed on the molding surface S of the vulcanization mold. That is, the rib 111 extends in the tire circumferential direction to form the circumferential groove 11. The ribs 122 and 123 extend in the tire width direction to form the center lug grooves 22 and 23, respectively. The area defined by a pair of ribs 111 and a pair of ribs 122 adjacent to each other in the tire circumferential direction is a center block molding space 121 for molding the center block 21. The ribs 132 and 133 extend in the tire width direction to form the side lug grooves 32 and 33, respectively. The area surrounded by each rib 111 and a pair of ribs 132 adjacent to each other in the tire circumferential direction is a side block molding space 131 for molding the side blocks 31.

[0035] In the above-described vulcanization mold, the ridges 111 are formed with a plurality of slits 141 that cross the ridges 111. That is, the slits 141 connect the center block molding space 121 and the side block molding space 131. In FIG. 4, the slits 141 are disposed only in the region above the tire equator position CL, but the slits 141 may also be provided in the region below the tire equator position CL. Similar slits 141 may also be provided in the ridges 122, 132, 133, etc., so as to be oriented substantially in the tire circumferential direction.

[0036] When manufacturing a solid tire 10 using such a vulcanization mold, as shown in FIG. 3, a rubber sheet is wound so as to be layered in the tire radial direction to form an unvulcanized solid tire 10x, and then the solid tire 10x is placed in a vulcanization mold, where the solid tire 10x is vulcanized. When vulcanizing the solid tire 10 in the vulcanization mold, the volume of the unvulcanized solid tire 10x must be equal to or greater than the volume of the mold in order to maintain pressure within the mold. As the vulcanization progresses, excess rubber composition squeezes out from vent holes 104, mold parting surfaces, and the like, thereby adjusting the weight. However, due to the viscosity, fluidity, and adhesiveness of the rubber composition, scorch time, green tire shape, press pressure, and other factors, the rubber may not be completely filled in the corners of the cavity, resulting in bare holes (depressions).

[0037] As described above, in a vulcanization mold having a molding surface S that molds the outer surface of the solid tire 10 and protrusions 111 and the like arranged on the molding surface S so as to mold grooves in the tread portion T of the solid tire 10, by providing a plurality of slit portions 141 formed so as to cross the protrusions 111 and the like, the movement of air and the rubber composition is permitted on both sides of the protrusions 111 and the like, thereby promoting the flow of the rubber composition that constitutes the tread rubber layer 1, suppressing air from remaining inside the vulcanization mold, and reducing poor appearance of the solid tire 10.

[0038] However, if excessive vent holes 104 are provided in an attempt to reduce poor appearance, the internal pressure will decrease, which will in turn cause poor appearance. Furthermore, the position of the vent holes 104 needs to be changed depending on the tire size, making this an incomplete solution. Furthermore, if any rubber composition remains in the vent holes 104, it must be cleaned after each vulcanization. Unlike pneumatic tires, the internal pressure during vulcanization is significantly higher in a vulcanization mold for vulcanizing a solid tire 10, and the mold is very thick. Therefore, the vent holes 104 do not penetrate the mold. Therefore, if the rubber composition clogs the vent holes 104, cleaning them is time-consuming. In contrast, if slits 141 are provided in the protrusions 111, etc., the inconveniences associated with providing vent holes 104 are eliminated. In other words, there is no need to provide extra vent holes 104, and extra cleaning is also unnecessary. Also, the work of cutting out the plate-shaped rubber pieces 41 (see FIG. 2) formed by the slit portions 141 from the solid tire 10 after vulcanization can be reduced. The rubber pieces 41 formed by the slit portions 141 will wear out early in the tire's running even if they are not cut out from the solid tire 10, and will not affect tire performance. Moreover, the work of forming the slit portions 141 in the protrusions 111 and the like can be easily performed using a sander or the like.

[0039] In the vulcanization mold, it is preferable that the slit portions 141 are arranged in 30 to 60 locations on the molding surface S. By optimizing the number of slit portions 141 arranged, it is possible to effectively reduce defects in appearance of the solid tire 10. If the number of slit portions 141 arranged is less than 30, the occurrence of defects in appearance increases. On the other hand, if the number of slit portions 141 arranged exceeds 60, the effect saturates, and not only does the number of slit portions 141 increase unnecessarily, but many plate-shaped rubber pieces 41 made of the rubber composition that flowed into the slit portions 141 remain, which is undesirable in terms of appearance. In particular, it is preferable that the slit portions 141 are arranged in 40 to 50 locations on the molding surface S.

[0040] In the above-described vulcanization mold, when the protrusions 111 and the like are arranged so as to divide the tread portion T into a plurality of blocks 21, 31, the slits 141 are preferably arranged in positions adjacent to the corners and / or flat portions of the blocks 21, 31. That is, the slits 141 are preferably arranged in positions adjacent to the corners and / or flat portions of the center block molding space 121 or the side block molding space 131. The protrusions 111 and the like surrounding the blocks 21, 31 form a closed space, which makes the blocks 21, 31 prone to having poor appearance. However, by arranging the slits 141 in positions adjacent to the corners and / or flat portions of the blocks 21, 31, the occurrence of poor appearance in the blocks 21, 31 can be effectively reduced. In particular, it is desirable that the slits 141 be arranged in positions adjacent to the corners of the blocks 21, 31.

[0041] In the vulcanization mold, as shown in Fig. 6, the depth D of the slit portion 141 is preferably 50% or more of the height H of the ridges 111 and the like from the molding surface S. By optimizing the depth D of the slit portion 141, it is possible to effectively reduce defects in the appearance of the solid tire 10. Here, if the depth D of the slit portion 141 is less than 50%, the amount of movement of the rubber composition decreases, making it difficult to fill every corner of the cavity with the rubber composition.

[0042] In the vulcanization mold, as shown in FIG. 6, the width W of the slit portion 141 is preferably in the range of 0.5 mm to 5.0 mm. By optimizing the width W of the slit portion 141, it is possible to effectively reduce the appearance defects of the solid tire 10. Here, if the width W of the slit portion 141 is less than 0.5 mm, the amount of movement of the rubber composition is reduced, thereby reducing the effect of reducing the appearance defects. Furthermore, if the width W of the slit portion 141 is less than 0.5 mm, rubber pieces are likely to remain in the slit portion 141 during demolding, which requires removal of the remaining rubber pieces, which is undesirable. On the other hand, if the width W of the slit portion 141 exceeds 5.0 mm, the effect of promoting the flow of the rubber composition is not further enhanced, and instead, the appearance is deteriorated due to the rubber pieces 41 formed in the slit portion 141. In particular, it is desirable that the width W of the slit portion 141 be in the range of 0.7 mm to 2.5 mm.

[0043] In the vulcanization mold, the length L of the slit portion 141 is preferably 40.0 mm or less, as shown in Fig. 5. If the length L of the slit portion 141 exceeds 40.0 mm, the rubber composition that flows into the slit portion 141 during vulcanization is likely to remain when the mold is demolded, requiring the removal of the remaining rubber pieces. However, by optimizing the length L of the slit portion 141, the removal of the remaining rubber pieces can be reduced. Furthermore, if the length L of the slit portion 141 is too large, the flow resistance of the rubber composition increases, reducing the effect of reducing appearance defects.

[0044] In the vulcanization mold, as shown in Fig. 5, it is preferable that the angle θ that the slit portions 141 form with respect to the width direction of the ridges 111, etc., is 45° or less. If the angle θ of the slit portions 141 exceeds 45°, the flow resistance of the rubber composition flowing inside the slit portions 141 increases, but by optimizing this angle, it is possible to effectively reduce defects in the appearance of the solid tire. Furthermore, if the angle θ of the slit portions 141 exceeds 45°, the remaining rubber pieces inside the slit portions 141 are likely to tear off when the tire is demolded, making it necessary to remove the remaining rubber pieces remaining in the mold, which is undesirable.

[0045] In the vulcanization mold, the slit portions 141 are preferably arranged on the protrusions 111 extending in the tire circumferential direction. When the mold is closed in the vulcanization process, the rubber composition that constitutes the tread rubber layer 1 tends to flow in the tire width direction (see the arrow in FIG. 3 ). That is, the rubber composition that constitutes the tread rubber layer 1 tends to flow in the direction from the lower mold 101 along the segments 103 toward the upper mold 102. Therefore, the protrusions 111 extending in the tire circumferential direction are a major factor in hindering the flow of the rubber composition. In contrast, by arranging the slit portions 141 on the protrusions 111 extending in the tire circumferential direction, the flow of the rubber composition that constitutes the tread rubber layer 1 is smoothed, and poor appearance of the solid tire 10 can be effectively reduced.

[0046] When manufacturing a solid tire 10 having a complex tread pattern as shown in FIG. 2, a sectional type vulcanization mold equipped with segments 103 for molding the tread portion T is usually used. However, when manufacturing a solid tire 10 having a simple tread pattern such as a lug pattern, a two-piece vulcanization mold equipped with a lower mold 101 for molding one half of the solid tire 10 and an upper mold 102 for molding the other half of the solid tire 10, as shown in FIG. 7, is used. In this case, when the molds are closed in the vulcanization step, the rubber composition constituting the tread rubber layer 1 tends to flow in the tire width direction (see the arrow in FIG. 7). In such a vulcanization mold, for example, it is also possible to provide slit portions 141 extending substantially in the tire circumferential direction with respect to the protrusions 122 extending in the tire width direction.

[0047] FIG. 8 shows a tread molding surface S of a vulcanization mold for molding a solid tire 10 having a rib lug pattern. In FIG. 8, the molding surface S is formed with protrusions 111 extending in the tire circumferential direction and protrusions 132 extending in the tire width direction. The area defined by a pair of protrusions 111 is a center rib molding space 124. The area surrounded by the protrusions 111 and a pair of protrusions 132 adjacent to each other in the tire circumferential direction is a side block molding space 131. In this case, too, it is meaningful to provide multiple slits 141 in the protrusions 111 extending in the tire circumferential direction. Similar slits 141 can also be provided in the protrusions 132 so as to be oriented approximately in the tire circumferential direction.

[0048] The solid tire 10 targeted by the present invention preferably has an inner diameter of 8 inches or more. In a solid tire 10 with a small inner diameter, the amount of movement of the rubber composition during vulcanization is small, so that poor appearance hardly occurs, but in a solid tire with a large inner diameter, poor appearance is likely to occur, so providing the slit portion 141 provides a significant effect.

[0049] In the solid tire 10, the rubber composition constituting the tread rubber layer 1 preferably contains, as a polymer, styrene butadiene rubber (SBR) and / or butadiene rubber (BR) in addition to natural rubber (NR), and carbon black and / or silica as a reinforcing material. A rubber composition containing only natural rubber as a polymer has poor fluidity, but the fluidity can be improved by adding styrene butadiene rubber and / or butadiene rubber of appropriate viscosity. Adding carbon black and / or silica as a reinforcing material also contributes to improving the fluidity of the rubber composition. The Mooney viscosity [ML(1+4)100°C] of the rubber composition constituting the tread rubber layer 1 is preferably in the range of 40 to 80, and particularly preferably in the range of 50 to 70. Furthermore, the above combination not only effectively reduces poor appearance of the solid tire 10, but also provides suitable tire performance as a new match type cushion tire. The tire performance referred to here includes longitudinal rigidity, lateral rigidity, rolling resistance, wear resistance, uneven wear resistance, heat buildup, resistance to defects (chips, chipping, etc.), ride comfort, etc.

[0050] In the solid tire 10, the rubber composition forming the tread rubber layer 1 preferably contains, as a polymer, styrene-butadiene rubber and / or butadiene rubber in addition to natural rubber, with the blending amount of natural rubber in the polymer being 30 to 70 wt %, and further contains, as a reinforcing material, 30 to 70 phr of carbon black having a DBP absorption of 85 to 160 ml / 100 g in the HAF class. By configuring the rubber composition of the tread rubber layer 1 as described above, it is possible to effectively reduce defects in the appearance of the solid tire 10 and further to enable the tread rubber layer 1 to exhibit suitable physical properties. Here, if the blending amount of natural rubber in the polymer is less than 30 wt %, it becomes difficult to exhibit sufficient tire performance, while conversely, if it exceeds 70 wt %, the viscosity increases, reducing the fluidity of the rubber composition and making it more likely to exhibit defects in appearance.

[0051] Carbon black with a DBP absorption of 85 to 160 ml / 100 g in the HAF class improves the abrasion resistance and fluidity of the rubber composition. A DBP absorption below 85 ml / 100 g reduces abrasion resistance, while a DBP absorption above 160 ml / 100 g increases viscosity, reducing the fluidity of the rubber composition and increasing the likelihood of poor appearance. Furthermore, a DBP absorption above 160 ml / 100 g increases modulus, making chipping and chipping more likely to occur in the tread rubber layer 1. A carbon black content below 30 phr reduces rubber hardness, tire rigidity, and increased tire heat generation, as well as worsening abrasion resistance and uneven wear resistance. Conversely, a carbon black content above 70 phr increases viscosity, reducing the fluidity of the rubber composition and increasing the likelihood of poor appearance, making it difficult to knead the rubber, deteriorating processability, and further increasing tire rigidity, resulting in poor ride comfort and increased tire heat generation, which are undesirable.

[0052] Alternatively, in the solid tire 10, the rubber composition forming the tread rubber layer 1 preferably contains, as a polymer, styrene-butadiene rubber and / or butadiene rubber in addition to natural rubber, with the amount of natural rubber in the polymer being 30 to 70% by weight, and further contains, as a reinforcing material, 35 to 55 phr of silica having a VN3 class particle size of 28 to 37 nm and a DBP absorption of 150 to 210 ml / 100 g, and 6 to 13% by weight of a silane coupling agent relative to the silica. By configuring the rubber composition of the tread rubber layer 1 as described above, it is possible to effectively reduce poor appearance of the solid tire 10 and further to exhibit suitable physical properties as the tread rubber layer 1. Here, if the amount of natural rubber in the polymer is less than 30% by weight, it becomes difficult to fully exhibit tire performance, while conversely, if it exceeds 70% by weight, the viscosity increases, reducing the fluidity of the rubber composition and making it more likely to exhibit poor appearance.

[0053] VN3-class silica with a particle size of 28–37 nm and DBP absorption of 150–210 ml / 100 g improves the abrasion resistance and fluidity of rubber compositions. Particle sizes below 28 nm are too fine, resulting in increased viscosity, decreased fluidity, and poor appearance. Particle sizes above 37 nm are too coarse, resulting in decreased abrasion resistance. DBP absorption below 150 ml / 100 g results in a poor abrasion resistance due to the particle structure being too small. Conversely, DBP absorption above 210 ml / 100 g results in a poor appearance due to the particle structure being too large. A silica content below 35 phr reduces the hardness of the rubber composition, resulting in decreased tire stiffness, abrasion resistance, and uneven wear resistance. Conversely, a silica content above 55 phr increases viscosity, decreases fluidity, and leads to poor appearance. The resulting hardness also increases tire chipping, chipping, and poor ride comfort.

[0054] When using such silica, a silane coupling agent is used to bond it to the polymer. Bis[3-(triethoxysilyl)propyl]tetrasulfide is a preferred silane coupling agent. Other examples include vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and γ-mercaptopropyltrimethoxysilane. The silane coupling agent is used in an amount of 6 to 13% by weight of the silica. If the amount of silane coupling agent is less than 6% by weight of the silica, the viscosity increases, fluidity decreases, and poor appearance becomes more likely. Conversely, if the amount exceeds 13% by weight of the silica, the reinforcing properties become too strong and the modulus becomes too high, making the tire more susceptible to chipping and chipping.

[0055] The present invention is applicable not only to pneumatic cushion tires for industrial vehicles specified in Chapter F of the JATMA Yearbook, but also to solid tires (press-on type) for industrial vehicles specified in Chapter F. Furthermore, the present invention is applicable to various solid tires including cure-on type solid tires specified in JIS-D6405. [Example]

[0056] Solid tires (tire sizes: 5.00-8, 7.00-12) having the tread pattern shown in Figure 2 were manufactured under different conditions. Examples of the rubber composition formulations used in the tread rubber layer are shown in Tables 1 and 2. In the conventional example, no slits were formed in the protrusions on the molding surface of the vulcanization mold. In each example, slits were formed in the protrusions extending in the circumferential direction of the tire on the molding surface of the vulcanization mold.

[0057] [Table 1] In Table 1 Styrene butadiene rubber: Nippon Zeon Nipol R1502 Butadiene rubber: UBE Elastomers Corporation BR150 Carbon Black N330: Asahi Carbon Black Asahi #70 Carbon Black N220: Asahi Carbon Black Asahi #80

[0058] [Table 2] In Table 2 Styrene butadiene rubber: Nippon Zeon Nipol R1502 Butadiene rubber: UBE Elastomers Corporation BR150 White carbon VN3: Evonik ULTRASILRVN3 Silane coupling agent: Bis[3-(triethoxysilyl)propyl]tetrasulfide

[0059] First, the following settings were common to all the solid tires (reference example, Examples 1 to 4), and the number of slit portions was set as shown in Table 3. The number of appearance defects (bare count) was visually checked for the solid tires obtained, and the results are also shown in Table 3. Tread rubber layer composition: R3 Slit width: 2mm Ratio of slit depth to ridge height: 70% Angle of slit with respect to width direction of protrusion: 0° Number of vent holes: 16

[0060] [Table 3]

[0061] As can be seen from Table 3, in comparison with the reference example, poor appearance of the solid tires could be reduced in Examples 1 to 4. In particular, good results were obtained when the number of slit portions was 30 to 60.

[0062] Next, solid tires were vulcanized (Examples 11 to 14) with the following common settings and the ratio of the slit depth to the ridge height set as shown in Table 4. The resulting solid tires were visually inspected for the number of appearance defects (bare count), and the results are also shown in Table 4. Tread rubber layer composition: R3 Number of slits: 45 Slit width: 2mm Angle of slit with respect to width direction of protrusion: 0° Number of vent holes: 16

[0063] [Table 4]

[0064] As can be seen from Table 4, in comparison with the reference example, Examples 11 to 14 were able to reduce defects in the appearance of the solid tires. In particular, good results were obtained when the ratio of the depth of the slits to the height of the protrusions was 50% or more.

[0065] Next, solid tires were vulcanized (Examples 21 to 28) with the following common settings and the width of the slit portion set as shown in Table 5. The number of appearance defects (bare count) of the obtained solid tires was visually confirmed, and the results are also shown in Table 5. Tread rubber layer composition: R3 Number of slits: 45 Ratio of slit depth to ridge height: 80% Angle of slit with respect to width direction of protrusion: 0° Number of vent holes: 16

[0066] [Table 5]

[0067] As can be seen from Table 5, Examples 21 to 28 were able to reduce defects in the appearance of the solid tires compared to the reference example. In particular, good results were obtained when the slit width was 0.5 mm to 5.0 mm. In Example 21, because the slit width was small, rubber pieces remained in some of the slits when the tire was demolded. In Example 28, the rubber pieces formed in positions corresponding to the slits of the solid tire were somewhat noticeable.

[0068] Next, solid tires were vulcanized (Examples 31 to 34) with the following common settings and the angle of the slit portion relative to the width direction of the protrusions set as shown in Table 6. The number of appearance defects (bare count) of the obtained solid tires was visually checked, and the results are also shown in Table 6. Tread rubber layer composition: R3 Number of slits: 45 Slit width: 0.7 mm Ratio of slit depth to ridge height: 60% Number of vent holes: 16

[0069] [Table 6]

[0070] As can be seen from Table 6, in comparison with the reference example, Examples 31 to 34 were able to reduce defects in the appearance of the solid tires. In particular, good results were obtained when the angle of the slit portion relative to the width direction of the protrusion was 45° or less.

[0071] Next, the following settings were common to all the examples, and the formulation of the rubber composition constituting the tread rubber layer was set as shown in Table 7, and solid tires were vulcanized (Examples 41 to 45). The number of appearance defects (bare count) of the obtained solid tires was visually confirmed, and the results are also shown in Table 7. Number of slits: 45 Slit width: 1.0 mm Ratio of slit depth to ridge height: 85% Angle of slit with respect to width direction of protrusion: 0° Number of vent holes: 16

[0072] [Table 7]

[0073] As can be seen from Table 7, Examples 41 to 45 were able to reduce poor appearance of solid tires compared to the reference example. In particular, good results were obtained when rubber compositions R3, R4, and R5 were used. In Example 41, the number of bare holes increased slightly because the compounding amount of natural rubber was high and the flowability of the rubber composition was poor. In Example 42, the carbon black N220 was ISAF grade, and the viscosity of the rubber composition increased, so the number of bare holes increased slightly.

[0074] Next, the following settings were common to all the examples, and the formulation of the rubber composition constituting the tread rubber layer was set as shown in Table 8, and solid tires were vulcanized (Examples 51 to 55). The number of appearance defects (bare count) of the obtained solid tires was visually confirmed, and the results are also shown in Table 8. Number of slits: 45 Slit width: 1.0 mm Ratio of slit depth to ridge height: 85% Angle of slit with respect to width direction of protrusion: 0° Number of vent holes: 16

[0075] [Table 8]

[0076] As can be seen from Table 8, Examples 51 to 55 were able to reduce poor appearance of solid tires compared to the reference example. In particular, good results were obtained when rubber compositions R13, R14, and R15 were used. In Example 51, the number of bare holes increased slightly because the compounded amount of natural rubber was high and the rubber composition had poor fluidity. In Example 52, the compounded amount of white carbon VN3 was high and the rubber composition had high viscosity, so the number of bare holes increased slightly.

[0077] The present disclosure includes the following inventions [1] to

[13] . Invention [1] is a vulcanization mold for a solid tire, which has a molding surface that molds the outer surface of the solid tire and protrusions arranged on the molding surface so as to mold grooves in the tread portion of the solid tire, and is characterized by having a plurality of slits formed so as to cross the protrusions. Invention [2] is the solid tire vulcanization mold according to invention [1], characterized in that the slit portions are arranged at 30 to 60 locations on the molding surface. Invention [3] is a vulcanizing mold for a solid tire according to Invention [1] or [2], characterized in that the protrusions are arranged so as to divide the tread portion into a plurality of blocks, and the slit portions are arranged at positions adjacent to the corners and / or flat portions of the blocks. Invention [4] is a vulcanizing mold for a solid tire according to any one of inventions [1] to [3], characterized in that the depth of the slit portion is 50% or more of the height of the ridge. Invention [5] is the vulcanizing mold for a solid tire according to any one of inventions [1] to [4], characterized in that the width of the slit portion is in the range of 0.5 mm to 5.0 mm. Invention [6] is the vulcanizing mold for a solid tire according to any one of inventions [1] to [5], characterized in that the length of the slit portion is 40.0 mm or less. Invention [7] is a vulcanizing mold for a solid tire according to any one of inventions [1] to [6], characterized in that the angle formed by the slit portion with respect to the width direction of the protrusion is 45° or less. Invention [8] is the vulcanizing mold for a solid tire according to any one of inventions [1] to [7], characterized in that the slit portion is arranged on a protrusion extending in the tire circumferential direction. Invention [9] is a method for manufacturing a solid tire using a vulcanization mold according to any one of Inventions [1] to [8], characterized in that an unvulcanized solid tire is molded, the solid tire is placed in the vulcanization mold, and the solid tire is vulcanized in the vulcanization mold. Invention

[10] is the method for manufacturing a solid tire according to invention [9], characterized in that the inner diameter of the solid tire is 8 inches or more. Invention

[11] is a method for manufacturing a solid tire according to Invention [9] or

[10] , characterized in that the rubber composition constituting the tread rubber layer of the solid tire contains, as a polymer, styrene-butadiene rubber and / or butadiene rubber in addition to natural rubber, and contains, as a reinforcing material, carbon black and / or silica. Invention

[12] is a method for manufacturing a solid tire according to any one of Inventions [9] to

[11] , characterized in that the rubber composition constituting the tread rubber layer of the solid tire contains, as a polymer, styrene-butadiene rubber and / or butadiene rubber in addition to natural rubber, the blending amount of the natural rubber in the polymer is 30 to 70 wt %, and further contains, as a reinforcing material, 30 to 70 phr of carbon black having a DBP absorption of 85 to 160 ml / 100 g in HAF class. Invention

[13] is a method for producing a solid tire according to any one of Inventions [9] to

[11] , characterized in that the rubber composition constituting the tread rubber layer of the solid tire contains, as a polymer, styrene-butadiene rubber and / or butadiene rubber in addition to natural rubber, the blending amount of the natural rubber in the polymer is 30 to 70% by weight, and further contains, as a reinforcing material, 35 to 55 phr of silica that is VN3 class, has a particle size of 28 to 37 nm, and has a DBP absorption of 150 to 210 ml / 100 g, and a silane coupling agent in an amount of 6 to 13% by weight of the silica. [Explanation of symbols]

[0078] 1 Tread rubber layer 2 base rubber layer 3 Bead Core 10 Solid Tires 101 Lower mold 102 Upper mold 103 segments 104 Vent Hole 111,122,123,132,133 Projection 121 Center block molding space 131 Side block molding space 141 Slit section S molding surface T Tread

Claims

1. A vulcanizing mold for a solid tire, comprising a molding surface for molding the outer surface of a solid tire and protrusions arranged on said molding surface so as to mold grooves in the tread portion of said solid tire, characterized in that the mold has a plurality of slits formed so as to cross said protrusions.

2. 2. The solid tire vulcanization mold according to claim 1, wherein the slit portions are arranged at 30 to 60 locations on the molding surface.

3. 2. The vulcanization mold for a solid tire according to claim 1, wherein the protrusions are arranged so as to divide the tread portion into a plurality of blocks, and the slit portions are arranged at positions adjacent to corners and / or flat portions of the blocks.

4. 2. The vulcanizing mold for a solid tire according to claim 1, wherein the depth of the slit portion is 50% or more of the height of the ridge.

5. 2. The solid tire vulcanizing mold according to claim 1, wherein the width of the slit portion is in the range of 0.5 mm to 5.0 mm.

6. 2. The vulcanizing mold for a solid tire according to claim 1, wherein the length of the slit portion is 40.0 mm or less.

7. 2. The vulcanization mold for a solid tire according to claim 1, wherein the angle formed by the slit portion with respect to the width direction of the ridge is 45 degrees or less.

8. 2. The vulcanizing mold for a solid tire according to claim 1, wherein the slits are arranged on a ridge extending in the tire circumferential direction.

9. A method for manufacturing a solid tire using the vulcanization mold according to any one of claims 1 to 8, comprising molding an unvulcanized solid tire, placing the solid tire in the vulcanization mold, and vulcanizing the solid tire in the vulcanization mold.

10. 10. The method for manufacturing a solid tire according to claim 9, wherein the inside diameter of the solid tire is 8 inches or more.

11. 10. The method for manufacturing a solid tire according to claim 9, wherein the rubber composition constituting the tread rubber layer of the solid tire contains, as a polymer, styrene-butadiene rubber and / or butadiene rubber in addition to natural rubber, and contains, as a reinforcing material, carbon black and / or silica.

12. 10. The method for manufacturing a solid tire according to claim 9, wherein the rubber composition constituting the tread rubber layer of the solid tire contains, as a polymer, styrene-butadiene rubber and / or butadiene rubber in addition to natural rubber, the blending amount of the natural rubber in the polymer is 30 to 70 wt %, and further contains, as a reinforcing material, 30 to 70 phr of carbon black having a DBP absorption of 85 to 160 ml / 100 g in HAF class.

13. 10. The method for manufacturing a solid tire according to claim 9, wherein the rubber composition constituting the tread rubber layer of the solid tire contains, as a polymer, styrene-butadiene rubber and / or butadiene rubber in addition to natural rubber, the blending amount of the natural rubber in the polymer is 30 to 70% by weight, and further contains, as a reinforcing material, 35 to 55 phr of silica of VN3 class, having a particle size of 28 to 37 nm and a DBP absorption of 150 to 210 ml / 100 g, and 6 to 13% by weight of a silane coupling agent based on the silica.

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