Manufacturing method for pneumatic tires
By employing compounds with controlled vulcanization rates and gauges, and low-temperature steam vulcanization, the method addresses the trade-off between rolling resistance and vulcanization time in tire manufacturing, achieving efficient tire production.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- THE YOKOHAMA RUBBER CO LTD
- Filing Date
- 2024-12-16
- Publication Date
- 2026-06-26
AI Technical Summary
Existing methods for manufacturing pneumatic tires face a trade-off between reducing rolling resistance and shortening vulcanization time, as lowering vulcanization temperature to reduce resistance leads to longer processing times, thereby deteriorating productivity.
A method involving the use of specific compounds with controlled vulcanization rates and gauges, combined with low-temperature steam vulcanization, to achieve reduced rolling resistance and shortened vulcanization time.
This approach effectively reduces rolling resistance and shortens vulcanization time by optimizing the vulcanization process with compounds having defined vulcanization rates and gauges, thereby improving tire manufacturing efficiency.
Smart Images
Figure 2026105178000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a method for manufacturing a pneumatic tire using a vulcanization mold, and more particularly, to a method for manufacturing a pneumatic tire that reduces the rolling resistance of the pneumatic tire and enables shortening of the vulcanization time.
Background Art
[0002] When manufacturing a pneumatic tire, an unvulcanized tire is inserted into a mold, and vulcanization of the tire is performed while introducing a pressurized heating medium inside a bladder inserted into the tire. In such a vulcanization process, the vulcanization time is set in consideration of the temperature of the green tire, the tire total gauge, the vulcanization rate of the rubber, etc. (for example, see Patent Document 1).
[0003] In recent years, there has been a strong demand to reduce the rolling resistance of passenger car tires. Therefore, as a countermeasure in the vulcanization process, reducing the vulcanization temperature to avoid over-vulcanization of tire constituent members has been studied to reduce the rolling resistance. However, when the vulcanization temperature is lowered, naturally the vulcanization time becomes longer, and there is a demerit that the productivity of the tire deteriorates.
Prior Art Documents
Patent Documents
[0004]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0005] An object of the present invention is to provide a method for manufacturing a pneumatic tire that reduces the rolling resistance of the pneumatic tire and enables shortening of the vulcanization time.
Means for Solving the Problems
[0006] To achieve the above objective, the present invention provides a method for manufacturing a pneumatic tire, comprising: forming an unvulcanized tire containing a cap tread compound whose vulcanization rate to reach a degree of vulcanization of 90% at a vulcanization temperature of 160°C is 10.0 minutes or less, and in which the total gauge at the center position and shoulder position of the tread portion is 14.5 mm or less; placing the unvulcanized tire into a vulcanization mold; and setting the temperature of the steam used to heat the vulcanization mold to 160°C or less. [Effects of the Invention]
[0007] The inventors of this invention conducted extensive research on the vulcanization process of pneumatic tires and discovered that, under low-temperature vulcanization conditions, by defining the factors influencing the vulcanization time—namely, the vulcanization rate of the compound in the vulcanization-limiting section and the total tire gauge—they could achieve low-temperature, short-time vulcanization and maximize the effect of reducing rolling resistance. This led to the present invention.
[0008] In other words, in this invention, an unvulcanized tire is formed in which the vulcanization rate to reach 90% vulcanization at a vulcanization temperature of 160°C for the cap tread compound is 10.0 minutes or less, and the total gauge at the center position and shoulder position of the tread is 14.5 mm or less. By setting the temperature of the steam used to heat the vulcanization mold into which the unvulcanized tire is placed to 160°C or less, it is possible to reduce the rolling resistance of the pneumatic tire and shorten the vulcanization time.
[0009] In the present invention, it is preferable that the unvulcanized tire includes a belt compound whose vulcanization rate to reach 90% vulcanization at a vulcanization temperature of 160°C is 13.0 minutes or less. If the vulcanization rate of the cap tread compound is fast, the vulcanization rate-limiting portion shifts to the belt compound. Therefore, by setting an upper limit on the vulcanization rate of the belt compound as well, it is possible to further promote the reduction of rolling resistance and the shortening of vulcanization time.
[0010] In the present invention, it is preferable that the unvulcanized tire includes an undertread compound in which the vulcanization rate to reach 90% vulcanization at a vulcanization temperature of 160°C is 7.0 minutes or less. By defining the vulcanization rate of the undertread compound, which can be the rate-limiting part of the vulcanization process, it is possible to further promote the reduction of rolling resistance and the shortening of the vulcanization time.
[0011] In the present invention, it is preferable that the unvulcanized tire includes a belt cover compound in which the vulcanization rate to reach 90% vulcanization at a vulcanization temperature of 170°C is 5.0 minutes or less. By defining the vulcanization rate of the belt cover compound, which can be the rate-limiting part of the vulcanization process, it is possible to further promote the reduction of rolling resistance and the shortening of the vulcanization time.
[0012] In this invention, the vulcanization rate (minutes) of the compound is measured in accordance with JIS-K6296-3 using a rotaryless vulcanization tester (RLR). [Brief explanation of the drawing]
[0013] [Figure 1] This is a meridian cross-sectional view showing an example of a pneumatic tire according to the present invention. [Figure 2] This is a meridian cross-sectional view showing a tire vulcanization apparatus used in the manufacturing method of the pneumatic tire of the present invention. [Figure 3] This is a meridian cross-sectional view showing a tire vulcanization apparatus used in the manufacturing method of the pneumatic tire of the present invention. [Modes for carrying out the invention]
[0014] The configuration of the present invention will be described in detail below with reference to the attached drawings. Figure 1 shows an example of a pneumatic tire according to the present invention.
[0015] As shown in Figure 1, this pneumatic tire T comprises a tread portion 1 that extends in the circumferential direction of the tire and forms an annular shape, a pair of sidewall portions 2, 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3, 3 arranged radially inward of these sidewall portions 2.
[0016] A carcass layer 4 is mounted between a pair of bead sections 3, 3. This carcass layer 4 includes multiple carcass cords extending in the radial direction of the tire, which are folded back from the inside to the outside of the tire around the bead core 5 located in each bead section 3. A bead filler 6 made of a rubber composition with a triangular cross-section is placed on the outer circumference of the bead core 5.
[0017] On the other hand, multiple belt layers 7 are embedded on the outer circumference of the carcass layer 4 in the tread portion 1. These belt layers 7 include multiple belt cords that are inclined with respect to the tire circumferential direction, and the belt cords are arranged so as to intersect each other between layers. The multiple belt layers 7 include a first belt layer 7A located on the innermost side in the tire radial direction and a second belt layer 7B located outside the first belt layer 7A, with the width of the first belt layer 7A being wider than the width of the second belt layer 7B. In the belt layers 7, the inclination angle of the belt cords with respect to the tire circumferential direction is set to, for example, a range of 10° to 40°. Steel cords are preferably used as the belt cords of the belt layers 7.
[0018] On the outer circumference of the belt layer 7, at least one belt cover layer 8 is arranged, with reinforcing cords arranged at an angle of, for example, 5° or less with respect to the tire circumferential direction, for the purpose of improving high-speed durability. It is desirable that this belt cover layer 8 has a jointless structure in which a strip material made of at least one reinforcing cord aligned and covered with rubber is continuously wound at substantially 0° with respect to the tire circumferential direction. Organic fiber cords such as nylon or polyethylene terephthalate (PET) are preferably used as the reinforcing cords of the belt cover layer 8.
[0019] The above-described tire internal structure shows a typical example in the pneumatic tire T, but is not limited thereto. In the region from one bead portion 3 to the other bead portion 3 of the pneumatic tire T, an inner liner layer 9 is disposed along the carcass layer 4 inside the carcass layer 4. Further, a cap tread rubber layer R1c and an under tread rubber layer R1u are laminated outside the belt layer 7 and the belt cover layer 8 in the tread portion 1, a side rubber layer R2 is disposed outside the carcass layer 4 in the sidewall portion 2, and a rim cushion rubber layer R3 is disposed outside the carcass layer 4 in the bead portion 3.
[0020] Figures 2 and 3 show a tire vulcanizing apparatus used when manufacturing a pneumatic tire configured as described above.
[0021] As shown in Figures 2 and 3, this tire vulcanizing apparatus includes a vulcanizing mold 10 for shaping the outer surface of the pneumatic tire 1, a cylindrical bladder 20 inserted inside the pneumatic tire 1, a central mechanism 30 for operating the bladder 20, a heat medium supply unit 40 for supplying steam as a heat medium inside the bladder 20, a pressure medium supply unit 50 for supplying an inert gas as a pressure medium inside the bladder 20, a heating unit 60 for heating the mold 10, a driving unit 70 for driving the vulcanizing mold 10, and an exhaust unit 80 for discharging the steam and inert gas inside the bladder 20 to the outside of the system.
[0022] The vulcanizing mold 10 is composed of a lower side plate 11 and an upper side plate 12 for shaping the sidewall portion 2 of the pneumatic tire T, a lower bead ring 13 and an upper bead ring 14 for shaping the bead portion 3 of the pneumatic tire T, and a plurality of sectors 15 for shaping the tread portion 1 of the pneumatic tire T, and the pneumatic tire T is vulcanized and molded inside the vulcanizing mold 10. The structure of the vulcanizing mold 10 is not particularly limited, and in addition to the sectional type mold as shown in the figure, a split type mold can also be used.
[0023] The central mechanism 30 is composed of a center post 31 arranged at the central position of the pneumatic tire T and configured to be vertically movable, a lower clamping ring 32 arranged to be connected to the lower bead ring 13, a cylinder 33 arranged between the lower clamping ring 32 and the center post 31, an upper clamping ring 34 fixed to the upper part of the center post 31, and an auxiliary ring 35 attached to the upper clamping ring 34. In the cylinder 33, a medium supply passage (not shown) for supplying a heat medium and a pressure medium into the bladder 20 and a medium discharge passage (not shown) for discharging the heat medium and the pressure medium from the bladder 20 are formed.
[0024] The lower end of the bladder 20 is gripped between the lower bead ring 13 and the lower clamping ring 32, and the upper end thereof is gripped between the upper clamping ring 34 and the auxiliary ring 35. In the vulcanized state as shown in FIG. 2, the bladder 20 is in a state of expanding toward the outer side in the radial direction of the pneumatic tire T. However, when the pneumatic tire T is taken out of the vulcanizing mold 10 after vulcanization, the upper clamping ring 34 moves upward, and accordingly, the bladder 20 is withdrawn from the inside of the pneumatic tire T.
[0025] The heat medium supply unit 40 is composed of a steam supply source 41 that supplies steam adjusted to a predetermined temperature and pressure as the heat medium, a steam supply pipe 42 that guides the steam to the inside of the bladder 20, and a valve 43 provided in the middle of the steam supply pipe 42. On the other hand, the pressure medium supply unit 50 is composed of an inert gas supply source 51 that supplies an inert gas (for example, nitrogen gas) adjusted to a predetermined temperature and pressure as the pressure medium, an inert gas supply pipe 52 that guides the inert gas to the inside of the bladder 20, and a valve 53 provided in the middle of the inert gas supply pipe 52. The heat medium supplied from the heat medium supply unit 40 and the pressure medium supplied from the pressure medium supply unit 50 are introduced into the inside of the bladder 20 through the central mechanism 30. Based on the pressures of these heat medium and pressure medium, the pneumatic tire T is pressed against the inner surface of the vulcanizing mold 10 from the inside during vulcanization.
[0026] The heating section 60 consists of a lower platen 61 attached to the lower side plate 11, an upper platen 62 attached to the upper side plate 12, and a jacket 63 attached to the sector 15. Flow channels 61a, 62a, and 63a are formed inside the lower platen 61, upper platen 62, and jacket 63, respectively, into which steam is introduced. Therefore, by introducing steam at a predetermined temperature into the flow channels 61a, 62a, and 63a of the lower platen 61, upper platen 62, and jacket 63, the vulcanization of the pneumatic tire 1 is performed by heating the vulcanization mold 10 (lower side plate 11, upper side plate 12, and sector 15).
[0027] The drive unit 70 of the vulcanizing mold 10 is configured as follows: The lower side plate 11 is fixed to the lower support plate 71 via the lower platen 61 together with the lower bead ring 13. The upper side plate 12 is fixed to the upper support plate 72 together with the upper bead ring 14. A closing plate 74 equipped with a drive shaft 73 is connected to the center of the upper support plate 72. Therefore, by driving the drive shaft 73 in the vertical direction, the upper side plate 12 and the upper bead ring 14 move in the vertical direction.
[0028] Furthermore, segments 75 are mounted on the back side of each sector 15. The segments 75 are configured to slide freely along rails formed in the jacket 63, and the sliding surfaces between the segments 75 and the jacket 63 are inclined with respect to the vertical direction. The jacket 63 is fixed to the drive plate 76 via an upper platen 62. Therefore, by driving the drive plate 76 in the vertical direction, the jacket 63 moves in the vertical direction, and as the jacket 63 moves, the segments 75 and sectors 15 move in the tire radial direction and the tire axial direction.
[0029] The exhaust section 80 consists of an exhaust pipe 82 that guides steam and inert gas from the bladder 20 to the outside of the system, and a valve 83 provided in the middle of the exhaust pipe 82. The heat transfer medium and pressure transfer medium from the bladder 20 pass through the inside of the central mechanism 30 and are discharged to the outside of the system via the exhaust section 80.
[0030] When manufacturing a pneumatic tire T as shown in Figure 1 using the tire vulcanization apparatus described above, first, an unvulcanized tire corresponding to the pneumatic tire T is molded. In the unvulcanized tire, the cap tread compound that constitutes the cap tread rubber layer R1c is a compound that has a vulcanization rate of 10.0 minutes or less to reach 90% vulcanization at a vulcanization temperature of 160°C. In addition, the total gauges Gc and Gs at the center and shoulder positions of the tread section 1 are both set to 14.5 mm or less. Then, the unvulcanized tire satisfying these requirements is placed into the vulcanization mold 10, a bladder 20 is inserted inside the unvulcanized tire, and steam and inert gas are introduced inside the bladder 20, while steam is introduced into the flow paths 61a, 62a, and 63a of the lower platen 61, upper platen 62, and jacket 63 to heat the vulcanization mold 10. At this time, the temperature of the steam used to heat the vulcanization mold 10 is set to 160°C or less. This allows for a reduction in the rolling resistance of the pneumatic tire T by lowering the external temperature during vulcanization, while simultaneously shortening the vulcanization time by using a cap tread compound with a fast vulcanization rate and thinning the total gauge Gc,Gs of the tread section 1, which is the rate-limiting part of vulcanization.
[0031] Here, if the vulcanization rate to reach 90% vulcanization of the cap tread compound at a vulcanization temperature of 160°C exceeds 10.0 minutes, the vulcanization time will be longer. It is desirable that the vulcanization rate to reach 90% vulcanization of the cap tread compound at a vulcanization temperature of 160°C is in the range of 4.0 minutes to 10.0 minutes. Also, if the total gauge Gc and Gs at the center and shoulder positions of the tread section 1 exceed 14.5 mm, the vulcanization time will be longer. It is desirable that the total gauge Gc and Gs are in the range of 12.5 mm to 14.5 mm. Note that the total gauge Gc at the center position of the tread section 1 is the thickness from the outer surface to the inner surface of the tire at the center position in the tire width direction, and the total gauge Gs at the shoulder position of the tread section 1 is the thickness from the outer surface to the inner surface of the tire measured on a straight line perpendicular to the inner surface of the tire, passing 5 mm inward in the tire width direction from the edge of the second belt layer 7B counting from the inner liner layer 9 side. Furthermore, if the temperature of the steam used to heat the vulcanizing mold 10 exceeds 160°C, the effect of reducing rolling resistance becomes insufficient. It is desirable that the temperature of the steam used to heat the vulcanizing mold 10 be in the range of 140°C to 160°C.
[0032] In the manufacturing method of the pneumatic tire T described above, it is preferable to use a compound as the belt compound constituting the belt layer 7, in which the vulcanization rate to reach 90% vulcanization at a vulcanization temperature of 160°C is 13.0 minutes or less. If the vulcanization rate of the cap tread compound is fast, the vulcanization rate-limiting part shifts to the belt compound, so by setting an upper limit on the vulcanization rate of the belt compound as well, it is possible to further promote the reduction of rolling resistance and the shortening of vulcanization time. It is desirable that the vulcanization rate to reach 90% vulcanization at a vulcanization temperature of 160°C for the belt compound is in the range of 9.0 minutes to 13.0 minutes.
[0033] In the manufacturing method of the pneumatic tire T described above, it is preferable to use a compound as the undertread compound constituting the undertread rubber layer R1u, in which the vulcanization rate to reach 90% vulcanization at a vulcanization temperature of 160°C is 7.0 minutes or less. By defining the vulcanization rate of the undertread compound, which can be the rate-limiting part of vulcanization, it is possible to further promote the reduction of rolling resistance and the shortening of vulcanization time. It is desirable that the vulcanization rate to reach 90% vulcanization at a vulcanization temperature of 160°C for the undertread compound is in the range of 3.0 minutes to 7.0 minutes.
[0034] In the method for manufacturing the pneumatic tire T described above, it is preferable to use a compound as the belt cover compound constituting the belt cover layer 8, in which the vulcanization rate to reach 90% vulcanization at a vulcanization temperature of 170°C is 5.0 minutes or less. By defining the vulcanization rate of the belt cover compound, which can be the rate-limiting part of the vulcanization process, it is possible to further promote the reduction of rolling resistance and the shortening of the vulcanization time. It is desirable that the vulcanization rate to reach 90% vulcanization at a vulcanization temperature of 170°C for the belt cover compound is in the range of 2.0 minutes to 5.0 minutes.
[0035] In the manufacturing method of the pneumatic tire T described above, the vulcanization rate of the cap tread compound, belt compound, under tread compound, or belt cover compound is specified, but the specific formulation is not limited. Various compounds can contain rubber components commonly used in the tire industry, reinforcing agents such as carbon black and silica, vulcanizing agents such as sulfur, vulcanization accelerators, softeners such as oil, etc. For example, the vulcanization rate can be increased by increasing the amount of carbon black, sulfur, and vulcanization accelerators. [Examples]
[0036] In manufacturing pneumatic tires of size 255 / 40R21, the manufacturing methods for pneumatic tires of the Conventional Example, Comparative Examples 1-3 and Examples 1-5 were carried out, with the following settings: the temperature of the steam used to heat the vulcanization mold (external temperature), the vulcanization rate until the cap tread compound reaches 90% vulcanization at a vulcanization temperature of 160°C, the total gauge Gc at the center of the tread, the total gauge Gs at the shoulder of the tread, the vulcanization rate until the belt compound reaches 90% vulcanization at a vulcanization temperature of 160°C, the vulcanization rate until the under tread compound reaches 90% vulcanization at a vulcanization temperature of 170°C, and the conventional example, Comparative Examples 1-3, and Examples 1-5, respectively.
[0037] Regarding the manufacturing method of the pneumatic tire described above, the rolling resistance and vulcanization time of the obtained pneumatic tire were evaluated using the evaluation method described below, and the results are shown in Table 1.
[0038] Rolling resistance: The tires obtained using each manufacturing method were mounted on wheels with a rim size of 21 x rim width of 9.0 mm and placed on an indoor drum testing machine (drum diameter: 1707 mm). The air pressure was set to 250 kPa, and a load equivalent to 80% of the maximum load capacity at that air pressure as described in the JATMA / ETRTO yearbook was applied. The rolling resistance was measured when the machine was run at a speed of 80 km / h while the tires were pressed against the drum. The evaluation results are shown as an index with the conventional example set to 100. A smaller index value indicates lower rolling resistance.
[0039] Vulcanization time: The required vulcanization time for each manufacturing method was measured. The evaluation results are shown as an index with the conventional example set to 100. A smaller index value indicates a shorter vulcanization time.
[0040] [Table 1]
[0041] As can be seen from Table 1, in Examples 1 to 5, the rolling resistance of the pneumatic tire was reduced and the vulcanization time was shortened compared to the conventional example. On the other hand, in Comparative Example 1, the vulcanization speed of the cap tread compound was slow and the total gauges Gc and Gs were large, so the effect of reducing rolling resistance and shortening vulcanization time was not obtained. In Comparative Example 2, the external temperature was high and the total gauges Gc and Gs were large, so the effect of reducing rolling resistance was insufficient. In Comparative Example 3, the external temperature was high and the vulcanization speed of the cap tread compound was slow, so the effect of reducing rolling resistance and shortening vulcanization time was insufficient.
[0042] This disclosure encompasses the following inventions [1] to [4]. The invention [1] is a method for manufacturing a pneumatic tire, characterized by comprising a cap tread compound having a vulcanization rate of 10.0 minutes or less to reach a degree of vulcanization of 90% at a vulcanization temperature of 160°C, forming an unvulcanized tire having a total gauge of 14.5 mm or less at the center position and shoulder position of the tread portion, placing the unvulcanized tire into a vulcanization mold, and setting the temperature of the steam used to heat the vulcanization mold to 160°C or less. Invention [2] is a method for manufacturing a pneumatic tire according to Invention [1], characterized in that the unvulcanized tire includes a belt compound in which the vulcanization rate until the degree of vulcanization reaches 90% at a vulcanization temperature of 160°C is 13.0 minutes or less. Invention [3] is a method for manufacturing a pneumatic tire according to Invention [1] or [2], characterized in that the unvulcanized tire includes an undertread compound in which the vulcanization rate until the degree of vulcanization reaches 90% at a vulcanization temperature of 160°C is 7.0 minutes or less. Invention [4] is a method for manufacturing a pneumatic tire according to any one of Inventions [1] to [3], characterized in that the unvulcanized tire includes a belt cover compound in which the vulcanization rate until the degree of vulcanization reaches 90% at a vulcanization temperature of 170°C is 5.0 minutes or less. [Explanation of Symbols]
[0043] 1. Tread section 2 Sidewall section 3. Bead section 4. Carcass layer 5 Bead core 6. Bead Filler 7 Belt layer 8 Belt cover layer 9. Inner liner layer 10 Vulcanization mold 20 Bladder 30 Central mechanism 40 Heat medium supply section 50 Pressure medium supply unit 60 Heating section 70 Drive unit 80 Exhaust section T pneumatic tire
Claims
1. A method for manufacturing a pneumatic tire, comprising: forming an unvulcanized tire containing a cap tread compound whose vulcanization rate to reach 90% vulcanization at a vulcanization temperature of 160°C is 10.0 minutes or less, and in which the total gauge at the center position and shoulder position of the tread portion is 14.5 mm or less; placing the unvulcanized tire into a vulcanization mold; and setting the temperature of the steam used to heat the vulcanization mold to 160°C or less.
2. The method for manufacturing a pneumatic tire according to claim 1, characterized in that the unvulcanized tire includes a belt compound in which the vulcanization rate until a degree of vulcanization of 90% is reached at a vulcanization temperature of 160°C is 13.0 minutes or less.
3. The method for manufacturing a pneumatic tire according to claim 1 or 2, characterized in that the unvulcanized tire includes an undertread compound in which the vulcanization rate until a degree of vulcanization of 90% is reached at a vulcanization temperature of 160°C is 7.0 minutes or less.
4. The method for manufacturing a pneumatic tire according to claim 1 or 2, characterized in that the unvulcanized tire includes a belt cover compound in which the vulcanization rate until a degree of vulcanization of 90% is reached at a vulcanization temperature of 170°C is 5.0 minutes or less.