Pneumatic tire and manufacturing method therefor

Abstract

Provided are: a pneumatic tire in which thermal shrinkage of a belt cover layer due to heating during the formation of a sealant layer is suppressed and thus it is possible to reduce distortion in the tire and improve durability; and a manufacturing method therefor. In a pneumatic tire comprising a tread portion 1, a pair of sidewall portions 2, and a pair of bead portions 3, a belt layer 7 including belt cords inclined with respect to the circumferential direction of the tire, and a belt cover layer 8 which is disposed on the outer circumferential side of the belt layer 7 and includes organic fiber cords oriented in the circumferential direction of the tire are embedded in the tread portion 1. The thermal shrinkage of the organic fiber cords in the belt cover layer 8 at 180°C is in the range of 0.1-5.0%. A sealant layer 20 is formed on a tire inner surface 10 in the tread portion 1. A sealant in the sealant layer 20 is composed of a silicone-based composition.

Description

Pneumatic tire and manufacturing method thereof

[0001] The present invention relates to a pneumatic tire having a sealant layer on the inner surface of the tire in the tread portion, and a manufacturing method thereof. More specifically, the present invention relates to a pneumatic tire and a manufacturing method thereof that can reduce distortion occurring in the tire and improve durability by suppressing thermal shrinkage of a belt cover layer due to heating during the formation of the sealant layer.

[0002] It has been proposed to provide a sealant layer in a pneumatic tire radially inward of an inner liner layer in the tread portion of the tire. In such a pneumatic tire, when a foreign object such as a nail penetrates the tread portion, the sealant flows into the through-hole, thereby suppressing a decrease in air pressure and enabling the tire to continue running.

[0003] Conventionally, sealants constituting a sealant layer have generally been rubber compositions mainly containing butyl-based rubber (see, for example, Patent Documents 1 to 3). Examples of butyl-based rubber include butyl rubber (IIR) and halogenated butyl rubbers such as brominated butyl rubber (Br-IIR) and chlorinated butyl rubber (Cl-IIR). Such sealants are applied to the inner surface of a tire in a softened state by heating to a high temperature (see, for example, Patent Document 4).

[0004] However, in a pneumatic tire in which a belt cover layer containing organic fiber cords oriented in the tire circumferential direction is embedded in the tread portion, when a sealant heated to a high temperature is applied to the inner surface of the tire, the belt cover layer embedded in the tread portion is thermally contracted, resulting in distortion of the tire and further reducing the durability of the tire.

[0005] Japanese Patent No. 6583456 Japanese Patent No. 6620851 Japanese Patent No. 7319533 Japanese Patent No. 6124967

[0006] An object of the present invention is to provide a pneumatic tire and a method for manufacturing the same that can reduce distortion occurring in the tire and improve durability by suppressing thermal shrinkage of the belt cover layer due to heating during the formation of a sealant layer.

[0007] In order to achieve the above object, the pneumatic tire of the present invention includes a tread portion extending in a circumferential direction of the tire to form an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of bead portions arranged radially inward of the sidewall portions, wherein a belt layer including belt cords inclined with respect to the circumferential direction of the tire and a belt cover layer including organic fiber cords oriented in the circumferential direction of the tire on the outer circumferential side of the belt layer are embedded in the tread portion, the organic fiber cords of the belt cover layer having a heat shrinkage rate at 180°C in the range of 0.1% to 5.0%, and a sealant layer is formed on the inner surface of the tire in the tread portion, and the sealant of the sealant layer is composed of a silicone-based composition.

[0008] In order to achieve the above object, the method for manufacturing a pneumatic tire of the present invention is a method for manufacturing the above-mentioned pneumatic tire, characterized in that after manufacturing the pneumatic tire excluding the sealant layer, when applying a sealant made of a silicone-based composition to the inner surface of the tire in the tread portion to form the sealant layer, the temperature of the sealant applied to the inner surface of the tire is lowered to below 70°C.

[0009] In the present invention, in a pneumatic tire having a belt cover layer embedded in the tread portion and including organic fiber cords oriented in the tire circumferential direction, and the organic fiber cords of the belt cover layer having a heat shrinkage rate at 180°C in the range of 0.1% to 5.0%, a sealant layer including a sealant made of a silicone composition is formed on the tire inner surface in the tread portion, making it possible to lower the temperature of the sealant applied to the tire inner surface. For example, the temperature of the sealant applied to the tire inner surface can be lowered to less than 70°C. This suppresses thermal shrinkage of the belt cover layer due to heating during the formation of the sealant layer, thereby reducing distortion in the pneumatic tire and improving its durability.

[0010] In the present invention, the silicone composition is preferably a two-component curing silicone, which has a low viscosity immediately after mixing the two components, making it possible to apply the composition even at low temperatures.

[0011] In the present invention, it is preferable that the belt cover layer covers the entire area of ​​the belt layer. When the belt cover layer covers the entire area of ​​the belt layer, the influence of thermal shrinkage of the belt cover layer becomes significant, so it is effective to apply the above structure.

[0012] In the present invention, the width of the sealant layer is preferably 90% or more of the width of the belt layer. By making the width of the sealant layer sufficiently large, punctures of the pneumatic tire can be effectively prevented.

[0013] In the present invention, the thickness of the sealant layer is preferably in the range of 2.0 mm to 5.0 mm, which makes it possible to ensure puncture sealing performance while preventing deterioration of durability due to an increase in tire weight.

[0014] In the present invention, it is preferable that the distance L from the belt layer located at the innermost position in the tire radial direction to the sealant layer is 10 mm or less at all locations of the belt layer, which makes it easier for the sealant to flow into the belt layer when a foreign object such as a nail penetrates the tread portion, thereby ensuring good puncture sealing performance.

[0015] In the present invention, it is preferable that a sound-absorbing material be provided along the tire circumferential direction on the tire radially inner side of the sealant layer. In this case, the sound-absorbing material can be provided on the sealant layer applied at a low temperature, so that damage to the sound-absorbing material can be avoided and its sound-absorbing effect can be well maintained.

[0016] Fig. 1 is a meridian cross-sectional view showing a pneumatic tire according to an embodiment of the present invention. Fig. 2 is a cross-sectional view showing a main portion of the pneumatic tire of Fig. 1. Fig. 3 is a cross-sectional view showing a method for manufacturing the pneumatic tire of Fig. 1. Fig. 4 is a plan view showing a sealant layer formed on the inner surface of the tire in the tread portion of the pneumatic tire of Fig. 1. Fig. 5 is a meridian cross-sectional view showing a pneumatic tire according to another embodiment of the present invention.

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings, in which: Figures 1 and 2 show a pneumatic tire according to an embodiment of the present invention;

[0018] As shown in FIG. 1, the pneumatic tire of this embodiment includes a tread portion 1 extending circumferentially in a ring shape, a pair of sidewall portions 2, 2 disposed on both sides of the tread portion 1, and a pair of bead portions 3, 3 disposed radially inward of the sidewall portions 2.

[0019] A carcass layer 4 is mounted between the pair of bead portions 3, 3. This carcass layer 4 includes a plurality of carcass cords extending in the tire radial direction, and is folded back from the inside to the outside of the tire around a bead core 5 disposed in each bead portion 3. A bead filler 6 made of a rubber composition and having a triangular cross section is disposed on the outer periphery of the bead core 5.

[0020] On the other hand, a plurality of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. These belt layers 7 include a plurality of belt cords that are inclined with respect to the tire circumferential direction, and are arranged so that the belt cords cross each other between the layers. In the belt layers 7, the inclination angle of the belt cords with respect to the tire circumferential direction is set in the range of 10° to 40°, for example. Steel cords are preferably used as the belt cords of the belt layers 7.

[0021] At least one belt cover layer 8 is disposed on the outer periphery of the belt layer 7, with the aim of improving high-speed durability. The belt cover layer 8 preferably has a jointless structure in which a strip of at least one reinforcing cord, which is aligned and rubber-coated, is continuously wound at an angle of substantially 0° relative to the tire circumferential direction. The reinforcing cord of the belt cover layer 8 is preferably an organic fiber cord such as nylon or polyethylene terephthalate (PET). The organic fiber cord constituting the belt cover layer 8 has a heat shrinkage rate of 0.1% to 5.0% at 180°C. The heat shrinkage rate is the dry heat shrinkage rate (%) of a sample cord measured in accordance with JIS L1017, "Test Methods for Chemical Fiber Tire Cords," when the sample length is 500 mm and the sample is heated at 180°C for 30 minutes.

[0022] The tire internal structure described above is a typical example of a pneumatic tire, but is not limited thereto. Various grooves, including a plurality of main grooves 11 extending in the tire circumferential direction, are formed in the tread portion 1.

[0023] In the above-described pneumatic tire, a sealant layer 20 is formed continuously in the tire circumferential direction on the tire inner surface 10 in the tread portion 1. The center position of the sealant layer 20 in the tire width direction preferably coincides with the tire equator, but the center position may be offset from the tire equator to either side in the tire width direction. The distance in the tire width direction between the center position of the sealant layer 20 in the tire width direction and the tire equator is preferably 10 mm or less, more preferably 5 mm or less. This prevents the sealant layer 20 from adversely affecting tire balance. The sealant in the sealant layer 20 is composed of a silicone-based composition. The silicone-based composition includes a synthetic polymer compound having a main skeleton formed by siloxane bonds. In this pneumatic tire, a belt cover layer 8 including organic fiber cords oriented in the tire circumferential direction is embedded in the tread portion 1, and the heat shrinkage rate of the organic fiber cords of the belt cover layer 8 at 180°C is in the range of 0.1% to 5.0%. Therefore, a sealant layer 20 including a sealant made of a silicone-based composition is formed on the tire inner surface 10 in the tread portion 1, making it possible to lower the temperature of the sealant applied to the tire inner surface 10 during the formation of the sealant layer 20. This suppresses the thermal shrinkage of the belt cover layer 8 due to heating during the formation of the sealant layer 20, thereby reducing distortion in the pneumatic tire and improving its durability. Here, if the heat shrinkage rate at 180°C of the organic fiber cords constituting the belt cover layer 8 exceeds 5.0%, distortion in the pneumatic tire increases. Furthermore, using a silicone-based composition as the sealant in the sealant layer 20 has the advantages of excellent weather resistance and low temperature dependency of physical properties.

[0024] The above-described pneumatic tire can be manufactured by the following method. First, a pneumatic tire is manufactured, as described above, including the tread portion 1, a pair of sidewall portions 2, and a pair of bead portions 3. The pneumatic tire has the belt layer 7 and belt cover layer 8 embedded in the tread portion 1, and the organic fiber cords of the belt cover layer 8 have a heat shrinkage rate at 180°C in the range of 0.1% to 5.0%. Next, a sealant made of a silicone-based composition is applied to the tire inner surface 10 in the tread portion 1 to form the sealant layer 20. Since silicone-based compositions have good fluidity even at low temperatures, the temperature of the sealant applied to the tire inner surface 10 is set to be lower than 70°C. This suppresses thermal shrinkage of the belt cover layer 8 due to heating during the formation of the sealant layer 20. If this temperature is 70°C or higher, the distortion caused in the pneumatic tire increases, resulting in a deterioration in durability. In particular, it is desirable that the temperature of the sealant applied to the tire inner surface 10 be 40°C or lower. Furthermore, from the viewpoint of the fluidity of the silicone-based composition, the lower limit of the temperature of the sealant applied to the tire inner surface 10 is preferably 20°C.

[0025] FIG. 3 shows a specific manufacturing method for the pneumatic tire of FIG. 1 , and FIG. 4 shows a sealant layer formed on the tire inner surface in the tread portion. In FIG. 3 , a sealant extrusion device 31 mixes sealants supplied from pumps 32 and 33 and continuously discharges the mixed sealant as a strip 21 from a nozzle 34. The sealant extrusion device 31 is configured so that the position of the nozzle 34 can be freely changed. Therefore, by moving the nozzle 34 axially while rotating the tire from a state in which the nozzle 34 is close to the tire inner surface 10, the sealant strip 21 can be spirally arranged on the tire inner surface 10 while being inclined with respect to the tire circumferential direction Tc (see FIG. 4 ). The spirally arranged sealant strips 21 are in close contact with each other at their circumferential portions. The spirally arranged sealant strips 21 are integrated to form the sealant layer 20.

[0026] As the silicone-based composition constituting the sealant of the sealant layer 20, one-component curing silicone or two-component curing silicone can be used, but it is particularly preferable to use two-component curing silicone. An example of one-component curing silicone is moisture-curing silicone. Two-component curing silicone is composed of a first liquid and a second liquid, and a curing reaction begins by mixing these first and second liquids, ensuring the stability of the sealant layer 20 after curing. In the above-mentioned device, the first liquid and the second liquid of the two-component curing silicone are supplied from pumps 32 and 33, respectively. Two-component curing silicone has low viscosity immediately after mixing the two liquids, so it can be applied even at low temperatures.

[0027] Two-component curing silicones are composed of, for example, a condensation-curable silyl-terminated polymer, a silane crosslinker, a condensation catalyst, a filler, and the like. Examples of condensation-curable silyl-terminated polymers include polydialkylsiloxanes, alkylphenylsiloxanes, organic polymers having silyl groups (e.g., silyl polyethers, silyl acrylates), and polyisobutylenes having silyl groups. Examples of silane crosslinkers include alkoxy-functional silanes, oximosilanes, acetoxysilanes, and enoxysilanes. Examples of fillers include iron oxide, titanium dioxide, carbon black, and talc. Examples of condensation catalysts include titanates and zirconates. These condensation-curable silyl-terminated polymers, silane crosslinkers, condensation catalysts, and fillers are stored in a first and second liquid form in a combination that does not promote a curing reaction, and are mixed at the time of use. Examples of two-component curing silicones include those described in Japanese Patent Publication No. 2018-503725 and Japanese Patent Publication No. 2022-550962. As a commercially available two-component curing silicone, for example, SST-2650 manufactured by Dow can be used.

[0028] In the above pneumatic tire, the belt cover layer 8 may cover only a part of the belt layer 7 in the tire width direction (for example, edge portions on both sides of the belt layer in the tire width direction), but it is preferable that it covers the entire area in the tire width direction of the belt layer 7. In a structure in which the belt cover layer 8 covers the entire area of ​​the belt layer 7, the influence of thermal shrinkage of the belt cover layer 7 becomes significant, so it is effective to apply a sealant layer 20 made of a silicone-based composition.

[0029] In the above pneumatic tire, the width Ws of the sealant layer 20 is preferably 90% or more of the width Wb of the belt layer 7. By making the width Ws of the sealant layer 20 sufficiently larger than the width Wb of the belt layer 7, punctures in the pneumatic tire can be effectively prevented. Here, if the width Ws of the sealant layer 20 is smaller than 90% of the width Wb of the belt layer 7, puncture sealing performance decreases.

[0030] In the above-described pneumatic tire, as shown in FIG. 2, the thickness S of the sealant layer 20 is preferably in the range of 2.0 mm to 5.0 mm. This ensures puncture sealing while preventing a deterioration in durability due to increased tire weight. Here, if the thickness S of the sealant layer 20 is less than 2.0 mm, puncture sealing performance will be reduced, while if it is greater than 5.0 mm, increased tire weight may result in a deterioration in durability. The thickness S of the sealant layer 20 is the overall average thickness. The average thickness of the sealant layer 20 can be calculated, for example, by CT scanning eight tire meridian cross sections around the tire, measuring the thickness of the sealant layer 20 at five points in each image: the tire equator, outer edge positions (on both sides) 10 mm inward in the tire width direction from the edge of the sealant layer 20, and intermediate positions (on both sides) between the tire equator and the outer edge positions. This is done from measurements at a total of 40 points.

[0031] In the above pneumatic tire, as shown in Figure 2, it is preferable that the distance (shortest distance) L from the belt layer 7 located at the innermost position in the tire radial direction to the sealant layer 20 is 10 mm or less at all points of the belt layer 7. This makes it easier for the sealant to flow into the belt layer 7 when a foreign object such as a nail penetrates the tread portion 1, thereby ensuring good puncture sealing performance. If there is a portion where the distance L from the belt layer 7 to the sealant layer 20 is greater than 10 mm, there is a risk that the puncture sealing performance in that portion will be insufficient.

[0032] FIG. 5 shows a pneumatic tire according to another embodiment of the present invention. In FIG. 5, a sound-absorbing material 40 is installed along the tire circumferential direction on the tire radially inward side of the sealant layer 20. The sound-absorbing material 40 is made of a porous material with open cells, and has predetermined sound-absorbing characteristics based on its porous structure. Polyurethane foam is preferably used as the porous material for the sound-absorbing material 40. After the sealant layer 20 is formed, the sound-absorbing material 40 is attached to the sealant layer 20 using the adhesiveness of the sealant layer 20. In this case, because the sound-absorbing material 40 is installed on the sealant layer 20, which is applied at a low temperature, damage to the sound-absorbing material 40 is avoided and its sound-absorbing effect can be maintained satisfactorily.

[0033] Tires of Comparative Examples 1 to 4 and Examples 1 to 8 were manufactured for a pneumatic tire having a tire size of 255 / 45R19 and including a tread portion, a pair of sidewall portions, and a pair of bead portions, with the cord material of the belt cover layer, the heat shrinkage rate at 180°C of the organic fiber cord of the belt cover layer, the constituent material of the sealant layer, the sealant application temperature, and the ratio of the width of the sealant layer to the width of the belt layer being varied as shown in Table 1. The thickness S of the sealant layer was 3 mm, and the distance L from the belt layer to the sealant layer was 8 mm.

[0034] These test tires were evaluated for high speed durability and outer diameter distortion by the following test methods. The results are also shown in Table 1.

[0035] High-speed durability: Each test tire was mounted on a wheel with a rim size of 19 x 8.5J, inflated to 360 kPa, and mounted on an indoor drum testing machine (drum diameter 1707 mm). The ambient temperature was controlled at 38±3°C, and the running speed was increased from 120 km / h in 10 km / h increments under a load of 88% of the JATMA maximum load. The running test was conducted until the tire broke. The evaluation results were indicated as "○" for a speed of 340 km / h x 10 minutes or more, "△" for a speed of 320 km / h x 10 minutes or more but less than 340 km / h x 10 minutes, and "×" for a speed of less than 320 km / h x 10 minutes.

[0036] Outer diameter distortion: The outer diameter of each test tire was measured, and the error of the actual measurement value from the design value was calculated. The evaluation results were indicated by "◎" when the error of the actual measurement value from the design value was within ±0.3%, by "◯" when the error was within ±0.5%, by "△" when the error was within ±0.7%, and by "×" when the error was outside the ±0.7% range.

[0037]

[0038] As can be seen from Table 1, the tires of Examples 1 to 8 had small distortion and good durability because the heat shrinkage of the belt cover layer due to heating during the formation of the sealant layer was suppressed. In contrast, the tires of Comparative Examples 1 to 4 had large distortion and poor durability because the sealant application temperature had to be set high to form the sealant layer mainly made of butyl rubber.

[0039] DESCRIPTION OF SYMBOLS 1 tread portion 2 sidewall portion 3 bead portion 4 carcass layer 5 bead core 6 bead filler 7 belt layer 8 belt cover layer 10 tire inner surface 20 sealant layer 40 sound absorbing material

Claims

1. In a pneumatic tire comprising a tread portion extending in the circumferential direction of the tire and forming an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of bead portions arranged radially inward of these sidewall portions, The tread portion is embedded with a belt layer containing belt cords inclined with respect to the tire circumferential direction, and a belt cover layer containing organic fiber cords oriented in the tire circumferential direction on the outer circumference side of the belt layer, wherein the heat shrinkage rate of the organic fiber cords of the belt cover layer at 180°C is in the range of 0.1% to 5.0%. A pneumatic tire characterized in that a sealant layer is formed on the inner surface of the tire in the tread portion, and the sealant in the sealant layer is composed of a silicone-based composition.

2. The pneumatic tire according to claim 1, characterized in that the silicone composition is a two-component curable silicone.

3. The pneumatic tire according to claim 1 or 2, characterized in that the belt cover layer covers the entire area of ​​the belt layer.

4. The pneumatic tire according to claim 1 or 2, characterized in that the width of the sealant layer is 90% or more of the width of the belt layer.

5. The pneumatic tire according to claim 1 or 2, characterized in that the thickness of the sealant layer is in the range of 2.0 mm to 5.0 mm.

6. The pneumatic tire according to claim 1 or 2, characterized in that at all locations of the belt layer located on the innermost side in the radial direction of the tire, the distance L from the belt layer to the sealant layer is 10 mm or less.

7. The pneumatic tire according to claim 1 or 2, characterized in that a sound-absorbing material is installed on the inner side of the sealant layer in the radial direction of the tire, along the circumferential direction of the tire.

8. A method for manufacturing a pneumatic tire according to claim 1 or 2, After manufacturing a pneumatic tire excluding the sealant layer, A method for manufacturing a pneumatic tire, characterized in that, when applying a sealant made of a silicone-based composition to the inner surface of the tire in the tread portion to form the sealant layer, the temperature of the sealant applied to the inner surface of the tire is lower than 70°C.

9. The method for manufacturing a pneumatic tire according to claim 8, characterized in that a sound-absorbing material is installed on the inner side of the sealant layer in the radial direction of the tire, along the circumferential direction of the tire.