Pneumatic tire and manufacturing method therefor

Abstract

Provided are a pneumatic tire and a manufacturing method therefor, wherein ride comfort can be improved when a sealant layer is provided on a tire inner surface of a tread section. This pneumatic tire comprises: a tread section 1 that extends in the tire circumference direction and forms an annular shape; a pair of sidewall sections 2 that are positioned on both sides of the tread section 1; and a pair of bead sections 3 that are positioned to the inside of the sidewall sections 2 in the tire radius direction. Formed on a tire inner surface 10 of the tread section 1 is a sealant layer 20 that has a structure in which a strip material 21 of a sealant is positioned in a helical shape along the tire circumference direction. A starting point P1 and an ending point P2 of the strip material 21 are separated from each other in the tire circumference direction, and the narrow angle-side angle β that the starting point P1 and the ending point P2 of the strip material 21 form around the tire center axis O is greater than the narrow angle-side angle α that both end points X1, X2 of a ground contact region in the tire circumference direction form around the tire center axis.

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, and more particularly to a pneumatic tire that enables improvement in ride comfort and a manufacturing method thereof.

[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 primarily composed of butyl-based rubber (see, for example, Patent Documents 1 to 3). Examples of butyl-based rubbers 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). More specifically, a strip of sealant that has been softened by heating to a high temperature is spirally arranged on the inner surface of the tire in the circumferential direction of the tire to form a sealant layer.

[0004] However, according to the inventors' findings, in a sealant layer having a structure in which a strip of sealant is spirally arranged around the tire circumferential direction, if the start and end points of the strip are both within the contact patch, this can cause a deterioration in ride comfort.

[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 that makes it possible to improve ride comfort when a sealant layer is provided on the inner surface of the tire in the tread portion, and a method for manufacturing the same.

[0007] In order to achieve the above object, the pneumatic tire of the present invention includes a tread portion extending circumferentially in an annular shape, a pair of sidewall portions disposed on either side of the tread portion, and a pair of bead portions disposed radially inward of the sidewall portions, wherein a sealant layer having a structure in which a strip of sealant is spirally arranged along the circumferential direction of the tire is formed on the inner surface of the tire in the tread portion, the start and end points of the strip are spaced apart in the circumferential direction of the tire, and the narrow angle β formed by the start and end points of the strip around the tire center axis when the pneumatic tire is mounted on a normal rim and inflated to a normal internal pressure is larger than the narrow angle α formed by both end points of the tire circumferential direction of the contact patch around the tire center axis when the pneumatic tire is mounted on a normal rim and inflated to a normal internal pressure, and placed vertically on a flat surface and subjected to a normal load.

[0008] In order to achieve the above object, the method for manufacturing a pneumatic tire of the present invention includes the steps of: manufacturing a pneumatic tire having a tread portion extending circumferentially in an annular direction of the tire, a pair of sidewall portions disposed on either side of the tread portion, and a pair of bead portions disposed radially inward of the sidewall portions; applying a strip of sealant in a spiral manner along the tire circumferential direction to the inner surface of the tire in the tread portion to form a sealant layer; separating a start point and an end point of the strip from each other in the tire circumferential direction; and making the narrow-angle angle β formed by the start point and end point of the strip around the tire center axis when the pneumatic tire is mounted on a normal rim and inflated to a normal internal pressure larger than the narrow-angle angle α formed by both end points of the tire circumferential direction of the contact patch around the tire center axis when the pneumatic tire is mounted on a normal rim and inflated to a normal internal pressure and placed vertically on a flat surface and subjected to a normal load.

[0009] In the present invention, in a pneumatic tire having a sealant layer with a structure in which a strip of sealant is arranged spirally along the tire circumferential direction on the inner surface of the tire in the tread portion, the start and end points of the sealant strip are spaced apart from each other in the tire circumferential direction, and the narrow-angle angle β formed by the start and end points of the strip around the tire center axis is set larger than the narrow-angle angle α formed by both end points of the tire circumferential direction of the contact patch around the tire center axis, so that the start and end points of the strip are not simultaneously within the contact patch, thereby improving ride comfort.

[0010] In the present invention, the angle β is preferably in the range of 60° to 180°. By setting the angle β within the above range, the ride comfort can be effectively improved.

[0011] In the present invention, when a belt layer including belt cords inclined relative to the tire circumferential direction is embedded in the tread portion, the width of the sealant layer is preferably 90% or more of the width of the belt layer located at the outermost position in the tire radial direction. By increasing the width of the sealant layer in this way and positioning the start and end points of the sealant strip material further outward in the tire width direction, ride comfort can be effectively improved. Furthermore, by making the width of the sealant layer sufficiently large, good sealing performance can be ensured.

[0012] In the present invention, the storage modulus G' of the sealant at 100° C. is preferably 20 kPa or less. When the storage modulus G' of the sealant at 100° C. is small, vibration of the sealant layer is suppressed, improving the ride comfort.

[0013] In the present invention, it is preferable that the loss modulus G" of the sealant at 100°C is 5 kPa or less. When the loss modulus G" of the sealant at 100°C is small, heat generation in the sealant layer is suppressed, thereby reducing the impact on durability.

[0014] In the present invention, the thickness of the sealant layer is preferably in the range of 2.0 mm to 5.0 mm, thereby ensuring puncture sealing properties.

[0015] In the present invention, the sealant is preferably composed of a silicone-based composition. When the sealant is composed of a rubber composition primarily containing butyl rubber, the sealant cools before the circumferential portions of the sealant strip blend together, resulting in poor integration between the circumferential portions of the sealant strip, resulting in insufficient sealing by the sealant layer. Furthermore, when the circumferential portions of the sealant strip are poorly integrated, the sealant layer is more likely to flow toward the center of the tread due to the centrifugal force generated during tire rotation, which also contributes to reduced sealing. In contrast, when the sealant is composed of a silicone-based composition, the circumferential portions of the sealant strip blend together easily during the curing reaction process of the silicone-based composition, improving the integration between the circumferential portions of the sealant strip, thereby improving the sealing by the sealant layer. Furthermore, because the circumferential portions of the sealant strip are well integrated, the sealant layer is less likely to flow toward the center in the tire width direction due to the centrifugal force generated during tire rotation, which also contributes to improved sealing. Furthermore, sealants made from silicone-based compositions can be applied at low temperatures; for example, the temperature of the sealant applied to the inner surface of a tire can be lowered to below 70°C, which has the advantage of reducing the effects of heat on the tire and preventing deterioration of tire performance.

[0016] 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, allowing application even at low temperatures.

[0017] In the present invention, angle α is the narrow angle formed around the tire center axis by both end points of the tire circumferential direction of the contact patch, measured when a pneumatic tire is mounted on a regular rim, inflated to the regular internal pressure, placed vertically on a flat surface, and subjected to a regular load, and angle β is the narrow angle formed around the tire center axis by the start and end points of the strip material, when the pneumatic tire is mounted on a regular rim and inflated to the regular internal pressure. A "regular rim" is a rim defined for each tire by a standard system including the standard on which the tire is based, for example, a standard rim in the case of JATMA, a "Design Rim" in the case of TRA, or a "Measuring Rim" in the case of ETRTO. "Normal internal pressure" is the air pressure specified for each tire by the standard system including the standard on which the tire is based, such as the maximum air pressure in the case of JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and "INFLATION PRESSURE" in the case of ETRTO. "Normal load" is the load specified for each tire by the standard system including the standard on which the tire is based, such as the maximum load capacity in the case of JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and "LOAD CAPACITY" in the case of ETRTO.

[0018] In the present invention, the storage modulus G' and loss modulus G" of the sealant are measured in accordance with JIS-K6394 using a viscoelasticity spectrometer (manufactured by Toyo Seiki Seisakusho, Ltd.) under conditions of a frequency of 20 Hz, an initial strain of 10%, a dynamic strain of ±2%, and a temperature of 100°C.

[0019] 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. Figs. 5(a) and (b) respectively show the pneumatic tire of Fig. 1, Fig. 5(a) being a side view in a loaded state and Fig. 5(b) being a side view in an unloaded state. Fig. 6 is a meridian cross-sectional view showing a pneumatic tire according to another embodiment of the present invention.

[0020] 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;

[0021] 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.

[0022] 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.

[0023] Meanwhile, multiple 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 multiple 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. 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 on the outer side of the first belt layer 7A, and the width of the first belt layer 7A is 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 in the range of 10° to 40°, for example. Steel cords are preferably used as the belt cords of the belt layers 7.

[0024] 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 has at least one reinforcing cord arranged at an angle of, for example, 5° or less relative to the tire circumferential direction. 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).

[0025] 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.

[0026] In the pneumatic tire described above, 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 CL, but the center position may be offset from the tire equator CL 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 CL 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 layer 20 has a structure in which a sealant strip 21 is spirally arranged along the tire circumferential direction (see FIG. 4 ). The sealant of the sealant layer 20 may be composed of a rubber composition primarily containing butyl rubber, but is preferably composed of a silicone-based composition. The silicone-based composition includes a synthetic polymer compound having a main skeleton formed by siloxane bonds.

[0027] The above-described pneumatic tire can be manufactured by the following method. First, a pneumatic tire is manufactured as described above, which includes the tread portion 1, a pair of sidewall portions 2, and a pair of bead portions 3, and in which the belt layer 7 and the belt cover layer 8 are embedded in the tread portion 1. Next, a sealant made of, for example, a silicone-based composition is applied to the tire inner surface 10 of the tread portion 1 to form a sealant layer 20.

[0028] 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.

[0029] In forming the sealant layer 20 by applying a strip of sealant 21 spirally along the tire circumferential direction to the tire inner surface 10 in the tread portion 1, as shown in Fig. 4 , the start point P1 and end point P2 of the strip of material 21 are spaced apart from each other in the tire circumferential direction Tc, and the narrow-angle angle β formed by the start point P1 and end point P2 of the strip of material 21 around the tire center axis O is made larger than the narrow-angle angle α formed by both end points X1, X2 of the tire circumferential direction of the contact patch of the pneumatic tire around the tire center axis O. The angle α is the narrow-angle angle formed by both end points X1, X2 of the tire circumferential direction of the contact patch of the pneumatic tire around the tire center axis O, as measured when the pneumatic tire is mounted on a standard rim, inflated to a standard internal pressure, placed vertically on a flat surface, and subjected to a standard load, as shown in Fig. 5(a). As shown in Figure 5(b), angle β is the narrow angle formed by the start point P1 and end point P2 of the strip material 21 around the tire center axis O when the pneumatic tire is mounted on a standard rim and inflated to the standard internal pressure.

[0030] In the above-described pneumatic tire, the pneumatic tire includes a sealant layer 20 having a structure in which a strip of sealant 21 is spirally arranged along the tire circumferential direction on the tire inner surface 10 in the tread portion 1, and the start point P1 and end point P2 of the sealant strip 21 are spaced apart from each other in the tire circumferential direction, and the narrow-angle side angle β formed by the start point P1 and end point P2 of the strip 21 around the tire center axis O is set to be larger than the narrow-angle side angle α formed by both end points X1, X2 of the tire circumferential direction of the contact patch around the tire center axis O. This prevents the start point P1 and end point P2 of the strip 21 from being simultaneously within the contact patch, thereby improving ride comfort.

[0031] In the above pneumatic tire, the angle β is preferably in the range of 60° to 180°, more preferably in the range of 90° to 180°. By setting the angle β within this range, ride comfort can be effectively improved. If the angle β is too small, the effect of improving ride comfort decreases. On the other hand, the angle α is generally in the range of 20° to 50°. Furthermore, it is desirable that the difference between the angle β and the angle α satisfy the relationship β-α≧60°.

[0032] In the pneumatic tire described above, multiple belt layers 7 are embedded in the tread portion 1, each including belt cords inclined relative to the tire circumferential direction and arranged so that the belt cords cross each other between layers. When these belt layers 7 include a first belt layer 7A located radially innermost in the tire direction and a second belt layer 7B located radially outermost in the tire direction, as shown in FIG. 1 , the width Ws of the sealant layer 20 is preferably at least 90% of the width Wb of the radially outermost belt layer 7B. In particular, it is preferable that the ends of the sealant layer 20 be positioned outward in the tire width direction relative to the ends of the radially innermost belt layer 7A. By making the width Ws of the sealant layer 20 sufficiently larger than the width Wb of the belt layer 7B and positioning the start point P1 and end point P2 of the sealant strip material 21 further outward in the tire width direction, ride comfort can be effectively improved. Furthermore, by making the width Ws of the sealant layer 20 sufficiently large, good sealing performance can be ensured. If the width Ws of the sealant layer 20 is smaller than 90% of the width Wb of the belt layer 7B, the effect of improving the ride comfort will decrease and the puncture sealing performance will also decrease.

[0033] In the above-described pneumatic tire, the sealant is preferably composed of a silicone-based composition. A sealant layer 20 having a structure in which a sealant strip 21 is spirally arranged along the tire circumferential direction is formed on the tire inner surface 10 in the tread portion 1. By using a silicone-based sealant, the circumferential portions of the sealant strip 21 can easily blend together during the curing reaction process of the silicone-based composition, improving the integrity of the circumferential portions of the sealant strip 21, thereby improving the sealing performance of the sealant layer 20. Furthermore, because the circumferential portions of the sealant strip 21 are well-integrated, the sealant layer 20 is less likely to flow toward the center of the tire width direction due to centrifugal force generated during tire rotation, which also contributes to improved sealing performance. Furthermore, using a silicone-based composition as the sealant for the sealant layer 20 has the advantages of excellent weather resistance and low temperature dependency of physical properties.

[0034] Since silicone-based compositions have good fluidity even at low temperatures, it is preferable to set the temperature of the sealant applied to the tire inner surface 10 to be lower than 70°C. This reduces the thermal effect on the tire and prevents deterioration of tire performance. If this temperature is 70°C or higher, the thermal effect on the tire will be greater, which will cause deterioration of tire performance. In particular, it is desirable for the temperature of the sealant applied to the tire inner surface 10 to be 35°C or lower. Furthermore, from the viewpoint of the fluidity of the silicone-based composition, it is preferable for the lower limit of the temperature of the sealant applied to the tire inner surface 10 to be 20°C.

[0035] The silicone-based composition constituting the sealant of the sealant layer 20 can be either a one-component curing silicone or a two-component curing silicone, with two-component curing silicone being particularly preferred. Examples of one-component curing silicones include moisture-curing silicone. Two-component curing silicones are composed of a first and a second component, and mixing these components initiates a curing reaction, ensuring the stability of the sealant layer 20 after curing. In the above-described device, the first and second components of the two-component curing silicone are supplied from pumps 32 and 33, respectively. Two-component curing silicones have low viscosity immediately after mixing, allowing them to be applied even at low temperatures. In particular, two-component curing silicones that take at least five days to fully cure are preferred.

[0036] 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.

[0037] In the pneumatic tire, it is preferable that the storage modulus G' of the sealant at 100°C is 20 kPa or less. When the sealant has a small storage modulus G' at 100°C, vibration of the sealant layer 20 is suppressed, improving ride comfort. If the storage modulus G' of the sealant at 100°C is greater than 20 kPa, the effect of improving ride comfort decreases. In particular, it is preferable that the storage modulus G' of the sealant at 100°C is in the range of 5 kPa to 15 kPa.

[0038] In the above pneumatic tire, it is preferable that the loss modulus G" of the sealant at 100°C is 5 kPa or less. When the sealant has a small loss modulus G" at 100°C, heat generation in the sealant layer 20 is suppressed, thereby reducing the impact on durability. If the loss modulus G" of the sealant at 100°C is greater than 5 GP, the effect of improving durability decreases. In particular, it is preferable that the loss modulus G" of the sealant at 100°C is in the range of 1 kPa to 3 kPa.

[0039] 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 performance while suppressing deterioration of rolling resistance due to increased tire weight and suppressing uneven distribution of the sealant layer 20 caused by sealant flow. Here, if the thickness S of the sealant layer 20 is less than 2.0 mm, puncture sealing performance will be reduced. Conversely, if the thickness S is greater than 5.0 mm, increased tire weight will result in deterioration of rolling resistance and uneven distribution of the sealant layer 20 due to sealant flow. 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 and 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 a total of 40 measurements.

[0040] In the above pneumatic tire, as shown in Fig. 2, it is preferable that the distance (shortest distance) L from the belt layer 7A 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 7A. This makes it easier for the sealant to flow into the belt layer 7A 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 7A 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.

[0041] In the pneumatic tire, it is preferable that the ratio of the thickness S of the sealant layer 20 to the distance L from the belt layer 7A located at the innermost side in the tire direction to the sealant layer 20 satisfies the relationship S / L≧0.3. By making the thickness S of the sealant layer 20 sufficiently large relative to the distance L, good puncture sealing performance can be ensured. If the ratio S / L is less than 0.3, puncture sealing performance deteriorates.

[0042] FIG. 6 shows a pneumatic tire according to another embodiment of the present invention. In FIG. 6, a sound-absorbing material 40 is disposed along the tire circumferential direction on the radially inner side of the sealant layer 20. The sound-absorbing material 40 is composed of a porous material with open cells, and has predetermined sound-absorbing properties 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 based on the adhesiveness of the sealant layer 20. In particular, when the sealant of the sealant layer 20 is composed of a silicone-based composition, the sound-absorbing material 40 is disposed on the sealant layer 20, which is applied at a low temperature, thereby avoiding damage to the sound-absorbing material 40 and maintaining its sound-absorbing effect.

[0043] In 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, a sealant layer having a structure in which a strip of sealant is spirally arranged along the tire circumferential direction is formed on the inner surface of the tire in the tread portion, and tires of Comparative Examples 1 and 2 and Examples 1 to 8 were produced with various changes as shown in Table 1, such as the constituent material of the sealant layer, the narrow angle α formed around the tire center axis by both end points of the tire circumferential direction of the contact patch, the narrow angle β formed around the tire center axis by the start and end points of the strip, the ratio of the width of the sealant layer to the width of the belt layer (Ws / Wb × 100%), the storage modulus G' of the sealant at 100°C, the loss modulus G" of the sealant at 100°C, and the thickness S of the sealant layer.

[0044] The test tires were evaluated for ride comfort and puncture sealing performance by the following test methods, and the results are shown in Table 1.

[0045] Ride comfort: Each test tire was mounted on a wheel with a rim size of 19 x 8.5J and mounted on a test vehicle (SUV) with an engine displacement of 2400cc, and a test driver conducted a running test with the tire pressure set to 210 kPa and a load set to 100% of the maximum unbearable force, and then performed a sensory evaluation of the ride comfort. The evaluation results were expressed as an index, with Comparative Example 1 being set to 100. The higher the index value, the better the ride comfort.

[0046] Puncture sealing ability: Each test tire was mounted on a wheel with a rim size of 19 x 8.5J, the initial air pressure was set to 250 kPa, a nail with a diameter of 4.0 mm was driven into the tread portion, the nail was removed, and the tire was left for 1 hour after which the air pressure was measured again and the rate of pressure drop relative to the initial air pressure was determined. The evaluation results were indicated by "◎" when the pressure drop rate was 2% or less, "◯" when the pressure drop rate was more than 2% and 7% or less, "△" when the pressure drop rate was more than 7% and 20% or less, and "×" when the pressure drop rate was more than 20%.

[0047]

[0048] As can be seen from Table 1, the tires of Examples 1 to 8 had good puncture sealing properties and, in addition, were superior in ride comfort compared to Comparative Examples 1 and 2.

[0049] REFERENCE SIGNS LIST 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 21 sealant strip 40 sound absorbing material P1 starting point of strip P2 ending point of strip X1, X2 tire circumferential end points of contact area

Claims

1. A pneumatic tire comprising a tread portion extending circumferentially in an annular shape, a pair of sidewall portions disposed on either side of the tread portion, and a pair of bead portions disposed radially inward of the sidewall portions, wherein a sealant layer having a structure in which a strip of sealant is spirally arranged along the tire circumferential direction is formed on the inner surface of the tire in the tread portion, the start and end points of the strip are spaced apart in the tire circumferential direction, and the narrow angle β formed by the start and end points of the strip around the tire center axis when the pneumatic tire is mounted on a normal rim and inflated to the normal internal pressure is greater than the narrow angle α formed by both end points of the tire circumferential direction of the contact patch around the tire center axis when the pneumatic tire is mounted on a normal rim and inflated to the normal internal pressure, and placed vertically on a flat surface and subjected to a normal load.

2. The pneumatic tire according to claim 1, wherein the angle β is in the range of 60° to 180°.

3. A pneumatic tire as described in claim 1 or 2, characterized in that a belt layer including belt cords inclined relative to the tire circumferential direction is embedded in the tread portion, and the width of the sealant layer is 90% or more of the width of the belt layer located at the outermost side in the tire radial direction.

4. A pneumatic tire according to any one of claims 1 to 3, characterized in that the storage modulus G' of the sealant at 100°C is 20 kPa or less.

5. A pneumatic tire according to any one of claims 1 to 4, characterized in that the loss modulus G" of the sealant at 100°C is 5 kPa or less.

6. A pneumatic tire according to any one of claims 1 to 5, characterized in that the thickness of the sealant layer is in the range of 2.0 mm to 5.0 mm.

7. A pneumatic tire according to any one of claims 1 to 6, characterized in that the sealant is made of a silicone-based composition.

8. The pneumatic tire according to claim 7, wherein the silicone composition is a two-component curing silicone.

9. A method for manufacturing a pneumatic tire having a tread portion extending circumferentially in an annular shape, a pair of sidewall portions disposed on either side of the tread portion, and a pair of bead portions disposed radially inward of the sidewall portions, comprising: applying a strip of sealant in a spiral manner along the circumferential direction of the tire to the inner surface of the tire in the tread portion to form a sealant layer; separating a start point and an end point of the strip from each other circumferentially of the tire; and making the narrower angle β formed by the start point and end point of the strip around the tire center axis when the pneumatic tire is mounted on a normal rim and inflated to a normal internal pressure larger than the narrower angle α formed by both end points of the tire circumferential direction of the contact patch around the tire center axis when the pneumatic tire is mounted on a normal rim and inflated to a normal internal pressure and placed vertically on a flat surface and subjected to a normal load.

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