Pneumatic tire

Abstract

Provided is a pneumatic tire in which sealability in low-temperature environments can be ensured. The pneumatic tire includes an annular tread part 1 extending in a tire circumferential direction, a pair of side wall parts 2 located on both sides of the tread part 1, and a pair of bead parts 4 located on the inner sides of the side wall parts 2 in the tire radial direction. A sealant layer 20 is formed on the inner surface of the tire in the tread part 1, and the glass transition temperature of the sealant constituting the sealant layer 20 is equal to or lower than the glass transition temperature of the cap compound constituting the tread part 1.

Description

pneumatic tires

[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 more particularly to a pneumatic tire that can ensure sealing performance even in low-temperature environments.

[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 rubber include butyl rubber (IIR) and halogenated butyl rubbers such as brominated butyl rubber (Br-IIR) and chlorinated butyl rubber (Cl-IIR). Furthermore, 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), and for this purpose, a large amount of liquid polymer is blended into the sealant.

[0004] However, sealants containing a large amount of liquid polymer as described above tend to have a high glass transition temperature Tg, which makes it difficult to ensure sufficient sealing performance in low-temperature environments.Furthermore, there is a risk that the sealant may crack during driving, making it difficult to ensure tire durability.

[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 can ensure sealing performance even in low-temperature environments.

[0007] The pneumatic tire of the present invention that achieves the above-mentioned object is a pneumatic tire having a tread portion extending circumferentially in a ring 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 sealant layer is formed on the inner surface of the tire in the tread portion, and the glass transition temperature of the sealant that constitutes the sealant layer is lower than the glass transition temperature of the cap compound that constitutes the tread portion.

[0008] In the pneumatic tire of the present invention, the glass transition temperature of the sealant constituting the sealant layer is equal to or lower than the glass transition temperature of the cap compound constituting the tread portion, so that peeling of the sealant in a low-temperature environment can be prevented and sealing performance can be ensured. Note that, in the present invention, the "glass transition temperature" of each material (sealant, cap compound, and inner liner compound described below) is defined as the peak temperature when a graph of tan δ against temperature (tan δ temperature curve) of each material is plotted (tan δ can be measured using a viscoelastic spectrometer at an initial strain of 10%, an amplitude of ±2%, and a frequency of 20 Hz).

[0009] In the present invention, it is preferable that an inner liner layer is adjacent to the outer peripheral side of the sealant layer in the tread portion, and that the glass transition temperature of the sealant is lower than that of the inner liner compound constituting the inner liner layer. As described above, by setting the glass transition temperature of the sealant constituting the sealant layer not only lower than that of the cap compound constituting the tread portion but also lower than that of the inner liner compound, a good balance of the physical properties of the inner liner layer and the sealant layer is achieved, which is advantageous for preventing peeling of the sealant in low-temperature environments.

[0010] In the present invention, the glass transition temperature of the sealant is preferably −60° C. or lower. Setting the glass transition temperature of the sealant to a sufficiently low temperature in this manner is advantageous for preventing peeling of the sealant in a low-temperature environment and for ensuring sealing properties.

[0011] In the present invention, the sealant is preferably made of a silicone-based composition. Furthermore, it is preferable that this silicone-based composition be a two-component curing silicone. A sealant made of a silicone-based composition has a low glass transition temperature, excellent weather resistance, and low temperature dependency of physical properties, which is advantageous for preventing sealant peeling in low-temperature environments and ensuring sealing properties. In particular, two-component curing silicones have low viscosity immediately after mixing the two components, making them applicable even at low temperatures.

[0012] In the present invention, the tan δ of the sealant at 100° C. is preferably 0.5 or less, which can prevent the sealant from distorting during running and affecting tire balance.

[0013] In the present invention, it is preferable that a belt layer including belt cords inclined with respect to the tire circumferential direction is embedded in the tread portion, and 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 points of the belt layer. This 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.

[0014] 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.

[0015] In the pneumatic tire of the present invention, after manufacturing the pneumatic tire excluding the sealant layer, a sealant made of a silicone composition can be applied to the tire inner surface in the tread portion to form a sealant layer, and at this time, it is preferable to set the temperature of the sealant applied to the tire inner surface to lower than 70° C. By lowering the temperature of the sealant applied to the tire inner surface in this way, thermal shrinkage of the belt cover layer due to heating during the formation of the sealant layer is suppressed, thereby reducing distortion occurring in the pneumatic tire and improving its durability.

[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] The configuration of the present invention will be described in detail below with reference to the accompanying drawings.

[0018] As shown in Figure 1, the pneumatic tire of this embodiment includes a tread portion 1 that extends circumferentially in the tire circumferential direction and forms an annular shape, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3 arranged radially inward of the sidewall portions 2. Although not depicted in Figure 1 because it is a meridian cross section, the tread portion 1, sidewall portions 2, and bead portions 3 each extend circumferentially in the tire circumferential direction and form an annular shape, thereby constituting the basic toroidal structure of a pneumatic tire. The following explanation using Figure 1 will be based basically on the meridian cross section shown in the figure, but each tire constituent member also extends circumferentially in the tire circumferential direction and forms an annular shape.

[0019] A carcass layer 4 is mounted between the pair of bead portions 3. This carcass layer 4 includes a plurality of carcass cords extending in the tire radial direction, and is folded back from the inner side to the outer side in the tire width direction 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] 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 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 reinforcing layer 8 is disposed on the outer peripheral side of the belt layer 7 for the purpose of improving high-speed durability. The belt reinforcing layer 8 may have two layers: a full cover layer that covers the entire width of the belt layer 7 and an edge cover layer that locally covers the ends of the belt layer 7, as shown in the figure. The belt reinforcing layer 8 includes reinforcing cords oriented in the tire circumferential direction. In the belt reinforcing layer 8, the reinforcing cords are set at an angle of, for example, 0° to 5° with respect to the tire circumferential direction. The belt reinforcing layer 8 preferably has a jointless structure in which a strip material formed by aligning and rubber-coating at least one reinforcing cord is continuously wound at an angle of substantially 0° with respect to the tire circumferential direction. Organic fiber cords such as nylon and polyethylene terephthalate (PET) are preferably used as the reinforcing cord of the belt reinforcing layer 8.

[0022] An inner liner layer 9 is provided on the inner surface of the tire along the carcass layer 4. This inner liner layer 9 is a layer that prevents air filled in the tire from permeating outside the tire. The inner liner layer 9 is made of, for example, a rubber composition mainly made of butyl rubber that has air permeation prevention properties. Alternatively, the inner liner layer 9 can be made of a resin layer with a thermoplastic resin matrix. In the case of a resin layer, an elastomer component may be dispersed in a thermoplastic resin matrix.

[0023] In the tread portion 1, a tread rubber layer 11 is disposed on the outer peripheral side of the carcass layer 4, belt layer 7, and belt reinforcing layer 8. The tread rubber layer 11 may have a structure in which two types of rubber layers with different physical properties (a cap tread layer that forms the tread surface of the tread portion 1 and an undertread layer disposed on its inner peripheral side) are laminated in the tire radial direction. A side rubber layer 12 is disposed on the outer peripheral side (outer side in the tire width direction) of the carcass layer 4 in the sidewall portion 2, and a rim cushion rubber layer 13 is disposed on the outer peripheral side (outer side in the tire width direction) of the carcass layer 4 in the bead portion 3.

[0024] The above-described internal structure of a tire is a typical example of a pneumatic tire, and the tire of the present invention is not limited to this. Various grooves, such as multiple main grooves extending in the tire circumferential direction and lug grooves extending in the tire width direction, can be formed in the tread portion 1.

[0025] In the pneumatic tire described above, a sealant layer 20 is formed continuously in the tire circumferential direction on the inner surface of the tire in the tread portion 1 (inner peripheral side of the inner liner layer 9). The sealant of the sealant layer 20 can be composed of a rubber composition mainly containing butyl rubber or a silicone composition, with the use of a silicone composition being particularly preferable. Examples of butyl rubber that can be used include butyl rubber (IIR) and halogenated butyl rubbers such as brominated butyl rubber (Br-IIR) and chlorinated butyl rubber (Cl-IIR). Silicone compositions include synthetic polymer compounds having a main skeleton formed by siloxane bonds.

[0026] Whether the sealant constituting the sealant layer 20 is composed of the above-mentioned rubber composition or a silicone-based composition, its glass transition temperature is set to be equal to or lower than the glass transition temperature of the cap compound constituting the tread portion 1, and preferably lower than the glass transition temperature of the cap compound. Note that the cap compound refers to the rubber (vulcanized rubber) constituting the tread portion 1 (particularly the cap tread layer) (if the tread portion 1 does not have a laminated structure of a cap tread layer and an under tread layer, the rubber (vulcanized rubber) constituting the tread rubber layer 11 is the cap compound). Because the glass transition temperature of the sealant is thus low, peeling of the sealant in low-temperature environments can be prevented and sealing performance can be ensured.

[0027] The glass transition temperature of the sealant is preferably not only lower than the glass transition temperature of the cap compound but also lower than the glass transition temperature of the inner liner compound constituting the inner liner layer 9. This results in a good balance of the physical properties of the adjacent inner liner layer and sealant layer, which is advantageous for preventing peeling of the sealant in a low-temperature environment. Note that the inner liner compound refers to the rubber (vulcanized rubber) or resin constituting the inner liner layer 9.

[0028] The glass transition temperature of the sealant needs only to satisfy the above-mentioned relationship, but is preferably −60°C or lower, more preferably −90°C or lower, and even more preferably −90°C to −120°C. Setting the sealant's glass transition temperature to a sufficiently low temperature like this is advantageous for preventing sealant peeling in low-temperature environments and ensuring sealing performance. If the sealant's glass transition temperature exceeds −60°C, the effect of preventing sealant peeling in low-temperature environments and ensuring sealing performance will be limited. The glass transition temperature of the sealant can be set by adjusting the type and amount of liquid polymer (e.g., paraffin oil or aromatic oil) blended into the rubber composition or silicone-based composition that constitutes the sealant.

[0029] The glass transition temperatures of the cap compound and the inner liner compound are not particularly limited as long as they satisfy the above-mentioned relationship, but the glass transition temperature of the cap compound may be set, for example, to -20°C to -60°C, and the glass transition temperature of the inner liner compound may be set, for example, to -30°C to -60°C.

[0030] The sealant of the present invention not only has a glass transition temperature that satisfies the above relationship, but also preferably has a tan δ at 100°C of 0.5 or less, more preferably 0.5 to 0.3. This prevents distortion of the sealant layer 20 during running, which would affect tire balance. If the tan δ at 100°C of the sealant exceeds 0.5, handling stability will decrease.

[0031] 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, with the belt layer 7 and belt cover layer 8 embedded in the tread portion 1. Next, a sealant is applied to the tire inner surface (the inner peripheral side of the inner liner layer 9) in the tread portion 1 to form the sealant layer 20. In this case, since the sealant satisfies the above-described physical properties and has good fluidity even at low temperatures, the temperature of the sealant applied to the tire inner surface can be lowered to below 70°C. This makes it possible to suppress 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, deteriorating durability. In particular, it is desirable that the temperature of the sealant applied to the tire inner surface be 40°C or lower. From the viewpoint of fluidity at low temperatures, it is preferable that the sealant be made of a silicone-based composition. 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 is preferably 20°C.

[0032] FIG. 3 shows a specific manufacturing method for the pneumatic tire of FIG. 1 , and FIG. 4 shows a sealant layer 20 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, the sealant strip 21 can be arranged spirally on the tire inner surface 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.

[0033] 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 two-component curing silicone is particularly preferred. Examples of one-component curing silicone include moisture-curing silicone. Two-component curing silicone is composed of a first component 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 component and the second component 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 components, allowing it to be applied even at low temperatures.

[0034] 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 when used.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] The present invention will be further explained below with reference to examples, but the scope of the present invention is not limited to these examples.

[0040] Tires of Comparative Examples 1 to 3 and Examples 1 to 5 were manufactured with a tire size of 255 / 45R19, with different sealant formulations, cap compound types, and inner liner compound types as shown in Table 1. The formulations of the cap compounds and inner liner compounds are shown in Tables 2 and 3, and the numbers are listed in the column for the type of each material in Table 1. In all tires, 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.

[0041] The glass transition temperatures Tg (unit: °C) of the sealant, cap compound, and inner liner compound are also shown in Table 1. The glass transition temperature Tg of each material is defined as the peak temperature when a graph of tan δ against temperature (tan δ temperature curve) of each material is plotted, and tan δ was measured using a viscoelasticity spectrometer (manufactured by Toyo Seiki Seisakusho, Ltd.) at an initial strain of 10%, an amplitude of ±2%, and a frequency of 20 Hz.

[0042] Furthermore, Table 1 shows the tire breakdown temperature (test temperature used to evaluate low-temperature sealability, which will be described later) measured by the following method.

[0043] Tire Failure Temperature Each test tire was mounted on a wheel with a rim size of 8.5J, aired to a pressure of 230 kPa, and mounted on a test vehicle. The tire was then driven for 30 minutes at a speed of 60 km / h on a test road surface equipped with three φ9.5 mm cleats at a test temperature of 0°C. After that, the test temperature was lowered by 5°C every 30 minutes, and the tire was allowed to run until failure occurred. The temperature at which the tire failed was recorded as the "tire failure temperature."

[0044] The low temperature sealability of these test tires was evaluated by the following test method, and the results are shown in Table 1.

[0045] Low-Temperature Sealing Property Each test tire was mounted on a wheel with a rim size of 8.5J, and the tire was fitted to a test vehicle with an air pressure of 230 kPa. A nail with a diameter of 5 mm was driven into the main groove of the tread under the "tire destruction temperature" conditions of each test tire, and the vehicle was driven at a speed of 60 km / h for one hour with the nail still inserted. After that, the nail was removed and the tire was left to stand for 24 hours under the "tire destruction temperature" environment of each test tire, after which the air pressure was measured. The evaluation results were rated on the following three-point scale. 3: Air pressure after standing was 200 kPa or more 2: Air pressure after standing was 150 kPa or more and less than 200 kPa 1: Air pressure after standing was less than 150 kPa

[0046]

[0047] The types of raw materials used in Table 1 are as follows: Silicone rubber 1: KE-551-U manufactured by Shin-Etsu Chemical Co., Ltd. Silicone rubber 2: two-component curing silicone, DOWSIL SE930 manufactured by Dow Corporation Butyl rubber: CHLOROBUTYL1066 manufactured by JSR Corporation Paraffin oil: Hicol K-350 manufactured by Kaneda Co., Ltd. Aroma oil: Diana Process Oil AH-58 manufactured by Idemitsu Kosan Co., Ltd.

[0048]

[0049]

[0050] The types of raw materials used in Tables 2 and 3 are as follows: NR: Natural rubber, SIR20 SBR1: Styrene butadiene rubber, Nipol 1502 manufactured by Nippon Zeon Co., Ltd. SBR2: Styrene butadiene rubber, Nipol 9548 manufactured by Nippon Zeon Co., Ltd. CB: Carbon black, Carbon black N772 manufactured by Degussa-Huels Co., Ltd. Adhesive: YS Resin PX1000 manufactured by Yasuhara Chemical Co., Ltd. Butyl rubber: CHLOROBUTYL1066 manufactured by JSR Corporation Process oil: Diana Process Oil NP250 manufactured by Idemitsu Kosan Co., Ltd. Paraffin oil: Hicol K-350 manufactured by Kaneda Co., Ltd. Sulfur: Kinkaji oil-filled finely powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd.

[0051] As is clear from Table 1, Examples 1 to 5 exhibited excellent low-temperature sealing properties while preventing peeling of the sealant in a low-temperature environment. On the other hand, Comparative Examples 1 to 3 were unable to exhibit sufficient sealing properties in a low-temperature environment because the glass transition temperature of the sealant was higher than the glass transition temperature of the cap compound.

[0052] 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 9 inner liner layer 11 tread rubber layer 12 side rubber layer 13 rim cushion rubber layer 20 sealant layer 40 sound absorbing material

Claims

1. 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, wherein a sealant layer is formed on the inner surface of the tire in the tread portion, and the glass transition temperature of the sealant constituting the sealant layer is lower than or equal to the glass transition temperature of a cap compound constituting the tread portion.

2. A pneumatic tire as described in claim 1, characterized in that an inner liner layer is adjacent to the outer circumferential side of the sealant layer in the tread portion, and the glass transition temperature of the sealant is lower than the glass transition temperature of the inner liner compound constituting the inner liner layer.

3. The pneumatic tire according to claim 1 or 2, characterized in that the glass transition temperature of the sealant is -60°C or lower.

4. The pneumatic tire according to any one of claims 1 to 3, characterized in that the sealant is made of a silicone-based composition.

5. The pneumatic tire according to claim 4, wherein the silicone composition is a two-component curing silicone.

6. A pneumatic tire according to any one of claims 1 to 5, characterized in that the tan δ of the sealant at 100°C is 0.5 or less.

7. A pneumatic tire as described in any one of claims 1 to 6, characterized in that a belt layer including belt cords inclined relative to the tire circumferential direction is embedded in the tread portion, and the distance L from the belt layer to the sealant layer is 10 mm or less at all points of the belt layer located at the innermost side in the tire radial direction.

8. A pneumatic tire according to any one of claims 1 to 7, characterized in that a sound absorbing material is provided along the circumferential direction of the tire on the radially inner side of the sealant layer.

9. A method for producing a pneumatic tire as described in any one of claims 1 to 8, comprising the steps of: producing a pneumatic tire excluding the sealant layer; 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; and lowering the temperature of the sealant applied to the inner surface of the tire to less than 70°C.

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