Pneumatic tire and method for manufacturing same

Abstract

Provided are a pneumatic tire capable of suppressing the peeling of a sealant layer and improving tire balance, and a method for manufacturing the same. In a pneumatic tire comprising an annular tread part 1 extending in the circumferential direction of the tire, a pair of side wall parts 2 disposed on both sides of the tread part 1, and a pair of bead parts 3 disposed on the inside of the side wall parts 2 in the radial direction of the tire, a sealant layer 20 is formed on a tire inner surface 10 of the tread part 1, the sealant layer 20 having a structure in which a band material 21 of sealant is spirally disposed along the tire circumferential direction, at least one end portion of the band material 21 being thinner than the other portions thereof.

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 can suppress peeling of the sealant layer and improve tire balance, 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, in the sealant layer formed as described above, peeling may occur in the sealant layer starting from the edge of the sealant strip, and the weight of the tire may change around the edge of the sealant strip, which may cause the tire to become unbalanced.

[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 suppress peeling of a sealant layer and improve tire balance, and a method for manufacturing the same.

[0007] In order to achieve the above object, the pneumatic tire of the present invention comprises a tread portion extending circumferentially in a ring shape, a pair of sidewall portions arranged on either side of the tread portion, and a pair of bead portions arranged radially inward of the sidewall portions, wherein a sealant layer having a structure in which a strip of sealant is arranged spirally along the circumferential direction of the tire is formed on the inner surface of the tire in the tread portion, and at least one end of the strip is thinner than the other portions.

[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, a sealant layer having a structure in which a strip of sealant is arranged spirally around the tire circumferential direction is formed on the inner surface of the tire in the tread portion, and at least one end of the strip is thinner than the other parts, which makes it possible to suppress peeling of the sealant layer starting from the end of the strip, and further reduces weight changes that occur around the tire circumferentially around the end of the strip, thereby improving tire balance.

[0010] In the present invention, the strip material has a narrow portion formed at at least one end and a wide portion that is thicker than the narrow portion, the length of the narrow portion is preferably 30 mm or more, and the average width of the narrow portion is preferably in the range of 20% to 97% of the average width of the wide portion. By specifying the dimensions of the narrow portion in this manner, it is possible to sufficiently ensure the effect of suppressing peeling of the sealant layer and the effect of improving tire balance.

[0011] 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.

[0012] 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.

[0013] In the present invention, the glass transition temperature of the sealant is preferably in the range of −120° C. to −40° C. By using a sealant with a low glass transition temperature, good puncture sealing properties can be ensured in low-temperature environments.

[0014] 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 suppressing deterioration of rolling resistance due to increased tire weight and suppressing uneven distribution of the sealant layer due to sealant flow.

[0015] In the present invention, when a belt layer including belt cords inclined with respect 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 innermost side in the tire radial direction. In particular, it is preferable that the end of the sealant layer is located outward in the tire width direction than the end of the belt layer located at the innermost side in the tire radial direction. By making the width of the sealant layer sufficiently large, punctures of the pneumatic tire can be effectively prevented.

[0016] In the present invention, when a belt cover layer including organic fiber cords oriented in the tire circumferential direction on the outer peripheral side of the belt layer is embedded in the tread portion, it is preferable that the end of the sealant layer is disposed on the outer side in the tire width direction than the end of the belt cover layer. By making the width of the sealant layer sufficiently large, punctures of the pneumatic tire can be effectively prevented.

[0017] In the present invention, when a belt layer including belt cords inclined with respect to the tire circumferential direction is embedded in the tread portion, it is preferable that the inclination direction of the sealant strip with respect to the tire circumferential direction is opposite in phase to the inclination direction of the belt cords of the belt layer located at the innermost side in the tire radial direction. In pneumatic tires, plysteer occurs due to the orientation of the belt cords of the belt layer, but the orientation of the sealant strip also causes plysteer. Therefore, by making the inclination direction of the sealant strip with respect to the tire circumferential direction opposite in phase to the inclination direction of the belt cords of the belt layer located at the innermost side in the tire radial direction, it is possible to reduce plysteer.

[0018] 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.

[0019] In the present invention, it is preferable that the ratio of the thickness S of the sealant layer to the distance L from the belt layer located at the innermost side in the tire radial direction to the sealant layer satisfies the relationship S / L ≥ 0.3. By making the thickness S of the sealant layer sufficiently large relative to the distance L, good puncture sealing performance can be ensured.

[0020] In the present invention, the distance in the tire width direction between the center position of the sealant layer in the tire width direction and the tire equator is preferably 10 mm or less. By reducing the distance in the tire width direction between the center position of the sealant layer in the tire width direction and the tire equator, tire balance can be improved.

[0021] 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. The sealant layer can be used as an adhesive layer for the sound-absorbing material. In particular, when the sealant is made of a silicone-based composition, the sound-absorbing material can be provided on the sealant layer applied at a low temperature, which prevents damage to the sound-absorbing material and maintains its sound-absorbing effect.

[0022] 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 plan view showing the belt layer, belt cover layer, and sealant layer of the pneumatic tire of Fig. 1. Fig. 4 is a cross-sectional view showing a method for manufacturing the pneumatic tire of Fig. 1. Fig. 5 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. 6 is a meridian cross-sectional view showing a pneumatic tire according to another embodiment of the present invention.

[0023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings, in which: Figures 1 to 3 show a pneumatic tire according to an embodiment of the present invention.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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).

[0028] 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.

[0029] 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. As shown in FIG. 3 , the sealant layer 20 has a structure in which a sealant strip 21 is spirally arranged along the tire circumferential direction. 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.

[0030] 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.

[0031] FIG. 4 shows a specific manufacturing method for the pneumatic tire of FIG. 1 , and FIG. 5 shows a sealant layer formed on the tire inner surface in the tread portion. In FIG. 4 , 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 arranged spirally on the tire inner surface 10 while being inclined with respect to the tire circumferential direction Tc (see FIG. 5 ). 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 a sealant layer 20. In this sealant layer 20, at least one end of the sealant strip 21 (both ends in FIG. 5 ) is thinner than the other portions. The thickness of the strip 21 can be adjusted arbitrarily based on the relative rotation speed of the tire with respect to the nozzle 34 .

[0032] In the pneumatic tire described above, a sealant layer 20 having a structure in which a strip of sealant 21 is arranged spirally around the tire circumferential direction is formed on the tire inner surface 10 in the tread portion 1, and at least one end of the strip of sealant 21 is thinner than the other parts, which makes it possible to suppress peeling of the sealant layer 20 starting from the end of the strip of sealant 21, and furthermore, reduces the weight change that occurs between the front and rear of the tire circumferential direction, with the end of the strip of sealant 21 as the boundary, thereby improving tire balance.

[0033] In the pneumatic tire, the strip material 21 has a narrow portion 21X formed at at least one end and a wide portion 21Y that is wider than the narrow portion 21X. The length X of the narrow portion 21X is 30 mm or more, and the average width of the narrow portion 21X is set to a range of 20% to 97% of the average width of the wide portion 21Y. The narrow portion 21X may be tapered in stages toward the tip, or may be tapered gradually toward the tip. By specifying the dimensions of the narrow portion 21X in this manner, it is possible to sufficiently ensure the effect of suppressing peeling of the sealant layer 20 and the effect of improving tire balance.

[0034] Here, if the length X of the narrow width portion 21X is less than 30 mm, the effect of suppressing peeling of the sealant layer 20 and the effect of improving tire balance are reduced. In particular, the length X of the narrow width portion 21X is preferably 50 mm or more, with its upper limit being preferably 1 / 8 of the tire inner circumference. Furthermore, if the average width of the narrow width portion 21X is less than 20% of the average width of the wide width portion 21Y, it becomes difficult to form the sealant layer 20. Conversely, if it is greater than 97%, the effect of suppressing peeling of the sealant layer 20 and the effect of improving tire balance are reduced. In particular, it is preferable that the average width of the narrow width portion 21X be in the range of 20% to 50% of the average width of the wide width portion 21Y.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] In the above pneumatic tire, the glass transition temperature of the sealant in the sealant layer 20 is preferably in the range of −120°C to −40°C. By using a sealant with a low glass transition temperature, good puncture sealing performance in low-temperature environments can be ensured. If the glass transition temperature of the sealant is higher than −40°C, puncture sealing performance in low-temperature environments will be reduced.

[0040] 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.

[0041] In the above-described pneumatic tire, when belt layers 7 (7A, 7B) including belt cords inclined with respect to the tire circumferential direction are embedded in the tread portion 1 as shown in Fig. 3, it is preferable that the inclination direction of the sealant strip material 21 with respect to the tire circumferential direction be in the opposite phase to the inclination direction of the belt cords of the belt layer 7A located at the innermost side in the tire radial direction. In a pneumatic tire, plysteer occurs due to the orientation of the belt cords of the belt layer 7, but the orientation of the sealant strip material 21 also causes plysteer. Therefore, by making the inclination direction of the sealant strip material 21 with respect to the tire circumferential direction in the opposite phase to the inclination direction of the belt cords of the belt layer 7A located at the innermost side in the tire radial direction, it is possible to reduce plysteer.

[0042] In the above-described pneumatic tire, as shown in Fig. 1, the width Ws of the sealant layer 20 is preferably 90% or more of the width Wb of the belt layer 7A located at the innermost position in the tire radial direction. In particular, it is preferable that the end of the sealant layer 20 be located outward in the tire width direction than the end of the belt layer 7A located at the innermost position in the tire radial direction. By making the width Ws of the sealant layer 20 sufficiently larger than the width Wb of the belt layer 7A, punctures in the pneumatic tire can be effectively prevented. Here, if the width Ws of the sealant layer 20 is less than 90% of the width Wb of the belt layer 7A, puncture sealing performance is reduced.

[0043] For the same reason, when a belt cover layer 8 containing organic fiber cords oriented in the tire circumferential direction on the outer peripheral side of the belt layer 7 is embedded in the tread portion 1, it is preferable that the ends of the sealant layer 20 are positioned further outward in the tire width direction than the ends of the belt cover layer 8. By making the width of the sealant layer 20 sufficiently large, punctures of the pneumatic tire can be effectively prevented.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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 sealant strip 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 in the constituent material of the sealant layer, the presence or absence of narrow portions formed at both ends of the strip, the length of the narrow portions, the ratio of the average width of the narrow portions to the average width of the wide portions, the thickness S of the sealant layer, the ratio of the width of the sealant layer to the width of the belt layer, the inclination direction of the sealant strip, the distance L from the belt layer located at the innermost position in the tire radial direction to the sealant layer, and the ratio S / L, as shown in Table 1. In addition, a conventional tire not provided with a sealant layer on the inner surface of the tire in the tread portion was prepared.

[0048] Regarding the inclination direction of the sealant strip material, when the inclination direction of the sealant strip material with respect to the tire circumferential direction is in phase with the inclination direction of the belt cord of the belt layer located at the innermost side in the tire radial direction, it is indicated as "same," and when the inclination direction of the sealant strip material with respect to the tire circumferential direction is in opposite phase with the inclination direction of the belt cord of the belt layer located at the innermost side in the tire radial direction, it is indicated as "opposite."

[0049] These test tires were evaluated for sealant layer peel resistance, tire balance, rolling resistance, plysteer, and puncture sealing performance by the following test methods. The results are shown in Table 1.

[0050] Peeling resistance of sealant layer: Each test tire was mounted on a wheel with a rim size of 19 x 8.5J, inflated to 230 kPa, and mounted on an indoor drum testing machine (drum diameter 1707 mm). The ambient temperature was controlled to 38±3°C, and the running test was continued until a running distance of 2500 km was reached, at a speed of 80 km / h, under a load of 88% of the JATMA maximum load. After the test, peeling of the sealant layer starting from the end of the strip material was examined. The evaluation results were as follows: no peeling at all was indicated by "◎", peeling of the strip material was more than 0 mm but not more than 3 mm was indicated by "◯", peeling of the strip material was more than 3 mm but not more than 10 mm was indicated by "△", and peeling of the strip material was more than 10 mm was indicated by "X".

[0051] Tire balance: Each test tire was mounted on a wheel with a rim size of 19 x 8.5J and attached to a rolling resistance tester, and the radial force variation (RFV) was measured in accordance with JIS-D4233 at an air pressure of 210 kPa. The evaluation results were expressed as an index using the reciprocal of the measured value, with the conventional example being set at 100. The higher the index value, the better the tire balance.

[0052] Rolling resistance: Each test tire was mounted on a wheel with a rim size of 19 x 8.5J and attached to a rolling resistance tester, and the rolling resistance was measured in accordance with JIS-D4234 at an air pressure of 210 kPa. The evaluation results were expressed as an index using the reciprocal of the measured value, with the conventional example being set at 100. The larger the index value, the smaller the rolling resistance.

[0053] Plysteer: Each test tire was mounted on a wheel with a rim size of 19 x 8.5J and attached to a uniformity tester, and the plysteer was measured in accordance with JIS-D4233 at an air pressure of 200 kPa. The evaluation results were expressed as an index using the reciprocal of the measured value, with the conventional example being set at 100. The larger the index value, the smaller the plysteer.

[0054] 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%.

[0055]

[0056] As can be seen from Table 1, the tires of Examples 1 to 8 all had good resistance to peeling of the sealant layer and good tire balance. The tires of Examples 1 to 8 also achieved good results in terms of rolling resistance, plysteer, and puncture sealing. In contrast, the tires of Comparative Examples 1 and 2 did not have narrow portions formed at both ends of the sealant strip, so the sealant layer had insufficient resistance to peeling and the tire balance was poor.

[0057] 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 21X narrow width portion 21Y wide width portion 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 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, and at least one end of the strip is narrower than other portions.

2. The pneumatic tire according to claim 1, characterized in that the strip of material has a narrow portion formed on at least one end and a wide portion that is thicker than the narrow portion, the length of the narrow portion is 30 mm or more, and the average width of the narrow portion is in the range of 20% to 97% of the average width of the wide portion.

3. The pneumatic tire according to claim 1 or 2, characterized in that the sealant is composed of a silicone-based composition.

4. The pneumatic tire according to claim 3, characterized in that the silicone composition is a two-component curing silicone.

5. A pneumatic tire according to any one of claims 1 to 4, characterized in that the glass transition temperature of the sealant is in the range of -120°C to -40°C.

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 as described in any one of claims 1 to 6, characterized in that a belt layer including belt cords inclined relative to the circumferential direction of the tire 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 innermost position in the radial direction of the tire.

8. The pneumatic tire according to claim 7, characterized in that an end portion of the sealant layer is disposed on the outer side in the tire width direction than an end portion of the belt layer positioned on the innermost side in the tire radial direction.

9. A pneumatic tire according to claim 8, characterized in that a belt cover layer containing organic fiber cords oriented in the tire circumferential direction on the outer circumferential side of the belt layer is embedded in the tread portion, and an end of the sealant layer is positioned outward in the tire width direction than an end of the belt cover layer.

10. A pneumatic tire as described in any one of claims 1 to 9, characterized in that a belt layer including belt cords inclined relative to the tire circumferential direction is embedded in the tread portion, and the inclination direction of the sealant strip material relative to the tire circumferential direction is in opposite phase to the inclination direction of the belt cords of the belt layer located at the innermost side in the tire radial direction.

11. A pneumatic tire according to any one of claims 7 to 10, characterized in that at all points of the belt layer located radially innermost in the tire, the distance L from the belt layer to the sealant layer is 10 mm or less.

12. The pneumatic tire according to claim 11, characterized in that the ratio of the thickness S of the sealant layer to the distance L from the belt layer located at the innermost side in the tire radial direction to the sealant layer satisfies the relationship S / L ≧ 0.

3.

13. A pneumatic tire according to any one of claims 1 to 12, characterized in that the distance in the tire width direction between the center position of the sealant layer in the tire width direction and the tire equator is 10 mm or less.

14. A pneumatic tire according to any one of claims 1 to 13, 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.

15. A method for producing a pneumatic tire as described in any one of claims 1 to 13, 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 below 70°C.

16. The method for manufacturing a pneumatic tire according to claim 15, 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.

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