Pneumatic tire and production method therefor

Abstract

Provided are: a pneumatic tire which has improved adhesion between a tire inner surface and a sealant layer, thereby enabling an improvement in durability; and a production method for the pneumatic tire. The pneumatic tire includes a tread part 1 which is annular and extends along the tire circumferential direction, a pair of sidewalls 2 disposed on both sides of the tread part 1, and a pair of beads 3 disposed on the inner side of the sidewalls 2 in the tire radial direction. The pneumatic tire has a release layer 10 comprising a silicone-based composition on a tire inner surface Ts and has a sealant layer 20 formed on the tire-radial-direction inner side of the release layer 10 in the tread part 1. The sealant of the sealant layer 20 is made of a silicone-based composition. The absolute value of the difference between the contact angle of water on the release layer 10 and the contact angle of water on the sealant layer 20 is 30° or less.

Description

Pneumatic tire and manufacturing method thereof

[0001] The present invention relates to a pneumatic tire having a sealant layer on the tire inner surface in the tread portion, and a manufacturing method thereof. More specifically, the present invention relates to a pneumatic tire that can enhance adhesion between the tire inner surface and the sealant layer and improve tire durability, and a manufacturing method thereof.

[0002] Pneumatic tires with puncture sealing properties have been proposed, with a sealant layer made of an adhesive sealant disposed on the inner surface of the tire tread (see, for example, Patent Document 1). In pneumatic tires with such a sealant layer, when a foreign object such as a nail penetrates the tread, the adhesive sealant clings to the foreign object and, as the foreign object falls off, is guided to the puncture hole, thereby providing a sealing effect.

[0003] Meanwhile, in the manufacturing process of pneumatic tires, when a green tire is vulcanized using a bladder, the bladder tends to stick to the inner surface of the green tire, so a release agent is applied to the inner surface of the green tire to prevent sticking between the green tire and the bladder. However, if the compatibility between the tire inner surface to which the release agent is attached and the sealant layer is low, the two do not get along well, and the adhesion between the tire inner surface and the sealant layer is low, which causes a problem of adversely affecting tire durability.

[0004] Japanese Patent Application Publication No. 2003-080909

[0005] An object of the present invention is to provide a pneumatic tire that can enhance the adhesion between the inner surface of the tire and the sealant layer and improve the durability of the tire, and a method for manufacturing the same.

[0006] In order to achieve the above object, the pneumatic tire of the present invention includes a tread portion extending circumferentially in a ring-like shape in the tire circumferential direction, 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, the pneumatic tire having a release layer containing a silicone-based composition on the inner surface of the tire, a sealant layer formed radially inward of the release layer in the tread portion, the sealant in the sealant layer being composed of a silicone-based composition, and the absolute value of the difference between the contact angle of water with the release layer and the contact angle of water with the sealant layer being 30° or less.

[0007] In order to achieve the above object, the manufacturing method of 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 set to 70°C or less.

[0008] The present inventors discovered that, in order to improve the adhesion between the inner surface of a tire and a sealant layer, it is effective to use the contact angle of water as an index of the compatibility between the components and set the absolute value of the difference in the contact angles within a specific range, and thus arrived at the present invention.

[0009] In the present invention, a tire has a release layer containing a silicone-based composition on its inner surface, a sealant layer is formed on the tire radially inward side of the release layer in the tread portion, and the sealant in the sealant layer is composed of a silicone-based composition. Since both the release layer and the sealant layer contain a silicone-based composition, this contributes to improved compatibility. Furthermore, by setting the absolute value of the difference between the water contact angle with the release layer and the water contact angle with the sealant layer to a specific range (30° or less), compatibility can be significantly improved. This enhances the adhesion between the tire inner surface and the sealant layer, improving tire durability.

[0010] In the pneumatic tire of the present invention, the thickness of the release layer is preferably in the range of 0.1 μm to 100.0 μm, which can effectively improve the durability of the tire.

[0011] 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.

[0012] The silicone composition that constitutes the sealant is preferably a two-component curing silicone, which has low viscosity immediately after mixing the two components and can therefore be applied even at low temperatures.

[0013] 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 be 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.

[0014] 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 that is 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] 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 part of the pneumatic tire shown in Fig. 1. Figs. 3(a) and 3(b) show the contact angle θ of water. 10 , θ 20 Fig. 4 is a cross-sectional view illustrating an example of a method for manufacturing a pneumatic tire according to an embodiment of the present invention. 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. 4. Fig. 6 is a meridian cross-sectional view showing a pneumatic tire according to another embodiment of the present invention.

[0016] 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;

[0017] As shown in FIG. 1 , the pneumatic tire of this embodiment includes a tread portion 1 extending circumferentially of the tire to form an annular shape, a pair of sidewall portions 2 disposed on both sides of the tread portion 1, and a pair of bead portions 3 disposed radially inward of the sidewall portions 2.

[0018] At least one carcass layer 4 (one layer in FIG. 1 ) made up of a plurality of carcass cords arranged in the radial direction is mounted between a pair of bead portions 3. Organic fiber cords such as nylon or polyester are preferably used as the carcass cords that make up the carcass layer 4. An annular bead core 5 is embedded in each bead portion 3, and 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.

[0019] Meanwhile, multiple belt layers 7 (two layers in FIG. 1 ) are embedded on the tire outer circumferential side of the carcass layer 4 in the tread portion 1. The belt layers 7 include multiple reinforcing cords that are inclined with respect to the tire circumferential direction, and are arranged so that the reinforcing cords cross each other between the layers. In the belt layers 7, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set to a range of 10° to 40°, for example. Steel cords are preferably used as the reinforcing cords of the belt layers 7.

[0020] At least one belt cover layer 8 (two layers in FIG. 1 ) is disposed on the tire outer periphery side 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 material made of at least one reinforcing cord 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 aramid.

[0021] The tire internal structure described above is a typical example of a pneumatic tire, but is not limited thereto. As a component constituting the tire inner surface Ts, an inner liner layer 9 is disposed along the carcass layer 4.

[0022] In the pneumatic tire, a release layer 10 formed by applying or transferring a release agent is formed on the tire radially inner side of the tire inner surface Ts. The release layer 10 contains a silicone-based composition. Examples of silicone-based compositions include those containing synthetic polymer compounds having a main skeleton formed by siloxane bonds.

[0023] Furthermore, the sealant layer 20 is formed continuously in the tire circumferential direction on the tire radially inner side of the release layer 10 in the tread portion 1. That is, the sealant layer 20, the release layer 10, and the tire inner surface Ts (inner liner layer 9) are laminated in this order from the tire radially inner side. The center position of the sealant layer 20 in the tire width direction preferably coincides with the tire equator, but the center position may be offset from the tire equator to either side in the tire width direction. The tire widthwise distance between the center position of the sealant layer 20 in the tire width direction and the tire equator is preferably 10 mm or less, more preferably 5 mm or less. This prevents the sealant layer 20 from adversely affecting tire balance. The sealant of the sealant layer 20 is composed of a silicone-based composition. The silicone-based composition includes a synthetic polymer compound having a main skeleton formed by siloxane bonds.

[0024] In the release layer 10 and the sealant layer 20, the contact angle θ of water with respect to the release layer 10 10 and the contact angle θ of water on the sealant layer 20 20 The absolute values ​​of the contact angles θ of the release layer 10 are preferably in the range of 90° to 120°. 10 and the contact angle θ of the sealant layer 20 20 The absolute values ​​of are close to each other, and the contact angle θ 10 , θ 20 Absolute value of the difference between |θ 10 -θ 20 | is less than 30°. In particular, the absolute value of the difference |θ 10 -θ 20 is preferably 20° or less, more preferably 10° or less. The contact angle of water is an index of compatibility, and adherends with similar contact angles tend to have high adhesion. Therefore, the absolute value of the difference |θ10 -θ 20 When | is small, the adhesiveness is high, so that the sealant layer 20 can be prevented from falling off or lifting off during running, which is advantageous for the durability of the tire.

[0025] In the present invention, the contact angle of water θ 10 , θ 20 is measured in accordance with JIS R3257. For example, a cut sample is cut out from a product tire along the tire width direction, and the contact angle θ of water between the release layer and the sealant layer on the cut sample is measured. 10 , θ 20 Alternatively, the measurement can be performed using a sheet sample prepared by disassembling the tire inner surface and processing it into a sheet. Alternatively, a sheet prepared by processing a sealant to a certain thickness before application to the tire inner surface, or a rubber sheet to which a release agent used on the tire inner surface is attached, may be used. Water is dropped onto each of the release layer sample 51 and the sealant layer sample 52 obtained in this manner, and the contact angle θ of the water droplet WD is measured. 10 , θ 20 (See FIGS. 3(a) and 3(b)). In FIG. 3, the contact angle θ 20 The contact angle θ 10 Although the case where the contact angle θ 10 , θ 20 The magnitude relationship is not limited to this.

[0026] In the pneumatic tire described above, since both the release layer 10 and the sealant layer 20 contain a silicone-based composition, this contributes to improving compatibility. 10 and the contact angle θ of water with the sealant layer 20 20 Absolute value of the difference between |θ 10 -θ 20 By setting | in a specific range (30° or less), it is possible to improve the compatibility very much. This makes it possible to increase the adhesion between the tire inner surface Ts and the sealant layer 20 and improve the durability of the tire. Here, the absolute value of the difference |θ 10 -θ 20If | exceeds 30°, the release layer 10 and the sealant layer 20 do not easily become compatible with each other, which tends to reduce the adhesion between them and reduce the durability of the tire.

[0027] 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.

[0028] 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, and having a release layer 10 containing a silicone-based composition formed on the tire inner surface Ts. The method for forming the release layer 10 on the tire inner surface Ts is not particularly limited, but it can be formed, for example, by applying a release agent to the inner surface of a green tire during vulcanization. Next, a sealant made of a silicone-based composition is applied to the tire inner surface Ts of the tread portion 1 to form the sealant layer 20. Since silicone-based compositions have good fluidity even at low temperatures, the temperature of the sealant applied to the tire inner surface Ts is set to 70°C or lower. If this temperature exceeds 70°C, the pneumatic tire will be distorted significantly during the process of applying the sealant to the tire inner surface Ts, resulting in a deterioration in tire durability. In particular, the temperature of the sealant when applied to the tire inner surface Ts is preferably in the range of 5°C to 40°C, more preferably in the range of 10°C to 35°C, and most preferably in the range of 15°C to 30°C. This prevents over-vulcanization of the rubber member due to heating during the formation of the sealant layer 20. Furthermore, because the release layer 10 and the sealant layer 20 contain similar materials, they are compatible with each other, allowing the sealant layer 20 to adhere well to the tire inner surface Ts. Furthermore, because the sealant can be applied with the release agent still attached to the tire inner surface, there is no need to perform a process of removing the release agent by buffing or laser treatment, which also leads to improved productivity.

[0029] FIG. 4 shows a specific manufacturing method for a pneumatic tire according to an embodiment of the present invention, and FIG. 5 shows a sealant layer formed on the inner surface of the tire 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 inner surface Ts of the tire, the sealant strip 21 can be arranged spirally on the release layer 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 the sealant layer 20.

[0030] As the silicone-based composition constituting the sealant of the sealant layer 20, one-component curing silicone or two-component curing silicone can be used, but it is particularly preferable to use two-component curing silicone. An example of one-component curing silicone is moisture-curing silicone. Two-component curing silicone is composed of a first liquid and a second liquid, and a curing reaction begins by mixing these first and second liquids, ensuring the stability of the sealant layer 20 after curing. In the above-mentioned device, the first liquid and the second liquid of the two-component curing silicone are supplied from pumps 32 and 33, respectively. Two-component curing silicone has low viscosity immediately after mixing the two liquids, so it can be applied even at low temperatures.

[0031] 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.

[0032] In the above-described pneumatic tire, the belt cover layer 8 may cover only a portion of the belt layer 7 in the tire width direction (for example, the edge portions on both sides of the belt layer in the tire width direction), but it is preferable that the belt cover layer 8 covers the entire area of ​​the belt layer 7 in the tire width direction. This can further improve the durability of the tire, and can also suppress the amount of air leakage from the shoulder portion Sh even if a nail is pierced, thereby further improving puncture sealing performance. In the embodiment of Fig. 1, the belt cover layer 8 located on the inner side in the tire radial direction forms a full cover that covers the entire area of ​​the belt layer 7, and the belt cover layer 8 located on the outer side in the tire radial direction forms an edge cover that covers only the edge portions of the belt layer 7.

[0033] In the above-described pneumatic tire, the thickness g of the release layer 10 (see FIG. 2) is preferably in the range of 0.1 μm to 100.0 μm. By appropriately setting the thickness g of the release layer 10 in this manner, tire durability can be effectively improved. Here, if the thickness g of the release layer 10 is less than 0.1 μm, it will be difficult for the release layer 10 to blend in with the sealant layer 20, resulting in a deterioration in tire durability. Conversely, if the thickness g is greater than 100.0 μm, the release layer 10 will deform significantly when subjected to tire deformation, accelerating destruction of the release layer 10 and potentially causing the sealant layer 20 to fall off. The thickness g of the release layer 10 is an average thickness. The thickness g of the release layer 10 can be detected, for example, using an electron microscope. When measuring the thickness g of the release layer 10 using an electron microscope, a cut sample cut out from the tire along the tire width direction is used, and the thickness is measured at multiple locations on the cut sample (for example, four locations in the tire circumferential direction and three locations in the tire width direction).The thickness g of the release layer 10 can be calculated by averaging the measurements taken at these multiple locations.

[0034] Furthermore, the thickness S of the sealant layer 20 (see FIG. 2 ) is preferably in the range of 2.0 mm to 5.0 mm. This ensures sufficient puncture sealing in the center region as well as the shoulder region Sh. 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, the sealant layer 20 will flow due to the tire's centrifugal force, resulting in poor tire balance during running. 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 a tire meridian cross section at eight locations around the tire circumference, 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 end 20 e 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.

[0035] 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.

[0036] FIG. 6 shows a pneumatic tire according to another embodiment of the present invention. In FIG. 6, a sound-absorbing material 40 is installed along the tire circumferential direction on the 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, the sound-absorbing material 40 is installed on the sealant layer 20, which has been applied at a low temperature, so damage to the sound-absorbing material 40 is avoided and its sound-absorbing effect can be maintained satisfactorily.

[0037] 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 has a release layer containing a silicone-based composition on the tire inner surface, a sealant layer is formed on the tire inner surface in the tread portion, and a contact angle θ 10 , θ 20 The absolute value of the difference, the type of sealant, the thickness g of the release layer, and the distance L were set as shown in Table 1 to produce tires of the conventional example and examples 1 to 7.

[0038] The durability and puncture sealing performance of these test tires were evaluated by the following test methods, and the results are shown in Table 1.

[0039] Durability: Each test tire was mounted on a wheel with a rim size of 19 x 8.5J, and a running test was carried out using a drum testing machine under conditions of an air pressure of 120 kPa, 100% of the maximum load, a running speed of 80 km, and a running distance of 6,000 km, after which the condition of the sealant layer was visually confirmed. The evaluation results were indicated as "Excellent" when there was no lift in the sealant layer and the sealant function was still exhibited, "Good" when there was slight lift in the sealant layer but the sealant function was still exhibited, and "Poor" when the sealant layer had fallen off.

[0040] Puncture sealing property: Each test tire was mounted on a wheel with a rim size of 19 x 8.5J, and a nail with a diameter of 5 mm was driven into the tread portion under conditions of an initial air pressure of 250 kPa and a temperature of 23°C. After the nail was removed, the tire was left for two weeks, and the air pressure was measured. 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 puncture sealing property.

[0041]

[0042] As can be seen from Table 1, the pneumatic tires of Examples 1 to 7 had improved durability compared to the conventional tire.

[0043] REFERENCE SIGNS LIST 1 tread portion 2 sidewall portion 3 bead portion 4 carcass layer 5 bead core 6 bead filler 7 belt layer 10 release layer 20 sealant layer Ts tire inner surface θ 10 , θ 20 Water contact angle

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 these sidewall portions, the pneumatic tire having a release layer containing a silicone-based composition on the inner surface of the tire, a sealant layer formed on the radially inward side of the release layer in the tread portion, a sealant in the sealant layer being composed of a silicone-based composition, and the absolute value of the difference between the contact angle of water with respect to the release layer and the contact angle of water with respect to the sealant layer is 30° or less.

2. The pneumatic tire according to claim 1, wherein the thickness of the release layer is in the range of 0.1 μm to 100.0 μm.

3. The pneumatic tire according to claim 1 or 2, characterized in that the glass transition temperature of the sealant is in the range of -120°C to -40°C.

4. A pneumatic tire according to any one of claims 1 to 3, characterized in that the silicone composition constituting the sealant is a two-component curing silicone.

5. A pneumatic tire according to any one of claims 1 to 4, 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.

6. A pneumatic tire according to any one of claims 1 to 5, 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.

7. A method for producing a pneumatic tire as claimed in any one of claims 1 to 5, 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 setting the temperature of the sealant applied to the inner surface of the tire to 70°C or lower.

8. The method for manufacturing a pneumatic tire according to claim 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.

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