Composition for sealant and pneumatic tire

Abstract

To provide a composition for a sealant which enables formation of a sealant layer that is excellent in shape retention property and sealing characteristics.SOLUTION: A composition for a sealant contains, with respect to 100 pts.mass of a solid rubber component containing diene-based rubber, 95 to 150 pts.mass of a hydrocarbon resin, 20 to 100 pts.mass of a liquid plasticizer, and 0.05 to 1.5 pts.mass of sulfur. The composition for the sealant has dynamic storage shear elastic modulus G' at 25% strain, which is obtained by measuring a crosslinked object under the conditions of a temperature of 40°C and a frequency of 1.0 Hz, of 10 to 50 kPa.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a composition for a sealant and a pneumatic tire using the same.

Background Art

[0002] As a pneumatic tire having a puncture prevention function, a tire in which a sealant layer is disposed on the inner surface of the tire is known. In a tire provided with a sealant layer, when a foreign object such as a nail pierces the tread and a through hole is formed, the sealant layer automatically closes the through hole to prevent air leakage from the tire. The sealant layer can be formed, for example, by discharging a composition for a sealant from a nozzle of a coating device and applying it to the inner surface of the tire.

[0003] As such a composition for a sealant, for example, Patent Document 1 describes a composition containing an unsaturated diene elastomer, a hydrocarbon resin between 30 phr and 90 phr, a liquid plasticizer between 0 phr and 60 phr having a Tg lower than -20°C, and a filler between 0 and less than 30 phr. However, the composition for a sealant described in Patent Document 1 has high viscosity at the coating temperature and places a load on the coating device, so it is necessary to suppress the coating speed.

[0004] In order to improve the above coating speed, Patent Document 2 discloses increasing the content of the hydrocarbon resin, specifically, blending 95 to 150 parts by mass of the hydrocarbon resin, 20 to 60 parts by mass of the liquid plasticizer, and a specific filler with respect to 100 parts by mass of the solid rubber component.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

[0006] Tires with a sealant layer formed by a coating device are generally stored at room temperature in a stationary state. At that time, if the sealant layer is too soft, the sealant layer may flow and deform in the stationary state. Therefore, the sealant layer is required to have shape retention. On the other hand, when a foreign object such as a nail pierces the tread, the foreign object may be left pierced without being immediately pulled out. In that case, cracks may occur in the sealant layer over time, resulting in air leakage. Therefore, improvement of the sealing property against such air leakage over time is required.

[0007] In view of the above points, an embodiment of the present invention aims to provide a sealant composition capable of forming a sealant layer excellent in shape retention and sealing properties. [Means for Solving the Problems]

[0008] The present invention includes the following embodiments. [1] A sealant composition containing 95 to 150 parts by mass of a hydrocarbon resin, 20 to 100 parts by mass of a liquid plasticizer, and 0.05 to 1.5 parts by mass of sulfur with respect to 100 parts by mass of a solid rubber component containing a diene rubber, and having a dynamic storage shear modulus G' measured under the conditions of a temperature of 40°C, a frequency of 1.0 Hz, and a strain of 25% for the crosslinked product of 10 to 50 kPa. [2] The sealant composition according to [1], wherein the solid rubber component contains at least one selected from the group consisting of natural rubber, synthetic polyisoprene, polybutadiene, butadiene copolymer, and isoprene copolymer. [3] The sealant composition according to [1] or [2], wherein 100 parts by mass of the solid rubber component contains 40 to 100 parts by mass of natural rubber and / or synthetic polyisoprene and 0 to 60 parts by mass of polybutadiene. [4] The sealant composition according to any one of [1] to [3], wherein the hydrocarbon resin contains at least one selected from the group consisting of petroleum resins, styrene resins, and terpene resins. [5] The sealant composition according to any one of [1] to [4], wherein the liquid plasticizer contains oil and / or liquid rubber. [6] A pneumatic tire including a sealant layer formed of the sealant composition according to any one of [1] to [5].

Advantages of the Invention

[0009] According to an embodiment of the present invention, a sealant layer excellent in shape retention and sealing characteristics can be formed.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0011] The sealant composition according to this embodiment contains 95 to 150 parts by mass of a hydrocarbon resin, 20 to 100 parts by mass of a liquid plasticizer, and 0.05 to 1.5 parts by mass of sulfur with respect to 100 parts by mass of a solid rubber component containing a diene rubber. The dynamic storage shear modulus G' measured under the conditions of a temperature of 40 °C, a frequency of 1.0 Hz, and a strain of 25% for the crosslinked product is 10 to 50 kPa. In addition to such a combination of specific components, since the dynamic storage shear modulus G' at 40 °C is 10 kPa or more, the flow deformation of the sealant layer can be suppressed, and the shape retention can be improved. Further, since the dynamic storage shear modulus G' is 50 kPa or less, the generation of cracks over time can be suppressed, and air leakage can be suppressed, that is, the sealing performance can be improved. More specifically, it is considered that the flow is suppressed by crosslinking with a small amount of sulfur, and an appropriate softness is imparted to the sealant layer by the combination of the hydrocarbon resin and the liquid plasticizer, thereby improving the sealing performance. Note that the sealing performance refers to the performance of automatically closing through holes to prevent air leakage from the tire, and in this embodiment, it refers to the performance of suppressing air leakage over time as described above.

[0012] In this embodiment, the solid rubber component contains a diene rubber. The solid rubber component preferably contains a diene rubber as a main component. Therefore, the content ratio of the diene rubber in 100% by mass of the solid rubber component is preferably 50% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and may be 100% by mass. In this specification, "solid" means having no fluidity at 23 °C.

[0013] The diene rubber refers to a rubber having a repeating unit corresponding to a diene monomer having a conjugated double bond. Examples of the diene rubber in the solid rubber component include natural rubber (NR), synthetic polyisoprene (isoprene rubber; IR), polybutadiene (butadiene rubber; BR), butadiene copolymer, isoprene copolymer, and the like. Any one of these may be used alone or two or more of them may be used in combination. Modified diene rubbers at the terminals or main chains as required are also included in this concept.

[0014] Here, the butadiene copolymer is a copolymer of butadiene and other monomers, and examples thereof include styrene-butadiene rubber (SBR), butadiene-isoprene copolymer rubber, styrene-butadiene-isoprene copolymer rubber, and the like. The isoprene copolymer is a copolymer rubber of isoprene and other monomers, and examples thereof include styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, styrene-butadiene-isoprene copolymer rubber, and the like. For a copolymer rubber containing both isoprene and butadiene as monomers, it shall be included in the copolymer of the monomer with the higher molar ratio. That is, if the molar ratio of butadiene is higher than that of isoprene, it shall be included in the butadiene copolymer, and if the molar ratio of isoprene is higher than that of butadiene, it shall be included in the isoprene copolymer.

[0015] In one embodiment, it is preferable that 100 parts by mass of the solid rubber component contains 40 to 100 parts by mass of natural rubber and / or polyisoprene and 0 to 60 parts by mass of polybutadiene, where the polybutadiene may be 0 parts by mass. 100 parts by mass of the solid rubber component may contain 50 to 80 parts by mass of natural rubber and / or polyisoprene and 20 to 50 parts by mass of polybutadiene.

[0016] The solid rubber component may contain a solid rubber other than the diene rubber. Examples of such non-diene rubbers include butyl rubber, halogenated butyl rubber, ethylene-propylene rubber, and the like.

[0017] The hydrocarbon resin is a polymer essentially based on carbon and hydrogen. As the hydrocarbon resin, a solid thermoplastic resin having no fluidity at 23°C is preferably used. The hydrocarbon resin may be aliphatic, alicyclic, aromatic, or a combination thereof, such as aliphatic / aromatic. The hydrocarbon resin may be a petroleum resin, or a natural resin or synthetic resin not of petroleum origin.

[0018] Preferred examples of the hydrocarbon resin include petroleum resins, styrene resins, and terpene resins, and any one of these may be used alone or two or more of them may be used in combination. In one embodiment, the hydrocarbon resin preferably contains at least 60% by mass, more preferably at least 80% by mass, still more preferably at least 90% by mass, and may contain 100% by mass, of at least one selected from the group consisting of petroleum resins, styrene resins, and terpene resins.

[0019] A petroleum resin is a resin obtained by polymerizing a petroleum fraction. Examples include C5 aliphatic petroleum resins, C9 aromatic petroleum resins, and C5 / C9 aliphatic / aromatic copolymer petroleum resins, and any one of these may be used alone or two or more of them may be used in combination. The aliphatic petroleum resin is a resin obtained by polymerizing a petroleum fraction (C5 fraction) corresponding to 4 to 5 carbon atoms, and may be hydrogenated. The aromatic petroleum resin is a resin obtained by polymerizing a petroleum fraction (C9 fraction) corresponding to 8 to 10 carbon atoms, and may be hydrogenated. The aliphatic / aromatic copolymer petroleum resin is a resin obtained by copolymerizing a C5 fraction and a C9 fraction, and may be hydrogenated.

[0020] A styrene resin (styrene-based hydrocarbon resin) is a resin obtained by polymerizing a styrene-based monomer that is styrene or its derivative (e.g., α-methylstyrene, vinyltoluene, 4-tert-butylstyrene, etc.), and may also be a copolymer of a styrene-based monomer and another aromatic monomer or aliphatic monomer. Examples of the styrene resin include styrene / α-methylstyrene copolymer, α-methylstyrene homopolymer, styrene / aliphatic monomer copolymer, α-methylstyrene / aliphatic monomer copolymer, styrene / α-methylstyrene / aliphatic monomer copolymer, etc., and any one of these may be used alone or two or more of them may be used in combination.

[0021] Terpene resins (terpene hydrocarbon resins) are resins obtained by polymerizing terpene compounds and have units derived from terpene compounds. Examples of terpene compounds include α-pinene, β-pinene, limonene, dipentene, and the like. Examples of terpene resins include polyterpene resins obtained by polymerizing only terpene compounds, and modified terpene resins obtained by polymerizing terpene compounds and monomers other than terpenes. Any one of these may be used alone or in combination of two or more. Examples of modified terpene resins include aromatic modified terpene resins (for example, terpene-phenol resins) obtained by polymerizing terpene compounds and aromatic compounds. As the terpene resin, it is preferable to use a polyterpene resin, and more preferably a pinene resin having α-pinene and / or β-pinene as the main monomer.

[0022] The softening point of the hydrocarbon resin is not particularly limited, but is preferably 80 to 150°C, more preferably 80 to 130°C. In this specification, the softening point is a value measured in accordance with ASTM D6090, and in the examples, it is the value measured using "DP70" (automatic softening point measuring device) manufactured by Mettler Toledo.

[0023] The content of the hydrocarbon resin is 95 to 150 parts by mass, preferably 95 to 130 parts by mass, and more preferably 95 to 115 parts by mass with respect to 100 parts by mass of the solid rubber component. When the content of the hydrocarbon resin is 95 parts by mass or more, the viscosity during coating can be lowered, making it easier to improve the coating speed. Also, it can prevent the sealing layer from becoming too hard and improve the sealing properties. When the content of the hydrocarbon resin is 150 parts by mass or less, cracks are less likely to occur in the sealing layer, and the sealing properties can be improved.

[0024] A liquid plasticizer refers to a plasticizer that is liquid at 23°C. That is, "liquid" means having fluidity at 23°C. As the liquid plasticizer, it is preferable to use oil or liquid rubber, and oil and liquid rubber may be used in combination. In one embodiment, the liquid plasticizer preferably contains 60% by mass or more of oil and / or liquid rubber, more preferably 80% by mass or more, still more preferably 90% by mass or more, and may contain 100% by mass.

[0025] As the oil, various oils generally compounded in rubber compositions can be used, and examples include mineral oil, vegetable oil, polyolefin oil, and the like. Specific examples of preferred oils are mineral oils mainly composed of hydrocarbons, and for example, it is preferable to use at least one process oil selected from the group consisting of paraffin oil, naphthene oil, and aromatic oil.

[0026] Liquid rubber is rubber that is liquid at 23°C. Examples of liquid rubber include liquid polyisoprene rubber, liquid polybutadiene rubber, liquid styrene-butadiene rubber, liquid isoprene-butadiene rubber, liquid isoprene-styrene rubber, liquid isoprene-butadiene-styrene rubber, liquid isobutylene, liquid ethylene-propylene-diene rubber (EPDM), and the like. These liquid rubbers may be those modified by carboxylation, methacrylation, or the like. Any one of these liquid rubbers may be used, or two or more thereof may be used in combination. As the liquid rubber, liquid diene rubber is preferably used.

[0027] The weight average molecular weight (Mw) of the liquid rubber is not particularly limited, but is generally less than 100,000, and may be 1,000 to 80,000 or 2,000 to 60,000. The weight average molecular weight (Mw) of the diene rubber (including natural rubber) of the solid rubber component is generally 200,000 or more and is distinguished from the liquid rubber.

[0028] In this specification, the weight-average molecular weight (Mw) is a value measured by gel permeation chromatography (GPC). Specifically, for example, using "HLC8320-GPC" manufactured by Tosoh Corporation equipped with a differential refractive index detector (RI) as the measuring device, tetrahydrofuran (THF) as the solvent, "TSKgel SuperHZM-M" manufactured by Tosoh Corporation as the column, the measuring temperature is 40 °C, the flow rate is 0.35 mL / min, the concentration is 1.0 g / L, and the injection volume is 40 μL. It is calculated in terms of polystyrene using commercially available standard polystyrene.

[0029] The content of the liquid plasticizer is 20 to 100 parts by mass, preferably 30 to 80 parts by mass, more preferably 35 to 80 parts by mass, and still more preferably 40 to 70 parts by mass with respect to 100 parts by mass of the solid rubber component. When the content of the liquid plasticizer is 20 parts by mass or more, the viscosity during coating can be lowered, making it easier to improve the coating speed, and the sealing properties in the sealant layer can be improved. When the content of the liquid plasticizer is 100 parts by mass or less, it becomes easier to ensure the shape retention of the sealant layer.

[0030] Sulfur is blended as a crosslinking agent in the sealant composition according to this embodiment. Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersed sulfur, and the like.

[0031] The content of sulfur is 0.05 to 1.5 parts by mass, preferably 0.1 to 1.0 parts by mass, and more preferably 0.1 to 0.5 parts by mass with respect to 100 parts by mass of the solid rubber component. When the content of sulfur is 0.05 parts by mass or more, the flow deformation of the sealant layer can be suppressed by sulfur crosslinking to enhance the shape retention. When the content of sulfur is 1.5 parts by mass or less, it can prevent the sealant layer from becoming too hard and improve the sealing properties.

[0032] The vulcanization accelerator may be incorporated into the sealant composition according to this embodiment. Examples of the vulcanization accelerator include sulfenamide-based vulcanization accelerators, thiuram-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiourea-based vulcanization accelerators, guanidine-based vulcanization accelerators, dithiocarbamate-based vulcanization accelerators, etc. Among these, it is preferable to use at least one selected from the group consisting of sulfenamide-based vulcanization accelerators, thiazole-based vulcanization accelerators, and guanidine-based vulcanization accelerators, and more preferably to use a sulfenamide-based vulcanization accelerator.

[0033] Examples of the sulfenamide-based vulcanization accelerator include N-cyclohexyl-2-benzothiazolylsulfenamide (abbreviation: CZ), N-tert-butyl-2-benzothiazolylsulfenamide (abbreviation: NS), N-oxydiethylene-2-benzothiazolylsulfenamide (abbreviation: OBS), N,N-diisopropyl-2-benzothiazolesulfenamide (abbreviation: DZ). Any one of these may be used, or two or more of them may be used in combination.

[0034] The content of the vulcanization accelerator is not particularly limited and may be, for example, 0.5 to 10 parts by mass, 1 to 5 parts by mass, or 1 to 3 parts by mass with respect to 100 parts by mass of the solid rubber component.

[0035] In addition to the above components, various additives such as fillers, zinc oxide, stearic acid, processing aids, softeners, waxes, and anti-aging agents may be appropriately incorporated within the normal range into the sealant composition according to this embodiment.

[0036] Examples of the filler include carbon black and / or silica. The carbon black is not particularly limited, and various known types can be used. Similarly, the silica is not particularly limited, and examples thereof include wet silica such as wet precipitated silica and wet gelled silica. The content of the filler is not particularly limited. For example, it may contain 0 to 30 parts by mass, or 0 to 20 parts by mass, based on 100 parts by mass of the solid rubber component. In one embodiment, the sealant composition may not contain a filler, or may contain a small amount of carbon black for coloring purposes, for example, 0.5 to 8 parts by mass based on 100 parts by mass of the solid rubber component.

[0037] The content of zinc oxide is not particularly limited. For example, it may be 0 to 10 parts by mass, 0.5 to 5 parts by mass, or 1 to 4 parts by mass, based on 100 parts by mass of the solid rubber component.

[0038] The content of stearic acid is not particularly limited. For example, it may be 0 to 10 parts by mass, 0.5 to 5 parts by mass, or 1 to 4 parts by mass, based on 100 parts by mass of the solid rubber component.

[0039] The sealant composition according to the present embodiment can be produced by kneading in accordance with a conventional method using a kneader commonly used in the rubber industry. For example, in the first step, a compounding agent excluding a hydrocarbon resin and a crosslinking compounding agent (sulfur and a vulcanization accelerator) is added to and kneaded with the solid rubber component. Then, in the second step, the hydrocarbon resin and the crosslinking compounding agent are added and kneaded. Thereby, a sealant composition is obtained. The sealant composition according to the present embodiment may be a crosslinked product crosslinked by the sulfur contained therein, or may be an uncrosslinked product before crosslinking. In one embodiment, it is preferable that the sealant composition is uncrosslinked at the stage after discharge from the kneader in the second step.

[0040] In the first step, for example, a kneader such as a Banbury mixer, a roll mill, or a kneading extruder is used. In the first step, a liquid plasticizer is added to the kneader together with the solid rubber component, and further, a compounding agent excluding the hydrocarbon resin and the crosslinking compounding agent is optionally added, and kneading is performed while raising the temperature of the kneaded product. The discharge temperature of the kneaded product from the kneader in the first step is not particularly limited, but may be, for example, 120 to 160°C.

[0041] In the second step, for example, a kneading extruder such as a twin-screw kneading extruder or a conical kneader is used. In the second step, the hydrocarbon resin and the crosslinking compounding agent are added to the kneading extruder together with the kneaded product obtained in the first step and kneaded. The discharge temperature of the kneaded product from the kneader in the second step is not particularly limited, but it is preferably a temperature higher than the softening point of the hydrocarbon resin. Thereby, the dispersibility of the hydrocarbon resin can be improved. The discharge temperature in the second step is preferably 80 to 140°C, more preferably 100 to 130°C.

[0042] The dynamic storage shear modulus G' of the sealant composition according to the present embodiment, measured using its crosslinked product under the conditions of a temperature of 40°C, a frequency of 1.0 Hz, and a strain of 25%, is 10 to 50 kPa. In addition to the combination of specific components as described above, since the dynamic storage shear modulus G' is 10 kPa or more and 50 kPa or less, as described above, it is possible to achieve both the shape retention and the sealing characteristics of the sealant layer. The dynamic storage shear modulus G' is more preferably 15 to 47 kPa, more preferably 16 to 46 kPa, and still more preferably 20 to 45 kPa.

[0043] The dynamic storage shear modulus G’ can be in the range of 10 to 50 kPa by appropriately adjusting the types and amounts of the above components within the above ranges. For example, by using or increasing the amount of oil as a liquid plasticizer, using or increasing the amount of butadiene rubber as a diene rubber, reducing the amount of sulfur, or blending a hydrocarbon resin in the specified amount as above, G’ tends to decrease. By doing the opposite, G’ tends to increase. Therefore, by adjusting one or more of these, G’ can be set within the above numerical range. The measurement method of the dynamic storage shear modulus G’ is as described in the column of the examples.

[0044] The sealant composition according to this embodiment can be used to form a sealant layer on the inner surface of a pneumatic tire. Examples of pneumatic tires include pneumatic tires of various applications and various sizes, such as passenger car tires and heavy-duty tires used for trucks and buses.

[0045] An embodiment of a pneumatic tire having a sealant layer will be described with reference to FIG. 1. The pneumatic tire 1 includes an annular tread 2 that contacts the road surface, a pair of left and right bead portions 3, 3 located inside the tread 2 in the tire radial direction RD, and a pair of left and right sidewalls 4, 4 located between the tread 2 and the bead portions 3, 3. The tire 1 includes a bead core 5 embedded in the bead portion 3, a carcass ply 6 extending toroidally between the left and right bead portions 3, 3, a belt 7 and tread rubber 8 provided on the outer peripheral side of the carcass ply 6 in the tread 2, an inner liner 9 provided on the inner surface side of the carcass ply 6, and a sealant layer 10 provided on the inner surface side of the inner liner 9.

[0046] The sealant layer 10 is provided by being overlaid on the inner surface 1A of the pneumatic tire 1, specifically, on the inner side of the inner liner 9. In this example, the sealant layer 10 is provided from one end to the other end in the tire axial direction AD on the inner surface 1A of the tread 2. Thus, it is preferable that the sealant layer 10 is provided over the entire inner surface of the tread 2, and it may be provided only on the inner surface of the tread 2, or it may be provided in a wider range including the inner surface of the tread 2. That is, the sealant layer 10 is preferably provided on the inner surface 1A of the tire 1 including the inner surface of the tread 2.

[0047] The method for forming the sealant layer is not particularly limited, but preferably, the sealant composition is heated to a temperature higher than the softening point of the hydrocarbon resin (for example, 80 to 160 °C) and applied to the inner surface of the pneumatic tire using an application device. Specifically, for example, an uncrosslinked sealant composition is heated and crosslinked in an application device, the crosslinked sealant composition is discharged in a band shape from the nozzle of the application device, and the band-shaped material is applied along the tire circumferential direction while being displaced in the tire axial direction with respect to the tire inner surface. After application, by leaving it at room temperature, the fluidity of the sealant composition decreases and it adheres to the inner surface of the pneumatic tire, thereby forming the sealant layer.

[0048] The thickness of the sealant layer is not particularly limited, and for example, it may be 3 to 7 mm.

Examples

[0049] Examples are shown below, but the present invention is not limited to these examples.

[0050] Each component used in the examples and comparative examples is as follows. · IR: "IR2200" manufactured by JSR Corporation · BR: "UBEPOL BR150B" manufactured by UBE Industries, Ltd.

[0051] · Process oil 1: Aromatic oil, "Process NC140" manufactured by ENEOS Corporation · Process Oil 2: Paraffin oil, "Process P200" manufactured by ENEOS Corporation · Liquid Rubber: Liquid polyisoprene rubber, "LIR50" manufactured by Kuraray Co., Ltd.

[0052] · Petroleum Resin: Aliphatic / Aromatic petroleum resin, "Petrotac 90" manufactured by Tosoh Corporation, Softening Point = 95°C · Polyterpene Resin: Pinene resin, "Sylvatraxx 4125" manufactured by KRATON Corporation, Softening Point = 125°C · Styrenic Resin: α-Methylstyrene-based resin, "Sylvatraxx 4401" manufactured by KRATON Corporation, Softening Point = 85°C

[0053] · Zinc Oxide: "Zinc Oxide Type 2" manufactured by Mitsui Mining & Smelting Co., Ltd. · Stearic Acid: "Lunac S20" manufactured by Kao Corporation · Sulfur: "Powdered Sulfur" manufactured by Tsurumi Chemical Industry Co., Ltd. · Vulcanization Accelerator: "Soxeal CZ" manufactured by Sumitomo Chemical Co., Ltd.

[0054] [Examples 1 - 12, Comparative Examples 1 - 8] Sealant compositions of Examples 1 - 12 and Comparative Examples 1 - 8 were prepared according to the formulations (parts by mass) shown in Table 1 below. Specifically, first, in the first step, using a Banbury mixer, components excluding hydrocarbon resin and crosslinking agents (i.e., sulfur and vulcanization accelerator) were kneaded (discharge temperature 100°C). Then, in the second step, using a twin-screw kneading extruder, hydrocarbon resin and crosslinking agents were added to the kneaded product obtained in the first step and kneaded to obtain a sealant composition. In the second step, the discharge temperature from the twin-screw kneading extruder was 130°C and the kneading time was 3 minutes.

[0055] For each of the obtained sealant compositions, the dynamic storage shear modulus G' was measured, and the shape retention and sealing properties of the sealant layer were evaluated. The measurement method and evaluation method are as follows.

[0056] (1) Dynamic storage shear modulus G': The sealant composition was crosslinked by heating at 150 °C for 120 minutes. For the obtained crosslinked product, using the "D-RPA3000" manufactured by Montech conforming to ISO6502, the dynamic storage shear modulus G' was measured under the conditions of a temperature of 40 °C, a frequency of 1 Hz, and a strain of 25%. Specifically, as shown in Figure 2, using a double-cone sealed (bi-conical) die with conical surfaces facing each other, 5 g of the crosslinked product was placed as a sample on the lower die, sandwiched between the lower die and the upper die, and the lower die was rotated and vibrated under the conditions of a temperature of 40 °C, a frequency of 1.0 Hz, and a strain of 25% to conduct a dynamic viscoelasticity test, and the value of the dynamic storage shear modulus G' at 25% strain was obtained. Here, the inclination angle of the conical surface is 3.5833°. Let twice the inclination angle be Φ and the vibration angle of the lower die be θ, then the strain % is defined as 100θ / Φ. Therefore, strain 25% = 100θ / (2×3.5833°), and the oscillation amplitude angle θ of the lower die was set to 1.79165°.

[0057] (2) Shape retention: Using a material coating system manufactured by Nordson, after heating the sealant composition at 150 °C for 120 minutes, while discharging from the nozzle at a pressure of 4.0×10 5 Pa, it was applied to the inner surface of a pneumatic tire (tire size: 215 / 55R17) to form a sealant layer with a thickness of 4 mm. The pneumatic tire with the sealant layer formed was stacked flat at room temperature and stored statically for 2 weeks, and then the inner surface of the tire was observed to confirm whether the sealant layer had undergone flow deformation. Those that did not undergo flow deformation were indicated as "○" (good shape retention), and those that underwent flow deformation were indicated as "×" (poor shape retention).

[0058] (3) Sealing property: An inflated tire equipped with a sealant layer prepared in the same manner as the evaluation of the above shape retention property was used. The tire was mounted on a rim and filled with air at an internal pressure of 180 kPa. A nail (diameter 5.2 mm, length 50 mm) was passed through the tread, and after leaving it as it was for one week, the sealing property was evaluated based on whether there was air leakage or not. Those with a less than 5% drop in internal pressure were marked as "○" (good sealing property), and those with a 5% or more drop in internal pressure were marked as "×" (poor sealing property).

[0059]

Table 1

[0060] The results are as shown in Table 1. In Comparative Example 1, since sulfur was not compounded, the sealant layer underwent flow deformation during static storage and was inferior in shape retention property. In Comparative Example 2, the sulfur content was more than the specified amount, and although it was excellent in shape retention property, cracks occurred in the sealant layer and it was inferior in sealing property.

[0061] In Comparative Example 3, since the hydrocarbon resin was less than the specified amount, the sealant layer was hard at room temperature and was inferior in sealing property. In Comparative Example 4, since the hydrocarbon resin was more than the specified amount and the dynamic storage shear modulus G' was greater than the upper limit, cracks occurred in the sealant layer and it was inferior in sealing property.

[0062] In Comparative Example 5, since oil was not compounded and the dynamic storage shear modulus G' was greater than the upper limit, the sealant layer was hard at room temperature and was inferior in sealing property. In Comparative Example 6, since the oil was more than the specified amount, it was inferior in the shape retention property of the sealant layer.

[0063] In Comparative Example 7, although the contents of the liquid plasticizer, hydrocarbon resin, and sulfur satisfied the specified amounts, the dynamic storage shear modulus G' was smaller than the lower limit. Therefore, the sealant layer was prone to flow deformation and had poor shape retention. In Comparative Example 8, although the contents of the liquid plasticizer, hydrocarbon resin, and sulfur satisfied the specified amounts, the dynamic storage shear modulus G' was larger than the upper limit. Therefore, cracks occurred in the sealant layer and the sealing performance was poor.

[0064] On the other hand, in Examples 1 to 12, while containing a specified amount of a liquid plasticizer, a hydrocarbon resin, and sulfur as a vulcanizing agent, and having a dynamic storage shear modulus at 40°C within the specified range, the flow deformation of the sealant layer was suppressed, resulting in excellent shape retention. Also, the occurrence and growth of cracks over time in the nail driving test were suppressed, and the sealing performance was excellent.

[0065] Note that various numerical ranges described in the specification can be arbitrarily combined with their upper and lower limits, and all of these combinations are described in the specification as preferred numerical ranges. Also, the description of the numerical range "X to Y" means X or more and Y or less.

Explanation of Reference Numerals

[0066] 1... pneumatic tire, 2... tread, 3... bead portion, 4... sidewall, 5... bead core, 6... carcass ply, 7... belt, 8... tread rubber, 9... inner liner, 10... sealant layer

Claims

1. Based on 100 parts by mass of the solid rubber component containing diene rubber, 95 to 150 parts by mass of hydrocarbon resin, 20 to 100 parts by mass of liquid plasticizer, 0.05 to 1.5 parts by mass of sulfur, and includes, A sealant composition in which the dynamic storage shear modulus G' measured under the conditions of a temperature of 40°C, a frequency of 1.0 Hz, and a strain of 25% for the crosslinked product is 10 to 50 kPa.

2. The sealant composition according to claim 1, wherein the solid rubber component includes at least one selected from the group consisting of natural rubber, synthetic polyisoprene, polybutadiene, butadiene copolymer, and isoprene copolymer.

3. The sealant composition according to claim 1, wherein 100 parts by mass of the solid rubber component includes 40 to 100 parts by mass of natural rubber and / or synthetic polyisoprene and 0 to 60 parts by mass of polybutadiene.

4. The sealant composition according to claim 1, wherein the hydrocarbon resin includes at least one selected from the group consisting of petroleum resin, styrene resin, and terpene resin.

5. The sealant composition according to claim 1, wherein the liquid plasticizer includes oil and / or liquid rubber.

6. A pneumatic tire provided with a sealant layer formed of the sealant composition according to any one of claims 1 to 5.

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