Vulcanized rubber and pneumatic tires

Abstract

To provide vulcanized rubber capable of self-repairing damaged areas such as external damage and ozone cracks through heating, and a pneumatic tire equipped with said vulcanized rubber. [Solution] A vulcanized rubber manufactured by vulcanizing a rubber composition, wherein a measurement sample in the shape of a JIS No. 7 dumbbell is prepared, and the breaking strength is measured by performing a tensile test at room temperature in accordance with JIS K6251 (TS B ), the central portion of the long side of the measurement sample is cut in the thickness direction, the cut surfaces are immediately bonded together, heat-treated at 90°C for 100 minutes, and then the breaking strength is measured by performing a tensile test at room temperature in accordance with JIS K6251 (TS A ) When that is the case, (TS A ) / (TS B )≧0.05 Vulcanized rubber that meets the requirements.

Description

[Technical Field]

[0001] This invention relates to vulcanized rubber and pneumatic tires. [Background technology]

[0002] The side of a pneumatic tire is called the sidewall, and it can be damaged or develop ozone cracks during use. When such damage or ozone cracks occur, it is generally difficult to repair the affected area, and in most cases, the pneumatic tire itself must be replaced. Furthermore, in recent years, with growing environmental awareness, retreaded tires are sometimes produced by replacing the worn tread portion of used pneumatic tires. However, if there is damage or ozone cracks in the tire sidewall, it cannot be used as a base tire (a tire with the worn tread portion removed) for retreaded tires.

[0003] In Patent Document 1 below, a dumbbell-shaped test specimen conforming to ASTM D638 Type V with a thickness of 2 mm is used, containing a rubber component including an epoxidized diene rubber, an imidazole compound, and a carboxylic acid compound with a valency of 2 or more. When the elongation at break EB (%) and breaking strength TB (MPa) are measured in accordance with JIS K 6251, the TB and the EB repair rate (%) RR defined below are used. EB , and the TB repair rate (%) RR as defined below. TB However, each of these is a rubber composition for tires that satisfies formulas (1) to (3). TB≧0.40 (1) RR EB ≥20 (2) RR TB ≥20 (3) (RR EB This value is defined as EB (%) of the repaired specimen / EB (%) of the annealed specimen × 100. TBThis value is defined as TB (MPa) of the repaired specimen / TB (MPa) of the annealed specimen × 100. Here, a repaired specimen is a specimen that has been cut in the thickness direction at the center of its long side, the cut surfaces have been immediately bonded together, and then heat-treated at 80°C for 24 hours. An annealed specimen is a specimen that has been heat-treated at 80°C for 24 hours. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-174336 [Overview of the project] [Problems that the invention aims to solve]

[0005] In components such as the sidewalls of pneumatic tires, where repairing only that part after use is difficult, if the rubber itself could repair damaged areas such as external damage or ozone cracks through heating or other means, it would not only extend the product life during tire operation but also be useful when reusing them as retreaded tires. The technology described in Patent Document 1 above has been found to have room for further improvement regarding the self-healing properties of damaged areas in the rubber.

[0006] This invention has been made in view of the above circumstances, and its purpose is to provide vulcanized rubber that can self-repair damaged areas such as trauma and ozone cracks by heating, and a pneumatic tire equipped with said vulcanized rubber. [Means for solving the problem]

[0007] The above problems can be solved by the following configuration. That is, the present invention is a vulcanized rubber manufactured by vulcanizing a rubber composition, wherein a measurement sample in the shape of a JIS No. 7 dumbbell is prepared, and the breaking strength is measured by performing a tensile test at room temperature in accordance with JIS K6251 (TS B) Cut the central part of the long side of the measurement sample in the thickness direction, immediately bond the cut surfaces together, and after heat treatment at 90 °C for 100 minutes, measure the breaking strength by performing a tensile test at room temperature in accordance with JIS K6251, and take it as (TS A ) When it is (TS A ) / (TS B ) ≥ 0.05 It relates to a vulcanized rubber (1) characterized by satisfying the above.

[0008] In the above vulcanized rubber (1), a vulcanized rubber (2) having dynamic covalent bonds at at least a part of the crosslinking points and capable of repairing damaged parts by applying heat or light is preferable.

[0009] In the above vulcanized rubber (2), a vulcanized rubber (3) in which the dynamic covalent bond is an ester bond or a disulfide bond is preferable.

[0010] In any of the above vulcanized rubbers (1) to (3), a vulcanized rubber (4) in which the rubber composition contains a diene rubber is preferable.

[0011] In the above vulcanized rubber (4), a vulcanized rubber (5) in which the rubber composition contains an epoxidized natural rubber and a dicarboxylic acid is preferable.

[0012] In the above vulcanized rubber (5), when the total amount of the diene rubber is 100 parts by mass, a vulcanized rubber (6) containing 1 to 10 parts by mass of the dicarboxylic acid is preferable.

[0013] In any of the above vulcanized rubbers (4) to (6), a vulcanized rubber (7) in which the rubber composition further contains a filler is preferable.

[0014] In any of the above vulcanized rubbers (5) to (7), a vulcanized rubber (8) in which the dicarboxylic acid has at least a disulfide bond is preferable.

[0015] In any of the above vulcanized rubbers (5) to (8), the dicarboxylic acid is a compound described in the following general formula (1);

Chem.

Chem.

Chem.

Chem.

[0016] The pneumatic tire (10) including any of the above vulcanized rubbers (1) to (9) is preferred.

[0017] In the above pneumatic tire (10), the pneumatic tire (11) is preferred.

Advantages of the Invention

[0018] Since the retention rate of the breaking strength of the vulcanized rubber according to the present invention after heat treatment at 90 ° C for 100 minutes is 5% or more, it has excellent self-healing properties. Therefore, the vulcanized rubber according to the present invention is preferably used for a pneumatic tire that is likely to have a damaged portion due to trauma, ozone crack, etc. and has self-healing properties, particularly for the sidewall portion of a pneumatic tire.

[0019] The vulcanized rubber according to the present invention exhibits particularly excellent self-healing properties when it has dynamic covalent bonds at at least some of its crosslinking points. Dynamic covalent bonds (DCBs) include a type called vitrimer-type, in which the bonds can be swapped without temporarily dehiscating. When the vulcanized rubber according to the present invention has vitrimer-type dynamic covalent bonds at its crosslinking points, it becomes a crosslinked rubber in which the crosslinking points can be swapped. Even if a defect occurs in the polymer or crosslinking point (even if a scratch occurs), the scratch can be repaired by the swapping of the crosslinking points, resulting in particularly excellent self-healing properties. As a result, it can exhibit functions such as (i) scratch repair, (ii) remolding processability, (iii) adhesion, and (iv) shape memory that allows for shape renewal. The vulcanized rubber according to the present invention exhibits even better self-healing properties when it has ester bonds or disulfide bonds as dynamic covalent bonds. [Modes for carrying out the invention]

[0020] The vulcanized rubber according to the present invention is manufactured by vulcanizing and molding a rubber composition. Such a rubber composition will be described below.

[0021] The rubber composition used as a raw material for vulcanized rubber according to the present invention contains a diene rubber. The diene rubber is not particularly limited and includes, for example, natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, and styrene-isoprene-butadiene copolymer rubber. These can be used individually or in combination of two or more. In the present invention, the rubber composition used preferably contains epoxidized natural rubber as the diene rubber from the viewpoint of improving the self-healing properties of damaged parts of the vulcanized rubber. When the total amount of rubber components is 100 parts by mass, the content of epoxidized natural rubber is preferably 60 parts by mass or more, more preferably 80 parts by mass or more, and particularly preferably 100 parts by mass. Furthermore, the epoxidation rate of epoxidized natural rubber, which represents the ratio (mol%) of epoxidized double bonds to the total number of double bonds in the natural rubber before epoxidation, is preferably 5 to 50%.

[0022] The rubber composition used as a raw material for the vulcanized rubber according to the present invention preferably contains a dicarboxylic acid in addition to epoxidized natural rubber. The dicarboxylic acid acts as a crosslinking agent for the epoxidized natural rubber. The crosslinking reaction between the dicarboxylic acid and the epoxidized natural rubber forms ester bonds, which are covalent bonds. These ester bonds are dynamic covalent bonds, and the exchange reaction of ester bonds proceeds when heat or light is applied. Therefore, even if damage occurs in the vulcanized rubber due to trauma or ozone cracking, that is, if the rubber polymer network is partially broken, the ester bonds, which are dynamic covalent bonds, are regenerated when heat or light is applied, thereby repairing the rubber polymer network. As a result, the vulcanized rubber according to the present invention can self-repair damaged areas.

[0023] In the case where the rubber composition used as a raw material for the vulcanized rubber according to the present invention contains a dicarboxylic acid in addition to epoxidized natural rubber, and the dicarboxylic acid further has disulfide bonds, these disulfide bonds are dynamic covalent bonds, and an exchange reaction of disulfide bonds proceeds when heat or light is applied. Therefore, even if damage occurs in the vulcanized rubber due to trauma or ozone cracking, that is, if the rubber polymer network is partially broken, the disulfide bonds, which are dynamic covalent bonds, are regenerated when heat or light is applied, thereby repairing the rubber polymer network. As a result, the vulcanized rubber according to the present invention is capable of self-repair of damaged areas.

[0024] In the case where the rubber composition used as a raw material for vulcanized rubber according to the present invention contains a dicarboxylic acid in addition to epoxidized natural rubber, the dicarboxylic acid is a compound described in the following general formula (1); [ka] Compounds described in the following general formula (2); [ka] Compounds described in the following general formula (3); [ka] and the compounds listed in the following general formula (4); [ka] It is preferable that the dicarboxylic acid is selected from the group consisting of the above, as it acts more effectively as a crosslinking agent for epoxidized natural rubber. The crosslinking reaction between the above dicarboxylic acid and epoxidized natural rubber forms ester bonds and / or disulfide bonds, which are covalent bonds. These ester bonds and / or disulfide bonds are dynamic covalent bonds, and an exchange reaction of ester bonds and / or disulfide bonds proceeds when heat or light is applied. Therefore, even if a damaged area occurs in vulcanized rubber due to trauma or ozone cracking, that is, if the rubber polymer network is partially broken, the rubber polymer network is repaired by regenerating the ester bonds and / or disulfide bonds, which are dynamic covalent bonds, when heat or light is applied. As a result, the vulcanized rubber according to the present invention can more effectively self-repair damaged areas.

[0025] When the rubber composition used as a raw material for the vulcanized rubber according to the present invention contains dicarboxylic acid in addition to epoxidized natural rubber, the amount of dicarboxylic acid that acts as a crosslinking agent for the epoxidized natural rubber is preferably 1 to 10 parts by mass, based on 100 parts by mass of the total amount of diene-based rubber containing epoxidized natural rubber. By keeping the amount of dicarboxylic acid within the above range, the self-healing properties of the vulcanized rubber are more effectively exhibited.

[0026] When the rubber composition used as a raw material for the vulcanized rubber according to the present invention contains a dicarboxylic acid in addition to epoxidized natural rubber, it is preferable to include dimethylimidazole in the rubber composition to promote the crosslinking reaction between the epoxidized natural rubber and the dicarboxylic acid. The amount of dimethylimidazole added is preferably 1 to 10 parts by mass when the total amount of the diene-based rubber containing epoxidized natural rubber is 100 parts by mass.

[0027] When the rubber composition used as a raw material for the vulcanized rubber according to the present invention contains a dicarboxylic acid in addition to epoxidized natural rubber, it is preferable to include zinc(II) acetylacetonate in the rubber composition in order to promote the exchange reaction of ester bonds formed in the network of the rubber polymer and to enhance the self-healing properties of the vulcanized rubber. The amount of zinc(II) acetylacetonate added is preferably 0.2 to 2 parts by mass when the total amount of the diene-based rubber containing epoxidized natural rubber is 100 parts by mass.

[0028] The rubber composition used as a raw material for vulcanized rubber according to the present invention preferably further contains a filler. Examples of fillers include carbon black and silica.

[0029] As carbon black, in addition to carbon black commonly used in the rubber industry, such as SAF, ISAF, HAF, FEF, and GPF, conductive carbon blacks such as acetylene black and Ketjen black can be used. In the rubber composition that serves as the raw material for the vulcanized rubber according to the present invention, it is preferable that the carbon black content is 10 to 60 parts by mass when the total amount of diene-based rubber is 100 parts by mass.

[0030] As silica, wet silica, dry silica, sol-gel silica, and surface-treated silica, which are commonly used for rubber reinforcement, can be used. Among these, wet silica is preferred. In the rubber composition that serves as the raw material for the vulcanized rubber according to the present invention, the silica content is preferably 20 to 100 parts by mass when the total amount of diene-based rubber is 100 parts by mass.

[0031] When silica is included as a filler, it is also preferable to include a silane coupling agent. The silane coupling agent is not particularly limited as long as it contains sulfur in its molecule, and various silane coupling agents that are compounded together with silica in rubber compositions can be used. Examples include sulfidosilanes such as bis(3-triethoxysilylpropyl)tetrasulfide (e.g., "Si69" manufactured by Evonik Japan), bis(3-triethoxysilylpropyl) disulfide (e.g., "Si75" manufactured by Evonik Japan), bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triecethoxysilylbutyl) disulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, and bis(2-trimethoxysilylethyl) disulfide; mercaptosilanes such as γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, mercaptopropylmethyldimethoxysilane, mercaptopropyldimethylmethoxysilane, and mercaptoethyltriethoxysilane; and protected mercaptosilanes such as 3-octanoylthio-1-propyltriethoxysilane and 3-propionylthiopropyltrimethoxysilane. The amount of silane coupling agent is preferably 2 to 15% by mass, when the total amount of silica is considered to be 100% by mass.

[0032] The rubber composition used as a raw material for vulcanized rubber according to the present invention may further contain a vulcanizing agent. Preferably, sulfur and a vulcanization accelerator can be used as the vulcanizing agent.

[0033] Any sulfur suitable for rubber production is acceptable, such as powdered sulfur, precipitated sulfur, insoluble sulfur, or highly dispersible sulfur.

[0034] As a vulcanization accelerator, vulcanization accelerators commonly used for rubber vulcanization, such as sulfenamide-based vulcanization accelerators, thiram-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiourea-based vulcanization accelerators, guanidine-based vulcanization accelerators, and dithiocarbamate-based vulcanization accelerators, may be used individually or in appropriate mixtures.

[0035] The rubber composition used as a raw material for vulcanized rubber according to the present invention may further contain an antioxidant. Examples of antioxidants commonly used for rubber include aromatic amine-based antioxidants, amine-ketone-based antioxidants, monophenol-based antioxidants, bisphenol-based antioxidants, polyphenol-based antioxidants, dithiocarbamate-based antioxidants, and thiourea-based antioxidants.

[0036] The rubber composition used as a raw material for vulcanized rubber according to the present invention may contain, in addition to the rubber components and compounding agents exemplified above, zinc oxide, stearic acid, softeners such as waxes and oils, processing aids, and the like.

[0037] The rubber composition used as a raw material for vulcanized rubber according to the present invention is obtained by mixing the rubber components and compounding agents exemplified above, as well as zinc oxide, stearic acid, softeners such as waxes and oils, processing aids, etc., using a kneader commonly used in the rubber industry, such as a Banbury mixer, kneader, and rolls.

[0038] Furthermore, the method of combining the above components is not particularly limited. It may be a method in which the components other than the vulcanizing compounding agents such as dicarboxylic acid, sulfur, and vulcanization accelerator are kneaded in advance to form a masterbatch, and the remaining components are added and kneaded further; a method in which the components are added and kneaded in any order; or a method in which all components are added and kneaded simultaneously.

[0039] The vulcanized rubber according to the present invention exhibits excellent self-healing properties. Therefore, the vulcanized rubber according to the present invention is useful for pneumatic tires, particularly for the sidewall portion of pneumatic tires, where damage is likely to occur due to trauma or ozone cracking, and where self-healing properties are desirable. [Examples]

[0040] The present invention will be described in more detail below by illustrating some embodiments.

[0041] (Preparation of rubber composition) For the rubber composition used as a raw material for the vulcanized rubber according to the present invention, the rubber compositions of Examples 1 to 11 and Comparative Examples 1 to 4 were blended with 100 parts by mass of diene rubber (epoxidized natural rubber or natural rubber) according to the formulations in Tables 1 to 2, and the mixture was kneaded using a conventional Banbury mixer to prepare the rubber composition. The compounding agents listed in Tables 1 to 2 are shown below.

[0042] (Diene-based rubber) • Natural rubber: RSS#3 • Epoxy-modified natural rubber (epoxy content 25%): Product name "ENR25", manufactured by MRB, Malaysia. (Filler) • Carbon Black: Product name "N234 Seast 7HM", manufactured by Tokai Carbon Co., Ltd. (Dicarboxylic acid) • Suberic acid (compound listed in general formula (1)): Trade name "Suberic acid", manufactured by TCI. • Dithiodibutyric acid (compound listed in general formula (2)): Trade name "Dithiodibutyric acid", manufactured by TCI. • 2,2'-Dithiodibenzoic acid (compound listed in general formula (3)): Trade name "2,2'-Dithiodibenzoic acid", manufactured by TCI. • 5,5'-Dithiobis(2-nitrobenzoic acid) (compound listed in general formula (4)): Trade name "5,5'-Dithiobis(2-nitrobenzoic acid)", manufactured by TCI. (Other combination drugs) • Zinc oxide: Mitsui Mining & Smelting Co., Ltd.'s "3 types of zinc oxide" • Stearic acid: Kao Corporation's "Lunaq S-20" • Dimethylimidazole: Trade name "Dimethylimidazole", manufactured by TCI. • Zinc(II) acetylacetonate: Brand name "Zinc(II) acetylacetonate", manufactured by TCI. (Vulcanizing agent) • Sulfur: Manufactured by Tsurumi Chemical Industry Co., Ltd., product name "Powdered Sulfur" • Vulcanization accelerator: Manufactured by Sumitomo Chemical Co., Ltd., product name "Soxinol CZ"

[0043] (Manufacturing of vulcanized rubber) Comparative Examples 1-4 Using a laboplast mill, rubber compositions were prepared according to the formulations (parts by mass) shown in Tables 1 and 2. First, in the first mixing stage, all compounding agents except sulfur and vulcanization accelerator were added to the diene rubber and kneaded. Then, in the final mixing stage, sulfur and vulcanization accelerator were added to the resulting mixture and kneaded (discharge temperature = 90°C) to prepare the rubber compositions. Each of the obtained rubber compositions was vulcanized at 150°C for 25 minutes to obtain sheets with a thickness of 2 mm.

[0044] Examples 1-11 Using a laboplast mill, compounding agents were added to diene rubber according to the formulations (parts by mass) shown in Tables 1 and 2, and the mixture was kneaded to prepare rubber compositions. Each of the resulting rubber compositions was heated at 150°C for 90 minutes to obtain sheets with a thickness of 2 mm.

[0045] <Retention rate of tensile strength of vulcanized rubber> (1) Breaking strength (TS B Measurement (without cutting or heating (Cont.)) A JIS No. 7 dumbbell-shaped test specimen was punched out from a vulcanized rubber sheet, and a tensile test was performed at a tensile speed of 200 mm / min in accordance with JIS K6251, and the breaking strength [MPa] was measured at 23°C. This breaking strength was (TS B ) (2) Breaking strength (TS A ) Measurement (with cutting and heating) A dumbbell-shaped test piece (JIS No. 7) was punched out from a vulcanized rubber sheet. The center of the dumbbell piece was cut with a razor, and with the cut surfaces in contact, it was heated in a constant temperature bath at 90°C, 120°C, and 150°C for 100 minutes each. After cooling, a tensile test was performed at a tensile speed of 200 mm / min in accordance with JIS K6251, and the breaking strength [MPa] was measured at 23°C. This breaking strength was then calculated (TS A )

[0046] Measurements were taken after heating to each temperature (90°C, 120°C, 150°C) (TS A ) and (TS B The retention rate of the tensile strength of the vulcanized rubber was calculated by substituting ) into the following formula. (Repair rate (retention rate of fracture strength)) [%] = (TSA ) / (TS B ) × 100 The results are shown in Tables 1 and 2.

[0047] [Table 1]

[0048] The results in Table 1 show that the vulcanized rubbers of Examples 1 to 10 retained more than 5% of their tensile strength, indicating that the vulcanized rubber itself can self-repair damaged areas such as trauma and ozone cracks through heating.

[0049] [Table 2]

[0050] The results in Table 2 show that although the vulcanized rubber of Example 11 contains carbon black as a filler, it retains more than 5% of its tensile strength, indicating that the vulcanized rubber itself can self-repair damaged areas such as trauma and ozone cracks through heating.

Claims

1. A vulcanized rubber produced by vulcanizing a rubber composition, A measurement sample in the shape of a JIS No. 7 dumbbell was prepared, and the breaking strength was measured by performing a tensile test at room temperature in accordance with JIS K6251 (TS B The central portion of the long side of the measurement sample is cut in the thickness direction, the cut surfaces are immediately bonded together, and after heat treatment at 90°C for 100 minutes, the breaking strength is measured by performing a tensile test at room temperature in accordance with JIS K6251 (TS A ) When that is the case, (TS A ) / (TS B )≧0.05 A vulcanized rubber characterized by satisfying the following conditions.

2. The vulcanized rubber according to claim 1, wherein at least a portion of the crosslinking points have dynamic covalent bonds, and the damaged portion is repaired by applying heat or light.

3. The vulcanized rubber according to claim 2, wherein the dynamic covalent bond is an ester bond or a disulfide bond.

4. The vulcanized rubber according to claim 1, wherein the rubber composition contains a diene rubber.

5. The vulcanized rubber according to claim 4, wherein the rubber composition contains epoxidized natural rubber and a dicarboxylic acid.

6. The vulcanized rubber according to claim 5, wherein the total amount of the diene rubber is 100 parts by mass, and the dicarboxylic acid is contained in 1 to 10 parts by mass.

7. The vulcanized rubber according to claim 4, wherein the rubber composition further contains a filler.

8. The vulcanized rubber according to claim 5, wherein the dicarboxylic acid has at least a disulfide bond.

9. The dicarboxylic acid is a compound described in the following general formula (1); 【Chemistry 1】 Compounds described in the following general formula (2); 【Chemistry 2】 Compounds described in the following general formula (3); 【Transformation 3】 and the compounds listed in the following general formula (4); 【Chemistry 4】 The vulcanized rubber according to claim 5, which is at least one selected from the group consisting of the following.

10. A pneumatic tire comprising the vulcanized rubber described in claim 1.

11. A pneumatic tire comprising the vulcanized rubber described in claim 1 in at least the sidewall portion.

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