Rubber composition and tires

Abstract

Provided are a rubber composition and a tire that can improve the overall wet grip performance and dry grip performance. A rubber composition whose hardness changes reversibly with water, satisfies the following formulas (1) and (2), and has a breaking stress of 8.0 MPa or more. Dry hardness - wet hardness ≥ 1 (1) (In the formula, the hardness is the JIS-A hardness of the rubber composition at 25°C.) 0.90≦Wet volume / Dry volume≦1.01 (2) (In the formula, the volume is the volume of the rubber composition at 25°C.)

Description

[Technical Field]

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

[0002] In recent years, awareness of safety has been increasing as a common challenge for automobiles, and further improvements in wet grip performance are required. Various studies have been conducted to improve wet grip performance, and many inventions of silica-containing rubber compositions have been reported (for example, Patent Document 1). Since wet grip performance is greatly influenced by the performance of the rubber composition of the tread portion that contacts the road surface, technical improvements to tire rubber compositions such as treads have been widely considered and put into practical use. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2008-285524 [Overview of the project] [Problems that the invention aims to solve]

[0004] As a result of diligent research by the inventors, it has been found that while significant improvements have been made to the wet grip performance of tires through technical improvements to tread rubber compositions using silica, the change in grip performance when road surface changes, such as from a dry road surface to a wet road surface, or from a wet road surface to a dry road surface, remains a significant technical challenge, and there is room for improvement. In this regard, the inventors conducted thorough research and found that conventional rubber, when changing from a dry state to a wet state, either does not change in hardness or hardens when cooled by water. As a result, the contact area with the road surface decreases, and consequently, wet grip performance tends to decrease compared to dry grip performance. Thus, it has become clear that there is room for improvement in conventional technology in terms of comprehensively improving both wet and dry grip performance. The present invention aims to solve the aforementioned problems and provide a rubber composition and tire that can improve the overall performance of wet grip performance and dry grip performance. [Means for solving the problem]

[0005] The present invention relates to a rubber composition whose hardness changes reversibly with water, satisfies the following formulas (1) and (2), and has a breaking stress of 8.0 MPa or more. Dry hardness - Wet hardness ≥ 1 (1) (In the formula, hardness is the JIS-A hardness of the rubber composition at 25°C.) 0.90 ≤ Volume when wet / Volume when dry ≤ 1.01 (2) (In the formula, volume is the volume of the rubber composition at 25°C.)

[0006] Preferably, the rubber component contains at least one rubber component, and some or all of the rubber molecules of the rubber component are crosslinked by ionic bonds.

[0007] Preferably, the cation side of the ionic bond is derived from at least one element selected from the group consisting of metallic elements, metalloid elements, and nitrogen elements, and the anion side is derived from at least one element selected from the group consisting of halogen elements and oxygen elements.

[0008] In the aforementioned rubber composition, it is preferable that the proportion of crosslinks consisting of ionic bonds is 0.1 to 100% of the total crosslinking.

[0009] It is preferable that the rubber component contains at least 1.0 part by mass of at least one selected from the group consisting of carbon black and silica, per 100 parts by mass of rubber component.

[0010] It is preferable that it is a rubber composition for treads.

[0011] The present invention also relates to a tire having a tire member at least partially composed of the rubber composition.

[0012] Preferably, the tire member is a tread.

Advantages of the Invention

[0013] According to the present invention, since the rubber composition has a hardness that reversibly changes with water and satisfies the above formulas (1), (2), and a predetermined breaking stress, the overall performance of wet grip performance and dry grip performance can be improved.

Embodiments for Carrying Out the Invention

[0014] The rubber composition of the present invention has a hardness that reversibly changes with water and satisfies the following formulas (1), (2), and a breaking stress of 8.0 MPa or more. Thereby, the overall performance of wet grip performance and dry grip performance can be improved. Hardness at dry time - Hardness at water wet time ≥ 1 (1) (In the formula, the hardness is the JIS - A hardness of the rubber composition at 25°C.) 0.90 ≤ Volume at water wet time / Volume at dry time ≤ 1.01 (2) (In the formula, the volume is the volume of the rubber composition at 25°C.)

[0015] Although the above rubber composition exhibits the aforementioned effects, the reason for such effects is not necessarily clear, but is presumed as follows. The rubber composition of the present invention has a hardness that reversibly changes with water and satisfies the above formula (1). Here, the above formula (1) means that the hardness at water wet time is smaller than the hardness at dry time. That is, the rubber composition of the present invention has a hardness that reversibly changes with water and satisfies the above formula (1), which means that the hardness at water wet time is smaller than the hardness at dry time and the hardness reversibly changes due to the presence of water. Therefore, when changing from a dry road surface to a wet road surface, the rubber composition is wetted by water, the hardness of the rubber composition decreases, the decrease in grip performance (wet grip performance) can be suppressed, and good grip performance (wet grip performance) can be obtained. This is because it is easy to slip on a wet road surface, so sufficient grip performance cannot be obtained with the hardness suitable for a dry road surface. However, when the hardness decreases, the contact area with the road surface increases, the decrease in grip performance (wet grip performance) can be suppressed, and it is presumed that good grip performance (wet grip performance) can be obtained. On the other hand, when changing from a wet road surface to a dry road surface, the rubber composition wetted by water is dried, the hardness of the rubber composition increases, the decrease in grip performance (dry grip performance) can be suppressed, and good grip performance (dry grip performance) can be obtained. This is because it is difficult to slip on a dry road surface, so sufficient grip performance cannot be obtained with the hardness suitable for a wet road surface. However, when the hardness increases, it becomes the hardness suitable for a dry road surface, the decrease in grip performance (dry grip performance) can be suppressed, and it is presumed that good grip performance (dry grip performance) can be obtained. <000​​​​​​​​​​​

[0018] In this specification, "reversibly changing hardness due to water" means that the hardness of the rubber composition (after vulcanization) reversibly increases or decreases in the presence of water. For example, it is sufficient that the hardness changes reversibly when the state changes from dry to wet and then back to dry. The hardness does not have to be the same in the first and second drying states, nor does it have to be the same in the first and second drying states.

[0019] In this specification, dry hardness refers to the hardness of a rubber composition in a dry state (after vulcanization), and more specifically, it refers to the hardness of a rubber composition (after vulcanization) dried by the method described in the Examples. In this specification, water-wet hardness refers to the hardness of a rubber composition (after vulcanization) in a water-wet state, and more specifically, it refers to the hardness of a rubber composition (after vulcanization) that has been wetted with water by the method described in the examples.

[0020] Furthermore, in this specification, the volume at dry state refers to the volume of the rubber composition in a dry state (after vulcanization), and more specifically, it refers to the volume of the rubber composition (after vulcanization) dried by the method described in the Examples. In this specification, the volume when wet means the volume of the rubber composition (after vulcanization) when wet with water, and more specifically, the volume of the rubber composition (after vulcanization) that has been wet with water by the method described in the examples.

[0021] In this specification, the hardness (JIS-A hardness) of the rubber composition (after vulcanization) is measured at 25°C using a Type A durometer in accordance with JIS K6253-3 (2012) "Vulcanized rubber and thermoplastic rubber - Method for determining hardness - Part 3: Durometer hardness".

[0022] In this specification, the volume of a rubber composition (after vulcanization) refers to the volume calculated from the length, width, and thickness measured at 25°C in the case of a rectangular parallelepiped shape.

[0023] As shown in formula (1) above, (hardness in dry state - hardness in wet state (hardness of rubber composition (after vulcanization) in dry state - hardness of rubber composition (after vulcanization) in wet state)) is 1 or more, preferably 2 or more, more preferably 3 or more, even more preferably 4 or more, particularly preferably 5 or more, most preferably 6 or more, most preferably 8 or more, even more preferably 9 or more, particularly preferably 10 or more, and may also be 11 or more. The upper limit is not particularly limited, but is preferably 50 or less, more preferably 40 or less, even more preferably 30 or less, particularly preferably 28 or less, and most preferably 26 or less. The effect is more favorably obtained when it is within the above range.

[0024] The hardness at dry (hardness of the rubber composition (after vulcanization) at dry) can be adjusted as appropriate within the range that satisfies the above formula (1), but is preferably 20 or higher, more preferably 25 or higher, even more preferably 30 or higher, particularly preferably 40 or higher, most preferably 42 or higher, even more preferably 43 or higher, even more preferably 44 or higher, particularly preferably 45 or higher, and may also be 46 or higher, 47 or higher, or 48 or higher. Also, is preferably 95 or lower, more preferably 90 or lower, even more preferably 85 or lower, particularly preferably 75 or lower, most preferably 70 or lower, even more preferably 65 or lower, and even more preferably 60 or lower. When the above hardness is within the above range, the effect is more favorably obtained.

[0025] The hardness when wet (hardness of the rubber composition (after vulcanization) when wet) can be adjusted as appropriate within the range that satisfies formula (1) above, but is preferably 20 or higher, more preferably 25 or higher, even more preferably 28 or higher, particularly preferably 29 or higher, most preferably 30 or higher, even more preferably 31 or higher, even more preferably 32 or higher, particularly preferably 33 or higher, and may also be 34 or higher. Also, is preferably 70 or lower, more preferably 60 or lower, even more preferably 50 or lower, particularly preferably 40 or lower, most preferably 38 or lower, even more preferably 37 or lower, and even more preferably 36 or lower. When the hardness is within the above range, the effect is more favorably obtained.

[0026] As shown in formula (2) above, (volume when wet / volume when dry (volume of rubber composition (after vulcanization) when wet / volume of rubber composition (after vulcanization) when dry)) is 0.90 or more and 1.01 or less, preferably 0.95 or more and 1.01 or less, more preferably 0.99 or more and 1.01 or less, and particularly preferably 1.00 (no volume change). If the volume changes significantly after the hardness change, it will adversely affect other physical properties such as wear resistance, handling stability, and fuel efficiency. Therefore, it is important that there is almost no volume change before and after the hardness change in order to maintain the balance of tire performance.

[0027] Furthermore, the hardness change of the rubber composition represented by formula (1) above, and the reversible hardness change due to water, can be achieved, for example, by incorporating a substance that can reversibly break and reform the ionic bonds between rubber molecules by adding water and drying. More specifically, the hardness change of the rubber composition represented by formula (1) above, and the reversible hardness change due to water, can be achieved by using rubber containing halogens or oxygen in combination with compounds containing metals, metalloids, or nitrogen. This is because, with this combination, ionic bonds are formed between rubber molecules by cations derived from metals, metalloids, or nitrogen, and anions derived from halogens or oxygen. As a result, ionic bonds are broken when water is added and reformed when the water dries, leading to a decrease in hardness when wet and an increase in hardness when dry.

[0028] Dry hardness can be adjusted by the type and amount of chemicals (especially rubber components, fillers, and softeners such as oils) added to the rubber composition. For example, increasing the amount of softener tends to decrease dry hardness, increasing the amount of filler tends to increase dry hardness, and decreasing the amount of sulfur tends to decrease dry hardness. Dry hardness can also be adjusted by adjusting the ratio of sulfur to vulcanization accelerator. More specifically, increasing the amount of sulfur tends to increase dry hardness, and increasing the amount of vulcanization accelerator tends to increase dry hardness.

[0029] The hardness when wet can be adjusted, for example, by using rubber containing halogens or oxygen in combination with compounds containing metals, metalloids, or nitrogen.

[0030] Specifically, by adjusting the hardness in the dry state to a desired range, and then using rubber containing halogens or oxygen in combination with compounds containing metals, metalloids, or nitrogen, it is possible to achieve the hardness change of the rubber composition represented by formula (1) above, as well as a reversible hardness change due to water. Furthermore, the aforementioned hardness in the dry state and hardness when wet can also be achieved.

[0031] Even small volume changes in the rubber composition represented by formula (2) can be achieved, for example, by incorporating a substance that allows for the reversible cleavage and recombination of ionic bonds between rubber molecules through the addition and drying of water. More specifically, small volume changes in the rubber composition represented by formula (2) can be achieved by using rubber containing halogens or oxygen in combination with compounds containing metals, metalloids, or nitrogen. This is because ionic bonds are formed between rubber molecules by cations derived from metals, metalloids, or nitrogen and anions derived from halogens or oxygen, and the cleavage of ionic bonds between rubber molecules due to the addition of water occurs in such small amounts that the water absorption into the polymer does not affect the volume, and the recombination of ionic bonds due to the drying of water occurs in such small amounts that the dehydration into the polymer does not affect the volume, thereby suppressing the volume change of the rubber composition.

[0032] The rubber composition (dry rubber composition (after vulcanization)) has a breaking stress (tensile strength) of 8.0 MPa or higher from the viewpoint of rubber properties, etc. Preferably it is 8.2 MPa or higher, more preferably 8.3 MPa or higher, even more preferably 8.4 MPa or higher, particularly preferably 8.5 MPa or higher, most preferably 8.6 MPa or higher, even more preferably 8.8 MPa or higher, even more preferably 8.9 MPa or higher, particularly most preferably 9.0 MPa or higher, and may also be 9.1 MPa or higher, 9.2 MPa or higher, or 9.4 MPa or higher. There is no particular upper limit to the breaking stress, but a higher value is preferable. The fracture stress was measured using the rubber composition after vulcanization, in accordance with JIS K6251, at the standard test temperature (23±2℃), and can be measured specifically by the method described in the examples below.

[0033] The fracture stress (tensile strength) of a rubber composition above a certain level can be adjusted by the type and amount of chemicals (especially rubber components, fillers, and softeners such as oils) incorporated into the rubber composition. For example, reducing the amount of softener tends to increase the fracture stress, while increasing the amount of filler tends to increase the fracture stress.

[0034] The following describes the medications that can be used.

[0035] The rubber composition contains at least one rubber component. Preferably, the rubber composition is such that some or all of the crosslinks between the rubber molecules of the rubber component are crosslinked by ionic bonds. When ionic bonds are included in the crosslinks of the polymer component (rubber component), the hardness can be reduced only when wet due to the reversibility of ionic bonds, which are non-covalent bonds. Furthermore, since ionic bonds are the strongest bonds among non-covalent bonds, sufficient bonding strength can be maintained when dry.

[0036] The rubber composition preferably has a proportion of ionic bonds at 0.1% or more of the total crosslinking, more preferably 0.5% or more, and even more preferably 1% or more. Achieving a proportion above the lower limit tends to result in good wet and dry grip performance. The upper limit is not particularly limited and may be 100%, but is preferably 80% or less, more preferably 70% or less. The proportion of crosslinks consisting of ionic bonds can be measured by the method described in the examples below.

[0037] The ionic bonds between rubber molecules are not particularly limited. For example, an ionic bond in which the cation side originates from at least one element selected from the group consisting of metallic elements, metalloid elements, and nitrogen elements, and the anion side originates from at least one element selected from the group consisting of halogen elements and oxygen elements is possible. Specifically, combinations such as a combination where the cation side is a metallic element and the anion side is a halogen element, a combination where the cation side is a metallic element and the anion side is an oxygen element, a combination where the cation side is a metalloid element and the anion side is a halogen element, a combination where the cation side is a metalloid element and the anion side is an oxygen element, a combination where the cation side is a nitrogen element and the anion side is a halogen element, a combination where the cation side is a nitrogen element and the anion side is an oxygen element, etc., are all possible combinations of at least one element selected from the group consisting of metallic elements, metalloid elements, and nitrogen elements and at least one element selected from the group consisting of halogen elements and oxygen elements.

[0038] Examples of metal elements on the cation side include alkali metals (lithium, sodium, potassium, etc.) and alkaline earth metals (magnesium, calcium, strontium, etc.); examples of metalloid elements include silicon, boron, and germanium. Examples of compounds that can supply nitrogen atoms on the cation side include nitrogen-containing compounds that can form cations, such as quaternary ammonium salts (ammonia, amines, etc.). Examples of halogen elements on the anionic side include chlorine and bromine.

[0039] For example, by using a rubber component containing halogen or oxygen elements in combination with a compound containing metal elements, metalloid elements, or nitrogen elements, ionic bonds are formed between the rubber molecules. In this case, the halogen or oxygen elements in the rubber component constitute the anionic side of the ionic bond, while the metal elements, metalloid elements, or nitrogen elements in the compound constitute the cationic side of the ionic bond.

[0040] From the viewpoint of ensuring that the aforementioned effects are well exhibited, it is preferable to use a rubber composition that contains at least one element selected from the group consisting of halogen elements and oxygen elements as a rubber component.

[0041] Examples of rubber components containing halogen or oxygen elements include isoprene rubber, butadiene rubber (BR), styrene-butadiene rubber (SBR), styrene-isoprene-butadiene rubber (SIBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), and other diene rubbers containing halogen or oxygen elements in their molecules; and butyl rubbers containing halogen or oxygen elements in their molecules. The rubber components may be used individually or in combination of two or more. Among these, butyl rubbers containing halogen or oxygen elements in their molecules are preferred.

[0042] Examples of butyl rubbers containing halogen or oxygen elements in their molecules include brominated butyl rubber (BR-IIR), chlorinated butyl rubber (Cl-IIR), and other halogenated butyl rubbers (X-IIR). These may be used individually or in combination of two or more. Among these, BR-IIR is more preferred because it provides a more favorable effect.

[0043] Examples of butyl rubbers that can be used include products from ExxonMobil, JSR Corporation, and Nippon Butyl Co., Ltd.

[0044] The content of "rubber component having at least one element selected from the group consisting of halogen elements and oxygen elements" in 100% by mass of the rubber component is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. A higher content tends to yield good wet grip performance and dry grip performance. The upper limit is not particularly limited and may be 100% by mass. Similarly, the content of butyl rubber having at least one element selected from the group consisting of halogen elements and oxygen elements is also preferably within a similar range.

[0045] From the viewpoint of ensuring that the aforementioned effects are well exhibited, the rubber composition preferably contains a compound having at least one selected from the group consisting of metallic elements, metalloid elements, and nitrogen elements.

[0046] As the aforementioned compound, any compound capable of forming an ionic bond on the cation side can be used. Among these, compounds containing a nitrogen element are preferred, and examples include nitrogen-containing compounds that can form cations, such as quaternary ammonium salts.

[0047] Specific examples of compounds containing the nitrogen element include 1,2-dimethylimidazole, N-butylimidazole, N-(trimethylsilyl)imidazole, N-decyl-2-methylimidazole, N-hydroxyethylimidazole, N-(3-trimethoxysilylpropyl)imidazole, N-vinylimidazole, 1-butylbenzimidazole; trimethylamine, triethylamine, triisopropylamine, and tri-n-butylamine. ; These are some examples. These may be used individually or in combination of two or more. Among them, imidazole compounds such as N-butylimidazole are preferred.

[0048] For example, when brominated butyl rubber (BR-IIR) is used as a rubber component containing halogen or oxygen elements, and N-butylimidazole is used as a compound containing metallic, metalloid, or nitrogen elements, it is thought that an ionic bond represented by the following formula is formed. [ka]

[0049] The content of "a compound having at least one selected from the group consisting of metallic elements, metalloid elements, and nitrogen elements" is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, even more preferably 2 parts by mass or more, particularly preferably 3 parts by mass or more, most preferably 5 parts by mass or more, and also preferably 30 parts by mass or less, more preferably 20 parts by mass or less, even more preferably 10 parts by mass or less, and even more preferably 7 parts by mass or less. When the content is within the above range, a better effect tends to be obtained.

[0050] From the viewpoint of obtaining better effects, the rubber composition preferably contains at least one selected from the group consisting of carbon black and silica. In particular, it is preferable to include carbon black in order to obtain better wet grip performance and abrasion resistance. For example, a rubber composition containing a rubber component that satisfies all the above combinations regarding the cation side and anion side of the ionic bond, and at least one selected from the group consisting of carbon black and silica, or a rubber composition containing the rubber component and at least carbon black can be suitably used.

[0051] The content (total content) of "at least one selected from the group consisting of carbon black and silica" is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, even more preferably 30 parts by mass or more, and also preferably 150 parts by mass or less, more preferably 100 parts by mass or less, even more preferably 80 parts by mass or less, particularly preferably 60 parts by mass or less, and most preferably 50 parts by mass or less, based on 100 parts by mass of the rubber component. When the content is within the above range, a better effect tends to be obtained.

[0052] As for carbon black, common types used in the tire industry, such as GPF, HAF, ISAF, and SAF, can be used. These may be used individually or in combination of two or more types.

[0053] The BET specific surface area of ​​carbon black is preferably 50 m². 2 / g or more, comfortably 100m 2 / g or more, more preferably 120m 2 The value is 1 / g or more. Setting it above the lower limit tends to provide sufficient wet grip performance and wear resistance. The upper limit is preferably 200m. 2 / g or less, more preferably 180m 2 It is less than / g. Within the above range, better effects tend to be obtained. Below the upper limit, good dispersibility and excellent wear resistance tend to be obtained. The BET specific surface area of ​​carbon black is a value measured by the BET method in accordance with ASTM D6556.

[0054] The dibutyl phthalate oil absorption (DBP) of carbon black is preferably 50 ml / 100g or more, and more preferably 100 ml / 100g or more. Above the lower limit tends to provide sufficient wet grip performance and wear resistance. Furthermore, the DBP of carbon black is preferably 220 ml / 100g or less, and more preferably 180 ml / 100g or less. Below the upper limit tends to provide good dispersibility and excellent wear resistance. The DBP of carbon black is measured in accordance with JIS K6217-4:2001.

[0055] For carbon black, products from companies such as Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Shin-Nippon Chemical Carbon Co., Ltd., and Columbia Carbon can be used.

[0056] The carbon black content is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, even more preferably 30 parts by mass or more, per 100 parts by mass of rubber component, and also preferably 150 parts by mass or less, more preferably 100 parts by mass or less, even more preferably 80 parts by mass or less, particularly preferably 60 parts by mass or less, and most preferably 50 parts by mass or less. When the content is within the above range, a better effect tends to be obtained.

[0057] In the above rubber composition, the carbon black content in the total content of carbon black and silica (100% by mass) is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. The upper limit is not particularly limited and may be 100% by mass. Within the above range, the effect tends to be more favorably obtained.

[0058] Examples of the silica include dry-process silica (anhydrous silicic acid), wet-process silica (hydrous silicic acid), etc. Wet-process silica is preferred because it has many silanol groups. These may be used alone or in combination of two or more.

[0059] The nitrogen adsorption specific surface area (N2SA) of the silica is 40 m 2 / g or more, preferably 60 m 2 / g or more, more preferably 80 m 2 / g or more, still more preferably 160 m 2 / g or more. Also, the above N2SA is preferably 600 m 2 / g or less, more preferably 300 m 2 / g or less, still more preferably 250 m 2 / g or less, particularly preferably 200 m 2 / g or less. When it is within the above range, the effect tends to be obtained more suitably. Note that the N2SA of the silica is a value measured by the BET method in accordance with ASTM D3037-81.

[0060] Examples of the silica include products of Degussa, Rhodia, Tosoh Silica Corporation, Solvay Japan Limited, Tokuyama Corporation, etc.

[0061] The content of the silica is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, still more preferably 15 parts by mass or more, and also preferably 150 parts by mass or less, more preferably 100 parts by mass or less, still more preferably 80 parts by mass or less, particularly preferably 60 parts by mass or less, and most preferably 40 parts by mass or less with respect to 100 parts by mass of the rubber component. When it is within the above range, the effect tends to be obtained more favorably.

[0062] When the above rubber composition contains silica, it is preferable to further contain a silane coupling agent. The silane coupling agent is not particularly limited and includes, for example, bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(2-triethoxysilylethyl) trisulfide, bis(4-trimethoxysilylbutyl) trisulfide, bis(3-triethoxysilylpropyl) disulfide, bis(2-triethoxysilylethyl) disulfide, bis(4-triethoxysilylbutyl) disulfide, bis(3-trimethoxysilylpropyl) disulfide, bis(2-trimethoxysilylethyl) disulfide, bis(4-trimethoxysilylbutyl) disulfide, and 3-trimethoxysilylpropyl-N Examples include sulfide compounds such as N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, and 3-triethoxysilylpropyl methacrylate monosulfide; mercapto compounds such as 3-mercaptopropyltrimethoxysilane and 2-mercaptoethyltriethoxysilane; vinyl compounds such as vinyltriethoxysilane and vinyltrimethoxysilane; amino compounds such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; glycidoxy compounds such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro compounds such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro compounds such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Commercially available products include those from companies such as Degussa, Momentive, Shin-Etsu Silicone Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azumax Co., Ltd., and Toray Dow Corning Co., Ltd. These can be used individually or in combination of two or more types.Among these, sulfide-based silane coupling agents and mercapto-based silane coupling agents are preferred because they tend to yield better results, and disulfide-based silane coupling agents having a disulfide bond, such as bis(3-triethoxysilylpropyl)disulfide, are more preferred.

[0063] The content of the silane coupling agent is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and preferably 20 parts by mass or less, and more preferably 15 parts by mass or less, per 100 parts by mass of silica. Within this range, a better effect tends to be obtained.

[0064] The above rubber composition may contain oil. Examples of oils include process oils, vegetable oils, or mixtures thereof. Examples of process oils include paraffinic process oils, aromatic process oils, and naphthenic process oils. Examples of vegetable oils include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil. These may be used individually or in combination of two or more. Among these, process oils are preferred, and aromatic process oils are more preferred, because they provide good results.

[0065] As for the oil, products from companies such as Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., Japan Energy Co., Ltd., Orisoy Co., Ltd., H&R Co., Ltd., Toyokuni Oil Co., Ltd., Showa Shell Sekiyu K.K., and Fuji Kosan Co., Ltd. can be used.

[0066] The oil content is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 20 parts by mass or more, per 100 parts by mass of rubber component, and also preferably 50 parts by mass or less, and more preferably 35 parts by mass or less. Within this range, a better effect tends to be obtained. Note that the oil content includes the amount of oil contained in the rubber (oil-applied rubber).

[0067] The above rubber composition may contain resin. The resin used is not particularly limited as long as it is commonly used in the tire industry, and examples include rosin resins, coumarone indene resins, α-methylstyrene resins, terpene resins, pt-butylphenol acetylene resins, acrylic resins, C5 resins, and C9 resins. Commercially available products from companies such as Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical Company, Nippon Paint Chemical Co., Ltd., Nippon Shokubai Co., Ltd., JX Energy Corporation, Arakawa Chemical Industries, Ltd., Taoka Chemical Industries, Ltd., and Toagosei Co., Ltd. can be used. These can be used individually or in combination of two or more types.

[0068] The resin content is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and preferably 30 parts by mass or less, and more preferably 20 parts by mass or less, per 100 parts by mass of the rubber component. Within this range, a better effect tends to be obtained.

[0069] The above rubber composition may also contain wax. The wax is not particularly limited and includes petroleum-based waxes such as paraffin wax and microcrystalline wax; natural waxes such as plant-based waxes and animal-based waxes; and synthetic waxes such as polymers of ethylene and propylene. These may be used individually or in combination of two or more. Among these, petroleum-based waxes are preferred, and paraffin waxes are more preferred.

[0070] Examples of waxes that can be used include those from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., and Seiko Chemical Co., Ltd.

[0071] The wax content is preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, and preferably 20 parts by mass or less, and more preferably 10 parts by mass or less, per 100 parts by mass of rubber component. Within this range, a better effect tends to be obtained.

[0072] The above rubber composition may also contain an anti-aging agent. Examples of anti-aging agents include naphthylamine-based anti-aging agents such as phenyl-α-naphthylamine; diphenylamine-based anti-aging agents such as octylated diphenylamine and 4,4'-bis(α,α'-dimethylbenzyl)diphenylamine; N-isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, and N,N'-di-2-naphthyl-p-phenylenediamine. Examples include p-phenylenediamine-based antioxidants such as 2,2,4-trimethyl-1,2-dihydroquinoline polymers and other quinoline-based antioxidants; monophenol-based antioxidants such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis-, tris-, and polyphenol-based antioxidants such as tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. These may be used individually or in combination of two or more types. Among these, p-phenylenediamine-based antioxidants and quinoline-based antioxidants are preferred.

[0073] Products from companies such as Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Co., Ltd., and Flexis Co., Ltd. can be used as anti-aging agents.

[0074] The amount of the anti-aging agent is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component. Within this range, a better effect tends to be obtained.

[0075] The above rubber composition may contain stearic acid. Conventional known stearic acid can be used, such as products from NOF Corporation, NOF Corporation, Kao Corporation, Fujifilm Wako Pure Chemical Corporation, Chiba Fatty Acid Co., Ltd., etc.

[0076] The stearic acid content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component. Within this range, a better effect tends to be obtained.

[0077] The above rubber composition may contain zinc oxide. Conventional zinc oxides can be used, such as products from Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., and Sakai Chemical Industry Co., Ltd.

[0078] The zinc oxide content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component. Within this range, a better effect tends to be obtained.

[0079] The above rubber composition may contain sulfur. Examples of sulfur commonly used in the rubber industry include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and soluble sulfur. These may be used individually or in combination of two or more types.

[0080] For sulfur, products from companies such as Tsurumi Chemical Industries, Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemicals Co., Ltd., Flexis Co., Ltd., Nippon Dry Distillation Co., Ltd., and Hosoi Chemical Industries Co., Ltd. can be used.

[0081] The sulfur content is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less, per 100 parts by mass of the rubber component. A better effect tends to be obtained when the sulfur content is within the above range.

[0082] The above rubber composition may contain a vulcanization accelerator. Examples of vulcanization accelerators include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, and N-cyclohexyl-2-benzothiadylsulfenamide; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazolesulfenamide, N-tert-butyl-2-benzothiazolesulfenamide, N-oxyethylene-2-benzothiazolesulfenamide, N-oxyethylene-2-benzothiazolesulfenamide, and N,N'-diisopropyl-2-benzothiazolesulfenamide; and guanidine-based vulcanization accelerators such as diphenylguanidine, diortotrilguanidine, and orthotrilbiguanidine. These may be used individually or in combination of two or more. Among them, sulfenamide-based vulcanization accelerators and guanidine-based vulcanization accelerators are preferred because they provide a more favorable effect.

[0083] Products from companies such as Kawaguchi Chemical Co., Ltd. and Ouchi Shinko Chemical Co., Ltd. can be used as vulcanization accelerators.

[0084] The content of the vulcanization accelerator is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and preferably 10 parts by mass or less, and more preferably 7 parts by mass or less, per 100 parts by mass of the rubber component. Within this range, a better effect tends to be obtained.

[0085] In addition to the components mentioned above, the above rubber composition may further contain additives commonly used in the tire industry, such as organic peroxides; fillers such as calcium carbonate, talc, alumina, clay, aluminum hydroxide, and mica. The content of these additives is preferably 0.1 to 200 parts by mass per 100 parts by mass of the rubber component.

[0086] The above rubber composition can be manufactured, for example, by kneading each of the components using a rubber kneading device such as an open roll or Banbury mixer, and then vulcanizing them.

[0087] Regarding the mixing conditions, in the base mixing step where additives other than the vulcanizing agent and vulcanization accelerator are mixed, the mixing temperature is usually 100 to 180°C, preferably 120 to 170°C. In the finish mixing step where the vulcanizing agent and vulcanization accelerator are mixed, the mixing temperature is usually 120°C or lower, preferably 80 to 110°C. Furthermore, the composition mixed with the vulcanizing agent and vulcanization accelerator is usually subjected to a vulcanization treatment such as press vulcanization. The vulcanization temperature is usually 140 to 190°C, preferably 150 to 185°C. The vulcanization time is usually 5 to 15 minutes.

[0088] The above rubber composition can be used (as a tire rubber composition) in tire components such as the tread (cap tread), sidewall, base tread, under tread, shoulder, clinch, bead apex, breaker cushion rubber, carcass cord covering rubber, insulation, chafer, inner liner, etc., as well as the side reinforcement layer of run-flat tires. In particular, it is preferably used in components that may come into contact with water (tread, sidewall, shoulder), and more preferably in the tread. In the case of a tread composed of a cap tread and a base tread, it is preferably used in the cap tread. Components that may come into contact with water include those located on the outermost surface of the tire (tread, sidewall, and shoulder) when the tire is new or when wear is progressing during driving.

[0089] The tire (pneumatic tire, etc.) of the present invention is manufactured by conventional methods using the above-mentioned rubber composition. Specifically, the rubber composition, which may contain various additives as needed, is extruded in the unvulcanized stage to match the shape of each component of the tire (especially the tread (cap tread)), molded in conventional methods on a tire molding machine, bonded together with other tire components to form an unvulcanized tire, and then heated and pressurized in a vulcanizing machine to manufacture the tire.

[0090] Furthermore, the tire components of the above-mentioned tire (for example, the tread) may be composed of at least a portion of the above-mentioned rubber composition, or may be composed entirely of the above-mentioned rubber composition.

[0091] The above-mentioned tires are suitably used as passenger car tires, large passenger car tires, large SUV tires, truck and bus tires, motorcycle tires, racing tires, studless tires (winter tires), all-season tires, run-flat tires, aircraft tires, mining tires, etc. [Examples]

[0092] The present invention will be specifically described based on the examples provided, but the present invention is not limited to these examples.

[0093] The various chemicals used in the examples and comparative examples are described below. Bromobutyl rubber: BUROMOBUTYL 2244 manufactured by JSR Corporation Chlorobutyl rubber: HT-1068 manufactured by ExxonMobil Ltd. 1,2-Dimethylimidazole: Curazol 1.2DMZ, manufactured by Shikoku Chemicals Co., Ltd. 1-Butylimidazole: Commercially available product Carbon black: Seast 9H manufactured by Tokai Carbon Co., Ltd. (DBP oil absorption capacity 115 ml / g, BET specific surface area 110 m²) 2 / g) Silica: Evonik Degussa's UltraSil VN3 (N2SA175m 2 / g) Silane coupling agent: Si69 (bis(3-triethoxysilylpropyl)tetrasulfide) manufactured by Evonik Degussa. Stearic acid: Stearic acid "Tsubaki" manufactured by NOF Corporation Zinc oxide: Two types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industries Co., Ltd. Vulcanization accelerator 1: Noxellar NS (N-tert-butyl-2-benzothiadylsulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Noxellar D (1,3-diphenylguanidine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0094] (Examples and Comparative Examples) According to the formulations shown in each table, all chemicals except sulfur and vulcanization accelerator were mixed for 4 minutes at 160°C using a 1.7L Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a mixture. Next, sulfur and vulcanization accelerator were added to the mixture and kneaded for 4 minutes at 80°C using an open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press-vulcanized for 12 minutes under conditions of 170°C to obtain a vulcanized rubber composition.

[0095] The obtained vulcanized rubber compositions were evaluated as described below. The results are shown in each table. Table 1 is Comparative Example 1-1, and Table 2 is Comparative Example 2-1.

[0096] (Hardness of vulcanized rubber (Hs)) The Shore hardness (Hs) of vulcanized rubber compositions (test specimens) was measured using a Type A durometer in accordance with JIS K6253-3 (2012) "Vulcanized rubber and thermoplastic rubber - Method for determining hardness - Part 3: Durometer hardness" (JIS-A hardness). The measurements were performed at 25°C.

[0097] (Hardness when wet) A vulcanized rubber composition (a rectangular parallelepiped measuring 30 mm x 30 mm x 4 mm) was immersed in 20 ml of water at 25°C for 6 hours to obtain a vulcanized rubber composition after water wetting. The hardness of the obtained vulcanized rubber composition after water wetting was measured using the method described above and was defined as the hardness when wet.

[0098] (Hardness when dry) The vulcanized rubber composition, after being wetted with water, was dried under reduced pressure at 80°C and 1 kPa or less until it reached a constant weight, thereby obtaining the dried vulcanized rubber composition. After returning the temperature of the obtained dried vulcanized rubber composition to 25°C, the hardness of the dried vulcanized rubber composition was measured using the method described above and recorded as the hardness at the time of drying.

[0099] (Hardness when re-wetted) The dried vulcanized rubber composition (a rectangular parallelepiped measuring 30 mm × 30 mm × 4 mm) was immersed in 20 ml of water at 25°C for 6 hours to obtain a vulcanized rubber composition after rewatering. The hardness of the obtained rewatered vulcanized rubber composition was measured using the method described above and was defined as the hardness at the time of rewatering.

[0100] (Volume when wet and when dry) To determine the volume when wet, a vulcanized rubber composition (a rectangular parallelepiped with dimensions of 30.0 mm in length, 30.0 mm in width, and 0.50 mm in thickness) was immersed in 20 ml of water at 25°C for 12 hours to obtain a water-wetted vulcanized rubber composition. The length, width, and thickness of the obtained water-wetted vulcanized rubber composition were measured at 25°C, and the volume when wet was calculated from the measured length, width, and thickness. For the volume after drying, the vulcanized rubber composition after water wetting was air-dried at 25°C under normal pressure until it reached a constant weight, thereby obtaining the dried vulcanized rubber composition. After returning the temperature of the obtained dried vulcanized rubber composition to 25°C, the volume of the dried vulcanized rubber composition was measured using the method described above and was recorded as the volume after drying. Then, the volume when wet / volume when dry was calculated. "None" in the table indicates that there was no change in volume (volume when wet / volume when dry = 1.00).

[0101] (Tensile test) The breaking stress (tensile strength) was measured according to JIS K6251 "Vulcanized rubber and thermoplastic rubber - Method for determining tensile properties". A higher value indicates greater mechanical strength and superior rubber properties.

[0102] (Ionic bond ratio (proportion of crosslinks consisting of ionic bonds)) This can be determined from the proportions of each ingredient.

[0103] (Wet grip performance index) The obtained unvulcanized rubber composition sheet was molded into a tread shape, bonded with other tire components, and press-vulcanized at 170°C for 12 minutes to create a kart tire (tire size: 11x1.10-5). The kart tire was mounted on a kart, and the kart was driven for eight laps around a 2km test course with a pre-watered surface. The grip performance was evaluated by a test driver on a scale of 200 points, with the reference comparison set at 100 points.

[0104] (Dry grip performance index) The obtained unvulcanized rubber composition sheet was molded into a tread shape, bonded with other tire components, and press-vulcanized at 170°C for 12 minutes to create a kart tire (tire size: 11x1.10-5). The kart tire was mounted on a kart, and the kart was driven for 8 laps on a 2km test course on a dry surface. The grip performance was evaluated by a test driver on a scale of 200 points, with the reference comparison set at 100 points.

[0105] [Table 1]

[0106] [Table 2]

[0107] From each table, it was found that the examples in which the hardness changes reversibly with water, satisfy the above equations (1) and (2), and have a fracture stress of 8.0 MPa or higher can improve the overall performance of wet grip performance and dry grip performance (expressed as the sum of the two indices of wet grip performance and dry grip performance).

Claims

1. The hardness changes reversibly with water, satisfies the following equations (1) and (2), and has a fracture stress of 8.0 MPa or more. It contains at least one type of rubber component, and per 100 parts by mass of the rubber component, it contains 30 parts by mass or more of carbon black and 5 parts by mass or more of silica. Some of the rubber molecules in the aforementioned rubber component are crosslinked by ionic bonds, A vulcanized rubber composition for treads, wherein the cation side of the ionic bond is derived from at least one element selected from the group consisting of metallic elements, metalloid elements, and nitrogen elements, and the anion side is derived from at least one element selected from the group consisting of halogen elements and oxygen elements. Dry hardness - Wet hardness ≥ 8 (1) (In the formula, hardness is the JIS-A hardness of the vulcanized rubber composition at 25°C.) 0.90 ≤ Volume when wet / Volume when dry ≤ 1.01 (2) (In the formula, volume is the volume of the vulcanized rubber composition at 25°C.)

2. The vulcanized rubber composition according to claim 1, wherein the proportion of crosslinks consisting of ionic bonds out of 100% total crosslinks is 0.1 to 80%.

3. A tire having a tire member composed of at least a portion of the vulcanized rubber composition described in claim 1 or 2.

4. The tire according to claim 3, wherein the tire member is a tread.

Images