Rubber composition and pneumatic tire

Abstract

To provide a rubber composition which serves as a raw material of a vulcanized rubber for tires improved in heat build-up properties and reinforcing properties in a well-balanced manner, and to provide a pneumatic tire comprising a vulcanized rubber of the rubber composition.SOLUTION: The rubber composition contains a diene rubber, carbon black, and a vegetable oil. The ratio (N2SA / IA) of the nitrogen adsorption specific surface area (N2SA) m2 / g of the carbon black to the iodine adsorption amount (IA) mg / g thereof is 0.9 m2 / mg or less. The vegetable oil is a glycerol fatty acid triester. The carbon black is preferably recycled carbon black. The vegetable oil preferably has an iodine value of 90 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber composition and a pneumatic tire. [Background technology]

[0002] In response to recent demands for resource conservation, pneumatic tires are required to have low fuel consumption, and therefore, improved heat generation properties that contribute to low fuel consumption are required. Furthermore, from the perspective of improving durability, pneumatic tires are also required to have reinforcement properties.

[0003] In recent years, companies, regardless of their applications, such as pneumatic tires, have been required to work on the Sustainable Development Goals (SDGs). There are 17 SDGs, one of which is SDG 12-5 (By 2030, significantly reduce waste generation through prevention, reduction, recycling and reuse).

[0004] Patent Document 1 listed below describes a rubber composition containing at least a rubber component, carbon black, and sodium (2Z)-4-[(4-aminophenyl)amino]-4-oxo-2-butenoate, and containing, as the carbon black, at least carbon black having a surface activity ((N2SA) / (IA)) of 1.0 or more.

[0005] Patent Document 2 listed below describes carbon black for use in rubber compositions, in which (N2SA) / (IA) is 1.10 to 1.50.

[0006] Patent Document 3 below describes a rubber composition for belt coating rubber, which contains a rubber component, carbon black having an (N2SA) / (IA) ratio of 1.2 or less, and a resin component consisting of a phenol resin and a methylene donor. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2020-23646 [Patent Document 2] Patent No. 7087219 [Patent Document 3] Patent No. 7280003 Summary of the Invention [Problem to be solved by the invention]

[0008] When carbon black with low surface activity is used as a reinforcing agent, it tends to be less effective in improving the rubber properties when the final vulcanized rubber is obtained. Therefore, it is presumed that the techniques described in Patent Documents 1 to 3 take this tendency into consideration and use carbon black with high surface activity. However, the techniques described in Patent Documents 1 and 2 are expected to result in poor heat buildup in the final vulcanized rubber, which in turn will result in poor fuel economy when the final vulcanized rubber is made into a pneumatic tire. Furthermore, the technique described in Patent Document 3 specifically exemplifies a rubber composition containing carbon black with an (N2SA) / (IA) ratio of 0.95 to 1.33, which also results in poor heat buildup in the final vulcanized rubber, which in turn will result in poor fuel economy when the final vulcanized rubber is made into a pneumatic tire.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a rubber composition that serves as a raw material for vulcanized rubber for tires, which has a well-balanced improvement in heat buildup and reinforcement properties, and a pneumatic tire equipped with vulcanized rubber of the rubber composition. [Means for solving the problem]

[0010] The above-mentioned problems can be solved by the following constitution: That is, the present invention is a rubber composition containing a diene rubber, carbon black, and vegetable oil, wherein the carbon black has a nitrogen adsorption specific surface area (N2SA) m 2 / g to the iodine adsorption (IA) mg / g ratio (N2SA / IA) is 0.9m 2 / mg or less, and the vegetable oil is a glycerin fatty acid triester.

[0011] In the rubber composition (1), the carbon black is preferably recycled carbon black.

[0012] In the rubber composition (1) or (2), the vegetable oil preferably has an iodine value of 90 or less (rubber composition (3)).

[0013] The present invention also relates to a pneumatic tire (4) comprising at least the vulcanized rubber of the rubber compositions (1) to (3). [Effects of the Invention]

[0014] For carbon black, nitrogen adsorption specific surface area (N2SA) m 2 The ratio (N2SA / IA) of the nitrogen adsorption specific surface area (N2SA) m / g to the iodine adsorption amount (IA) mg / g represents the surface activity of carbon black; the larger this value, the higher the surface activity, and the smaller this value, the lower the surface activity. Carbon black with low surface activity has low reinforcing properties for rubber and also leads to deterioration in filler dispersibility and processability, so when it is finally made into vulcanized rubber, it tends to be inferior in improving the rubber properties. Here, in the present invention, carbon black with a nitrogen adsorption specific surface area (N2SA) m 2 / g to the iodine adsorption (IA) mg / g ratio (N2SA / IA) is 0.9m 2 Such carbon black has low surface activity and is expected to deteriorate the rubber properties of the final vulcanized rubber. However, the rubber composition of the present invention has a nitrogen adsorption specific surface area (N2SA) m 2 / g to the iodine adsorption (IA) mg / g ratio (N2SA / IA) is 0.9m 2The rubber contains a glycerin fatty acid triester as a vegetable oil, along with carbon black with a surface activity of 0.1 mg or less. As a result, contrary to expectations, the heat buildup and reinforcing properties of the final vulcanized rubber are improved in a balanced manner. While the reason for this effect is unclear, one possible explanation is that glycerin fatty acid triester has a moderate amount of double bonds compared to mineral oil. When carbon black with low surface activity and a glycerin fatty acid triester with a moderate amount of double bonds are kneaded with a diene rubber, the decrease in rubber viscosity during kneading is suppressed, and the dispersibility of the carbon black, even with its low surface activity, is improved.

[0015] In the rubber composition according to the present invention, when recycled carbon black is used as the carbon black, the N2SA / IA value tends to be low because recycled carbon has a high ash content, and in addition, the rubber viscosity during kneading is likely to increase due to the ash content. 2 When recycled carbon black with a viscosity of 0.1g / mg or less and glycerin fatty acid triester are blended into a rubber composition, the rubber viscosity during mixing can be adjusted within an appropriate range, resulting in a balanced improvement in the heat buildup and reinforcement properties of the final vulcanized rubber, even when recycled carbon black is used.In addition, the use of recycled carbon black can significantly reduce waste generation by preventing, reducing, recycling, and reusing waste, in line with the requirements of the SDGs.

[0016] In the rubber composition according to the present invention, when a glycerin fatty acid triester having an iodine value of 90 or less is blended as a vegetable oil, the occurrence of premature crosslinking (scorch) during vulcanization of diene rubber can be suppressed. Furthermore, since the vegetable oil contributes to the development of an effect as a plasticizer and to the improvement of the dispersibility of carbon black, even if the carbon black has low surface activity, it can compensate for the low interaction with diene rubber, resulting in a more balanced improvement in the heat buildup and reinforcement properties of the final vulcanized rubber.

[0017] The vulcanized rubber of the rubber composition according to the present invention has a well-balanced improvement in heat buildup and reinforcement properties, and is therefore particularly useful for use as a tread for pneumatic tires. DETAILED DESCRIPTION OF THE INVENTION

[0018] The rubber composition according to the present invention contains a diene rubber, carbon black, and vegetable oil.

[0019] The diene rubber is not particularly limited, and examples thereof include 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, styrene-isoprene-butadiene copolymer rubber, etc. These may be used alone or in combination of two or more.

[0020] The rubber composition according to the present invention has a nitrogen adsorption specific surface area (N2SA) m 2 / g to the iodine adsorption (IA) mg / g ratio (N2SA / IA) is 0.9m 2 The lower limit of N2SA / IA of the carbon black used is 0.50 m 2 / mg, and preferably 0.70m 2 The upper limit of N2SA / IA of the carbon black used is 0.85 m 2 The nitrogen adsorption specific surface area (N2SA) and iodine adsorption capacity (IA) can be measured based on JIS K6217-2 and JIS K6217-1, respectively. In the present invention, in consideration of the environment and in response to the demands of the SDGs, it is preferable that N2SA / IA is 0.9 m 2 It is preferable to use recycled carbon black having a nitrogen adsorption specific surface area (NSA) m 2 / g to the iodine adsorption (IA) mg / g ratio (N2SA / IA) is 0.9m 2The lower limit of the amount of carbon black, which is not more than 1 / mg, is preferably 3 parts by mass, and more preferably 5 parts by mass, when the total amount of the rubber components is 100 parts by mass. On the other hand, the upper limit of the amount is preferably 100 parts by mass, and more preferably 90 parts by mass, when the total amount of the rubber components is 100 parts by mass. In the present invention, when the N2SA / IA is 0.9 m 2 Carbon black having an N2SA / IA of 0.9 m / mg can also be used, but in order to fully achieve the effects of the present invention, the carbon black used should have an N2SA / IA of 0.9 m / mg. 2 The amount of carbon black used that exceeds 1 / mg is preferably 75% by mass or less, and more preferably 70% by mass or less.

[0021] The rubber composition according to the present invention has a nitrogen adsorption specific surface area (N2SA) m 2 / g to the iodine adsorption (IA) mg / g ratio (N2SA / IA) is 0.9m 2This rubber composition is characterized by the incorporation of a glycerin fatty acid triester as a vegetable oil together with carbon black having an iodine value of 90 or less. Among glycerin fatty acid triesters, when a glycerin fatty acid triester with an iodine value of 90 or less is incorporated, the glycerin fatty acid triester has a moderate double bond content, which can suppress premature crosslinking (scorch) during the vulcanization of diene rubber. Furthermore, by contributing to the manifestation of its plasticizer effect and the improvement of carbon black dispersibility, the heat buildup and reinforcement properties of the final vulcanized rubber are improved in a balanced manner. If the iodine value of the glycerin fatty acid triester is too low, the melting point tends to rise significantly, resulting in poor handling. Therefore, the lower limit of the iodine value is preferably 60, and more preferably 65. On the other hand, if the iodine value of the glycerin fatty acid triester is too high, the amount of double bonds increases, which may make it difficult to suppress premature crosslinking (scorch) during the vulcanization of diene rubber. From the viewpoint of improving the processability of the rubber composition while improving heat buildup and reinforcement in a balanced manner, sunflower oil and palm oil are particularly preferred as the glycerin fatty acid triester used in the present invention. The lower limit of the blending amount of the vegetable oil (glycerin fatty acid triester) used in the present invention is preferably 3 parts by mass, more preferably 5 parts by mass, based on 100 parts by mass of the total amount of the rubber component. On the other hand, the upper limit of the blending amount of the vegetable oil (glycerin fatty acid triester) used in the present invention is preferably 30 parts by mass, more preferably 25 parts by mass, based on 100 parts by mass of the total amount of the rubber component.

[0022] The rubber composition according to the present invention may contain, in addition to the rubber component, carbon black, and vegetable oil, silica, a silane coupling agent, a vulcanizing agent, a vulcanization accelerator, an antioxidant, stearic acid, a softener such as wax or oil, a processing aid, and the like.

[0023] As the silica, wet silica, dry silica, sol-gel silica, surface-treated silica, and the like, which are commonly used for rubber reinforcement, are used. Among these, wet silica is preferred. However, from the viewpoint of maintaining a high level of the effect of improving the dispersibility of carbon black, the rubber composition for a tire according to the present invention preferably does not contain silica. Even if silica is contained, the compounding amount thereof is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, when the total amount of the rubber components is 100 parts by mass.

[0024] When silica is contained as a filler, it is also preferable to contain a silane coupling agent. The silane coupling agent is not particularly limited as long as it contains sulfur in the molecule, and various silane coupling agents that are compounded together with silica in rubber compositions can be used. Examples of the silane include sulfide silanes such as bis(3-triethoxysilylpropyl)tetrasulfide (e.g., "Si69" manufactured by Evonik Japan Co., Ltd.), bis(3-triethoxysilylpropyl)disulfide (e.g., "Si75" manufactured by Evonik Japan Co., Ltd.), bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)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.

[0025] As the vulcanizing agent, sulfur can be suitably used. The sulfur may be any ordinary sulfur for rubber, such as powdered sulfur, precipitated sulfur, insoluble sulfur, or highly dispersible sulfur. In the rubber composition for tires according to the present invention, the content of the vulcanizing agent is preferably 0.5 to 3.5 parts by mass when the total amount of the rubber components is taken as 100 parts by mass.

[0026] As the vulcanization accelerator, vulcanization accelerators commonly used for rubber vulcanization, such as sulfenamide-based vulcanization accelerators, thiuram-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiourea-based vulcanization accelerators, guanidine-based vulcanization accelerators and dithiocarbamate-based vulcanization accelerators, may be used alone or in appropriate mixtures.

[0027] As the antiaging agent, antiaging agents commonly used for rubber, such as aromatic amine antiaging agents, amine-ketone antiaging agents, monophenol antiaging agents, bisphenol antiaging agents, polyphenol antiaging agents, dithiocarbamate antiaging agents, and thiourea antiaging agents, may be used alone or in appropriate mixtures.

[0028] The rubber composition according to the present invention can be obtained by kneading a rubber component, carbon black, a vegetable oil, silica, a silane coupling agent, a vulcanizing agent, a vulcanization accelerator, zinc oxide, an antioxidant, stearic acid, a softener such as wax, a processing aid, and the like, using a kneading machine typically used in the rubber industry, such as a Banbury mixer, a kneader, or a roll.

[0029] The method for compounding the above-mentioned components is not particularly limited, and any of the following may be used: a method in which the compounding components other than the vulcanization-based compounding agents, such as the vulcanizing agent and vulcanization accelerator, are pre-mixed to form a master batch, and the remaining components are then added and further kneaded; a method in which the components are added in any order and kneaded; or a method in which all the components are added simultaneously and kneaded.

[0030] The vulcanized rubber of the rubber composition according to the present invention has a well-balanced improvement in heat buildup and reinforcement properties, and is therefore useful for pneumatic tire components in general, and is particularly useful for tread applications. [Example]

[0031] The present invention will be explained in more detail below by way of examples.

[0032] (Preparation of Rubber Composition for Tires) Rubber compositions for tires were prepared by compounding the rubber compositions of Examples 1 to 7 and Comparative Examples 1 to 6 with 100 parts by mass of the rubber component according to the compounding recipes in Tables 1 to 5 and kneading them using a conventional Banbury mixer. The compounding ingredients listed in Tables 1 to 5 are shown below.

[0033] (rubber component) Natural rubber (NR): RSS#3 Butadiene rubber (BR): Product name "BR150B" (manufactured by UBE Elastomers) Styrene-butadiene rubber (SBR (ESBR (emulsion-polymerized SBR))): Product name "SBR1502" (manufactured by ENEOS Materials Co., Ltd.) (carbon black) CB1 (HAF): Product name "Seast 3" (manufactured by Tokai Carbon Co., Ltd.), (N2SA) 75m 2 / g, (IA) 80mg / g, (N2SA / IA) 0.94m 2 / mg CB2: Product name "SC31" (manufactured by CSRC), (N2SA) 74m 2 / g, (IA) 87mg / g, (N2SA / IA) 0.85m 2 / mg ·CB3: Product name "SC51" (manufactured by CSRC), (N2SA) 39m 2 / g, (IA) 46mg / g, (N2SA / IA) 0.85m 2 / mg ·CB4: Product name "SC61" (manufactured by CSRC), (N2SA) 37m 2 / g, (IA) 42mg / g, (N2SA / IA) 0.88m 2 / mg CB5 (recycled carbon black): Product name "PB-365" (manufactured by Enrestec), (N2SA) 73m 2 / g, (IA) 92mg / g, (N2SA / IA) 0.79m 2 / mg (vegetable oil) Vegetable oil 1 (sunflower oil): (Nisshin Oillio Co., Ltd.) Iodine value: 84, Oleic acid: 82% by weight Vegetable oil 2 (PL65 (palm olein)): (Nisshin Oillio Co., Ltd.) Iodine value: 65, Oleic acid: 48% by weight (Other ingredients) Mineral oil (naphthenic oil): Product name "Process NC140" (manufactured by JOMO) Silica: Product name "Nipsil AQ" (manufactured by Tosoh Corporation) Silane coupling agent: Product name "Si69" (manufactured by Evonik Japan Co., Ltd.) Zinc oxide: Product name "Zinc Oxide No. 1" (manufactured by Mitsui Mining & Smelting Co., Ltd.) Stearic acid: product name "Lunac S-20" (Kao Corporation) Wax: Product name "OZOACE0355" (manufactured by Nippon Seiro Co., Ltd.) Anti-aging agent 1: Product name "Nocrac 6C" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) Anti-aging agent 2: Product name "Antage RD" (Kawaguchi Chemical Industry Co., Ltd.) Hydrocarbon resin: Product name "Petrotack 90" (manufactured by Tosoh Corporation) Vulcanization accelerator 1: Trade name "Soxinor CZ" (manufactured by Sumitomo Chemical Co., Ltd.) Vulcanization accelerator 2: Product name "Noccela NS-P" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) Sulfur: Powdered sulfur (manufactured by Tsurumi Chemical Industry Co., Ltd.)

[0034] Unvulcanized samples of the rubber compositions of Examples 1 to 7 and Comparative Examples 1 to 6 obtained above were prepared, and then the viscosity (processability) of the unvulcanized rubber compositions, heat buildup (rolling resistance) of the vulcanized rubber, and reinforcing properties of the vulcanized rubber were evaluated under the following conditions.

[0035] (Viscosity of Unvulcanized Rubber Composition (Processability)) In accordance with JIS K6300, unvulcanized rubber was preheated at 100°C for 1 minute and the torque value after 4 minutes was measured in Mooney units using a rotorless Mooney measuring machine manufactured by Toyo Seiki Co., Ltd. Example 1 and Comparative Example 1 are expressed as an index with the value of Comparative Example 2 set to 100, Examples 2 and 3 are expressed as an index with the value of Comparative Example 3 set to 100, Example 4 is expressed as an index with the value of Comparative Example 4 set to 100, Examples 5 and 6 are expressed as an index with the value of Comparative Example 5 set to 100, and Example 7 is expressed as an index with the value of Comparative Example 6 set to 100. Smaller values indicate lower viscosity of the unvulcanized rubber and better processability.

[0036] (Reinforcement of vulcanized rubber (tensile product)) Tensile tests were conducted using JIS No. 3 dumbbells in accordance with JIS K6251 to determine the tensile product (tensile strength (MPa) × elongation at break (%)). For Example 1 and Comparative Example 1, the value for Comparative Example 2 was expressed as an index of 100; for Examples 2 and 3, the value for Comparative Example 3 was expressed as an index of 100; for Example 4, the value for Comparative Example 4 was expressed as an index of 100; for Examples 5 and 6, the value for Comparative Example 5 was expressed as an index of 100; and for Example 7, the value for Comparative Example 6 was expressed as an index of 100. A larger value indicates a larger tensile product of the vulcanized rubber and superior reinforcement of the carbon black.

[0037] (Heat generation of vulcanized rubber (rolling resistance)) Using a viscoelasticity tester manufactured by Toyo Seiki Seisakusho, the loss factor tanδ was measured at a frequency of 10 Hz, static strain of 10%, dynamic strain of 1%, and temperature of 60°C. For Example 1 and Comparative Example 1, the value for Comparative Example 2 is expressed as an index of 100, for Examples 2 and 3, the value for Comparative Example 3 is expressed as an index of 100, for Example 4, the value for Comparative Example 4 is expressed as an index of 100, for Examples 5 and 6, the value for Comparative Example 5 is expressed as an index of 100, and for Example 7, the value for Comparative Example 6 is expressed as an index of 100. Smaller values indicate less heat generation and better rolling resistance performance.

[0038] [Table 1]

[0039] From the results in Table 1, N2SA / IA is 0.94m 2 The vulcanized rubber of the rubber composition of Comparative Example 1, which was blended with CB1 having a N2SA / IA of 0.85 mg and mineral oil (naphthenic oil), had an N2SA / IA of 0.85 mg. 2 It can be seen that, compared to the vulcanized rubber of the rubber composition of Comparative Example 2, which contains CB2 with an N2SA / IA of 0.85 mg and mineral oil (naphthenic oil), the reinforcement is improved, but the heat buildup is significantly worse. 2 It can be seen that the vulcanized rubber of the rubber composition of Example 1, which is blended with CB2 having a molecular weight of 1 / mg and vegetable oil 1 (sunflower oil), has improved reinforcement properties and also has significantly improved heat buildup.

[0040] [Table 2]

[0041] From the results in Table 2, N2SA / IA is 0.85m 2 / mg and mineral oil (naphthenic oil) were blended in the vulcanized rubber of the rubber composition of Comparative Example 3, and the N2SA / IA was 0.85 m 2 The vulcanized rubber of the rubber composition of Example 2, which was blended with CB3 having a viscosity of 1000 psi / mg and vegetable oil 1 (sunflower oil), and the vulcanized rubber of Example 2, which was blended with CB3 having a viscosity of 1000 psi / mg and vegetable oil 1 (sunflower oil), 2 It can be seen that the vulcanized rubber of the rubber composition of Example 3, which is compounded with CB2 and vegetable oil 2 (palm olein) at 1000 kJ / mg, exhibits improved reinforcement and significantly improved heat buildup.

[0042] [Table 3]

[0043] The compounding system in Table 3 is one in which the diene rubber type has been changed and the amount of carbon black compounded has been increased compared to the compounding system in Table 2. From the results in Table 3, it can be seen that N2SA / IA is 0.85m 2 / mg and mineral oil (naphthenic oil) were blended in the vulcanized rubber of the rubber composition of Comparative Example 4, and the N2SA / IA was 0.85 m 2 It can be seen that the vulcanized rubber of the rubber composition of Example 4, which is blended with CB3 having a molecular weight of 1 / mg and vegetable oil 1 (sunflower oil), has improved reinforcement properties and also has significantly improved heat buildup.

[0044] [Table 4]

[0045] The blending system in Table 4 is N2SA / IA 0.94m 2 / mg CB1 and N2SA / IA are 0.88m 2 The results in Table 4 show that compared to the vulcanized rubber of the rubber composition of Comparative Example 5, which was blended with mineral oil (naphthenic oil), the vulcanized rubber of the rubber composition of Example 5, which was blended with vegetable oil 1 (sunflower oil), and the vulcanized rubber of the rubber composition of Example 6, which was blended with vegetable oil 2 (palm olein), both showed improved reinforcement and greatly improved heat buildup.

[0046] [Table 5]

[0047] The blending system in Table 5 is N2SA / IA 0.94m 2 / mg CB1 and N2SA / IA are 0.79m 2 / mg, and this system uses recycled carbon black CB5 in combination. The results in Table 5 show that the vulcanized rubber of the rubber composition of Example 7, which contains vegetable oil 1 (sunflower oil), has improved reinforcement properties and significantly improved heat buildup, compared to the vulcanized rubber of the rubber composition of Comparative Example 6, which contains mineral oil (naphthenic oil).

Claims

1. A rubber composition containing a diene rubber, carbon black, and a vegetable oil, The carbon black has a nitrogen adsorption specific surface area (N ２ SA)m ２ / g and the ratio of iodine adsorption (IA) mg / g (N ２ SA / IA) is 0.9m ２ / mg or less, The rubber composition is characterized in that the vegetable oil is a glycerin fatty acid triester.

2. The rubber composition according to claim 1 , wherein the carbon black is recycled carbon black.

3. The rubber composition according to claim 1, wherein the vegetable oil has an iodine value of 90 or less.

4. A pneumatic tire comprising at least a vulcanized rubber of the rubber composition according to claim 1.

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