JP7757721B2 - Rubber composition and tire - Google Patents

Description

The present disclosure relates to a rubber composition and a tire.

Natural rubber contains large amounts of non-rubber components such as proteins, lipids, and sugars, which can cause foul odors when these components spoil during storage of the raw materials or decompose due to thermal decomposition during the drying process.

Methods proposed for reducing the odor of natural rubber include, for example, setting the removal temperature when masticating natural rubber in a Banbury mixer to 145°C or lower (see, for example, Patent Document 1), and adding at least one antioxidant selected from tocopherol and phenol to natural rubber latex before coagulation, followed by drying at a temperature of 115°C to 100°C (see, for example, Patent Document 2). However, these methods are insufficient to suppress the odor of rubber compositions containing natural rubber, and there is room for improvement.

Japanese Patent Application Laid-Open No. 2006-257237 JP 2011-74392 A

The present disclosure aims to solve the above problems and provide a rubber composition and tire that have excellent odor-suppressing properties and processability despite containing natural rubber.

The present disclosure relates to a rubber composition comprising a rubber component containing natural rubber and rice husk ash, wherein the rice husk ash has an ash content of 40% by mass or more, and the content of the rice husk ash is 0.1 to 3.0 parts by mass per 100 parts by mass of the rubber component.

According to the present disclosure, the rubber composition includes a rubber component containing natural rubber and rice husk ash, where the rice husk ash has an ash content of 40% by mass or more and the rice husk ash content is 0.1 to 3.0 parts by mass per 100 parts by mass of the rubber component. Therefore, despite the inclusion of natural rubber, a rubber composition and tire can be provided that have excellent odor suppression properties and processability.

The present disclosure relates to a rubber composition that contains a rubber component containing natural rubber and rice husk ash, and in which the ash content and content of the rice husk ash are specified. Despite containing natural rubber, the rubber composition exhibits excellent odor suppression and processability.

The odor of natural rubber is thought to be caused by the spoilage of non-rubber components of natural rubber, such as proteins, lipids, and sugars, during storage or decomposition during drying, which produces odor-causing lower fatty acids and other odorous substances. However, this disclosure was completed based on the discovery that blending a specified amount of rice husk ash with a rubber composition containing such natural rubber can result in a rubber composition with excellent odor-suppressing properties without compromising processability. Furthermore, the rubber composition of this disclosure is capable of suppressing odors originating from natural rubber as well as odors originating from substances other than natural rubber.

[Rubber component]
The natural rubber (NR) is not particularly limited, and can be any rubber commonly used in the rubber industry, such as SIR20, RSS#3, TSR20, SVR5S, deproteinized natural rubber (DPNR), highly purified natural rubber (UPNR), epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, etc.; however, in the present disclosure, by blending a predetermined amount of rice husk ash with a predetermined ash content into the rubber composition, excellent odor suppression properties can be exhibited without deteriorating processability, and therefore even when SIR20, RSS#3, TSR20, SVR5S, etc. are used as the natural rubber, the odor of the rubber composition can be sufficiently suppressed without deteriorating processability.

The NR content in 100% by mass of the rubber component is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 55% by mass or more, even more preferably 60% by mass or more, even more preferably 70% by mass or more, and particularly preferably 95% by mass or more, and may even be 100% by mass. Within the above range, better effects tend to be obtained.

The rubber composition may contain rubber components other than NR. Examples of other rubber components that can be used include other diene-based rubbers. Examples of other diene-based rubbers include isoprene-based rubbers other than NR, butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR). Other examples include butyl-based rubber and fluororubber. These may be used alone or in combination of two or more types. However, from the perspective of rubber physical properties, it is preferable to use BR, for example.

Examples of isoprene-based rubbers other than NR include isoprene rubber (IR) and modified IR. IR is not particularly limited, and can be, for example, IR2200 or other commonly used rubber in the rubber industry. Modified IR includes epoxidized isoprene rubber, hydrogenated isoprene rubber, grafted isoprene rubber, etc. These may be used alone or in combination of two or more types.

The BR is not particularly limited, and examples that can be used include high-cis BR with a high cis content, BR containing syndiotactic polybutadiene crystals, and BR synthesized using a rare earth catalyst (rare earth BR). These may be used alone or in combination of two or more. Of these, high-cis BR with a cis content of 90% by mass or more is preferred because it improves abrasion resistance. These may be used alone or in combination of two or more.

The BR may be unmodified or modified.
The modified BR may be any BR having a functional group that interacts with a filler such as silica, and examples thereof include terminal-modified BR in which at least one terminal of the BR has been modified with a compound (modifying agent) having the above functional group (terminal-modified BR having the above functional group at the terminal), main-chain-modified BR in which the main chain has the above functional group, main-chain-terminal-modified BR in which the main chain and the above functional group have been modified with the above modifier, and main-chain-terminal-modified BR in which the main chain has the above functional group and at least one terminal has been modified with the above modifier, and terminal-modified BR in which the BR has been modified (coupled) with a polyfunctional compound having two or more epoxy groups in the molecule and into which a hydroxyl group or an epoxy group has been introduced.

Examples of the functional group include amino, amide, silyl, alkoxysilyl, isocyanate, imino, imidazole, urea, ether, carbonyl, oxycarbonyl, mercapto, sulfide, disulfide, sulfonyl, sulfinyl, thiocarbonyl, ammonium, imide, hydrazo, azo, diazo, carboxyl, nitrile, pyridyl, alkoxy, hydroxyl, oxy, and epoxy groups. These functional groups may have a substituent. Among these, amino groups (preferably amino groups in which the hydrogen atoms of the amino group are substituted with alkyl groups having 1 to 6 carbon atoms), alkoxy groups (preferably alkoxy groups having 1 to 6 carbon atoms), and alkoxysilyl groups (preferably alkoxysilyl groups having 1 to 6 carbon atoms) are preferred.

For example, products from Ube Industries, Ltd., JSR Corporation, Asahi Kasei Corporation, Zeon Corporation, etc. can be used as BR.

When the rubber component of the rubber composition contains BR, the BR content per 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and particularly preferably 25% by mass or more. The upper limit is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. Within the above range, better effects tend to be obtained.

When the rubber component of the rubber composition contains BR, the total content of NR and BR in 100% by mass of the rubber component is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more, and may even be 100% by mass. Within the above range, better effects tend to be obtained.

[Filler]
The rubber composition contains rice husk ash.
Rice husk ash can be obtained by carbonizing rice husks. The carbonization method is not particularly limited, and known methods can be used, such as a method of heating rice husks.
Commercially available rice husk ash may be used, such as rice husk ash manufactured by Kansai Sangyo Co., Ltd.

The main components contained in rice husk ash are carbon and ash, but the proportions of carbon and ash in rice husk ash can be adjusted by changing the carbonization conditions, such as the heating temperature and heating time. For example, by increasing the heating temperature and/or increasing the heating time, the carbonization reaction can be promoted more rapidly, making it possible to prepare rice husk ash with a higher ash content.

In the present disclosure, the rice husk ash contains 40% by mass or more of ash. That is, the ash content in 100% by mass of rice husk ash is 40% by mass or more. By setting the ash content of the rice husk ash within this range, the rubber composition can be made to have excellent odor suppression properties. The ash content in 100% by mass of rice husk ash is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 75% by mass or more, and particularly preferably 85% by mass or more. Furthermore, the ash content in 100% by mass of rice husk ash is preferably 99.7% by mass or less, more preferably 99.5% by mass or less, even more preferably 99.3% by mass or less, and particularly preferably 99.0% by mass or less.
In this specification, the ash content of rice husk ash can be measured by the method described in the examples below.

The carbon content in 100% by mass of rice husk ash is preferably 0.3% by mass or more, more preferably 0.5% by mass or more, even more preferably 0.7% by mass or more, and particularly preferably 1.0% by mass or more. It is also preferably 60% by mass or less, more preferably 50% by mass or less, even more preferably 40% by mass or less, even more preferably 25% by mass or less, and particularly preferably 15% by mass or less. If the carbon content in 100% by mass of rice husk ash is within the above range, the effects of the present disclosure can be further enhanced.
In this specification, the carbon content of rice husk ash is calculated as the amount remaining after subtracting the ash content in the rice husk ash.

The most common pore size of rice husk ash is preferably 0.50 to 0.80 nm. It is more preferably 0.55 nm or more, and even more preferably 0.60 nm or more. It is also more preferably 0.75 nm or less, even more preferably 0.70 nm or less, and even more preferably 0.65 nm or less. By setting the most common pore size of rice husk ash within the above range, the effects of the present disclosure can be further enhanced.

The maximum pore diameter of the rice husk ash is preferably 2.0 to 2.5 nm. It is more preferably 2.1 nm or more, and even more preferably 2.2 nm or more. It is also more preferably 2.4 nm or less, and even more preferably 2.3 nm or less. By setting the maximum pore diameter of the rice husk ash within the above range, the effects of the present disclosure can be further enhanced.

The minimum pore diameter of the rice husk ash is preferably 0.10 to 0.30 nm. It is more preferably 0.12 nm or more, and even more preferably 0.14 nm or more. It is more preferably 0.25 nm or less, even more preferably 0.20 nm or less, and even more preferably 0.17 nm or less. By setting the minimum pore diameter of the rice husk ash within the above range, the effects of the present disclosure can be further enhanced.
In the present disclosure, the most frequent pore size, maximum pore size, and minimum pore size of rice husk ash can be measured by the method described in the examples below.

The pore diameters (modal pore diameter, maximum pore diameter, minimum pore diameter) of rice husk ash can be adjusted by washing the rice husk ash with acid or alkali. Specifically, washing the rice husk ash with acid can reduce the modal pore diameter and minimum pore diameter and increase the maximum pore diameter. Furthermore, washing the rice husk ash with alkali can reduce the modal pore diameter and minimum pore diameter and increase the maximum pore diameter.

Methods for washing rice husk ash with acid or alkali include, for example, applying an acidic solution of pH 1 to 3 (such as an aqueous solution of an acidic compound or an alcohol solution) or a basic (alkaline) solution of pH 6 to 9 (such as an aqueous solution of a basic compound or an alcohol solution) to the rice husk ash, spraying it with a spray or shower, or immersing the rice husk ash in the acidic or basic solution, thereby bringing the rice husk ash into contact with the acidic or basic solution, and then removing the acidic or basic solution remaining on the surface of the rice husk ash.

The contact time and temperature between the rice husk ash and the acidic or basic solution are not particularly limited and can be adjusted as appropriate. Furthermore, the concentration of the acidic or basic solution is not particularly limited and can be adjusted as appropriate.

The method for removing the acidic or basic solution remaining on the surface of the rice husk ash is not particularly limited, but examples include placing the rice husk ash that has been in contact with the acidic or basic solution in running water, diluting the rice husk ash that has been in contact with the acidic or basic solution with water and then centrifuging it, and leaving the rice husk ash that has been in contact with the acidic or basic solution in a water bath to float it, and then draining off only the aqueous phase to remove the rice husk ash.

The acidic compound is not particularly limited and may be, for example, an inorganic acid such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, polyphosphoric acid, metaphosphoric acid, boric acid, boronic acid, sulfanilic acid, or sulfamic acid; or formic acid, acetic acid, glycolic acid, oxalic acid, propionic acid, malonic acid, succinic acid, adipic acid, maleic acid, malic acid, tartaric acid, citric acid, benzoic acid, phthalic acid, isophthalic acid, glutaric acid, gluconic acid, lactic acid, aspartic acid, glutamic acid, salicylic acid, methanesulfonic acid, itaconic acid, benzenesulfonic acid, or toluenesulfonic acid. Examples of organic acids include naphthalenedisulfonic acid, trifluoromethanesulfonic acid, styrenesulfonic acid, trifluoroacetic acid, barbituric acid, acrylic acid, methacrylic acid, cinnamic acid, 4-hydroxybenzoic acid, aminobenzoic acid, naphthalenedisulfonic acid, hydroxybenzenesulfonic acid, toluenesulfinic acid, benzenesulfinic acid, α-resorcylic acid, β-resorcylic acid, γ-resorcylic acid, gallic acid, phloroglycine, sulfosalicylic acid, ascorbic acid, erythorbic acid, and bisphenolic acid.

The basic compound is not particularly limited, and examples thereof include metal hydroxides such as alkali metal hydroxides and alkaline earth metal hydroxides; metal carbonates such as alkali metal carbonates and alkaline earth metal carbonates; metal hydrogencarbonates such as alkali metal hydrogencarbonates; metal phosphates such as alkali metal phosphates; metal acetates such as alkali metal acetates; metal hydrides such as alkali metal hydrides; and ammonia.
Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide.
Examples of the alkaline earth metal hydroxide include magnesium hydroxide, calcium hydroxide, and barium hydroxide.
Examples of the alkali metal carbonate include lithium carbonate, sodium carbonate, and potassium carbonate.
Examples of the alkaline earth metal carbonate include magnesium carbonate, calcium carbonate, and barium carbonate.
Examples of the alkali metal hydrogen carbonate include lithium hydrogen carbonate, sodium hydrogen carbonate, and potassium hydrogen carbonate.
Examples of the alkali metal phosphate include sodium phosphate and sodium hydrogen phosphate.
Examples of the alkali metal acetate include sodium acetate and potassium acetate.
Examples of the alkali metal hydride include sodium hydride and potassium hydride.

The rice husk ash content is 0.1 to 3.0 parts by mass per 100 parts by mass of the rubber component. By setting the rice husk ash content within this range, the rubber composition can be made to have excellent odor suppression and processability. The rice husk ash content is preferably 0.2 parts by mass or more, and more preferably 0.3 parts by mass or more, per 100 parts by mass of the rubber component. It is also preferably 2.5 parts by mass or less, more preferably 2.0 parts by mass or less, even more preferably 1.5 parts by mass or less, even more preferably 1.0 part by mass or less, and particularly preferably 0.6 parts by mass or less.

The rubber composition may contain carbon black.
Examples of carbon black include, but are not limited to, GPF, FEF, HAF, ISAF, SAF, etc. Commercially available products include those from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Shin-Nichika Carbon Co., Ltd., Columbia Carbon Co., Ltd., etc. These may be used alone or in combination of two or more.

The nitrogen adsorption specific surface area ( _N2SA ) of carbon black is preferably 20 ^m2 /g or more, more preferably 50 ^m2 /g or more, and even more preferably 70 ^m2 /g or more. There is no particular upper limit to the _N2SA of carbon black, but it is preferably 150 ^m2 /g or less, more preferably 130 ^m2 /g or less, and even more preferably 120 ^m2 /g or less. Within the above range, better effects tend to be obtained.
The nitrogen adsorption specific surface area of carbon black is determined in accordance with JIS K6217-2:2001.

In the rubber composition, the carbon black content is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 40 parts by mass or more, and particularly preferably 50 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, the carbon black content is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, even more preferably 100 parts by mass or less, and particularly preferably 90 parts by mass or less. Within the above range, better effects tend to be obtained.

Fillers other than carbon black that can be used in the rubber composition include those known in the rubber field, such as silica, calcium carbonate, talc, alumina, clay, aluminum hydroxide, aluminum oxide, and mica. Of these, silica is preferred.

In the rubber composition, the filler content (total amount) is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 40 parts by mass or more, and particularly preferably 50 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, even more preferably 100 parts by mass or less, and particularly preferably 90 parts by mass or less. Within the above range, better effects tend to be obtained.

The carbon black content in 100% by mass of the filler contained in the rubber composition is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. Within the above range, better effects tend to be obtained.

Examples of silica that can be used in the rubber composition include dry-process silica (anhydrous silica) and wet-process silica (hydrated silica). Among these, wet-process silica is preferred because it contains a large number of silanol groups.

In the rubber composition, the silica content is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 40 parts by mass or more, and particularly preferably 50 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, the silica content is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, even more preferably 100 parts by mass or less, and particularly preferably 90 parts by mass or less. Within the above range, better effects tend to be obtained.

The nitrogen adsorption specific surface area ( _N2SA ) of silica is preferably ^50m2 /g or more, more preferably ^100m2 /g or more, and even more preferably ^150m2 /g or more. The _N2SA of silica is preferably ^250m2 /g or less, more preferably ^220m2 /g or less, and even more preferably ^200m2 /g or less. Within the above ranges, the effect tends to be more favorable.
The N ₂ SA of silica is a value measured by the BET method in accordance with ASTM D3037-93.

For example, products from Degussa, Rhodia, Tosoh Silica Co., Ltd., Solvay Japan Co., Ltd., Tokuyama Corporation, etc. can be used as silica.

[Silane coupling agent]
The rubber composition preferably contains a silane coupling agent together with silica.
The silane coupling agent is not particularly limited, and examples thereof include sulfide-based agents such as bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, and bis(3-trimethoxysilylpropyl)tetrasulfide, mercapto-based agents such as 3-mercaptopropyltrimethoxysilane, vinyl-based agents such as vinyltriethoxysilane, amino-based agents such as 3-aminopropyltriethoxysilane, glycidoxy-based agents such as γ-glycidoxypropyltriethoxysilane, nitro-based agents such as 3-nitropropyltrimethoxysilane, and chloro-based agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Of these, sulfide-based agents are preferred from the viewpoint of obtaining better effects.

Examples of silane coupling agents that can be used include products from Degussa, Momentive, Shin-Etsu Silicones, Tokyo Chemical Industry, Azumax, and Dow Corning Toray.

In the rubber composition, the content of the silane coupling agent per 100 parts by mass of silica is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 8 parts by mass or more, and is preferably 25 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less. Within the above ranges, better effects tend to be obtained.

[Plasticizer]
The rubber composition may contain a plasticizer.
In this specification, the term "plasticizer" refers to a material that imparts plasticity to a rubber component, and is a concept that includes liquid plasticizers (plasticizers that are liquid (liquid) at 25°C) and solid plasticizers (plasticizers that are solid at 25°C). Specifically, it is a component that can be extracted from a rubber composition using acetone. These may be used alone or in combination of two or more types.

In the rubber composition, the total content of plasticizers (total content of liquid plasticizer and solid plasticizer) is preferably 5.0 parts by mass or more, more preferably 8.0 parts by mass or more, even more preferably 10.0 parts by mass or more, and particularly preferably 12.0 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit is preferably 50.0 parts by mass or less, more preferably 30.0 parts by mass or less, and even more preferably 20.0 parts by mass or less. Within the above range, better effects tend to be obtained.
The amount of plasticizer included also includes the amount of oil contained in rubber (oil-extended rubber), sulfur (oil-containing sulfur), etc.

Liquid plasticizers include oils, liquid polymers (diene-based, olefin-based, ester-based, etc.), liquid resins, essential oils derived from natural products such as turpentine, and ester-based plasticizers. Solid plasticizers include solid resins commonly used in the tire industry that are solid at 25°C. These may be used alone or in combination of two or more. Of these, oils, liquid polymers, and liquid resins are preferred, with oils being more preferred and process oils being even more preferred.

The oil is not particularly limited, and conventionally known oils can be used, such as process oils such as paraffin-based process oil, aromatic process oil, naphthenic process oil, low PCA (polycyclic aromatic) process oil such as TDAE or MES, vegetable oil, and mixtures thereof. These may be used alone or in combination of two or more. Of these, aromatic process oil is preferred.

As oils, products from, for example, Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., Japan Energy Co., Ltd., Orisoi Co., Ltd., H&R Corporation, Toyokuni Oil Mills Co., Ltd., Showa Shell Sekiyu K.K., Fuji Kosan Co., Ltd., etc. can be used.

Examples of liquid resins include terpene-based resins (including terpene-phenolic resins and aromatic-modified terpene resins) that are liquid at 25°C, rosin resins, styrene-based resins, C5-based resins, C5C9-based resins, coumarone-indene-based resins (including coumarone and indene simple resins), olefin-based resins, polyurethane resins, and acrylic resins.

Liquid resins that can be used include products from Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical Company, Nitto Chemical Co., Ltd., Nippon Shokubai Co., Ltd., JXTG Nippon Oil & Energy Corporation, Arakawa Chemical Industries, Ltd., and Taoka Chemical Co., Ltd.

Examples of liquid diene polymers include liquid styrene butadiene copolymers (liquid SBR), liquid butadiene polymers (liquid BR), liquid isoprene polymers (liquid IR), liquid styrene isoprene copolymers (liquid SIR), liquid styrene butadiene styrene block copolymers (liquid SBS block polymers), and liquid styrene isoprene styrene block copolymers (liquid SIS block polymers), which are liquid at 25°C. The terminals or main chains of these polymers may be modified with polar groups.

Liquid diene polymers that can be used include products from Sartomer, Kuraray Co., Ltd., and others.

In the rubber composition, the content of the liquid plasticizer (preferably oil) is preferably 5.0 parts by mass or more, more preferably 8.0 parts by mass or more, even more preferably 10.0 parts by mass or more, and particularly preferably 12.0 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit is preferably 50.0 parts by mass or less, more preferably 30.0 parts by mass or less, and even more preferably 20.0 parts by mass or less. Within the above range, the effect tends to be more favorably obtained.
The amount of plasticizer included also includes the amount of oil contained in rubber (oil-extended rubber), sulfur (oil-containing sulfur), etc.

Solid plasticizers can be solid resins commonly used in tire compounds. Specific examples include terpene resins, rosin resins, styrene resins, olefin resins, C5 resins, C9 resins, C5/C9 resins, coumarone resins, indene resins, coumarone-indene resins, acrylic resins, and urethane resins. These may be used alone or in mixtures of two or more types, or the resin itself may be a copolymer of monomer components derived from multiple sources.

Examples of solid plasticizers that can be used include products from Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical Company, Nitto Chemical Co., Ltd., Nippon Shokubai Co., Ltd., JXTG Nippon Oil & Energy Corporation, Arakawa Chemical Industries, Ltd., and Taoka Chemical Co., Ltd.

The softening point of the solid plasticizer is preferably 30° C. or higher, more preferably 50° C. or higher, even more preferably 80° C. or higher, and is preferably 200° C. or lower, more preferably 160° C. or lower, even more preferably 140° C. or lower, particularly preferably 120° C. or lower. By setting the softening point within the above range, the above-mentioned effects tend to be more suitably obtained.
In this specification, the softening point of a solid plasticizer is the temperature at which the ball drops when the softening point specified in JIS K 6220-1:2001 is measured using a ring and ball softening point tester.

When the rubber composition contains a solid plasticizer (preferably a resin), the content of the solid plasticizer per 100 parts by mass of the rubber component is preferably 5.0 parts by mass or more, more preferably 8.0 parts by mass or more, even more preferably 10.0 parts by mass or more, and particularly preferably 12.0 parts by mass or more. The upper limit is preferably 50.0 parts by mass or less, more preferably 30.0 parts by mass or less, and even more preferably 20.0 parts by mass or less. Within the above range, better effects tend to be obtained.

[Other ingredients]
The rubber composition preferably contains zinc oxide from the viewpoint of obtaining better effects. As the zinc oxide, a conventionally known product can be used, for example, a product manufactured by Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc.

In the rubber composition, the zinc oxide content is preferably 1.0 part by mass or more, more preferably 1.5 parts by mass or more, even more preferably 2.0 parts by mass or more, and particularly preferably 2.5 parts by mass or more, per 100 parts by mass of the rubber component, from the viewpoint of obtaining better effects. There is no particular upper limit, but it is preferably 10.0 parts by mass or less, more preferably 7.0 parts by mass or less, and even more preferably 5.0 parts by mass or less. Within the above range, better effects tend to be obtained.

The rubber composition preferably contains a vulcanizing agent.
The vulcanizing agent may be one commonly used in the rubber industry, such as sulfur. Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and soluble sulfur, which are commonly used in the rubber industry. These may be used alone or in combination of two or more.

Examples of vulcanizing agents that can be used include products from Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flexis Corporation, Nippon Kanzuri Kogyo Co., Ltd., and Hosoi Chemical Industry Co., Ltd.

In the rubber composition, the content of the vulcanizing agent (preferably sulfur) is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and even more preferably 1.5 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, the content is preferably 10.0 parts by mass or less, more preferably 7.0 parts by mass or less, even more preferably 5.5 parts by mass or less, and particularly preferably 4.0 parts by mass or less. Within the above range, better effects tend to be obtained.

The rubber composition preferably contains a vulcanization accelerator.
Examples of vulcanization accelerators include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole and di-2-benzothiazolyl disulfide; 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-benzothiazolylsulfenamide, N-t-butyl-2-benzothiazolylsulfenamide, N-oxyethylene-2-benzothiazolesulfenamide, and N,N'-diisopropyl-2-benzothiazolesulfenamide; and guanidine-based vulcanization accelerators such as diphenylguanidine, di-orthotolylguanidine, and orthotolylbiguanidine. These may be used alone or in combination of two or more. Of these, sulfenamide-based vulcanization accelerators are preferred.

Examples of vulcanization accelerators that can be used include products manufactured by Kawaguchi Chemical Co., Ltd., Ouchi Shinko Chemical Co., Ltd., and Rhein Chemie AG.

In the rubber composition, the content of the vulcanization accelerator is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, and even more preferably 1.0 part by mass or more, per 100 parts by mass of the rubber component, and is preferably 10.0 parts by mass or less, more preferably 5.0 parts by mass or less, and even more preferably 4.0 parts by mass or less. Within the above ranges, better effects tend to be obtained.

The rubber composition preferably contains stearic acid.
As the stearic acid, conventionally known products can be used, for example, products available from NOF Corporation, Kao Corporation, Fujifilm Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., etc.

In the rubber composition, the content of stearic acid per 100 parts by mass of the rubber component is preferably 1.0 part by mass or more, more preferably 2.0 parts by mass or more, and even more preferably 3.0 parts by mass or more. Furthermore, the content is preferably 8.0 parts by mass or less, more preferably 6.0 parts by mass or less, and even more preferably 5.0 parts by mass or less. Within the above range, better effects tend to be obtained.

The rubber composition may contain an antioxidant.
Examples of the antioxidant include naphthylamine-based antioxidants such as phenyl-α-naphthylamine; diphenylamine-based antioxidants 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 of antioxidants include p-phenylenediamine-based antioxidants such as quinoline; quinoline-based antioxidants such as polymers of 2,2,4-trimethyl-1,2-dihydroquinoline; 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 antioxidants may be used alone or in combination of two or more. Of these, p-phenylenediamine-based antioxidants and quinoline-based antioxidants are preferred, and p-phenylenediamine-based antioxidants are more preferred.

As antioxidants, products from, for example, Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Industry Co., Ltd., Flexis, etc. can be used.

In the rubber composition, the content of the antioxidant is preferably 1.0 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2.0 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 10.0 parts by mass or less, more preferably 5.0 parts by mass or less, and even more preferably 4.0 parts by mass or less. Within the above ranges, better effects tend to be obtained.

The rubber composition may contain a wax.
The wax is not particularly limited, and examples thereof include petroleum waxes such as paraffin wax and microcrystalline wax; natural waxes such as vegetable wax and animal wax; and synthetic waxes such as polymers of ethylene, propylene, etc. These may be used alone or in combination of two or more.

For example, products from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., Seiko Chemical Co., Ltd., etc. can be used as wax.

In the rubber composition, the wax content is preferably 0.5 parts by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2.0 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, the wax content is preferably 10.0 parts by mass or less, more preferably 7.0 parts by mass or less, and even more preferably 5.0 parts by mass or less. Within the above range, better effects tend to be obtained.

In addition to the above components, the rubber composition can contain additives commonly used in the tire industry, such as vulcanizing agents other than sulfur (e.g., organic crosslinking agents, organic peroxides). The content of each of these components is preferably 0.1 parts by mass or more and preferably 200 parts by mass or less per 100 parts by mass of the rubber component.

The rubber composition can be produced, for example, by kneading the components using a rubber kneading device such as an open roll or Banbury mixer, and then vulcanizing the mixture.

As for kneading conditions, in the base kneading process, in which additives other than the crosslinking agent (vulcanizing agent) and vulcanization accelerator are kneaded, the kneading temperature is typically 100 to 180°C, preferably 120 to 170°C. In the finish kneading process, in which the vulcanizing agent and vulcanization accelerator are kneaded, the kneading temperature is typically 120°C or lower, preferably 80 to 110°C. Furthermore, the composition kneaded with the vulcanizing agent and vulcanization accelerator is typically subjected to a vulcanization process such as press vulcanization. The vulcanization temperature is typically 140 to 190°C, preferably 150 to 185°C. The vulcanization time is typically 5 to 15 minutes.

The rubber composition can be used (as a rubber composition for tires) in tire components such as treads, sidewalls, base treads, undertreads, shoulders, clinches, bead apexes, breaker cushion rubber, carcass cord covering rubber, insulation, chafers, inner liners, and side reinforcing layers of run-flat tires. In particular, it is particularly suitable for use in treads (particularly the portion that comes into contact with the road surface during driving (cap tread)) and sidewalls.

〔tire〕
The tire of the present disclosure is manufactured by a conventional method using the rubber composition. That is, the rubber composition, to which various additives are optionally blended, is extruded in an unvulcanized state to match the shapes of the tire components such as the tread, molded in a tire building machine by a conventional method, and laminated together with other tire components to form an unvulcanized tire, which is then heated and pressurized in a vulcanizer to manufacture the tire.

Tires are not particularly limited, and examples include pneumatic tires, solid tires, and airless tires. Of these, pneumatic tires are preferred.

The tires can be used as passenger car tires, large passenger car tires, large SUV tires, heavy-duty tires (truck and bus tires, etc.), motorcycle tires, racing tires, winter tires (studless tires, snow tires, studded tires), all-season tires, run-flat tires, aircraft tires, mining tires, etc.

The present disclosure will be specifically explained based on examples, but the present disclosure is not limited to these examples.

[Ash content measurement]
The dried rice husk ash was placed in an alumina crucible and heated for 4 hours in an electric furnace at 550° C. Thereafter, the ash content was calculated using the following formula.
Ash content (mass%) = (mass of rice husk ash after heating/mass of rice husk ash before heating) x 100

[Pore size distribution measurement]
The pore size was measured by a nitrogen adsorption test and analyzed by the MP method. The MP method is a method in which the pore size is calculated based on the correlation with the adsorption layer thickness, assuming that the pores are cylindrical. The measurement device used was a BELSORP MAX manufactured by Microtrac-Bell Corporation.

The various chemicals used in the examples and comparative examples will be collectively described below.
NR: TSR20
BR: BR150B (cis content: 98% by mass) manufactured by Ube Industries, Ltd.
Carbon black: Showblack N220 (N ₂ SA: 111 m ² /g) manufactured by Cabot Japan Co., Ltd.
Rice husk ash A: Prepared by carbonizing rice husks at a temperature range of 500 to 700°C
(Ash content: 60% by mass, carbon content: 40% by mass, modem pore diameter: 0.75nm, maximum pore diameter: 2.0nm, minimum pore diameter: 0.23nm)
Rice husk ash B: Prepared by further burning rice husk ash A at 700°C or higher (ash content: 99.0% by mass, carbon content: 1.0% by mass, mode pore size: 0.75 nm, maximum pore size: 2.0 nm, minimum pore size: 0.23 nm)
Rice husk ash C: Prepared by washing rice husk ash A with an acidic solution (pH 1-3)
(Ash content: 60% by mass, Carbon content: 40% by mass, Modest pore diameter: 0.70nm, Maximum pore diameter: 2.1nm, Minimum pore diameter: 0.20nm)
Rice husk ash D: Prepared by washing rice husk ash B with an acidic solution (pH 1 to 3) (ash content: 99.0% by mass, carbon content: 1.0% by mass, mode pore size: 0.70 nm, maximum pore size: 2.1 nm, minimum pore size: 0.20 nm)
Rice husk ash E: Prepared by washing rice husk ash A with an alkaline solution (pH 6-9)
(Ash content: 60% by mass, carbon content: 40% by mass, modem pore diameter: 0.65nm, maximum pore diameter: 2.3nm, minimum pore diameter: 0.17nm)
Rice husk ash F: Prepared by washing rice husk ash B with an alkaline solution (pH 6 to 9) (ash content: 99.0% by mass, carbon content: 1.0% by mass, mode pore size: 0.65 nm, maximum pore size: 2.3 nm, minimum pore size: 0.17 nm)
Aroma oil: Diana Process AH-24 (aromatic process oil) manufactured by Idemitsu Kosan Co., Ltd.
Stearic acid: NOF Corporation's "Tsubaki" stearic acid
Zinc oxide: Zinc oxide type 2 manufactured by Mitsui Mining & Smelting Co., Ltd. Antioxidant: Antigen 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Sulfur: powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator: Noccela NS (N-tert-butyl-2-benzothiazylsulfenamide (TBBS)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

Examples and Comparative Examples
According to the formulation shown in Table 1, chemicals other than sulfur and vulcanization accelerator were kneaded using a Banbury mixer to obtain a kneaded mixture. Next, sulfur and vulcanization accelerator were kneaded into the obtained kneaded mixture using an open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press-vulcanized at 170°C for 12 minutes to produce a vulcanized rubber sheet with a thickness of 2 mm.

The resulting vulcanized rubber sheets were evaluated as follows. The evaluation results are shown in Table 1.

(Odor rating)
20 g of the vulcanized rubber sheet was placed in a 200 mL glass airtight container and heated in an oven at 60°C for 3 hours, after which a sensory evaluation was carried out according to the following criteria. The sensory evaluation was carried out by two people, and the average score of the two people was used as the sensory evaluation score.
The evaluation criteria were as follows: Comparative Example 1, which had a strong putrid odor, was 5 points;
4 points: A putrid smell is detected. 3 points: A slightly faint putrid smell is detected. 2 points: If you smell carefully, a slight putrid smell can be detected. 1 point: Odorless (no putrid smell is detected).
It was judged as such.

(Mooney viscosity (ML1+4, 130°C) (processability))
Processability was evaluated by measuring the Mooney viscosity (ML1+4, 130°C). The Mooney viscosity of the unvulcanized rubber composition was measured at 130°C in accordance with JIS K6300. The smaller the measured value, the better the processability.

Table 1 shows that the rubber compositions of the examples, which contain a rubber component containing natural rubber and rice husk ash, and in which the ash content of the rice husk ash is a specified amount, have excellent odor suppression properties and processability, despite containing natural rubber.

The present disclosure (1) relates to a rubber composition comprising a rubber component containing natural rubber and rice husk ash, wherein the rice husk ash contains an ash content of 40% by mass or more, and the content of the rice husk ash is 0.1 to 3.0 parts by mass per 100 parts by mass of the rubber component.

Disclosure (2) is a rubber composition described in Disclosure (1), in which the rice husk ash has a most frequent pore size of 0.50 to 0.80 nm, a maximum pore size of 2.0 to 2.5 nm, and a minimum pore size of 0.10 to 0.30 nm.

The present disclosure (3) is a tire having a tread and/or sidewalls made of the rubber composition described in the present disclosure (1) or (2).

Claims (2)

The rubber component contains natural rubber and rice husk ash,
The rice husk ash contains 40% by mass or more of ash, has a mode pore size of 0.50 to 0.80 nm, a maximum pore size of 2.0 to 2.5 nm, and a minimum pore size of 0.10 to 0.30 nm;
The content of the rice husk ash in the rubber composition is 0.1 to 3.0 parts by mass per 100 parts by mass of the rubber component. A tire having a tread and/or sidewalls made from the rubber composition of claim 1 .