Rubber composition

Abstract

To provide a rubber composition excellent in friction on ice, and hardly causing deterioration with time and poor appearance.SOLUTION: A rubber composition includes, based on 100 parts by mass of a diene-based rubber, 55 parts by mass or more of a filler in total, more than 4.0 parts by mass of an amine-based antioxidant having a specific structure, and 0.5 to 30 parts by mass of a crystallizable cellulose agglomerate, wherein the crystallizable cellulose agglomerate has a secondary agglomerate structure in which primary particles of crystallizable cellulose are agglomerated and which has a void between the primary particles, and the crystallizable cellulose agglomerate has an average particle size (D50) of 5 μm or more and 200 μm or less. As the amine-based antioxidant having a specific structure, N - (1, 3-dimethylbutyl) - N ' - phenyl-p-phenylenediamine (6PPD) is preferably used.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Studless tires are required to have high frictional force (friction on ice) even on icy surfaces such as icy roads. As studless tires become harder with age, their friction on ice can decrease. One known method of preventing this is to increase the amount of antioxidants added to the tires.

[0003] However, increasing the blending amount of antioxidant increases the likelihood of the antioxidant precipitating on the tire surface, which can lead to problems such as brown discoloration of the surface and other appearance defects. In light of this background, for example, Patent Document 1 discloses a rubber composition that contains a rubber component including an isoprene-based rubber and a butadiene rubber, silica, an aromatic oil, benzothiazole and / or dibenzothiazyl disulfide having one or two substituents selected from alkyl groups, aryl groups, and aralkyl groups on the benzene ring, and a thiuram-based vulcanization accelerator, in which the silica content is 15 to 80 parts by mass and the aromatic oil content is 15 to 80 parts by mass per 100 parts by mass of the rubber component, and the rubber composition has improved heat resistance and a long life without reducing performance on snow and ice, and provides good performance on snow and ice, wet grip performance, and abrasion resistance, and furthermore can shorten the vulcanization time and improve crosslinking efficiency, without increasing the amount of antioxidant. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-219124 Summary of the Invention [Problem to be solved by the invention]

[0005] However, there is room for further improvement in the rubber compositions used in such studless tires in terms of both improving friction on ice and suppressing deterioration over time. In particular, there is a need for the development of technology that makes it less likely for poor appearance to occur even when the amount of antioxidant is increased.

[0006] Therefore, an object of the present invention is to provide a rubber composition that has excellent friction on ice and is less susceptible to deterioration over time and poor appearance. [Means for solving the problem]

[0007] In order to solve the above problems, the present inventors have conducted extensive research and have discovered a rubber composition comprising a rubber composition comprising a total of 55 parts by mass or more of a filler, more than 4.0 parts by mass of an amine-based antioxidant represented by the general formula (1) described below, and 0.5 to 30 parts by mass of crystalline cellulose aggregates, relative to 100 parts by mass of a diene-based rubber, wherein the crystalline cellulose aggregates have a secondary aggregate structure in which primary particles of crystalline cellulose are aggregated and have voids between the primary particles, and further wherein the average particle diameter (D 50 The present inventors have found that a rubber composition having a particle size of 5 μm or more and 200 μm or less has excellent friction on ice and is less susceptible to deterioration over time and poor appearance, and have completed the present invention.

[0008] That is, the present invention provides the following: <1> ~ <7> This includes embodiments of the present invention. <1> The rubber composition contains a total of 55 parts by mass or more of a filler, more than 4.0 parts by mass of an amine-based antioxidant represented by general formula (1) described below, and 0.5 to 30 parts by mass of crystalline cellulose aggregates, relative to 100 parts by mass of a diene-based rubber, The crystalline cellulose aggregate has a secondary aggregate structure in which primary particles of crystalline cellulose are aggregated and have voids between the primary particles, and the average particle diameter (D 50 ) is 5 μm or more and 200 μm or less. <2> The bulk density of the crystalline cellulose aggregate is 0.30 g / cm 3 is less than <1> The rubber composition according to claim 1. <3> The average particle diameter (D 50 ) is 10 μm or more and less than 100 μm, <1> or <2> The rubber composition according to claim 1. <4> The white filler is contained in an amount of 50 parts by mass or more relative to 100 parts by mass of the diene rubber. <1> ~ <3> The rubber composition according to any one of the above. <5> The diene rubber contains 50% by mass or more of butadiene rubber (BR). <1> ~ <4> The rubber composition according to any one of the above. <6> A tread portion extending in the tire circumferential direction and forming an annular shape, <1> ~ <5> A studless tire comprising the rubber composition according to any one of the above items. <7> the tire comprises a tread portion extending in a circumferential direction of the tire and forming an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed radially inward of the sidewall portions, a carcass layer is installed between the pair of bead portions, a belt layer including belt cords inclined with respect to the circumferential direction of the tire is disposed on the outer peripheral side of the carcass layer in the tread portion, and a belt cover layer is disposed on the outer peripheral side of the belt layer, The shortest distance in the tire radial direction between the groove bottom of the tire circumferential main groove in the tread portion and the belt layer is 5 mm or less. <6> Studless tires as described above. [Effects of the Invention]

[0009] According to the present invention, a rubber composition can be obtained that has excellent friction on ice and is less susceptible to deterioration over time and poor appearance. By using this rubber composition, an excellent studless tire can be obtained. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a meridian cross-sectional view showing an embodiment of a studless tire of the present invention. [Figure 2] FIG. 2 is an enlarged cross-sectional view of the vicinity of a main groove in the tread portion of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will now be described. The present invention relates to a rubber composition comprising, relative to 100 parts by mass of a diene rubber, a total of 55 parts by mass or more of a filler, more than 4.0 parts by mass of an amine-based antioxidant represented by the general formula (1) described below, and 0.5 to 30 parts by mass of crystalline cellulose aggregates, wherein the crystalline cellulose aggregates have a secondary aggregate structure in which primary particles of crystalline cellulose are aggregated and have voids between the primary particles, and further, the average particle diameter (D 50 and a studless tire having a tread portion extending in the tire circumferential direction and forming an annular shape, the tread portion being made of this rubber composition. Hereinafter, these will also be referred to as the "rubber composition of the present invention" and the "studless tire of the present invention."

[0012] In the present invention, unless otherwise specified, a numerical range expressed using "to" means a numerical range in which the numerical value before "to" is the lower limit and the numerical value after "to" is the upper limit.

[0013] The components contained in the rubber composition of the present invention, their contents, etc. will be described in detail below.

[0014] [Diene rubber] The diene rubber contained in the rubber composition of the present invention is a rubber component having a double bond in the polymer main chain, and specific examples thereof include natural rubber (NR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), isoprene rubber (IR), acrylonitrile-butadiene copolymer rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, isoprene-butadiene copolymer rubber, etc. In the rubber composition of the present invention, such diene rubbers can be used alone or in combination of two or more.

[0015] In the rubber composition of the present invention, it is preferable that the diene rubber contains 45% by mass or more, more preferably 50% by mass or more, of butadiene rubber (BR), that is, 45% by mass or more, more preferably 50% by mass or more of the total amount of diene rubber contained in the rubber composition of the present invention is butadiene rubber, because this makes it easier to exhibit the effect of friction on ice.

[0016] In the above embodiment, the diene rubber contains a predetermined amount or more of butadiene rubber, and it is more preferable that the diene rubber further contains natural rubber (NR), since this facilitates the production of a rubber composition with better mechanical properties. The content of natural rubber in the diene rubber is more preferably 35% by mass or more, even more preferably 40% by mass or more, and even more preferably 45% by mass or more of the total amount of the diene rubber.

[0017] The weight average molecular weight of the diene rubber contained in the rubber composition of the present invention is preferably 50,000 to 3,000,000, and more preferably 100,000 to 2,000,000. In the present invention, the "weight average molecular weight" refers to a value measured in terms of standard polystyrene by gel permeation chromatography (GPC) using tetrahydrofuran as a solvent. The GPC measurement is carried out at 40°C using a column (MIXED-B, manufactured by Polymer Laboratories) as a measuring instrument.

[0018] Furthermore, the diene rubber contained in the rubber composition of the present invention preferably has an average glass transition temperature (Tg) of -100 to -50°C, more preferably -90 to -60°C, because this facilitates further improvement of friction on ice. Here, the average glass transition temperature (Tg) of this diene rubber is a value obtained by multiplying the glass transition temperature of each component contained in the diene rubber by the mass% of each component and adding the results together. In this calculation, the sum of the mass% of each component is set to 1.0. The glass transition temperature of each diene rubber is determined by measuring a thermogram by differential scanning calorimetry (DSC) at a heating rate of 20°C / min, and the temperature at the intersection of the low-temperature baseline and the extension of the slope of the transition region (inclined straight line).When the diene rubber is an oil-extended product, the glass transition temperature is the diene rubber's glass transition temperature in a state that does not contain an oil-extending component (oil).

[0019] The rubber composition of the present invention may contain rubber components other than diene-based rubber, but it is preferable that 85% by mass or more of the rubber components contained are diene-based rubber, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably that the rubber components contained consist of diene-based rubber (100% by mass of diene-based rubber).

[0020] [Filler] The filler contained in the rubber composition of the present invention is not particularly limited, and any known filler that is blended into rubber compositions for use in tires, etc. Examples of such fillers include white fillers and carbon black.

[0021] The rubber composition of the present invention contains the above-described fillers in a total amount of 55 parts by mass or more per 100 parts by mass of the diene rubber. The lower limit is preferably 60 parts by mass or more, more preferably 65 parts by mass or more, even more preferably 70 parts by mass or more, and even more preferably 75 parts by mass or more. The upper limit is preferably 100 parts by mass or less, even more preferably 95 parts by mass or less, even more preferably 90 parts by mass or less, and even more preferably 85 parts by mass or less. If the total amount (total content) of the fillers is less than 55 parts by mass per 100 parts by mass of the diene rubber, the effects of the present invention may not be fully achieved.

[0022] [White filler] The white filler is also not particularly limited, and any known white filler blended into rubber compositions for applications such as tires can be used. Specific examples include silica, calcium carbonate, magnesium carbonate, clay, mica, talc, alumina, aluminum hydroxide, titanium oxide, calcium sulfate, and barium sulfate. These white fillers may be used alone or in combination of two or more. In particular, the rubber composition of the present invention more easily exhibits the effects of the present invention (especially the effect of improving friction on ice). Therefore, it is preferable to use silica (more preferably, more than 50 mass% of the white filler is silica) and, for example, it is preferable to use silica alone or silica in combination with at least one selected from the above-listed materials. Specific examples of silica include wet silica, dry silica, fumed silica, and diatomaceous earth. Silica produced using biomass materials such as rice husks as raw materials may also be used. These silicas may be used alone or in combination of two or more. Furthermore, from the viewpoint of the effects of the present invention, the CTAB specific surface area of ​​the silica contained in the rubber composition of the present invention is 110 to 200 m 2 / g is more preferable, and 150 to 180m 2 It is more preferable that the saturation rate is / g. Here, the CTAB adsorption specific surface area of ​​silica is a value measured in accordance with JIS K 6430:2008, Appendix G. When one type of silica is used alone, this value is the value of the CTAB adsorption specific surface area of ​​that silica. When two or more types are used in combination, this value is the value obtained by multiplying the CTAB adsorption specific surface area of ​​each silica used in combination by its use ratio (mass ratio) and adding up the results. In this calculation, the sum of the use ratios of each silica is set to 1.0.

[0023] In the rubber composition of the present invention, it is more preferable that the total amount of fillers satisfies the above-mentioned range, and that the total amount of the white fillers is 50 parts by mass or more per 100 parts by mass of the diene rubber. That is, it is more preferable that the total amount of the white fillers is 50 parts by mass or more per 100 parts by mass of the diene rubber. The lower limit is more preferably 55 parts by mass or more, and even more preferably 60 parts by mass or more. The upper limit is more preferably 100 parts by mass or less, more preferably 95 parts by mass or less, and even more preferably 90 parts by mass or less. Furthermore, although not limited thereto, from the viewpoint of friction on ice, etc., it is more preferable that the proportion of this white filler (mass proportion of the total amount of white filler) of the total amount of fillers contained in the rubber composition of the present invention is more than 50 mass% (the amount of white filler is more than 50 mass% of the total amount of the above fillers), even more preferably 55 mass% or more, even more preferably 60 mass% or more, even more preferably 65 mass% or more, even more preferably 70 mass% or more, and even more preferably 75 mass% or more. In particular, in the rubber composition of the present invention, it is more preferable that silica is used as the white filler and the content and ratio of this silica are within the above ranges.

[0024] [Carbon black] The carbon black is not particularly limited, and any known carbon black compounded in rubber compositions for applications such as tires can be used. Specific examples of carbon black that can be used include SAF-HS, SAF, ISAF-HS, ISAF, ISAF-LS, IISAF-HS, HAF-HS, HAF, HAF-LS, and FEF. These carbon blacks may be used alone or in combination of two or more. The nitrogen adsorption specific surface area (N2SA) of the carbon black is not particularly limited, but is preferably 50 to 200 m 2 / g, and 70 to 130m 2 / g is more preferred. Here, "carbon black" refers to fine carbon particles consisting of primary particles with a diameter of approximately 3 to 500 nm, which are manufactured under industrial quality control. The nitrogen adsorption specific surface area (N2SA) of this carbon black is a value measured in accordance with JIS K 6217-2:2017. When a single carbon black is used, this value is the nitrogen adsorption specific surface area (N2SA) of that carbon black. When two or more carbon blacks are used in combination, this value is calculated by multiplying the nitrogen adsorption specific surface area (N2SA) of each carbon black used by its respective proportion (mass proportion) and adding the results together. In this calculation, the sum of the proportions of each carbon black used is assumed to be 1.0.

[0025] [Amine-based antioxidant] The rubber composition of the present invention further contains a predetermined amount of an amine-based antioxidant represented by the following general formula (1). This sufficiently exhibits the effect of preventing deterioration over time. 1 and R 2 Each of the represents a hydrocarbon group, and examples thereof include those containing an alkyl group, a cycloalkyl group, a phenyl group, etc., but it is more preferable that at least one of them is a hydrocarbon group containing a phenyl group. The number of carbon atoms in this hydrocarbon group is not particularly limited, but is preferably 1 to 20, more preferably 3 to 10, and even more preferably 3 to 8.

[0026] [ka] [In the formula, R 1 and R 2 Each of these represents a hydrocarbon group.

[0027] Specific examples of this amine-based antioxidant include N,N'-diphenyl-p-phenylenediamine, N-phenyl-N'-isopropyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) represented by the following formula (2), N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (77PD) represented by the following formula (3), and N,N'-dicyclohexyl-p-phenylenediamine (CCPD). These amine-based antioxidants can be used alone or in combination. In particular, it is more preferable to use N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) represented by the following formula (2) as the amine-based antioxidant in view of the effects of the present invention.

[0028] [ka]

[0029] [ka]

[0030] The rubber composition of the present invention contains the above-described amine-based antioxidant in an amount of more than 4.0 parts by mass per 100 parts by mass of the diene rubber. The lower limit is preferably 4.5 parts by mass or more, and may be more than 5.0 parts by mass, 6.0 parts by mass or more, or even 8.0 parts by mass or more. The upper limit is preferably 20 parts by mass or less, more preferably 16 parts by mass or less, even more preferably 14 parts by mass or less, and even more preferably 12 parts by mass or less. The rubber composition of the present invention is also characterized in that, even when the blending amount of the specified amine-based antioxidant is within the above-described range, poor appearance is unlikely to occur due to the action of the specified crystalline cellulose aggregates described below. If the content of the amine-based antioxidant is 4.0 parts by mass or less per 100 parts by mass of the diene rubber, the effect of inhibiting deterioration over time may be insufficient.

[0031] [Crystalline cellulose aggregates] The crystalline cellulose aggregate contained in the rubber composition of the present invention is an aggregate having a secondary aggregate structure in which primary particles (plural primary particles) of crystalline cellulose are aggregated and have voids between the primary particles. The average particle diameter (D 50 ) is between 5 μm and 200 μm. The crystalline cellulose constituting this crystalline cellulose aggregate is cellulose obtained by hydrolysis of pulp or other raw materials to extract and refine the crystalline regions, and is an insoluble cellulose possessing both hydrophilic and lipophilic surfaces. Although the mechanism behind the crystalline cellulose aggregates described above is unclear, it is believed that the lipophilic surfaces of the crystalline cellulose and other factors contribute to their high dispersibility in diene-based rubber components, and that the structure and size of the crystalline cellulose aggregates also contribute to their high affinity with specific amine-based antioxidants. It is believed that the crystalline cellulose aggregates can capture the specific amine-based antioxidants in the rubber composition and suppress their excessive surface deposition, thereby suppressing poor appearance and fully demonstrating the effect of suppressing aging degradation even at the above-mentioned compounding amounts. Furthermore, it is believed that the relatively low bulk density of the aggregates significantly increases friction on ice. Furthermore, it is believed that the average particle diameter (D 50 ), not only is it highly dispersible in the diene rubber component, but it is also easy to maintain the mechanical properties of the rubber composition at a high level.

[0032] The average particle size of this crystalline cellulose aggregate (D 50 The lower limit of the average particle diameter (D) is more preferably 10 μm or more, even more preferably 15 μm or more, and even more preferably 20 μm or more. The upper limit is more preferably 150 μm or less, even more preferably 120 μm or less, and even more preferably less than 100 μm. For example, 50 ) is more preferably 10 μm or more and less than 100 μm. Here, this "average particle diameter (D 50) is the volume-based average particle diameter (50% volume cumulative distribution diameter (D 50 )).

[0033] Furthermore, the crystalline cellulose aggregate has a bulk density of 0.50 g / cm because the effects of the present invention are more easily exhibited. 3 The upper limit of the bulk density is preferably 0.40 g / cm or less. 3 More preferably, it is 0.35 g / cm or less. 3 More preferably, it is 0.30 g / cm or less. 3 The lower limit is more preferably less than 0.05 g / cm 3 More preferably, it is 0.10 g / cm or more. 3 More preferably, it is equal to or greater than this. Here, the bulk density is the density (mass per unit volume) when a container of a certain volume is filled to capacity with crystalline cellulose aggregates (powder) without applying any additional physical external force (without pushing, tapping, etc.), and is the volume when the internal volume is taken as the volume, and is a value measured by the container method.

[0034] Furthermore, although not limited thereto, the crystalline cellulose aggregates preferably have an average aspect ratio (the ratio of the length in the long axis direction to the length in the short axis direction in the smallest rectangle circumscribing the aggregate) of 1 to 50, since this makes it easier to exhibit the effects of the present invention (particularly the effect of improving friction on ice).The upper limit of this average aspect ratio is more preferably 45 or less, and even more preferably 40 or less. Here, this average aspect ratio is obtained by obtaining an electron microscope image by TEM or SEM observation, setting an appropriate magnification depending on the size of the crystalline cellulose aggregate, and calculating the ratio of the long axis length to the short axis length of the smallest circumscribing rectangle for at least 50 aggregates in the image, and then taking the average of these ratios.

[0035] The shape of the crystalline cellulose aggregate is not particularly limited as long as it satisfies the above conditions, and may be, for example, spherical (approximately spherical) or fibrous. Furthermore, the aggregate may have an uncontrolled shape. From the viewpoint of the effects of the present invention, it is more preferable that the aggregate be spherical (approximately spherical) with an average aspect ratio of 1 to 2 as described above.

[0036] The rubber composition of the present invention contains 0.5 to 30 parts by mass of the above-described crystalline cellulose aggregates per 100 parts by mass of the diene rubber. The lower limit is preferably 1.0 part by mass or more, more preferably 2.0 parts by mass or more, even more preferably 3.0 parts by mass or more, and even more preferably 5.0 parts by mass or more. The upper limit is preferably 25 parts by mass or less, even more preferably 20 parts by mass or less, even more preferably 15 parts by mass or less, and even more preferably 12 parts by mass or less. If the content of the crystalline cellulose aggregates per 100 parts by mass of the diene rubber is less than 0.5 parts by mass, the friction on ice may not be sufficiently improved, and the suppression of poor appearance may not be sufficient.

[0037] Although not limited thereto, the rubber composition of the present invention preferably contains 5 to 20 parts by mass of the crystalline cellulose aggregates per 100 parts by mass of the total white filler, because this facilitates the interaction (particularly the effect of friction on ice) between the white filler and the specified crystalline cellulose aggregates. The lower limit is more preferably 6 parts by mass or more, and the upper limit is more preferably 17 parts by mass or less. Furthermore, it is more preferable that the rubber composition of the present invention contains silica, and the crystalline cellulose aggregates are contained in the above range per 100 parts by mass of the silica, from the viewpoint of the interaction between them.

[0038] [Other ingredients] The rubber composition of the present invention may further contain appropriate amounts of various additives that are generally used in rubber compositions, such as resin components (e.g., thermoplastic resins), oils (process oils), zinc oxide (zinc white), stearic acid, wax, lecithin, plasticizers (liquid diene polymers), curing agents, vulcanizing agents (e.g., sulfur), vulcanization accelerators, and vulcanization accelerator aids, within the range that does not significantly affect the effects of the present invention, and these additives can be kneaded by known methods to form a rubber composition.

[0039] For example, the content of the oil and the plasticizer (each content or total amount) in the rubber composition of the present invention is preferably 10 to 90 parts by mass, more preferably 20 to 80 parts by mass, and even more preferably 25 to 75 parts by mass, per 100 parts by mass of the diene rubber. This allows the hardness of the rubber composition of the present invention to be adjusted, and its processability to be further improved. The content of the stearic acid and the zinc oxide in the rubber composition of the present invention is preferably 1 to 5 parts by mass per 100 parts by mass of the diene rubber. Furthermore, the content of the resin component in the rubber composition of the present invention is preferably 1 part by mass or more but less than 20 parts by mass per 100 parts by mass of the diene rubber, and this resin component is preferably a C5 / C9 thermoplastic resin (e.g., a thermoplastic resin containing more than 50% by mass of a C5 / C9 resin). The C5 / C9 resin is a copolymerized petroleum resin (C5C9 copolymerized petroleum resin) obtained by copolymerizing a C5 petroleum resin (an aliphatic petroleum resin obtained by polymerizing fractions such as isoprene, 1,3-pentadiene, cyclopentadiene, methylbutene, and pentene) with a C9 petroleum resin (an aromatic petroleum resin obtained by polymerizing fractions such as α-methylstyrene, o-vinyltoluene, m-vinyltoluene, and p-vinyltoluene). The average glass transition temperature (Tg) of the resin is preferably 70°C or lower, more preferably 60°C or lower, and may even be 50°C or lower, since this facilitates the exertion of the effects of the present invention (particularly the effect of improving friction on ice). The lower limit is not particularly limited, but may be, for example, 20°C or higher, 30°C or higher, or 40°C or higher. The weight-average molecular weight is more preferably 1,000 to 3,000, from the viewpoint of suppressing deterioration over time. Here, the average glass transition temperature (Tg) and the weight average molecular weight are values ​​that are measured and calculated in the same manner as the average glass transition temperature or weight average molecular weight of the diene rubber described above.

[0040] The content (total amount) of vulcanizing agents in the rubber composition of the present invention is preferably 0.3 to 3.0 parts by mass, more preferably 0.5 to 2.5 parts by mass, per 100 parts by mass of the diene rubber. The content of the vulcanization accelerator in the rubber composition of the present invention, either as a primary accelerator alone or as a blend with a secondary accelerator, is preferably 0.5 to 3.5 parts by mass, more preferably 1.0 to 3.0 parts by mass, and even more preferably 2.0 to 3.0 parts by mass, per 100 parts by mass of the diene rubber.

[0041] The rubber composition of the present invention may further contain a silane coupling agent to enhance the dispersibility of silica when silica is used as a white filler. The silane coupling agent is not particularly limited as long as it is a silane compound having a hydrolyzable group and an organic functional group. The hydrolyzable group is also not limited, but examples include an alkoxy group, a phenoxy group, a carboxy group, and an alkenyloxy group. An alkoxysilyl group in which the alkoxy group is bonded to a silicon atom is preferred. When the hydrolyzable group is an alkoxysilyl group, the alkoxy group preferably has 1 to 16 carbon atoms, more preferably 1 to 4 carbon atoms. Examples of alkoxy groups having 1 to 4 carbon atoms include a methoxy group, an ethoxy group, and a propoxy group.

[0042] The organic functional group is not limited, but may be any group capable of forming a chemical bond with an organic compound, such as an epoxy group, a vinyl group, an acryloyl group, a methacryl group, an amino group, a sulfide group (particularly, a polysulfide group (-S n - (n is an integer of 2 or more), a mercapto group, a blocked mercapto group (protected mercapto group) (for example, an octanoylthio group), and the like. Among these, a sulfide group (particularly a disulfide group or a tetrasulfide group), a mercapto group, and a blocked mercapto group are preferred. Such silane coupling agents may be used alone or in combination of two or more thereof. The silane coupling agent is preferably a sulfur-containing silane coupling agent.

[0043] The rubber composition of the present invention preferably contains 1 to 20 parts by mass, and more preferably 2 to 10 parts by mass, of the silane coupling agent per 100 parts by mass of the silica.

[0044] [Manufacturing method etc.] The method for producing the rubber composition of the present invention may be a conventional method and is not particularly limited. As an example of the production method, the rubber composition of the present invention can be produced by kneading and mixing a diene rubber, a filler, a predetermined amine-based antioxidant, a predetermined crystalline cellulose aggregate, and, if necessary, other components, at room temperature or at an elevated temperature using a kneading machine such as a Banbury mixer, kneader, or roll mill, in a predetermined blend. When vulcanization-related components (sulfur, vulcanization accelerator, vulcanization accelerator aid, etc.) are used, it is preferable to first mix the other components at an elevated temperature, cool the mixture, and then mix the vulcanization-related components. The predetermined crystalline cellulose aggregate can be compounded in a powder state.

[0045] The rubber composition of the present invention obtained as described above has excellent friction on ice and is less susceptible to deterioration over time and poor appearance due to the interactions between the diene rubber, filler, specified amine-based antioxidant, and specified crystalline cellulose aggregates.

[0046] The studless tire of the present invention can be obtained by using the rubber composition of the present invention to form a tread portion that extends circumferentially in the tire and forms an annular shape, which is the tire component that comes into contact with the road surface. The rubber composition of the present invention may also be used for other tire components. In other words, the rubber composition of the present invention is suitable as a rubber composition for tires that forms each tire component. The studless tire of the present invention is preferably a pneumatic tire, and the gas that can be filled into the pneumatic tire can be, for example, air, inert gases such as nitrogen, argon, and helium, or other gases.

[0047] 1 and 2, the rubber composition of the present invention is preferably used to form the tread portion of a studless tire as follows: Specifically, the rubber composition of the present invention is more preferably used to form the tread portion 1 of a studless tire, the tread portion 1 having an annular shape extending in the tire circumferential direction, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3 arranged radially inward of the sidewall portions 2, a carcass layer 4 mounted between the pair of bead portions 3, a belt layer 7 (preferably a plurality of belt layers 7) including belt cords inclined with respect to the tire circumferential direction arranged on the outer circumferential side of the carcass layer 4 in the tread portion 1, and a belt cover layer 8 (preferably a belt cover layer 8 including organic fiber cords oriented in the tire circumferential direction) arranged on the outer circumferential side of the belt layer 7, and the shortest radial distance between the bottom of a circumferential main groove (e.g., 11, 12, 13, or 14) in the tread portion 1 and the belt layer 7 is 5 mm or less. If the shortest distance in the tire radial direction between the groove bottom of the main groove and the belt layer is short, this can contribute to reducing the tire weight, but it can also cause groove cracks. However, by using the rubber composition of the present invention containing a predetermined amount or more of an antioxidant, groove cracks can be sufficiently suppressed and poor appearance is also less likely to occur. The dimensional ratios of the components in FIGS. 1 and 2 may differ from the actual dimensional ratios in order to facilitate understanding of the invention.

[0048] Here, the main groove in the circumferential direction of the tire in the tread portion is defined as a groove that is required to display a wear indicator as specified by JATMA, and has a lateral width (groove width) of 4.0 mm or more and a groove depth of 6.2 mm or more.

[0049] The groove width is measured as the maximum distance between opposing groove walls at a groove opening on the tread surface when the studless tire of the present invention is mounted on a specified rim, inflated to a specified internal pressure, and in an unloaded state. In a configuration in which the groove opening has a notch or chamfer, the groove width is measured using the intersection of an extension of the tread surface and an extension of the groove wall as an endpoint in a cross-sectional view parallel to the groove width direction and the groove depth direction.

[0050] Furthermore, the groove depth is measured as the maximum distance from the tread surface to the groove bottom when the studless tire of the present invention is mounted on a specified rim, inflated to a specified internal pressure, and under no load. In addition, if the tire has partial unevenness or sipes at the groove bottom, the groove depth is measured excluding these.

[0051] The specified rim refers to the "standard rim" specified by JATMA, the "design rim" specified by TRA, or the "measuring rim" specified by ETRTO. The specified internal pressure refers to the "maximum air pressure" specified by JATMA, the maximum value of the "tire load limits at various cold inflation pressures" specified by TRA, or the "inflation pressures" specified by ETRTO. However, in JATMA, the specified internal pressure for passenger car tires is 180kPa.

[0052] The shortest distance in the tire radial direction between the groove bottom of the tire circumferential main groove in the tread portion and the belt layer is the shortest linear distance (separation distance) in the tire radial direction between the surface of the area forming the bottom of the main groove and the belt layer when the studless tire of the present invention described above is mounted on a specified rim and inflated to a specified internal pressure in an unloaded state; for example, in the embodiment of Figure 2, it is the shortest linear distance L in the tire radial direction between the groove bottom 22 of the main groove and the belt layer 7. In addition, in the studless tire of the present invention, the same effect can be achieved even in an embodiment in which the distance (straight-line distance) in the tire radial direction between the groove bottom of the main groove in the tire circumferential direction in the tread portion and the belt layer is 5 mm or less.

[0053] Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples, and various modifications are possible within the technical concept of the present invention. [Example]

[0054] (Production and Evaluation of Rubber Composition and Studless Tire) Rubber compositions having the formulations shown in Table 1 below and studless tires using the same in the tread portion were produced.

[0055] Specifically, the components (excluding sulfur and vulcanization accelerator) in the parts by weight shown in the upper row of Table 1 below were mixed for 5 minutes using a 1.7-liter internal Banbury mixer (maintaining the temperature at 150-160°C for 4-5 minutes to promote the reaction between the silica and the silane coupling agent), then the mixture was discharged from the mixer and cooled to room temperature. Each cellulose was compounded in powder form. Furthermore, using the Banbury mixer, predetermined amounts of sulfur and vulcanization accelerator were mixed and kneaded, and the mixture was formed into a sheet using a two-roll mill. This was then press-vulcanized in a predetermined mold at 170°C for 10 minutes to produce the rubber compositions (vulcanized rubber test pieces) of the Reference Example, Comparative Examples 1-5, and Examples 1-10. Furthermore, each of the specified studless tires having a tread portion made of the rubber composition shown in the upper part of Table 1 below was also produced by a conventional method.

[0056] The resulting rubber compositions (vulcanized rubber test pieces) of the Standard Example, Comparative Examples 1 to 5, and Examples 1 to 10 were evaluated for friction on ice and deterioration over time as follows.

[0057] <Friction on ice> Each vulcanized rubber test piece obtained was attached to a flat cylindrical rubber base and tested using an inside drum type ice friction tester at a measurement temperature of -3.0°C and a load of 5.5 kg / cm. 3 The coefficient of friction on ice was measured at a drum rotation speed of 25 km / h. The results are shown in the bottom row of Table 1 below. The results are expressed as an index, with the standard example value being 100. The higher the index, the greater the friction force on ice (the easier it is to stop on ice).

[0058] <Aging deterioration (tensile strength retention rate after aging)> Immediately after preparation, each vulcanized rubber test piece was subjected to a tensile test in accordance with JIS K 6251 (2017) to measure the initial tensile strength (TB: MPa). Next, each vulcanized rubber test piece was left to age at 80°C for 240 hours, and after this aging, each test piece was subjected to a tensile test in accordance with JIS K 6251 (2017) to measure the tensile strength (TB: MPa) after aging. From the initial tensile strength (TB) and the tensile strength (TB) after aging, the retention rate of tensile strength (TB) after aging was calculated according to the following formula (4). (4) Tensile strength (TB) retention rate after aging = Tensile strength (TB) after aging / Initial tensile strength (TB) × 100 (%) The results are also shown in the bottom row of Table 1 below. The results are expressed as an index where the standard example has a value of 100. In other words, the higher the index, the more resistant the product is to deterioration over time.

[0059] <Appearance> After each of the studless tires was produced, it was left to stand at room temperature for one month, and then the appearance was visually inspected and evaluated according to the following evaluation criteria. ○: No visible change in surface color. △: The surface is slightly discolored when visually inspected. ×: Brown or white color is clearly visible on the surface when visually inspected.

[0060] [Table 1]

[0061] The details of each component in Table 1 above are as follows: NR: Natural rubber (STR20, glass transition temperature (Tg): -65°C, manufactured by Bonbandit) BR: Butadiene rubber (Nipol BR1220, glass transition temperature (Tg): -110°C, manufactured by Zeon Corporation) Carbon black: Show Black N339 (Nitrogen adsorption specific surface area (N2SA): 88m 2 / g, manufactured by Gabot Japan) ·Silica: Zeosil 1165MP (CTAB adsorption specific surface area: 165m 2 / g, manufactured by Solvay) Crystalline cellulose 1 (crystalline cellulose aggregate): CEOLUS TG-101 (average particle size (D 50 ) 50 μm, shape uncontrolled, bulk density 0.29 g / cm 3 , manufactured by Asahi Kasei Corporation) Crystalline cellulose 2 (crystalline cellulose aggregate): CEOLUS PH-102 (average particle size (D 50 ) 90 μm, shape uncontrolled, bulk density 0.30 g / cm 3 , manufactured by Asahi Kasei Corporation) Crystalline cellulose 3 (crystalline cellulose aggregate): CEOLUS TG-F20 (average particle size (D 50 ) 20 μm, shape uncontrolled, bulk density 0.23 g / cm 3 , manufactured by Asahi Kasei Corporation) Crystalline cellulose 4 (crystalline cellulose aggregate): CEOLUS UF-F711 (average particle size (D 50 ) 50 μm, spherical, bulk density 0.22 g / cm 3 , manufactured by Asahi Kasei Corporation) Crystalline cellulose 5 (crystalline cellulose aggregate): CEOLUS ST-100 (average particle size (D 50 ) 50 μm, fibrous, bulk density 0.12 g / cm 3 , manufactured by Asahi Kasei Corporation) *Crystalline cellulose 1 to 5 are all crystalline cellulose aggregates with a secondary aggregate structure in which primary particles of crystalline cellulose aggregate and there are voids between these primary particles. Porous cellulose (porous cellulose particles): Viscopearl (average particle diameter (D 50 ) 400 μm, shape uncontrolled, bulk density 0.3 g / ml, manufactured by Rengo Co., Ltd. Thermoplastic resin: T-REZ RD104 (C5 / C9 resin, glass transition temperature (Tg): 44°C, weight average molecular weight: 2460, manufactured by ENEOS Corporation) Silane coupling agent: Si69 (bis(3-triethoxysilylpropyl)tetrasulfide, manufactured by Evonik Degussa) Process oil: Extract No. 4S (Shell Lubricants Japan) Zinc oxide: Three types of zinc oxide (manufactured by Seido Chemical Industry Co., Ltd.) Stearic acid: Beads Stearic Acid YR (NOF Corporation) Antioxidant 1: Amine-based antioxidant (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine: Santoflex 6PPD, manufactured by Flexis) Antioxidant 2: Amine-based antioxidant (N,N'-bis-(1,4-dimethylpentyl)-p-phenylenediamine: Santoflex 77PD, manufactured by Flexis) Sulfur: Oil-treated sulfur (Hosoi Chemicals) Vulcanization accelerator 1: CZ (Suncerer CM-G, manufactured by Sanshin Chemical Industry Co., Ltd.) Vulcanization accelerator 2: DPG (Suncerer DG, manufactured by Sanshin Chemical Industry Co., Ltd.)

[0062] These results show that by incorporating predetermined amounts of a specified crystalline cellulose aggregate, a specified amine-based antioxidant, and a filler (Examples 1 to 10), the friction on ice is superior and the product is less susceptible to deterioration over time and poor appearance compared to the standard example. On the other hand, when crystalline cellulose aggregates were used without using an antioxidant, friction on ice improved but the product was prone to deterioration over time (Comparative Example 1), and when an amine-based antioxidant was simply used or increased without using crystalline cellulose aggregates, friction on ice did not improve and the appearance deteriorated (Comparative Examples 2 and 3). Furthermore, when porous cellulose particles with large particle sizes that were not obtained by isolating and purifying the crystalline regions were used instead of crystalline cellulose aggregates, reducing the amount of silica did not improve friction on ice (Comparative Example 4), and increasing the amount of amine-based antioxidant deteriorated the appearance (Comparative Example 5). [Explanation of symbols]

[0063] 100 studless tires 1 Tread section 2 Sidewall 3 Bead section 4 carcass layers 5 bead core 6 Bead filler 7 Belt Layer 8 Belt cover layer 11, 14 Circumferential shoulder main grooves 12, 13 Circumferential center main groove 22 Bottom of main groove 31 Belt cord

Claims

1. The rubber composition contains a total of 55 parts by mass or more of a filler, more than 4.0 parts by mass of an amine-based antioxidant represented by the following general formula (1), and 0.5 to 30 parts by mass of crystalline cellulose aggregates, relative to 100 parts by mass of a diene-based rubber, The crystalline cellulose aggregate has a secondary aggregate structure in which primary particles of crystalline cellulose are aggregated and have voids between the primary particles, and the average particle diameter (D 50 ) is 5 μm or more and 200 μm or less. 【Chemistry 1】 [In the formula, R 1 and R 2 Each of the represents a hydrocarbon group.

2. The bulk density of the crystalline cellulose aggregate is 0.30 g / cm 3 The rubber composition of claim 1 , wherein the tensile strength is less than 1000 kJ / cm 2 .

3. The average particle size (D 50 3. The rubber composition according to claim 1, wherein the average particle diameter is 10 μm or more and less than 100 μm.

4. The rubber composition according to claim 1 or 2, further comprising 50 parts by mass or more of a white filler per 100 parts by mass of the diene rubber.

5. The rubber composition according to claim 1 or 2, wherein the diene rubber contains 50% by mass or more of butadiene rubber (BR).

6. A studless tire having a tread portion extending in a circumferential direction of the tire to form an annular shape, the tread portion being made of the rubber composition according to claim 1 or 2.

7. the tire comprises the tread portion, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed radially inward of the sidewall portions, a carcass layer is installed between the pair of bead portions, a belt layer including belt cords inclined with respect to the tire circumferential direction is disposed on the outer peripheral side of the carcass layer in the tread portion, and a belt cover layer is disposed on the outer peripheral side of the belt layer, The studless tire according to claim 6, wherein the shortest distance in the tire radial direction between the bottom of a main groove in the tire circumferential direction in the tread portion and the belt layer is 5 mm or less.

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