Rubber composition

Abstract

To provide a rubber composition excellent in friction on ice and hard to break.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 and 0.5 to 30 parts by mass of a crystallizable cellulose agglomerate, wherein a proportion of a white filler in a total amount of the filler is 85.0% by mass or more, the crystallizable cellulose agglomerate has a secondary agglomerate structure in which primary particles of the crystallizable cellulose are agglomerated and which has voids between the primary particles, and an average particle size (D50) of the crystallizable cellulose agglomerate is 5 μm or more and 200 μm or less.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 a high frictional force (friction on ice) even on ice such as icy roads, etc. Various rubber compositions for use in such studless tires have been developed.

[0003] For example, Patent Document 1 discloses a rubber composition for tires that combines 30 to 100 parts by mass of carbon black and / or white filler and 0.1 to 30 parts by mass of thermally expandable microcapsules with 100 parts by mass of diene rubber, and that has a 5-day biodegradability (De1) of more than 0% as measured in accordance with JIS K 6950:2000, thereby enabling improved performance on ice while reducing environmental impact. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2024-082917 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the industry is seeking further improvements in the friction on ice of rubber compositions used in studless tires, and in addition to improvements in friction on ice, further improvements in breaking characteristics, etc. The rubber composition for tires described in Patent Document 1 above is excellent in that it enables improved performance on ice while reducing the environmental load, but there is still room for further improvement.

[0006] Therefore, an object of the present invention is to provide a rubber composition that has excellent friction on ice and is resistant to breakage. [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 filler in a total amount of 55 parts by mass or more and 0.5 to 30 parts by mass of crystalline cellulose aggregates relative to 100 parts by mass of diene rubber, wherein the proportion of white filler in the total amount of the fillers is 85.0% by mass or more, 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 in which the average particle size is 5 μm or more and 200 μm or less has excellent friction on ice and is resistant to breakage, and have completed the present invention.

[0008] That is, the present invention provides the following: <1> ~ <6> This includes embodiments of the present invention. <1> The rubber composition contains a total of 55 parts by mass or more of a filler and 0.5 to 30 parts by mass of a crystalline cellulose aggregate per 100 parts by mass of a diene rubber, The proportion of the white filler in the total amount of the filler is 85.0% by mass or more, 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 diene rubber contains 35% by mass or more of natural rubber (NR), <1> ~ <3> The rubber composition according to any one of the above. <5> The aromatic modified terpene resin is contained in an amount of 0.5 to 10 parts by mass relative to 100 parts by mass of the diene rubber. <1> ~ <4> The rubber composition according to any one of the above. <6> <1> ~ <5> A studless tire using the rubber composition according to any one of the above. [Effects of the Invention]

[0009] According to the present invention, a rubber composition that exhibits excellent friction on ice and is resistant to breakage can be obtained. By using this rubber composition, an excellent studless tire can be obtained. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will now be described. The present invention relates to a rubber composition comprising a total of 55 parts by mass or more of a filler and 0.5 to 30 parts by mass of crystalline cellulose aggregates relative to 100 parts by mass of a diene rubber, wherein the proportion of the white filler in the total amount of the fillers is 85.0% by mass or more, 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 ) is 5 μm or more and 200 μm or less, and a studless tire using 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."

[0011] 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.

[0012] The components contained in the rubber composition of the present invention, their contents, etc. will be described in detail below.

[0013] [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.

[0014] In the rubber composition of the present invention, it is more preferable that the diene rubber contains 35% by mass or more of natural rubber (NR), that is, 35% by mass or more of the total amount of diene rubber contained in the rubber composition of the present invention is natural rubber, because this makes it easier to obtain a rubber composition that is less susceptible to breakage. In particular, it is more preferable that the diene rubber contains 40% by mass or more, and even more preferably 45% by mass or more, of natural rubber.

[0015] In the above embodiment, in which the diene rubber contains 35% by mass or more of natural rubber, it is more preferable that the diene rubber further contains butadiene rubber (BR) from the viewpoint of friction on ice, etc. The content of butadiene rubber (BR) in the diene rubber is preferably 35% by mass or more, more preferably 40% by mass or more, and even more preferably 45% by mass or more of the total amount of diene rubber. The upper limit is more preferably 65% ​​by mass or less, even more preferably 60% by mass or less, and even more preferably 55% by mass or less.

[0016] 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.

[0017] 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).

[0018] 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).

[0019] [Filler] The filler contained in the rubber composition of the present invention is not limited as long as it contains a white filler described below in a predetermined proportion, and any known filler that is compounded in rubber compositions for use in tires, etc. Examples of fillers include carbon black in addition to the white filler, which is an essential component.

[0020] 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.

[0021] [White filler] The white filler, an essential component of the rubber composition of the present invention, is not limited as long as it satisfies the above requirements. Any known white filler compounded in 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 preferably uses silica as the white filler (more preferably, more than 50% by mass of the white filler is silica) because this more easily achieves the effects of the present invention. For example, it is preferable to use silica alone or silica in combination with at least one selected from the above-listed fillers. 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.

[0022] In the rubber composition of the present invention, the proportion of this white filler in the total amount of the above-mentioned fillers (the mass proportion of the total amount of white filler in the total amount of fillers) is 85.0 mass% or more. In other words, the amount of white filler in the total amount of fillers contained in the rubber composition of the present invention is 85.0 mass% or more (the white filler accounts for 85.0 mass% or more). This results in excellent friction on ice due to interactions with the predetermined crystalline cellulose aggregates described below. The proportion of this white filler is more preferably 87.5 mass% or more, even more preferably 90.0 mass% or more, even more preferably 92.5 mass% or more, and even more preferably 93.5 mass% or more. Note that if the proportion of this white filler is less than 85.0 mass%, friction on ice may not be sufficiently improved. It has been conventionally recognized that increasing the proportion of white filler in the total amount of filler to the above range may result in a decrease in processability during vulcanization. However, one of the features of the rubber composition of the present invention is that, due to the action of the specified crystalline cellulose aggregates described below, the white filler is less likely to break and has excellent processability during vulcanization even when the proportion of the white filler is within the above range. The total amount of the white filler is not limited as long as the above conditions are satisfied, but is preferably 50 parts by mass or more, more preferably 55 parts by mass or more, even more preferably 60 parts by mass or more, even more preferably 65 parts by mass or more, and even more preferably 68 parts by mass or more, relative to 100 parts by mass of the diene rubber. The upper limit is more preferably 95 parts by mass or less, even more preferably 90 parts by mass or less, even more preferably 85 parts by mass or less, and even more preferably 80 parts by mass or less. In particular, in the rubber composition of the present invention, it is more preferable to use silica as the white filler, and the proportion and content of this silica are within the above ranges.

[0023] [Carbon black] When carbon black is used in the rubber composition of the present invention, there are no particular limitations, 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 various grades such as 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 this carbon black is not particularly limited, but is preferably 50 to 200 m 2 / g, and 70 to 150m 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.

[0024] [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 extracting crystalline regions from pulp or other raw materials through hydrolysis and purifying them, and is an insoluble cellulose having 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 make them highly dispersible in diene rubber components, and that the interaction with the white filler significantly increases friction on ice. Furthermore, despite the presence of the voids described above, the aggregate structure is relatively stable, which likely contributes to improved breaking properties. Furthermore, 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.

[0025] 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 )).

[0026] Furthermore, the crystalline cellulose aggregate is more likely to exhibit the effects of the present invention (particularly the effect of improving friction on ice), and therefore, the bulk density of the aggregate is preferably 0.50 g / cm. 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 not particularly limited, but for example, it is 0.05 g / cm 3 The above is an example, and 0.10 g / cm 3 It may be more than that. 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.

[0027] 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.

[0028] 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.

[0029] 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, and more preferably 3.0 parts by mass or more. The upper limit is preferably 25 parts by mass or less, 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. If the content of the crystalline cellulose aggregates per 100 parts by mass of the diene rubber is more than 30 parts by mass, the rupture properties may not be sufficiently improved.

[0030] 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 between the white filler and the specified crystalline cellulose aggregates. The lower limit is preferably 6 parts by mass or more, and even more preferably 7 parts by mass or more, and the upper limit is preferably 17 parts by mass or less. Furthermore, if 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, this is more preferable from the viewpoint of the interaction and effects between them.

[0031] [Aromatic modified terpene resin] It is more preferable that the rubber composition of the present invention further contains a predetermined amount of aromatic-modified terpene resin. This is because it can further increase the dispersibility of white fillers and crystalline cellulose aggregates and further improve breaking properties. In particular, when the diene-based rubber contains natural rubber, the effects of this aromatic-modified terpene resin are more likely to be exhibited. As the aromatic-modified terpene resin, for example, an aromatic-modified terpene resin obtained by polymerizing a terpene resin such as α-pinene, β-pinene, dipentene, or limonene with an aromatic compound such as styrene, α-methylstyrene, vinyltoluene, or indene can be used.

[0032] Furthermore, since this aromatic modified terpene resin is more likely to exhibit the effects of the present invention (particularly the effect of improving friction on ice), it is more preferable that its average glass transition temperature (Tg) is 85° C. or lower, even more preferably 75° C. or lower, and even more preferably 70° C. or lower. There is no particular lower limit for this average glass transition temperature (Tg), but it may be, for example, 20° C. or higher, 30° C. or higher, or 40° C. or higher. The average glass transition temperature (Tg) of this aromatic modified terpene resin is also a value that is measured and calculated in the same manner as the average glass transition temperature of the diene rubber described above.

[0033] The rubber composition of the present invention preferably contains 0.5 to 10 parts by mass of the aromatic modified terpene resin per 100 parts by mass of the diene rubber. The lower limit is more preferably 1.0 part by mass or more, and even more preferably 3.0 parts by mass or more. The upper limit is more preferably 8.0 parts by mass or less, and even more preferably 5.0 parts by mass or less. If the content of the aromatic modified terpene resin is less than 0.5 parts by mass per 100 parts by mass of the diene rubber, the above-mentioned effect may not be fully exhibited. If the content of the aromatic modified terpene resin is more than 10 parts by mass per 100 parts by mass of the diene rubber, the effect of improving friction on ice tends to be less fully exhibited.

[0034] [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 other than those described above, oils (process oils, etc.), zinc oxide (zinc white), stearic acid, wax, lecithin, antioxidants, plasticizers (liquid diene polymers, etc.), curing agents, vulcanizing agents (e.g., sulfur), vulcanization accelerators, and vulcanization acceleration aids, within the range that does not significantly affect the effects of the present invention, and these additives can be kneaded together to form a rubber composition.

[0035] 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. The content of the stearic acid, zinc oxide, and antioxidant in the rubber composition of the present invention is preferably 1 to 5 parts by mass each, per 100 parts by mass of the diene rubber. 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] [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 containing a predetermined ratio of white filler, 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 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 components. The predetermined crystalline cellulose aggregate can be compounded in a powder state.

[0040] The rubber composition of the present invention obtained as described above has excellent friction on ice and is resistant to breakage due to the interaction between the diene rubber, the filler containing a predetermined or higher proportion of white filler, and the predetermined crystalline cellulose aggregates. Furthermore, this breakage characteristic also improves processability during vulcanization, resulting in excellent processability even when the compounding ratio of white filler such as silica is high (even when the compounding amount of carbon black is low). Furthermore, it may also be possible to improve wet performance and rolling performance.

[0041] The studless tire of the present invention can be obtained by using the rubber composition of the present invention, for example, in the tread portion (the cap tread portion extending circumferentially in the tire to form an annular shape) that comes into contact with the road surface. The rubber composition of the present invention may also be used in other tire components (for example, the sidewall portion that constitutes the tire side surface). In other words, the rubber composition of the present invention is suitable as a tire rubber composition that constitutes 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 may be, for example, air, inert gases such as nitrogen, argon, and helium, or other gases.

[0042] 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]

[0043] (Preparation and Evaluation of Rubber Compositions) Rubber compositions having the formulations shown in Table 1 below were prepared.

[0044] 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 1-4, and Examples 1-9.

[0045] The obtained rubber compositions (vulcanized rubber test pieces) of the Standard Example, Comparative Examples 1 to 4, and Examples 1 to 9 were evaluated for friction on ice and energy to break as follows.

[0046] <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 value, the greater the friction force on ice (the easier it is to stop on ice).

[0047] <Breaking energy> For each vulcanized rubber composition obtained, a JIS No. 3 dumbbell-shaped test piece (thickness: 2 mm) was cut out in accordance with JIS K 6251 (2017). Using these, a tensile test was carried out in accordance with JIS K 6251 (2017) at a temperature of 23°C and a tensile speed of 500 mm / min. The breaking strength (TB: MPa) and breaking elongation (EB: %) were measured, and the product of these values ​​was calculated as the breaking energy. The results are also shown in the lower part of Table 1 below. The results are expressed as an index, with the value of the standard example being 100. The larger the index value, the greater the energy required at tensile breakage, meaning that the breaking properties are excellent (less likely to break).

[0048] [Table 1]

[0049] 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) Thermally expandable microcapsules: Microsphere F-100D (Matsumoto Yushi Pharmaceutical Co., Ltd.) 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. Aromatic modified terpene resin: YS Resin TO-105 (glass transition temperature (Tg): 58°C, manufactured by Yasuhara Chemical Co., Ltd.) 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: Amine-based antioxidant (Santoflex 6PPD, 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.)

[0050] These results show that by including the predetermined amounts of crystalline cellulose aggregates and filler and by configuring the filler so that the ratio of silica in the white filler is equal to or greater than a predetermined value (Examples 1 to 9), rubber compositions with superior ice friction and rupture properties can be obtained compared to the standard example. These rubber compositions are also recognized as suitable for use in studless tires. On the other hand, when the silica content of the filler was increased in a formulation using thermally expandable microcapsules, the friction on ice improved but the breaking properties decreased (Comparative Example 1), and the same was true when the amount of filler was reduced in a formulation using crystalline cellulose aggregates (Comparative Example 2).Furthermore, when the silica content of the filler was reduced below a certain level in a formulation using crystalline cellulose aggregates, the breaking properties improved but the friction on ice decreased (Comparative Example 3), and when porous cellulose particles with a large particle size that were not obtained by isolating and purifying the crystalline region were used instead of crystalline cellulose aggregates, the friction on ice improved but the breaking properties decreased (Comparative Example 4).

Claims

1. The rubber composition contains a total of 55 parts by mass or more of a filler and 0.5 to 30 parts by mass of a crystalline cellulose aggregate per 100 parts by mass of a diene rubber, The proportion of the white filler in the total amount of the filler is 85.0% by mass or more, 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 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, wherein the diene rubber contains 35% by mass or more of natural rubber (NR).

5. The rubber composition according to claim 1 or 2, comprising 0.5 to 10 parts by mass of an aromatic modified terpene resin per 100 parts by mass of the diene rubber.

6. A studless tire using the rubber composition according to claim 1 or 2.

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