Studless tire

Abstract

To provide a studless tire having excellent processability and exhibiting excellent on-ice braking and wet braking.SOLUTION: A studless tire comprising a tread portion extending in a tire circumferential direction to form an annular shape, wherein a rubber composition constituting the tread portion comprises 0.5 to 30 parts by mass of a crystalline cellulose aggregate per 100 parts by mass of a diene rubber, A hardness Hs (-20 °C.) is from 50 to 60, the crystalline-cellulose aggregates have a secondary-aggregate structure in which primary particles of the crystalline cellulose are aggregated and which has voids between the primary particles, an average particle size (D50) of the crystalline-cellulose aggregates is from 5 μm to 200 μ m, and a groove area ratio of the tread portion is from 20 to 30%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a studless tire. [Background technology]

[0002] Studless tires are required to have high frictional force even on ice surfaces such as icy roads (ice performance). At the same time, high levels of wet performance (grip performance on wet road surfaces) are often required. Rubber compositions for use in such studless tires have therefore been developed.

[0003] For example, Patent Document 1 discloses a rubber composition for tires that can be used in studless tires and has excellent wet grip performance and braking performance on ice, which contains 3 to 30 parts by mass of a diene rubber that is liquid at room temperature and 0.3 to 20 parts by mass of porous cellulose particles with a porosity of 75 to 95%, per 100 parts by mass of a diene rubber that is solid at room temperature. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-091839 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the industry, there is a demand for further improvements in studless tires' performance on ice and wet surfaces, as well as for improvements in their processability, etc. In other words, there is room for further improvement in the above-mentioned aspects of studless tires.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a studless tire that is easy to process and has excellent braking performance on both ice and wet surfaces. [Means for solving the problem]

[0007] In order to solve the above problems, the present inventors have conducted extensive research and have discovered a studless tire having a tread portion extending in a circumferential direction of the tire and forming an annular shape, wherein the rubber composition constituting the tread portion contains 0.5 to 30 parts by mass of crystalline cellulose aggregates per 100 parts by mass of diene rubber and has a hardness Hs (-20°C) of 50 to 60, 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 The present inventors have found that a studless tire having a groove area ratio of 20 to 30% in the tread portion has excellent processability and excellent braking performance on both ice and wet surfaces, and have completed the present invention.

[0008] That is, the present invention provides the following: <1> ~ <5> This includes embodiments of the present invention. <1> A studless tire having a tread portion extending in a tire circumferential direction and forming an annular shape, the rubber composition constituting the tread portion contains 0.5 to 30 parts by mass of crystalline cellulose aggregates per 100 parts by mass of diene rubber, and has a hardness Hs (-20°C) of 50 to 60; 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, The groove area ratio of the tread portion is 20 to 30%. Studded tires. <2> The bulk density of the crystalline cellulose aggregate contained in the rubber composition is 0.30 g / cm 3 is less than <1> Studless tires as described above. <3> The average particle diameter (D 50) is 10 μm or more and less than 100 μm, <1> or <2> Studless tires as described above. <4> The rubber composition contains 65 parts by mass or more of a white filler per 100 parts by mass of the diene rubber. <1> ~ <3> Studless tires described in any one of the above. <5> The rubber composition contains 10 parts by mass or more of a thermoplastic resin per 100 parts by mass of the diene rubber. <1> ~ <4> Studless tires described in any one of the above. [Effects of the Invention]

[0009] According to the present invention, a studless tire can be obtained which has excellent processability and excellent braking performance on both ice and wet surfaces. [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 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 studless tire having a tread portion extending in a circumferential direction of the tire and forming an annular shape, wherein the rubber composition constituting the tread portion contains 0.5 to 30 parts by mass of crystalline cellulose aggregates per 100 parts by mass of diene rubber and has a hardness Hs (-20°C) of 50 to 60, 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 the groove area ratio of the tread portion is 20 to 30%. Hereinafter, this will also be referred to as the "studless tire of the present invention." In addition, the rubber composition constituting the tread portion of the studless tire of the present invention will also be referred to as the "rubber composition 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] First, the components contained in the rubber composition of the present invention that constitutes the tread portion of the studless tire of the present invention, their contents, physical properties, 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 butadiene rubber (BR), since this makes it easier to achieve braking effects on ice. Furthermore, in the above embodiment in which the diene rubber contains butadiene rubber, it is preferable that the diene rubber further contains natural rubber (NR), since this makes it easier to obtain a rubber composition that is less likely to break and has better processability. The content of both butadiene rubber and natural rubber 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.

[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 braking 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 that can be used 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.

[0020] The rubber composition of the present invention preferably 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 more preferably 60 parts by mass or more, more preferably 65 parts by mass or more, more preferably 70 parts by mass or more, and even more preferably 75 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, more preferably 90 parts by mass or less, and even more preferably 85 parts by mass or less.

[0021] [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, in the rubber composition of the present invention, silica is preferably used as the white filler (more preferably, more than 50% by mass of the white filler is silica) because this more easily exhibits synergistic effects with the predetermined crystalline cellulose aggregates described below, thereby improving braking performance on ice. 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.

[0022] In the rubber composition of the present invention, the total amount of the white filler 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 70 parts by mass or more, relative to 100 parts by mass of the diene rubber. The upper limit is 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, from the viewpoint of braking on ice, it is more preferable to use silica as a white filler and to have the silica content as described above (for example, 60 parts by mass or more, or even 65 parts by mass or more, per 100 parts by mass of the diene rubber described above). Additionally, also from the viewpoint of braking on ice, 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 preferable that it is 55 mass% or more, even more preferable that it is 60 mass% or more, even more preferable that it is 65 mass% or more, even more preferable that it is 70 mass% or more, even more preferable that it is 75 mass% or more, even more preferable that it is 80 mass% or more, and even more preferable that it is more than 85 mass%.

[0023] [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 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 the 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 the like through hydrolysis and refining, and is an insoluble cellulose having both hydrophilic and lipophilic surfaces. Although the mechanism of the crystalline cellulose aggregates made of this crystalline cellulose is unclear, it is presumed that the lipophilic surfaces of the crystalline cellulose make them highly dispersible in diene rubber components, and that the aggregates have a relatively low bulk density, which in turn enhances braking performance on ice through a synergistic effect with the hardness Hs (-20°C) described below. Furthermore, despite having the voids described above, the aggregate structure is relatively stable, which improves breaking properties and facilitates excellent processability. In addition, 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 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 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 of 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 braking 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, braking performance 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, breaking properties may not be sufficiently improved.

[0030] Although not limited thereto, it is more preferable that the rubber composition of the present invention contains 5 to 20 parts by mass of the crystalline cellulose aggregates per 100 parts by mass of the white filler, since 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, 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.

[0031] [Thermoplastic resin] The rubber composition of the present invention preferably further contains a thermoplastic resin. This is because it can further enhance the dispersibility of crystalline cellulose aggregates and improve breaking properties. The thermoplastic resin is not particularly limited, and can be a thermoplastic resin with a weight-average molecular weight of several hundred to several thousand (e.g., 500 to 5,000), such as a petroleum-based resin or an aromatic resin, which is typically incorporated into rubber compositions for applications such as tires. Examples of petroleum-based resins include C5 petroleum resins (aliphatic petroleum resins obtained by polymerizing fractions such as isoprene, 1,3-pentadiene, cyclopentadiene, methylbutene, and pentene), C9 petroleum resins (aromatic petroleum resins obtained by polymerizing fractions such as α-methylstyrene, o-vinyltoluene, m-vinyltoluene, and p-vinyltoluene), and C5 / C9 resins (C5C9 copolymer petroleum resins) obtained by copolymerizing these resins. Examples of aromatic resins include coumarone resins, phenolic resins, alkylphenolic resins, terpene resins, aromatic-modified terpene resins, rosin resins, novolac resins, resol resins, and aromatic indene copolymers. Among aromatic resins, terpene resins and aromatic-modified terpene resins (resins obtained by polymerizing terpene resins and aromatic compounds) are preferred. These resins can be used alone or as a blend of multiple resins. The C9 petroleum resins mentioned above are also classified as aromatic resins. Among these, from the viewpoint of the above-mentioned effects, it is more preferable to include an aromatic modified terpene resin or a C5 / C9 resin (for example, the proportion of either of these exceeds 50 mass% of the total amount of thermoplastic resins contained in the rubber composition of the present invention, or the combined proportion of these exceeds 50 mass%), and this thermoplastic resin may essentially consist of one or more selected from aromatic modified terpene resins and C5 / C9 resins.

[0032] Furthermore, since the above-mentioned effects are more easily exhibited, the thermoplastic resin preferably has an average glass transition temperature (Tg) of 85° C. or less, more preferably 75° C. or less, and may even have an average glass transition temperature (Tg) of 70° C. or less. There is no particular restriction on the lower limit of the average glass transition temperature (Tg), but it may be, for example, 20° C. or more, 30° C. or more, or 40° C. or more. There is also no restriction on the weight average molecular weight, but it is more preferably 1,000 to 3,000. 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.

[0033] The rubber composition of the present invention preferably contains the above-mentioned thermoplastic resin in an amount of 5 parts by mass or more, more preferably 10 parts by mass or more, per 100 parts by mass of the diene rubber. The upper limit is more preferably 40 parts by mass or less, even more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less. However, the rubber composition of the present invention may also be substantially free of this thermoplastic resin.

[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 oil (process oil, etc.), zinc oxide (zinc white), stearic acid, wax, lecithin, antioxidants, plasticizers (liquid diene-based polymers, etc.), 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.

[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 also makes it possible to adjust the hardness Hs (-20°C) of the rubber composition of the present invention. Although not limited thereto, the total amount of the thermoplastic resin, the oil, and the plasticizer is more preferably 30 to 100 parts by mass per 100 parts by mass of the diene rubber, since this makes it easier to exhibit the effects of the present invention, and the lower limit is more preferably 35 parts by mass or more, more preferably 40 parts by mass or more, and even more preferably more than 45 parts by mass. 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, even more preferably 80 parts by mass or less, even more preferably 75 parts by mass or less, and even more preferably 70 parts by mass or less. The contents of stearic acid, zinc oxide, and antioxidant in the rubber composition of the present invention are each preferably 1 to 5 parts by mass per 100 parts by mass of the diene rubber. Furthermore, the content of vulcanizing agent 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. Additionally, the content of 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] [Hardness Hs(-20℃)] The rubber composition of the present invention has the above-mentioned configuration, and its hardness Hs (-20°C) is 50 to 60. This allows the rubber composition to have high braking performance on ice with a given configuration. The upper limit is more preferably 58 or less, and even more preferably 56 or less. The lower limit is more preferably 52 or more, and even more preferably 54 or more. In studless tires, lowering the hardness Hs (-20°C) of the rubber composition constituting the tread tends to improve braking on ice, but lowering the hardness Hs (-20°C) of the rubber composition constituting the tread also tends to reduce the breaking characteristics and processability. However, one of the features of the studless tire of the present invention is that, because the tread is made of the rubber composition of the present invention, it is possible to achieve a high level of both processability and braking on ice. Here, the hardness Hs (-20°C) is a durometer hardness measured using a test piece of the rubber composition of the present invention in accordance with JIS K 6253 (2023) using a durometer type A at a temperature of -20°C.

[0040] [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, a diene rubber, a predetermined crystalline cellulose aggregate, and, if necessary, other components are kneaded and mixed in a predetermined blend at room temperature or at an elevated temperature using a kneading machine such as a Banbury mixer, kneader, or roll mill, to produce a rubber composition of the present invention having a predetermined hardness Hs (-20°C). 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, then cool the mixture, and then mix the vulcanization components. The predetermined crystalline cellulose aggregate can be compounded in a powder state.

[0041] Next, the configuration of the studless tire of the present invention will be described in detail.

[0042] The studless tire of the present invention has a circumferentially extending annular tread portion made of the rubber composition of the present invention. The tread portion has a groove area ratio of 20 to 30%. From the viewpoint of wet braking, the lower limit of this groove area ratio is preferably 21% or more, more preferably 22% or more, and even more preferably 23% or more. From the viewpoint of braking on ice, the upper limit of this groove area ratio is preferably 29% or less, more preferably 28% or less, and even more preferably 27% or less. In studless tires, reducing the groove area ratio of the tread tends to improve braking on ice, but on the other hand, reducing the groove area ratio of the tread tends to reduce wet braking. However, the studless tire of the present invention, whose tread is made of the rubber composition of the present invention, has excellent wet braking even when the groove area ratio of the tread is within the above-mentioned range, and one of its features is that it can achieve a high level of both braking on ice and braking in wet conditions.

[0043] Here, the "groove area ratio" of the tread portion is a value calculated by the formula (groove area / ground contact area) × 100 (%) for the surface of the region of the tread portion that comes into contact with the road surface or the like under specified conditions (tread contact surface). This ground contact area is the area of ​​the tread contact surface, and is the area measured between the ground contact edges, based on the plane where the pneumatic studless tire and the flat plate contact each other, when the studless tire of the present invention is mounted on a standard rim, inflated to the standard internal pressure, placed perpendicular to a flat plate in a stationary state, and a load corresponding to a standard load is applied. The groove area is also the total opening area of ​​the grooves in the tread contact surface. However, this groove area does not include the openings of sipes (those formed in the shape of fine grooves on the surface of the tread portion, etc., which, when the fine grooves are positioned on the flat portion under the load described above or when the land portions where the fine grooves are formed collapse, bring the wall surfaces of the fine grooves, or at least parts of the portions provided on the wall surfaces, into contact with each other due to deformation of the land portions).

[0044] For example, taking the embodiment shown in Figures 1 and 2 as an example, a studless tire 100 of the present invention as shown in Figure 1 is mounted on a standard rim, inflated to the standard internal pressure, and placed in a stationary state with the tire radial direction perpendicular to a flat plate.When a load corresponding to the standard load (see Figure 1) is applied, the plane of the tread portion 1 that comes into contact with the flat plate (the surface of the tread portion 1 in the tire contact area T in Figure 1) is used as a reference, and the area measured between the contact edges based on this (contact area) and the sum of the opening areas of the grooves 11 to 14 there (A1, A2, etc. in Figure 2) (groove area) are measured and calculated. 1 and 2 may differ from the actual dimensional ratios, etc., in order to facilitate understanding of the invention. In addition, in Fig. 2, the plane of the groove opening is indicated by a dotted line.

[0045] The above-mentioned "genuine rim" refers to the "standard rim" defined by JATMA, the "design rim" defined by TRA, or the "measuring rim" defined by ETRTO. Furthermore, the above-mentioned normal 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. Furthermore, the above-mentioned normal load refers to the "maximum load capacity" specified by JATMA, the maximum value of the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified by TRA, or the "LOAD CAPACITY" specified by ETRTO. However, in JATMA, for passenger car tires, the normal internal pressure is 180kPa and the normal load is 88% of the maximum load capacity.

[0046] The studless tire of the present invention may also use the rubber composition of the present invention in tire components other than the tread portion. As described above, the studless tire of the present invention is preferably a pneumatic tire, and the gas to be filled in the pneumatic tire may be, for example, air, inert gas such as nitrogen, argon, or helium, or other gases.

[0047] The studless tire of the present invention as described above exhibits excellent braking performance on both ice and wet surfaces due to the interaction between the predetermined crystalline cellulose aggregate contained in the rubber composition constituting the tread, its hardness Hs (-20°C), and the groove area ratio of the tread. Furthermore, the rupture properties of the rubber composition also contribute to excellent processability.

[0048] 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]

[0049] (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 were produced.

[0050] Specifically, the components (excluding sulfur and vulcanization accelerator) in the amounts shown in the upper part 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 1-13. Furthermore, studless tires each having a tread portion with grooves that are made of the rubber composition shown in the upper part of Table 1 below and have the groove area ratios shown in the middle part of Table 1 below when measured using the above-mentioned measurement method were also produced by a conventional method.

[0051] The rubber compositions (vulcanized rubber test pieces) and studless tires obtained in the Standard Example, Comparative Examples 1 to 4, and Examples 1 to 13 were evaluated for hardness Hs, braking on ice, braking on wet ground, and breaking energy as follows.

[0052] <Hardness Hs (-20℃)> Using each of the obtained vulcanized rubber test pieces, the hardness Hs (-20°C) was measured at a temperature of -20°C with a durometer type A in accordance with JIS K 6253 (2023). The results are shown in the lower part of Table 1 below.

[0053] <Braking on ice> Each studless tire obtained was mounted on a standard rim and inflated to a predetermined air pressure (standard internal pressure) to obtain a test tire. This was mounted on a test vehicle and driven on a test course (straight road) consisting of an ice and snow surface. The vehicle was braked at an initial speed of 25 km / h, and the braking distance from 20 km / h to 5 km / h was measured. The results are shown in the bottom row of Table 1 below. The results are expressed as an index with the standard example value set at 100, and the shorter the braking distance, the higher the index. In other words, the higher the index, the better the braking performance on ice.

[0054] <Wet braking> Each studless tire was mounted on a standard rim and inflated to a specified air pressure (standard internal pressure) to obtain a test tire. This was mounted on a test vehicle and driven on an asphalt road sprayed with water 1 mm deep, and the braking distance from an initial speed of 40 km / h was measured. The results are shown in the bottom row of Table 1 below. The results are expressed as an index with the standard example value set at 100, and the shorter the braking distance, the higher the index. In other words, the higher the index, the better the wet braking performance.

[0055] <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).

[0056] [Table 1]

[0057] 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. Thermally expandable microcapsules: Microsphere F-100D (Matsumoto Yushi Pharmaceutical Co., Ltd.) Thermoplastic resin A: YS Resin TO-105 (aromatic modified terpene resin, glass transition temperature (Tg): 58°C, weight average molecular weight: 1450, manufactured by Yasuhara Chemical Co., Ltd.) Thermoplastic resin B: T-REZ RD104 (C5 / C9 resin, glass transition temperature (Tg): 44°C, weight average molecular weight: 2460, manufactured by ENEOS Corporation) Process oil: Extract No. 4S (Shell Lubricants Japan) Silane coupling agent: Si69 (bis(3-triethoxysilylpropyl)tetrasulfide, manufactured by Evonik Degussa) 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.)

[0058] These results show that in studless tires, by constructing a tread portion with a predetermined groove area ratio using a rubber composition with a predetermined hardness Hs (-20°C) containing a predetermined amount of crystalline cellulose aggregates (Examples 1 to 13), both ice braking and wet braking are superior compared to the standard example, and further, the rubber composition is less likely to break and has excellent processability. On the other hand, simply reducing the groove area ratio in the tread improved braking on ice but reduced wet braking (Comparative Example 1). Also, increasing the groove area ratio in the tread made with a rubber composition formulated with crystalline cellulose aggregates or increasing the hardness Hs (-20°C) of that rubber composition reduced braking on ice in both cases (Comparative Examples 2 and 3). Furthermore, when the tread was made with a rubber composition that used porous cellulose particles with a large particle size and not obtained by isolating and refining the crystalline region instead of the crystalline cellulose aggregates, braking on ice decreased and the breaking characteristics were significantly reduced (Comparative Example 4). [Explanation of symbols]

[0059] 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 groove

Claims

1. A studless tire having a tread portion extending in a tire circumferential direction and forming an annular shape, the rubber composition constituting the tread portion contains 0.5 to 30 parts by mass of crystalline cellulose aggregates per 100 parts by mass of diene rubber, and has a hardness Hs (-20°C) of 50 to 60; 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, The groove area ratio of the tread portion is 20 to 30%. Studded tires.

2. The bulk density of the crystalline cellulose aggregate contained in the rubber composition is 0.30 g / cm 3 The studless tire according to claim 1, wherein the tread width is less than 1 / 2 mm.

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

4. The studless tire according to claim 1 or 2, wherein the rubber composition contains 65 parts by mass or more of a white filler per 100 parts by mass of the diene rubber.

5. The studless tire according to claim 1 or 2, wherein the rubber composition contains 10 parts by mass or more of a thermoplastic resin per 100 parts by mass of the diene rubber.

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