tire

Abstract

The present invention provides a tire having a sidewall section in which a reinforcing core is embedded, which has excellent sidewall reinforcement performance and high interfacial adhesion with the adjacent rubber compound. [Solution] The above problem is solved by providing a tire that has a sidewall portion in which a reinforcing core portion is embedded, and the rubber compound of the sidewall portion is composed of a rubber composition (a) made of diene rubber reinforced with carbon black, which constitutes the region adjacent to the reinforcing core portion and surrounding its periphery, and a rubber composition (b) made of diene rubber reinforced with carbon black and nanocellulose and / or kraft pulp, which constitutes the reinforcing core portion, and the mass ratio of the rubber composition (b) to the total mass of the rubber compound of the sidewall portion is 10 to 50%.

Description

Technical Field

[0001] The present invention relates to a tire having a sidewall portion buried with a reinforcing material core portion.

Background Art

[0002] In tires for underground mines, construction vehicles, etc., the sidewall portion is often used in a harsh environment where it is rubbed or pressed against rock masses, rocks, etc. Therefore, high cut resistance, etc. is also required for the sidewall portion. And in such a background, technologies for reinforcing the sidewall portion of such tires and technologies for enhancing the reinforcing effect have been developed.

[0003] For example, Patent Document 1 discloses a pneumatic tire for a construction vehicle in which at least two convex protectors extending in the tire circumferential direction are provided in a range of 30 to 65% of the tire section height on at least one sidewall portion, an elastic reinforcing material is buried inside the protector, and the 100% modulus of the elastic reinforcing material is 5 to 25 times the 100% modulus of the rubber composition of the adjacent sidewall portion.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in this industry, there is a demand for further improvements in the reinforcing performance of the tire sidewall and the reinforcing material (reinforcing core) contained within it, as well as further improvements in the interfacial adhesion between this reinforcing material and the adjacent rubber compound. In other words, there is room for further improvement in the tire sidewall in the manner described above.

[0006] Therefore, the present invention aims to provide a tire having a sidewall portion in which a reinforcing core portion is embedded, which has excellent sidewall reinforcement performance and high interfacial adhesion with adjacent rubber compounds. [Means for solving the problem]

[0007] To solve the above problems, the inventors diligently conducted research and found that a tire having a sidewall portion in which a reinforcing core is embedded, wherein the rubber compound of the sidewall portion is composed of a rubber composition (a) made of diene rubber reinforced with carbon black, which constitutes the region adjacent to and surrounding the periphery of the reinforcing core portion, and a rubber composition (b) made of diene rubber reinforced with carbon black and nanocellulose and / or kraft pulp, which constitutes the reinforcing core portion, and furthermore, the mass ratio of the rubber composition (b) to the total mass of the rubber compound of the sidewall portion is 10 to 50%, has excellent sidewall portion reinforcement performance and a sidewall portion in which a reinforcing core is embedded, which has high interfacial adhesion with adjacent rubber compounds, and thus completed the present invention.

[0008] In other words, the present invention is as follows <1> ~ <6> Includes embodiments. <1> A tire having a sidewall portion in which a reinforcing core portion is embedded, The rubber compound of the sidewall portion is composed of a rubber composition (a) in which diene rubber is reinforced with carbon black, constituting a region adjacent to and surrounding the periphery of the reinforcing core portion, and a rubber composition (b) in which diene rubber is reinforced with carbon black and nanocellulose and / or kraft pulp, constituting the reinforcing core portion. The mass ratio of the rubber composition (b) to the total mass of the rubber compound in the sidewall portion is 10 to 50%. tire. <2> Both rubber composition (a) and rubber composition (b) have a carbon black content of 40 to 60 phr. <1> The tires listed. <3> The rubber composition (b) has a total content of 5 to 20 phr of nanocellulose and kraft pulp. <1> or <2> The tires listed. <4> The reinforcing core portion is embedded in the sidewall portion in the tire circumferential direction such that it forms a closed annular shape with a columnar form. <1> ~ <3> The tire listed in any one of the following. <5> When the sidewall portion is divided into a region on the tire surface side and a region on the tire inner side at the center of its thickness in the tire width direction, 90% or more of the reinforcing core portion is embedded in the region on the tire surface side. <1> ~ <4> The tire listed in any one of the following. <6> These are tires for underground mines. <1> ~ <5> The tire listed in any one of the following. [Effects of the Invention]

[0009] According to the present invention, it is possible to obtain a tire having a sidewall portion in which a reinforcing core portion is embedded, which has excellent sidewall reinforcement performance and high interfacial adhesion with adjacent rubber compounds. [Brief explanation of the drawing]

[0010] [Figure 1] This is a perspective view showing some embodiments of the tire of the present invention. [Figure 2]This is a meridian cross-sectional view showing a part of an embodiment of the tire of the present invention. [Figure 3] This is an enlarged cross-sectional view showing a portion of the cross-section of the sidewall portion in an embodiment of the tire of the present invention. [Figure 4] This is an enlarged cross-sectional view showing a portion of the cross-section of the sidewall in a modified embodiment of the tire of the present invention. [Modes for carrying out the invention]

[0011] The present invention will now be described. The present invention provides a sidewall portion in which a reinforcing core is embedded, and the rubber compound of the sidewall portion is composed of a rubber composition (a) made of diene rubber reinforced with carbon black, which constitutes the region adjacent to and surrounding the periphery of the reinforcing core portion, and a rubber composition (b) made of diene rubber reinforced with carbon black and nanocellulose and / or kraft pulp, which constitutes the reinforcing core portion, wherein the mass ratio of rubber composition (b) to the total mass of the rubber compound of the sidewall portion is 10 to 50%. Hereinafter, this will also be referred to as "the tire of the present invention".

[0012] In this invention, the "sidewall portion" of a tire refers to the "rubber layer between the shoulder and the bead" as defined in the Selection, Use, and Maintenance Standards for Automobile Tires (2023) Truck and Bus Tires Edition / Small Truck Tires Edition published by JATMA. Furthermore, in this invention, unless otherwise specified, a numerical range represented using "~" means a numerical range where the number written before "~" is the lower limit and the number written after "~" is the upper limit.

[0013] First, the components and their contents in the rubber composition (*a*) that constitutes the region surrounding the periphery adjacent to the reinforcing material core part in the rubber compound of the sidewall part in which the reinforcing material core part of the tire of the present invention is embedded, and the rubber composition (*b*) that constitutes the reinforcing material core part (hereinafter, these may be collectively referred to as "the rubber composition of the present invention" or "the rubber compound of the present invention") will be described in detail. Note that "constituting" means substantially consisting of the rubber composition, but embodiments containing trace additives (trace components different from the components of the rubber composition) are not excluded. The same applies hereinafter.

[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. Specifically, natural rubber (NR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), synthetic isoprene rubber (IR), acrylonitrile-butadiene copolymer rubber (nitrile rubber, NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, isoprene-butadiene copolymer rubber, etc. are exemplified. And in the rubber composition of the present invention, such diene rubbers can be used alone or in combination of two or more.

[0015] And in any of the rubber compositions of the present invention, when this diene rubber contains natural rubber (NR) and / or synthetic isoprene rubber (IR), the effects of the present invention are more likely to be exhibited, so it is suitable. Also, the ratio of the total amount of natural rubber and synthetic isoprene rubber in this diene rubber (when only one of them is included, the ratio of that amount) is more preferably more than 50% by mass, further preferably 70% by mass or more, still further preferably 90% by mass or more, still further preferably 95% by mass or more, and most preferably substantially 100% by mass (substantially consisting of natural rubber and / or synthetic isoprene rubber). Further, although not limited, the diene rubber of the rubber composition of the present invention (particularly rubber composition (b)) is more preferably in an embodiment that substantially does not contain acrylonitrile-butadiene copolymer rubber (NBR) from the viewpoint of interfacial adhesion and the like.

[0016] In addition, the weight average molecular weight of this diene rubber is preferably 50,000 to 3,000,000, and more preferably 100,000 to 2,000,000. Here, in the present invention, the "weight average molecular weight" means that measured in terms of standard polystyrene by gel permeation chromatography (GPC) using tetrahydrofuran as a solvent. Further, this GPC measurement is performed at 40 °C using a column (manufactured by Polymer Laboratories, MIXED-B) as a measuring instrument.

[0017] And all of the rubber compositions of the present invention are rubber compositions in which the above-described diene rubber is reinforced with at least carbon black. That is, it is a rubber composition in which at least carbon black is blended as a filler into the above-described diene rubber and reinforced. Hereinafter, this carbon black will be described.

[0018] [Carbon Black] The carbon black for reinforcing the diene rubber as described above is not particularly limited, and any known carbon black blended in a rubber composition for applications such as tires can be used. For example, as specific examples of carbon black, various grades such as SAF-HS, SAF, ISAF-HS, ISAF, ISAF-LS, IISAF-HS, HAF-HS, HAF, HAF-LS, and FEF can be used. And this carbon black 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 more preferably 70 to 150 m 2 / g. Here, "carbon black" refers to carbon nanoparticles consisting of primary particles with a diameter of approximately 3 to 500 nm, manufactured with industrial quality control. The nitrogen adsorption specific surface area (N2SA) of this carbon black is measured according to JIS K 6217-2:2017. Note that this value is the nitrogen adsorption specific surface area (N2SA) of the carbon black used alone, and when two or more types are used in combination, it is the value obtained by multiplying the nitrogen adsorption specific surface area (N2SA) of each carbon black used by its respective usage ratio (mass ratio) and adding them together. In this calculation, the sum of the usage ratios of each carbon black is set to 1.0.

[0019] Furthermore, from the viewpoint of the effects of the present invention, it is more preferable that both rubber compositions of the present invention (rubber composition (a) and rubber composition (b)) contain the above-mentioned carbon black in an amount of 40 to 60 parts by mass per 100 parts by mass of the aforementioned diene-based rubber. In other words, it is more preferable that the carbon black content relative to the diene-based rubber is 40 to 60 phr (parts per hundred parts of rubber), and more specifically, it is more preferable that rubber composition (a) contains 40 to 60 parts by mass of the above-mentioned carbon black per 100 parts by mass of the diene-based rubber, and that rubber composition (b) also contains 40 to 60 parts by mass of the above-mentioned carbon black per 100 parts by mass of the diene-based rubber. Furthermore, it is even more preferable that the lower limit is 45 parts by mass or more, and the upper limit is even more preferable that it is 55 parts by mass or less.

[0020] Furthermore, among the rubber compositions of the present invention, rubber composition (b) has a different composition and physical properties from rubber composition (a) in order to constitute a predetermined reinforcing core, and is a diene-based rubber reinforced with the above-mentioned carbon black and nanocellulose and / or kraft pulp. In other words, it is a rubber composition in which the above-mentioned diene-based rubber is reinforced by compounding at least carbon black with nanocellulose and / or kraft pulp. These will be explained below.

[0021] [Nanocellulose] Nanocellulose refers to extremely fine cellulose fibers with an average fiber diameter of 1 to 1000 nm. Examples include cellulose nanofibers (CNF, e.g., Cellenpia from Nippon Paper Industries) with an average fiber diameter of 1 to 50 nm and an average fiber length of several hundred nm to about 1 μm, and microfibrillated cellulose (MFC, e.g., Exilva from Borregaard) with an average fiber diameter of more than 50 nm but less than or equal to 200 nm and an average fiber length of several tens of μm.

[0022] As mentioned above, the average fiber diameter of this nanocellulose is 1 to 1000 nm, but it is more preferably 1 to 200 nm. The average aspect ratio (average fiber length / average fiber diameter) of this nanocellulose is preferably 10 to 1000, more preferably 30 to 500, and even more preferably 50 to 300. If the average fiber diameter is less than the above range and / or the average aspect ratio is greater than the above range, the dispersibility of the nanocellulose tends to decrease. Also, if the average fiber diameter exceeds the above range and / or the average aspect ratio is less than the above range, the reinforcing performance of the nanocellulose tends to decrease.

[0023] Here, the "average fiber diameter" and "average fiber length" of this nanocellulose refer to the average values ​​of the fiber diameter and fiber length obtained by TEM observation or SEM observation, where the magnification is appropriately set according to the size of the constituent fibers, and measurements are taken on at least 50 fibers in these images. Then, the average aspect ratio is calculated from the average fiber length and average fiber diameter obtained in this way.

[0024] The cellulose used as the raw material for this nanocellulose can be derived from wood or from non-wood sources (bacteria, algae, cotton, etc.), and is not particularly limited. Examples of methods for producing nanocellulose include adding water to the raw material cellulose, processing it with a mixer or the like to prepare a slurry in which the cellulose is dispersed in water, and then finely defibrating it by applying mechanical shear force directly using a device such as a high-pressure or ultrasonic device, or subjecting the slurry to chemical treatment such as oxidation, alkali treatment or acid hydrolysis to modify the cellulose and make it easier to defibrate, and then finely defibrating it by applying mechanical shear force with a disperser or the like. By performing chemical treatment in this way before defibration, the cellulose can be finer and more homogeneously defibrated with lower energy, and chemically modified nanocellulose can be easily obtained. Chemical treatments can include, for example, treatment with chemical agents such as 2,2,6,6-tetramethylpiperidine-1-oxyl (hereinafter referred to as "TEMPO"), 4-acetamido-TEMPO, 4-carboxy-TEMPO, 4-amino-TEMPO, 4-hydroxy-TEMPO, 4-phosphonooxy-TEMPO, phosphate esters, periodic acid, alkali metal hydroxide, and carbon disulfide. Alternatively, chemical treatment may be performed after mechanical defibration of the cellulose. Furthermore, in addition to the aforementioned chemical treatments, cellulase treatment, carboxymethylation, esterification, and treatment with cationic polymers can be performed after the defibration process to further enhance affinity with rubber components.

[0025] In the present invention, it is preferable to use chemically modified nanocellulose having anion-forming groups (for example, one or more selected from the group consisting of carboxyl groups, phosphate ester groups, phosphite ester groups, xantate groups, sulfone groups, sulfate groups, and thiolate groups) from the viewpoint of making nanocellulose aggregation difficult during manufacturing, and it is more preferable to use chemically modified nanocellulose having carboxyl groups.

[0026] [Kraft pulp] Kraft pulp is a cellulose fiber with an average fiber diameter of 5 to 50 μm and an average fiber length of approximately 500 μm or less, obtained by alkali treatment of wood. Examples include softwood-derived pulp, such as bleached softwood kraft pulp (NBKP) or unbleached softwood kraft pulp (NUKP), and hardwood-derived pulp, such as bleached hardwood kraft pulp (LBKP). Commercial products include KC Floc (a product of Nippon Paper Industries). It should be noted that if the average fiber diameter is below the above range, or if the average fiber length is above the above range, the reinforcing performance tends to decrease. Furthermore, the average aspect ratio (average fiber length / average fiber diameter) is more preferably 1 to 800, even more preferably 2 to 500, even more preferably 3 to 200, and even more preferably 3 to 100.

[0027] Here, the "average fiber diameter" and "average fiber length" of this kraft pulp also refer to the average values ​​of the fiber diameter and fiber length obtained by obtaining electron microscope images by TEM observation or SEM observation, setting the magnification appropriately according to the size of the constituent fibers, and measuring them in at least 50 or more fibers in these images.

[0028] Furthermore, if this kraft pulp is a powdered material, the average particle size (D) of the powder is... 50 The average particle diameter (D) is preferably 1000 μm or less, more preferably 800 μm or less, more preferably 600 μm or less, more preferably 400 μm or less, more preferably 250 μm or less, and more preferably 100 μm or less, as this makes it easier to exhibit the effects of the present invention. The lower limit may be 10 μm or more, and even more preferably 20 μm or more. 50 )" refers to the average particle diameter based on volume (50% diameter (D) measured by a laser diffraction / scattering particle size distribution analyzer. 50 )) is.

[0029] Furthermore, in rubber composition (b), from the viewpoint of the effects of the present invention, it is more preferable that the above-mentioned nanocellulose and / or kraft pulp are contained in a total amount of 5 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the aforementioned diene rubber. That is, it is more preferable that the total content of nanocellulose and kraft pulp relative to the above-mentioned diene rubber is 5 to 20 phr, and more specifically, it is more preferable that rubber composition (b) contains the above-mentioned nanocellulose and / or kraft pulp in a total amount of 5 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the diene rubber. Therefore, this amount is the content of nanocellulose in embodiments that substantially do not contain kraft pulp, and the content of kraft pulp in embodiments that substantially do not contain nanocellulose. The lower limit is more preferably 6 parts by mass or more, and even more preferably 8 parts by mass or more. The upper limit is more preferably 15 parts by mass or less, and even more preferably 12 parts by mass or less.

[0030] Furthermore, although not limited thereto, it is more preferable that rubber composition (b) contains a total of 0.10 to 0.40 parts by mass of the nanocellulose and / or kraft pulp per 1 part by mass of carbon black, as this allows both the effects of the carbon black and the effects of the nanocellulose and / or kraft pulp to be more easily exerted, and also facilitates their interactions. The "total" of nanocellulose and / or kraft pulp has the same meaning as above. The lower limit is more preferably 0.15 parts by mass or more, and the upper limit is more preferably 0.35 parts by mass or less, even more preferably 0.30 parts by mass or less, and even more preferably 0.25 parts by mass or less.

[0031] Furthermore, the rubber compositions of the present invention may further contain fillers other than those listed above, to the extent that they do not significantly affect the effects of the present invention. For example, they may contain silica, clay, mica, talc, alumina, calcium carbonate, magnesium carbonate, aluminum hydroxide, calcium sulfate, barium sulfate, etc. Alternatively, they may be composed of materials that are substantially free of fillers other than those listed above. Furthermore, although not limited thereto, from the viewpoint of cost and manufacturing, the aforementioned rubber composition (a) is more preferably an embodiment that substantially does not contain nanocellulose and kraft pulp, and even more preferably an embodiment that substantially does not contain cellulose (cellulose-containing material).

[0032] [Other ingredients] Each rubber composition of the present invention may further contain appropriate amounts of various additives commonly used in rubber compositions, such as oils (process oils, etc.), zinc oxide (zinc oxide), resin components, stearic acid, waxes, lecithin, antioxidants, plasticizers, curing agents, vulcanizing agents (e.g., sulfur), vulcanization accelerators, and vulcanization accelerators, to the extent that they do not significantly affect the effects of the present invention. In particular, from the viewpoint of interfacial adhesion and other factors, it is more preferable that all rubber compositions of the present invention use sulfur as a vulcanizing agent (especially those that use substantially only sulfur as a vulcanizing agent).

[0033] For example, the oil content in the rubber composition of the present invention is preferably 1 to 20 parts by mass, and more preferably 5 to 15 parts by mass, per 100 parts by mass of the aforementioned diene rubber. Furthermore, the content of stearic acid, zinc oxide, and antioxidant in the rubber composition of the present invention is preferably 0.5 to 10 parts by mass, and more preferably 1 to 5 parts by mass, per 100 parts by mass of the aforementioned diene rubber. In addition, the content of vulcanizing agent (especially sulfur) in the rubber composition of the present invention is preferably 0.5 to 3.5 parts by mass, and more preferably 1.0 to 3.0 parts by mass, per 100 parts by mass of the aforementioned diene rubber. Moreover, the content of vulcanization accelerator in the rubber composition of the present invention, either as a primary accelerator alone or in a blend with a secondary accelerator, is also preferably 0.5 to 3.5 parts by mass, and more preferably 1.0 to 3.0 parts by mass, per 100 parts by mass of the aforementioned diene rubber.

[0034] [Manufacturing method etc.] The manufacturing method for the rubber composition (rubber compound of the present invention) of the present invention is not particularly limited and can be any conventional method. As an example of a manufacturing method, diene rubber, carbon black, and other components as needed are kneaded and mixed at room temperature or high temperature using a mixing machine such as a Banbury mixer, kneader, or roll, in predetermined proportions, and then extruded or otherwise performed by conventional methods to produce the rubber composition (or rubber compound for the sidewall portion) of the present invention by press vulcanization in a predetermined shape and arrangement. When using vulcanizing components (sulfur, vulcanization accelerator, vulcanization accelerator aid, etc.), it is preferable to mix the other components at high temperature first, cool them, and then mix in the vulcanizing components.

[0035] Next, the structure of the tire of the present invention will be described in detail with reference to the drawings. In all drawings, the same reference numerals are used for similar components, however, in some drawings, reference numerals are omitted for convenience. Furthermore, the dimensional ratios shown in the drawings may differ from the actual dimensional ratios in order to facilitate understanding of the invention.

[0036] The tire of the present invention comprises a sidewall portion in which a reinforcing core is embedded on at least one side (more preferably both sides), and the rubber compound of this sidewall portion is composed of the above-described rubber composition (b) that constitutes the reinforcing core portion and the above-described rubber composition (a) that constitutes the region adjacent to (i.e., adjacent to and in contact with) the reinforcing core portion and surrounding its periphery. The mass ratio of rubber composition (b) to the total mass of the rubber compound of this sidewall portion is 10 to 50%. With this configuration, the interfacial adhesion between the reinforcing core made of rubber composition (b) and the region made of rubber composition (a) adjacent to and surrounding its periphery is very good because they are made of predetermined rubber compositions, even without an adhesive layer. Furthermore, the excellent sidewall reinforcement performance of the reinforcing core made of predetermined composition and quantity further improves the trauma resistance of the sidewall.

[0037] For example, although not limited thereto, an embodiment is exemplified in which a tire comprises, as shown in Figures 1 and 2, a tread portion 1 extending in the circumferential direction of the tire and forming an annular shape, a pair of sidewall portions 2 arranged on both sides of the tread portion 1 (arranged via a shoulder portion), and a pair of bead portions 3 arranged radially inward of these sidewall portions 2, a carcass layer 4 (not included in the sidewall portions 2) mounted between these pair of bead portions 3, a plurality of belt layers 10 including belt cords inclined with respect to the circumferential direction of the tire arranged on the outer circumference side of the carcass layer 4 in the tread portion 1, and a belt cover layer 11 arranged on the outer circumference side of these belt layers 10, wherein at least one of the pair of sidewall portions 2 is provided with one or more convex protectors 7 extending in the circumferential direction of the tire, made of the rubber composition (a) described above, and a predetermined amount of reinforcing core portions 8 made of the rubber composition (b) described above is embedded inside the protector 7. In this embodiment, the rubber compound of the sidewall portion 2 excluding the reinforcing core portion 8 (that is, the entire rubber compound of the sidewall portion 2 including the region adjacent to and surrounding its periphery, excluding the reinforcing core portion 8; in other words, the entire rubber compound of the sidewall portion 2 other than the reinforcing core portion 8) is made of the above-mentioned rubber composition (a). The above-mentioned convex protector 7 may be formed in an annular shape with continuous grooves in the circumferential direction of the tire, for example, in a range of 30 to 65% of the tire cross-sectional height.

[0038] Furthermore, this sidewall portion may be a composite of materials other than rubber compound as auxiliary materials. For example, embodiments may include metal cords or organic fiber cords. However, in the tire of the present invention, the effects of the present invention are fully realized even in embodiments in which the entire sidewall portion substantially does not contain materials other than rubber compound (substantially consists of rubber compound). In each of the above embodiments, it is preferable that the entire rubber compound of the sidewall portion excluding the reinforcing core portion, including the region adjacent to and surrounding its periphery, is composed of the above-described rubber composition (a), and the reinforcing core portion is composed of the above-described rubber composition (b).

[0039] Furthermore, from the viewpoint of sidewall reinforcement performance, the lower limit of the mass ratio of rubber composition (b) to the total mass of the rubber compound in this sidewall portion is more preferably 15% or more, even more preferably 20% or more, and even more preferably 25% or more. From the same viewpoint, the upper limit is more preferably 45% or less, even more preferably 40% or less, and even more preferably 35% or less. Here, "total mass of the rubber compound in the sidewall" refers to the total mass of the rubber compound contained in the sidewall. If the sidewall contains materials other than rubber compound, the mass of those materials is not included in the above calculation.

[0040] Furthermore, from the viewpoint of sidewall reinforcement performance, it is even more preferable that the reinforcing core portion is embedded in the sidewall portion in a closed annular shape that encircles the tire in the circumferential direction. In other words, it is preferable that the reinforcing core portion is embedded in the sidewall portion in a closed annular shape that encircles (extends in a circular manner) along the tire circumferential direction and has a columnar shape in this circumferential direction. This makes it easier for the effects such as damage resistance to be fully exhibited even when the sidewall portion comes into contact with rock or the like when the tire rotates. However, in the case where the reinforcing core portion has a columnar shape that encircles the tire in the circumferential direction of the sidewall portion, it may also be an open annular shape with a portion missing rather than a closed annular shape.

[0041] Furthermore, the shape of this reinforcing core portion in the tire circumferential direction (columnar shape) may be cylindrical (including approximately cylindrical or approximately elliptical shapes) or prismatic (including polygonal prismatic shapes such as flat or plate-like shapes). In other words, the shape of the cross-section of this reinforcing core portion perpendicular to the tire circumferential direction may be approximately circular or approximately polygonal. Examples of embodiments that make the above effect easier to achieve include, for example, an embodiment shown in Figure 3 in which the reinforcing core portion is cylindrical and forms a closed annular shape around the tire circumferential direction of the sidewall portion, and the reinforcing core portion is embedded inside each of several convex protectors extending in the tire circumferential direction, and an embodiment shown in Figure 4 in which the reinforcing core portion is prismatic (approximately flat, approximately square prismatic, or approximately plate-like) and forms a closed annular shape around the tire circumferential direction of the sidewall portion.

[0042] Furthermore, it is more preferable that the tire of the present invention, when the sidewall portion is divided into a region on the tire surface side and a region on the tire inner side at the center of the thickness in the tire width direction (a line or plane connecting the centers of the thickness), has 90% or more of the reinforcing material core portion (90% or more of the total volume of the reinforcing material core portion), more preferably the entire reinforcing material core portion embedded in the region on the tire surface side. This is because the reinforcing material core portion, which has high interfacial adhesion with the peripheral rubber compound and excellent sidewall reinforcement performance, is embedded in a region closer to the outer surface of the tire, which not only improves resistance to punctures (pressure) by rocks and the like, but also makes it easier to improve resistance to abrasion (rubbing) by rocks and the like.

[0043] Here, the "center of the thickness in the tire width direction" of the sidewall portion refers to a line or plane connecting the centers of line segments representing the thickness of the sidewall portion in the tire width direction (thickness parallel to the tire width direction). In the above embodiment, when the region of the sidewall portion is divided into two parts, the tire surface side and the tire inner surface side, with this "center of the thickness in the tire width direction" as the boundary, at least 90% of the reinforcing material core portion, and more preferably the entire reinforcing material core portion, is embedded in the region on the tire surface side. For example, in the embodiment of Figure 3, when the sidewall portion 2 is divided into two regions as described above, the entire reinforcing material core portion 8 is embedded in the region on the tire surface side. Furthermore, an embodiment in which, when the volume of this sidewall portion is divided equally into a region on the tire surface side and a region on the tire inner side in the tire width direction by a plane perpendicular to the tire width direction, 90% or more of the reinforcing material core portion, more preferably the entire portion, is embedded within the region on the tire surface side is also equally suitable.

[0044] Furthermore, the tire components other than the sidewall portion are not particularly limited, as long as they can perform their function as a tire and do not significantly affect the effects of the present invention. The tire of the present invention is more preferably a pneumatic tire, and as the gas filled into this pneumatic tire, for example, air, nitrogen, argon, helium or other inert gases, and other gases can be used.

[0045] The tire of the present invention, as described above, has excellent resistance to trauma due to a predetermined reinforcing core embedded in its sidewall. At the same time, the sidewall also exhibits very good interfacial adhesion between the reinforcing core and the adjacent region. The tire of the present invention is more suitable for use in vehicles used in underground mine tunnels where bedrock is exposed (underground mining tires), as the above effects are more easily demonstrated in such applications. However, the tire of the present invention may also be used for other types of tires where resistance to trauma is required.

[0046] The following describes embodiments of the present invention, but the present invention is not limited to the following embodiments, and various modifications are possible within the technical concept of the present invention. [Examples]

[0047] First, each component (excluding sulfur and vulcanization accelerator) in mass parts shown in Table 1(a) below was mixed for 5 minutes using a 1.7-liter sealed Banbury mixer, then released from the mixer and cooled to room temperature. Furthermore, using the same Banbury mixer, predetermined amounts of sulfur and vulcanization accelerator were mixed and kneaded to prepare the unvulcanized rubber compounds of Comparative Examples 1-3 and Examples 1-13 (unvulcanized rubber compounds consisting of rubber composition (a)). Furthermore, the unvulcanized rubber compounds of Comparative Examples 1-3 and Examples 1-13 (unvulcanized rubber compounds for reinforcing cores consisting of rubber composition (b)) were also prepared by similarly mixing and kneading each component by mass shown in Table 1(b) below. Then, using these, the following tests were conducted and evaluated.

[0048] <Adhesiveness> A sheet-like laminate of unvulcanized rubber compound was prepared by laminating a layer of the unvulcanized rubber compound (reinforcement core portion) made of rubber composition (b) and an adjacent layer of the unvulcanized rubber compound made of rubber composition (a) into a sheet with a thickness of 2 mm and a width of 1 inch × length of 6 inches. Synthetic fibers were arranged longitudinally in a curtain-like pattern as a reinforcing backing material above and below to reinforce the laminate. This laminate was then press-vulcanized in a predetermined mold at 170°C for 10 minutes to obtain strip-shaped adhesiveness evaluation samples (Comparative Examples 1-3 and Examples 1-13). The reinforcement core portion layer and the adjacent rubber compound layer were peeled off by a 180° peel test, and the fracture state of the peeled surface was visually confirmed. The results are shown in the lower section of Table 1 below. Note that results indicating interfacial fracture were marked with ×, and results indicating material fracture were marked with ○.

[0049] <Trauma resistance> Using the unvulcanized rubber compound (reinforcement core) made of rubber composition (b) and the unvulcanized rubber compound made of rubber composition (a), the layer of the reinforcement core was embedded in a predetermined position within it in a predetermined shape (see Table 1 below), with the unvulcanized rubber compound made of rubber composition (a) adjacent to and surrounding its periphery, and the layer of the reinforcement core embedded within it in a predetermined shape (see Table 1 below). Furthermore, the mass ratio (content) of the reinforcement core (i.e., rubber composition (b)) to the total mass of the sheet was set to the value shown in Table 1 below. After molding into a sheet with a thickness of 20 mm, a width of 40 mm, and a length of 125 mm, it was press-vulcanized in a predetermined mold at 170°C for 10 minutes to obtain strip-shaped samples for evaluating trauma resistance (Comparative Examples 1-3 and Examples 1-13). In Example 13, the entire reinforcing core portion was embedded in the surface layer of the sheet (within the surface region when the sheet thickness is divided into a surface region and a back region at the center), while in the other cases, the reinforcing core portion was embedded approximately in the center of the sheet. Then, a chisel-like blade with a width of 80 mm, a cutting edge angle of 20°, and a weight attached to it, with a mass of 3 kg, was dropped from a height of 25 cm onto these samples (sheet surfaces), and the length of the cracks that entered the samples was measured and compared. The results are shown in the lower section of Table 1 below. The results are expressed as an index (index%) with the value of Comparative Example 1 set to 100, and a larger index indicates shorter crack length (better trauma resistance).

[0050] [Table 1]

[0051] The detailed contents of each component in Table 1 above are as follows: • NR: Natural rubber (TSR20, glass transition temperature (Tg): -62℃) • Hydrogenated NBR: Hydrogenated nitrile rubber (Zetpol 2030L, manufactured by Zeon Corporation) • Cellulose nanofibers: Oxidized cellulose nanofibers (manufactured by Nippon Paper Industries, Cellenpia; average fiber diameter: 3-4 nm; average fiber length: several hundred nm to 1 μm; average aspect ratio: approximately 100; chemically modified nanocellulose containing carboxyl groups) • Microfibrillated cellulose: Exilva (manufactured by Borregaard, average fiber diameter: approximately 100 nm, average fiber length: several tens of μm, average aspect ratio: approximately 300, mechanically defibrated nanocellulose) • Kraft pulp: KC Floc W-50GK (manufactured by Nippon Paper Industries, average particle size (D 50 (Approximately 45 μm in diameter, average fiber diameter: about 10 μm, average fiber length: 45 μm, average aspect ratio: about 4.5) • Carbon Black: Show Black N339 (Nitrogen adsorption specific surface area (N2SA): 88m²) 2 (Manufactured by Gabot Japan Co., Ltd.) • Stearic acid: Stearic acid YR (manufactured by NOF Corporation) • Zinc oxide: Zinc oxide (ZnO, manufactured by Seido Chemical Industry Co., Ltd.) • Anti-aging agent: Ozonone 6C (manufactured by Seiko Chemical Co., Ltd.) • Process oil: Extract No. 4 S (manufactured by Shell Lubricants Japan Co., Ltd.) • Vulcanization accelerator 1: Noxellar NS (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) • Vulcanization accelerator 2: Parkmill D-40 (manufactured by NOF Corporation) • Sulfur: Micron OT-20 (manufactured by Shikoku Chemicals Co., Ltd.)

[0052] These results demonstrate that by embedding a predetermined amount of a reinforcing core made of a predetermined rubber composition (b) in a predetermined rubber composition (a), the material exhibits excellent resistance to trauma, and also provides good interfacial adhesion between the layer of this reinforcing core and adjacent regions (Examples 1-13). On the other hand, when the reinforcing core was a peroxide crosslinked carbon black-reinforced hydrogenated NBR, the interfacial adhesion with adjacent regions decreased (Comparative Example 1). Also, when the mass ratio of the rubber composition (b) of the predetermined composition was too low or too high, the trauma resistance (i.e., the sidewall reinforcement performance) decreased in both cases (Comparative Examples 2 and 3). [Explanation of Symbols]

[0053] 100 tires 1. Tread section 2 Sidewall section 3. Bead section 4. Carcass layer 5 Bead core 7 Protectors 8. Reinforcement core section 10 Belt Layer 11 Belt cover layer

Claims

1. A tire having a sidewall portion in which a reinforcing core portion is embedded, The rubber compound of the sidewall portion is composed of a rubber composition (a) in which diene rubber is reinforced with carbon black, constituting a region adjacent to and surrounding the periphery of the reinforcing core portion, and a rubber composition (b) in which diene rubber is reinforced with carbon black and nanocellulose and / or kraft pulp, constituting the reinforcing core portion. The mass ratio of the rubber composition (b) to the total mass of the rubber compound in the sidewall portion is 10 to 50%. tire.

2. The tire according to claim 1, wherein both the rubber composition (a) and the rubber composition (b) have a carbon black content of 40 to 60 phr.

3. The tire according to claim 1 or 2, wherein the rubber composition (b) has a total content of 5 to 20 phr of the nanocellulose and the kraft pulp.

4. The tire according to claim 1 or 2, wherein the reinforcing core portion is embedded in the sidewall portion in the tire circumferential direction such that it forms a closed annular shape with a columnar form.

5. The tire according to claim 1 or 2, wherein when the sidewall portion is divided into a region on the tire surface side and a region on the tire inner side at the center of the thickness in the tire width direction, 90% or more of the volume of the reinforcing material core portion is embedded in the region on the tire surface side.

6. A tire for use in underground mines, as described in claim 1 or 2.

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