Rubber composition

Abstract

To provide a rubber composition which is excellent in both wear resistance and cut resistance and maintains hardness and whiteness.SOLUTION: The rubber composition contains a diene rubber, silica, titanium oxide, and cellulose fibers. The rubber composition contains 2-20 pts.mass of the cellulose fibers based on 100 pts.mass of the diene rubber.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber composition and a white cushion tire using the rubber composition in a tread rubber layer. [Background technology]

[0002] Cushion tires, also known as solid tires or solid tires, are tires that do not contain air and are made entirely of a rubber composition, even to the inside, and are primarily used on industrial vehicles such as forklifts for loading and unloading. The term "cushion tire" is applied not only to pneumatic cushion tires for industrial vehicles as specified in Chapter F of the JATMA Yearbook, but also to solid tires (press-on type) for industrial vehicles as specified in the same Chapter F, and further to various solid tires including cure-on type solid tires as specified in JIS D6405:1990.

[0003] For example, Patent Document 1 discloses a cushion tire having excellent durability, the surface of which is a cushion tire with an inner circumferential surface and a pair of side surfaces, the tire comprising a tread having a tread surface that comes into contact with the road surface, a base located radially inward of the tread, beads embedded in the base and extending circumferentially, and one or more reinforcing layers that include a plurality of cords arranged in parallel and extend circumferentially, the hardness of the base being the same as or greater than the hardness of the tread, and each reinforcing layer extending along at least one of the side surfaces and the inner circumferential surface. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-185647 Summary of the Invention [Problem to be solved by the invention]

[0005] Here, forklifts and the like in paper mills and the like may use white cushion tires, which are less likely to leave tire marks on the road surface and less likely to produce wear debris during wear. However, although these white cushion tires are used for vehicles such as cargo handling and transportation, they have room for improvement in terms of abrasion resistance and cut resistance because the rubber composition used cannot contain carbon black. In other words, there is room for improvement in this rubber composition in terms of improving its abrasion resistance and cut resistance while maintaining the hardness and whiteness required for use as a white cushion tire.

[0006] Therefore, an object of the present invention is to provide a rubber composition that is excellent in both abrasion resistance and cut resistance, and that maintains hardness and whiteness. [Means for solving the problem]

[0007] In order to solve the above problems, the present inventors have conducted extensive research and found that a rubber composition comprising a diene rubber, silica, titanium oxide, and cellulose fibers, in which the cellulose fibers are contained in an amount of 2 to 20 parts by mass per 100 parts by mass of the diene rubber, has excellent abrasion resistance and cut resistance, and also maintains hardness and whiteness, thereby completing the present invention.

[0008] That is, the present invention provides the following: <1> ~ <7> This includes embodiments of the present invention. <1> The composite material includes a diene rubber, silica, titanium oxide, and cellulose fibers, A rubber composition comprising 2 to 20 parts by mass of the cellulose fibers per 100 parts by mass of the diene rubber. <2> The cellulose fibers are nanocellulose having an average fiber diameter of 1 to 1000 nm and an average fiber length of 5 μm or less, and / or powdered cellulose having an average fiber diameter of 5 to 50 μm and an average fiber length of 500 μm or less. <1> The rubber composition according to claim 1. <3> Further, the present invention provides a method for manufacturing a soluble fiber blend comprising the step of: blending soluble fiber with a soluble fiber containing at least one selected from the group consisting of fatty acids, resin acids, a mixture of fatty acids and resin acids, and crude tall oil; <1> or <2> The rubber composition according to claim 1. <4> The total amount of the fatty acid, resin acid, mixture of fatty acid and resin acid, and crude tall oil is 1 to 10 parts by mass per 100 parts by mass of the diene rubber. <3> The rubber composition according to claim 1. <5> the cellulose fibers are surface-treated with at least one selected from the group consisting of fatty acids, resin acids, mixtures of fatty acids and resin acids, crude tall oil, and resole-type and / or novolac-type resorcinol-formaldehyde precondensates; <1> ~ <4> The rubber composition according to any one of the above. <6> The silica is contained in an amount of 20 to 70 parts by mass and the titanium oxide is contained in an amount of 15 to 45 parts by mass relative to 100 parts by mass of the diene rubber. <1> ~ <5> The rubber composition according to any one of the above. <7> <1> ~ <6> 1. A white cushion tire using the rubber composition according to any one of items 1 to 5 in a tread rubber layer. [Effects of the Invention]

[0009] According to the present invention, a rubber composition can be obtained that has excellent abrasion resistance and cut resistance while maintaining hardness and whiteness. By using this rubber composition in a tread rubber layer, a white cushion tire that has excellent abrasion resistance and cut resistance can be obtained. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will now be described. The present invention provides a rubber composition comprising a diene rubber, silica, titanium oxide, and cellulose fibers, the composition containing 2 to 20 parts by mass of the cellulose fibers per 100 parts by mass of the diene rubber. Hereinafter, this is also referred to as the "rubber composition 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 and materials 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. Specific examples include natural rubber (NR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), chloroprene rubber (CR), and synthetic isoprene rubber (IR). These diene rubbers can be used alone or in combination of two or more. In the rubber composition of the present invention, from the viewpoint of ease of mixing with cellulose fibers, the diene rubber is preferably one or more selected from the group consisting of NR, IR, SBR, NBR, and CR, which can be formed into a rubber latex. In particular, the diene rubber preferably contains 90% by mass or more of NR and / or IR, and more preferably 95% by mass or more of NR and / or IR.

[0014] The weight average molecular weight of each of these diene rubbers is preferably 50,000 to 3,000,000, and more preferably 100,000 to 2,000,000. Furthermore, each of these may be graft-modified with a vinyl monomer or epoxidized with an organic peracid. 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.

[0015] The rubber composition of the present invention may contain rubber components other than diene-based rubber, but it is preferable that 90% by mass or more of the rubber components contained are diene-based rubber, more preferably 95% by mass or more are diene-based rubber, and even more preferably that the rubber components contained consist of diene-based rubber (100% by mass of diene-based rubber).

[0016] [silica] The silica contained in the rubber composition of the present invention is not particularly limited, and any known silica used in applications such as tires can be used. Specific examples of silica that can be used include wet silica, dry silica, fumed silica, and diatomaceous earth. Silica produced using biomass materials such as rice husks as raw materials can also be used. One type of silica can be used alone, or two or more types can be used in combination. In addition, the CTAB specific surface area of ​​this silica is 130m, which makes it easier to improve wear resistance and cut resistance. 2 / g or more is more preferable, and 140m 2 / g or more is more preferable, and 150m 2 / g or more is more preferable. In other words, the smaller the particle size of silica, the more preferable. 2 / g or less is more preferable, and 180m 2 It is more preferable that the molecular weight is not more than 1 / g.

[0017] Here, "silica" refers to a particulate material made of silicon dioxide (SiO2) or containing silicon dioxide as the main component (e.g., 80% by mass or more, or even 90% by mass or more). The CTAB specific surface area of ​​silica is a value measured in accordance with JIS K6430:2008, Appendix G. When one type of silica is used alone, this value is the CTAB specific surface area of ​​that silica. When two or more types are used in combination, this value is the CTAB specific surface area of ​​each silica used multiplied by its respective usage ratio and added together. In this calculation, the sum of the usage ratios of each silica is set to 1.0.

[0018] The rubber composition of the present invention preferably contains 20 to 70 parts by mass of the silica per 100 parts by mass of the diene rubber. The lower limit of the silica content is more preferably 30 parts by mass or more, and even more preferably 40 parts by mass or more, per 100 parts by mass of the diene rubber. The upper limit is more preferably 60 parts by mass or less, and even more preferably 50 parts by mass or less. Here, the content of silica in the present invention means the total content of all silicas when multiple types of silica are contained.

[0019] [Titanium oxide] The titanium oxide contained in the rubber composition of the present invention is not particularly limited, and any known titanium oxide used in applications such as tires can be used. Titanium oxide particles treated with silica, alumina, zinc oxide, etc. can also be used. The average primary particle diameter of this titanium oxide (titanium oxide particles) is preferably 0.05 to 0.5 μm. Here, the "average primary particle diameter" refers to the particle diameter (μm) defined as the unidirectional diameter (the distance between two parallel lines in a fixed direction that sandwich a particle) in a 10,000-fold magnification field of view of a scanning electron microscope (SEM) photograph, and is calculated by measuring the unidirectional diameters of 150 to 1,000 primary particles in the SEM photograph and calculating the average value of their cumulative distribution.

[0020] The rubber composition of the present invention preferably contains 15 to 45 parts by mass of the titanium oxide as described above per 100 parts by mass of the diene rubber. From the viewpoint of maintaining whiteness while also achieving other physical properties, the lower limit of the titanium oxide content is more preferably 20 parts by mass or more, and even more preferably 25 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, and even more preferably 35 parts by mass or less.

[0021] In addition, since the rubber composition of the present invention more easily exhibits the effects of the present invention, it is preferable that the total amount of white filler, including the silica and titanium oxide, is 35 to 115 parts by mass per 100 parts by mass of the diene rubber. The lower limit of the total amount of white filler is more preferably 50 parts by mass or more, and even more preferably 65 parts by mass or more, per 100 parts by mass of the diene rubber. The upper limit is more preferably 100 parts by mass or less, and even more preferably 85 parts by mass or less. Examples of white fillers other than silica and titanium oxide include clay, mica, talc, alumina, calcium carbonate, magnesium carbonate, aluminum hydroxide, calcium sulfate, and barium sulfate.

[0022] Additionally, in the rubber composition of the present invention, the ratio of the total content of the white filler to the cellulose fiber content within a predetermined range (total content of white filler / content of cellulose fiber) is preferably within a range of 3.0 to 20, since this also makes it easier to achieve the effects of the present invention. The lower limit is more preferably 3.5 or more, more preferably 4.5 or more, even more preferably 5.0 or more, and even more preferably 6.0 or more. The upper limit is more preferably 15 or less, even more preferably 10 or less.

[0023] [Cellulose fiber] The cellulose fibers contained in the rubber composition of the present invention are fibrous cellulose, and preferred examples include fibrous nanocellulose and powdered cellulose obtained by powdering fibrous cellulose. As described above, these cellulose fibers are fibrous or powdered fibrous materials, and are not so-called porous. Even when powdered, the porosity (void ratio) of the particles is less than 30%, or even less than 20%. In particular, nanocellulose having an average fiber diameter of 1 to 1,000 nm and an average fiber length of 5 μm or less and / or powdered cellulose having an average fiber diameter of 5 to 50 μm and an average fiber length of 500 μm or less (powdered cellulose obtained by powdering cellulose fibers having an average fiber diameter of 5 to 50 μm and an average fiber length of 500 μm or less) is more preferred, as these fibers are more likely to exhibit the effects of the present invention. These are described below.

[0024] <Nanocellulose> This nanocellulose is an ultrafine fiber (ultrafine cellulose fiber) made of cellulose microfibrils with an average fiber diameter of 1 to 1000 nm and an average fiber length of 5 μm or less, and examples include cellulose nanofibers (CNF, such as Cellenpia manufactured by Nippon Paper Industries Co., Ltd.) containing amorphous regions.

[0025] As mentioned above, the average fiber diameter of this nanocellulose is 1 to 1,000 nm, but is more preferably 1 to 200 nm. The average aspect ratio of this nanocellulose (average fiber length / average fiber diameter) is preferably 10 to 1,000, more preferably 50 to 500. If the average fiber diameter is less than the above range and / or the average aspect ratio exceeds the above range, the dispersibility of the nanocellulose tends to decrease. If the average fiber length exceeds the above range, the dispersibility of the nanocellulose also tends to decrease. 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.

[0026] Here, the "average fiber diameter" and "average fiber length" of this nanocellulose refer to the average values ​​of fiber diameter and fiber length measured for at least 50 fibers in an electron microscope image obtained by TEM or SEM observation, with the magnification appropriately set according to the size of the constituent fibers. The average aspect ratio is then calculated from the average fiber length and average fiber diameter thus obtained.

[0027] The cellulose used as the raw material for nanocellulose can be derived from either wood or non-wood sources (bacteria, algae, cotton, etc.) and is not particularly limited. Examples of methods for producing nanocellulose include adding water to the raw cellulose and processing it in a mixer or other device to prepare a slurry in which the cellulose is dispersed in water, and then directly applying mechanical shear force using a high-pressure or ultrasonic device to finely defibrate the slurry; or chemically treating the slurry with oxidation, alkali, acid hydrolysis, or other methods to modify the cellulose and make it easier to defibrate, and then applying mechanical shear force using a disperser or other device to finely defibrate the cellulose. By subjecting the cellulose to chemical treatment in this way before defibrating it, the cellulose can be defibrated into finer, more uniform fibers with less energy, making it easy to obtain chemically modified nanocellulose. Examples of chemical treatments include treatments with chemical treating 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-phosphonoxy-TEMPO, phosphate esters, periodic acid, alkali metal hydroxides, and carbon disulfide. Alternatively, chemical treatments may be performed after mechanical defibration of cellulose. In addition to the aforementioned chemical treatments, cellulase treatment, carboxymethylation, esterification, or treatment with a cationic polymer may be performed after the defibration process to further enhance affinity with the rubber component.

[0028] In the present invention, it is preferable to use chemically modified nanocellulose having an anion-forming group (for example, one or more selected from the group consisting of a carboxy group, a phosphate ester group, a phosphite ester group, a xanthate group, a sulfone group, a sulfate group, and a thiolate group), because this increases the affinity with the surface treatment component described below. In particular, it is more preferable to use chemically modified nanocellulose having a carboxy group.

[0029] <Powdered cellulose> This powdered cellulose is made by powdering cellulose fibers having an average fiber diameter of 5 to 50 μm and an average fiber length of 500 μm or less, and an example of this is KC Flock (a product of Nippon Paper Industries Co., Ltd.) If the average fiber diameter is below the above range or if the average fiber length exceeds the above range, the reinforcing performance of the powdered cellulose tends to be easily reduced.

[0030] Here, the "average fiber diameter" and "average fiber length" of the cellulose fibers in this powdered cellulose also refer to the average values ​​of fiber diameter and fiber length when an electron microscope image is obtained by TEM or SEM observation at an appropriate magnification depending on the size of the constituent fibers and at least 50 fibers in the image are measured. The cellulose used as the raw material for this powdered cellulose may also be the same as the nanocellulose described above.

[0031] The average particle diameter of this powdered cellulose (D 50 ) is not limited, but is preferably 1000 μm or less, more preferably 800 μm or less, even more preferably 600 μm or less, even more preferably 400 μm or less, even more preferably 250 μm or less, and even more preferably 100 μm or less, since this makes it easier to exhibit the effects of the present invention. The lower limit may be 5 μm or more, or even 10 μm or more. This "average particle diameter (D 50 ) is the volume-based average particle diameter (50% volume cumulative distribution diameter (D 50 )).

[0032] In order to fully achieve the effects of the present invention, the rubber composition of the present invention contains 2 to 20 parts by mass of the above-mentioned cellulose fiber per 100 parts by mass of the diene rubber. The lower limit is preferably 5 parts by mass or more, and more preferably 8 parts by mass or more. The upper limit is preferably 15 parts by mass or less, and even more preferably 12 parts by mass or less. The content of cellulose fiber in the rubber composition of the present invention means the amount of cellulose fiber excluding the surface-treated component, even when surface-treated cellulose fiber (described below) is blended, and this amount is within the above range. If the content of the cellulose fibers is less than 2 parts by mass per 100 parts by mass of diene rubber, cut resistance may not be excellent, whereas if the content of the cellulose fibers is more than 20 parts by mass per 100 parts by mass of diene rubber, abrasion resistance may decrease.

[0033] [Fatty acids, resin acids, mixtures of fatty acids and resin acids, and crude tall oil] It is more preferable that the rubber composition of the present invention further contains at least one selected from the group consisting of fatty acids, resin acids, mixtures of fatty acids and resin acids, and crude tall oil in addition to the above-mentioned components, because this further improves the dispersibility of cellulose fibers and makes it easier to exhibit the effects of the present invention.

[0034] The fatty acid is preferably oleic acid and / or linoleic acid, and more preferably a mixture (fatty acid mixture) containing both oleic acid and linoleic acid in a larger amount than linoleic acid. Furthermore, the resin acid preferably includes one or more selected from the group consisting of abietic acid, neoabietic acid, palustric acid, pimaric acid, isopimaric acid, and dehydroabietic acid, and more preferably includes one or more selected from the group consisting of abietic acid, neoabietic acid, and palustric acid. Furthermore, a mixture of such fatty acids and resin acids is more preferred, and crude tall oil is one example of such a mixture. This "crude tall oil" is recovered as a by-product in the Kraft process, in which wood chips are added with chemicals such as sodium hydroxide and decomposed (alkaline decomposition) at high temperature and high pressure to extract pulp fibers. It can be obtained by neutralizing black liquor, which is a concentrated mixture of lignin, which solidifies the pulp fibers, resin components, and chemicals, with an acid such as sulfuric acid. Tall rosin and tall oil fatty acids are obtained by fractionating this crude tall oil, and distilled tall oil is recovered as a by-product when these are separated. The type of wood used as the raw material for crude tall oil is not particularly limited, but crude tall oil derived from pine is preferred. The type of pine is also not particularly limited, and examples include horse ear pine, Tudor pine, and Elliotti pine. However, for example, a raw material containing fatty acids and a raw material containing resin acids may be prepared separately and then mixed for use.

[0035] In particular, since the effects of the present invention are more easily exhibited, it is more preferable that the mixing ratio of the fatty acid and the resin acid is a mixture in which the mass ratio of resin acid to fatty acid (resin acid / fatty acid) is 0.9 or more, and it is even more preferable that the mixture is crude tall oil in which this mass ratio is 0.9 or more. The lower limit is more preferably 1.0 or more, and even more preferably 1.1 or more, and the upper limit is more preferably 2.0 or less, and even more preferably 1.8 or less, and even more preferably 1.5 or less.

[0036] The rubber composition of the present invention preferably contains 1 to 10 parts by mass of the fatty acid, resin acid, mixture of fatty acid and resin acid, and crude tall oil in total relative to 100 parts by mass of the diene rubber. That is, when the rubber composition of the present invention contains at least one selected from the group consisting of the fatty acid, resin acid, mixture of fatty acid and resin acid, and crude tall oil, the total content of these (if any) is preferably 1 to 10 parts by mass relative to 100 parts by mass of the diene rubber. In embodiments where only one of these is included, the content is set within the above range. The upper limit is more preferably 8.0 parts by mass or less, and even more preferably 6.0 parts by mass or less. The lower limit is more preferably 2.0 parts by mass or more, and even more preferably 4.0 parts by mass or more. In addition, while satisfying the above requirements, it is even more preferable that the total amount of the fatty acid, resin acid, mixture of fatty acid and resin acid, and crude tall oil is 0.1 to 1 part by mass per part by mass of the cellulose fiber. Even in this case, in an embodiment in which only one of these is contained, the amount is set to be within the above range.

[0037] In the rubber composition of the present invention, the cellulose fibers may be surface-treated with at least one selected from the group consisting of fatty acids, resin acids, mixtures of fatty acids and resin acids, crude tall oil, and resole and / or novolac resorcinol-formaldehyde precondensates. This similarly improves the dispersibility of the cellulose fibers, making it easier to achieve the effects of the present invention. In particular, it is more preferable to use cellulose fibers surface-treated with at least one selected from the group consisting of fatty acids, resin acids, mixtures of fatty acids and resin acids, and crude tall oil, as this makes it easier to maintain a high level of whiteness in the resulting rubber composition.

[0038] Here, "surface-treated cellulose fibers" refers to a treatment in which the above-mentioned components (surface treatment components) are placed in close proximity to at least a portion of the interface (surface) of the cellulose fibers through interactions such as hydrogen bonding between the interface (surface) of the cellulose fibers and the above-mentioned components (surface treatment components). This reinforces the interface of the cellulose fibers and facilitates improved dispersibility in diene rubber. This surface treatment may also be performed using other components as secondary components (components used in smaller amounts than the above-mentioned components). For example, resole-type and / or novolac-type resorcinol-formaldehyde precondensates may be used in combination with formaldehyde. Alternatively, the surface treatment may be performed using only the above-mentioned components.

[0039] The fatty acid, resin acid, mixture of fatty acid and resin acid, and crude tall oil used in the surface treatment can be the same as those described above. The resorcinol-formaldehyde precondensate (RF resin) is a condensate (oligomer) obtained by condensing resorcinol, a phenolic resin, with formaldehyde in the presence of a catalyst, and preferably has a degree of polymerization of approximately 5 to 15. The resorcinol-formaldehyde precondensate used may contain unreacted resorcinol and / or formaldehyde. Therefore, the rubber composition of the present invention may contain formaldehyde and other substances in addition to the RF resin, including when formaldehyde is used in the surface treatment described above (for example, approximately 0.02 to 0.4 parts by mass of formaldehyde per part by mass of cellulose fiber). A methylol-containing condensate obtained by condensation of resorcinol / formaldehyde in a molar ratio of 1 / 1 to 3 in the presence of an alkaline catalyst such as sodium hydroxide or sodium carbonate is called a resole-type resorcinol-formaldehyde precondensate (a condensate represented by the following formula (1) (where n is the degree of polymerization)). A methylol-free condensate obtained by condensation of resorcinol / formaldehyde in a molar ratio of 1 / 0.8 to 0.9 in the presence of an acid catalyst such as oxalic acid is called a novolac-type resorcinol-formaldehyde precondensate (a condensate represented by the following formula (2) (where m is the degree of polymerization). In this surface treatment, either a resole-type or a novolac-type resorcinol-formaldehyde precondensate may be used, with the novolac-type being preferred.

[0040] [ka]

[0041] [ka]

[0042] Even when such surface-treated cellulose fibers are used, the content of the cellulose fibers, excluding the surface treatment components, is within the aforementioned ranges. Furthermore, the total amount of fatty acids, resin acids, mixtures of fatty acids and resin acids, and crude tall oil used as surface treatment components is preferably 0.1 to 1 part by mass per 1 part by mass of cellulose fibers. Furthermore, the total amount of these, including the amount blended separately from the surface treatment components, is preferably within the aforementioned ranges per 100 parts by mass of diene rubber. Furthermore, the total amount of these, including the amount blended separately from the surface treatment components per 1 part by mass of cellulose fibers, is preferably within the aforementioned ranges. In addition, from the viewpoint of whiteness, the amount of RF resin used as a surface treatment component is preferably 0.1 to 0.5 parts by mass per 1 part by mass of cellulose fibers. Furthermore, when cellulose fibers surface-treated with RF resin are used, the content of titanium oxide is more preferably 20 parts by mass or more per 100 parts by mass of diene rubber. An example of a method for surface treating cellulose fibers is a method in which a predetermined amount of a surface treatment component (such as the above-mentioned crude tall oil or RF resin) is added to an aqueous dispersion of cellulose fibers and stirred and mixed.

[0043] [Other ingredients] The rubber composition of the present invention may further contain various additives commonly used in rubber compositions, such as organic fillers (organic fillers, for example, lecithin), resin components, process oil, zinc oxide (zinc white), stearic acid, antioxidants, plasticizers, curing agents, vulcanizing agents (for example, sulfur), vulcanization accelerators, and vulcanization accelerator aids, within the range that does not affect the effects of the present invention, and these additives can be kneaded by known methods to form the rubber composition. In particular, it is more preferable that the above-mentioned process oil is non-staining (its color tone is colorless to yellow and does not easily discolor the blend). However, the rubber composition of the present invention does not contain carbon black so that it can be used at least in the tread rubber layer of a white cushion tire. In other words, the rubber composition of the present invention is substantially free of carbon black. In addition, the rubber composition of the present invention is substantially free of any other components that would prevent the whiteness of the rubber composition of the present invention from being maintained at a level that would allow it to be used in the tread rubber layer of a white cushion tire. Here, "substantially free of" means that the content in the rubber composition of the present invention is less than 0.1% by mass.

[0044] The content of the process oil in the rubber composition of the present invention is preferably 1 to 10 parts by mass, more preferably 2 to 8 parts by mass, per 100 parts by mass of the diene rubber. This allows the hardness of the rubber composition of the present invention to be adjusted, and its processability to be further improved. In embodiments containing at least one selected from the group consisting of fatty acids, resin acids, mixtures of fatty acids and resin acids, and crude tall oil, it is more preferable that the total content of the process oil and these ingredients be within the above-mentioned ranges. The contents of the 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. The content of the 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 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 0.3 to 3.0 parts by mass, more preferably 0.5 to 2.0 parts by mass, per 100 parts by mass of the diene rubber.

[0045] The rubber composition of the present invention may further contain a silane coupling agent to further enhance the dispersibility of silica. 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 thereof 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.

[0046] Furthermore, 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.

[0047] In this embodiment, the silane coupling agent is preferably contained in an amount of 1 to 20 parts by mass, more preferably 2 to 10 parts by mass, per 100 parts by mass of silica.

[0048] [Manufacturing method etc.] The method for producing the rubber composition of the present invention may be conventional and is not particularly limited. One example of the production method involves mixing a rubber latex of a diene rubber with cellulose fibers or surface-treated cellulose fibers (e.g., the aforementioned aqueous dispersion of nanocellulose or powdered cellulose), and optionally other components, to obtain a cellulose fiber-containing masterbatch. This cellulose fiber-containing masterbatch, silica, titanium oxide, and optionally other components are then 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. The rubber composition of the present invention can be produced by mixing these components. 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 (vulcanization).

[0049] The rubber composition of the present invention obtained as described above is excellent in both abrasion resistance and cut resistance, and maintains or improves hardness and whiteness. Although not limited thereto, the whiteness of the rubber composition of the present invention can be measured in accordance with JIS Z8722:2009, CIE 1976(L * ,a * ,b * ) Lightness index L in color space * When the value is measured, this L * It is preferable that the value of L is 80% or more. * The value is an average value obtained by measuring 10 arbitrary points on the rubber composition of the present invention.

[0050] By using this rubber composition of the present invention in at least the tread rubber layer, a white cushion tire with excellent abrasion resistance and cut resistance can be obtained. In other words, a cushion tire with excellent abrasion resistance and cut resistance can be obtained in which at least the tread rubber layer is white (for example, its whiteness is within the above-mentioned range). The rubber composition of the present invention may be used partially in portions other than the tread rubber layer (for example, the base rubber layer), or the entire white cushion tire (all of the portions composed of the rubber composition) may be composed of the rubber composition of the present invention. Alternatively, a middle rubber layer composed of a non-staining (hardly discoloring objects in contact with it) and low-heat-generating black rubber may be provided as an intermediate layer between the tread rubber layer and the base rubber layer. By making the hardness of this middle rubber layer smaller than that of the tread rubber layer, ride comfort and other properties can be improved and heat generation in the tire can be suppressed.

[0051] 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]

[0052] (Preparation and Evaluation of Rubber Compositions) Rubber compositions having the formulations shown in Table 1 below were prepared.

[0053] Specifically, the components (excluding the vulcanization accelerator and sulfur) 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 discharged from the mixer and cooled to room temperature. For the cellulose fiber-containing compositions, natural rubber latex and an aqueous cellulose fiber dispersion or an aqueous surface-treated cellulose fiber dispersion were mixed and coagulated to form a masterbatch. For the cellulose fiber-free compositions, natural rubber latex was coagulated to form a masterbatch, and the resulting masterbatch was used for the above-mentioned mixing. The rubber compositions were then mixed with the specified amounts of vulcanization accelerator and sulfur using the Banbury mixer, kneaded, and formed into a sheet using a two-roll mill. The sheet was then press-vulcanized in a mold at 170°C for 10 minutes to produce the rubber compositions (vulcanized rubber test pieces) of Comparative Examples 1-4 and Examples 1-5.

[0054] The resulting rubber compositions (vulcanized rubber test pieces) of Comparative Examples 1 to 4 and Examples 1 to 5 were evaluated for 100% modulus, cut resistance, abrasion resistance, and whiteness as follows.

[0055] <100% modulus> A tensile test was carried out on each of the obtained vulcanized rubber test pieces at a tensile speed of 500 mm / min in accordance with JIS K6251:2010, and the 100% modulus (M100: MPa) was measured at room temperature (20°C). The results are shown in the upper bottom row of the following Table 1. The results are expressed as an index, with the M100 value of the vulcanized rubber test piece of Comparative Example 1 set to 100.

[0056] <Cut resistance> The flex crack growth resistance of each of the obtained vulcanized rubber test pieces was measured in accordance with JIS K6260:2017. The results are also shown in the upper bottom row of Table 1 below. The results are expressed as an index with the value of Comparative Example 1 being 100, and the index was converted so that the smaller the crack growth, the larger the index. In other words, the larger the index, the better the cut resistance.

[0057] <Wear resistance (Lambourn abrasion)> The amount of wear of each of the obtained vulcanized rubber test pieces was measured in accordance with JIS K6264-1, 2:2005 using a Lambourn abrasion tester (manufactured by Iwamoto Seisakusho Co., Ltd.) at a temperature of 20°C and a slip ratio of 50%. The results are also shown in the upper bottom row of Table 1 below. The results are expressed as an index with the value of Comparative Example 1 being 100, and the smaller the amount of wear, the larger the index. In other words, the larger the index, the more excellent the wear resistance.

[0058] <Whiteness> The whiteness of each vulcanized rubber test piece was measured according to JIS Z8722:2009 and CIE 1976(L * ,a * ,b * ) Lightness index L in color space * Measure the value and * The value was used as the evaluation standard for whiteness. * A value of 80% or more was evaluated as ◯, and a value of less than 80% was evaluated as X. The results are also shown in the upper bottom row of Table 1 below.

[0059] <Abrasion resistance (for use on dry floors)> The abrasion resistance of the tires was also evaluated. Specifically, a white cushion tire including a tread rubber layer (a tread rubber layer made of a rubber composition having a predetermined composition) having the composition shown in the upper row of Table 1 below was fitted onto a rim and mounted on a test vehicle, and a 3000 km actual vehicle running test was carried out using a dry floor surface (concrete surface). After that, the groove depth at predetermined positions in the tread rubber layer was measured, and the amount of wear was calculated. The results are also shown in the bottom row of Table 1 below. The results are expressed as an index with the value of Comparative Example 1 being 100, and the smaller the amount of wear, the larger the index. In other words, the larger the index, the more excellent the wear resistance.

[0060] [Table 1]

[0061] The details of each component in Table 1 above are as follows: NR: Natural rubber (rubber latex: HYTEX HA, high ammonia type, solid content 60% by mass, manufactured by SIME DARBY PLANTATION SDN BHD) *In Table 1, the solid content is shown. Cellulose nanofiber: Oxidized cellulose nanofiber (chemically modified nanocellulose with carboxyl groups, with an average fiber diameter of 1-1000 nm and an average fiber length of 5 μm or less; Cellenpia, manufactured by Nippon Paper Industries Co., Ltd.) Surface-treated cellulose nanofiber 1: 10 parts by mass of oxidized cellulose nanofiber (Nippon Paper Industries, Cellenpia) surface-treated with 5 parts by mass of the following pine-derived crude tall oil. Surface-treated cellulose nanofiber 2: 10 parts by mass of oxidized cellulose nanofiber (Nippon Paper Industries, Cellenpia) surface-treated with 5 parts by mass of novolac-type resorcinol-formaldehyde precondensate (RF resin (Sumikanol 700S), Sumitomo Chemical Co., Ltd.). Powdered cellulose: Powdered cellulose (KC Flock W-100GK, manufactured by Nippon Paper Industries Co., Ltd., average particle diameter (D 50 ): approx. 37μm) ·Silica: Zeosil 1165MP (CTAB adsorption specific surface area: 159m 2 / g, manufactured by Rhodia) Titanium oxide: R-650 (average primary particle size: 0.25 μm, manufactured by Sakai Chemical Industry Co., Ltd.) Silane coupling agent: Si69 (bis(3-triethoxysilylpropyl)tetrasulfide, manufactured by Evonik Degussa) Crude tall oil: Crude tall oil derived from pine. It contains a total of 80% by mass or more of fatty acids and resin acids, with a mass ratio of resin acids to fatty acids (resin acids / fatty acids) of approximately 1.2, of which approximately 50% is oleic acid and approximately 35% is linoleic acid, and contains at least abietic acid, neoabietic acid, and palustric acid as resin acids. Process oil: Extract No. 4 S (TDAE, Shell Lubricants Japan) Stearic acid: Stearic acid YR (NOF Corporation) Zinc oxide: Zinc oxide (ZnO, manufactured by Seido Chemical Industry Co., Ltd.) Anti-aging agent: Ozonone 6C (Seiko Chemical Co., Ltd.) Vulcanization accelerator: Noccela NS-P (Ouchi Shinko Chemical Industry Co., Ltd.) Sulfur: Myucron OT-20 (manufactured by Shikoku Chemicals Corporation)

[0062] These results demonstrate that rubber compositions containing predetermined amounts of natural rubber, silica, titanium oxide, and cellulose fiber can maintain or improve hardness and whiteness while providing excellent abrasion resistance and cut resistance (Examples 1 to 5). These rubber compositions are considered suitable for use in the tread rubber layer of white cushion tires. In particular, the whiteness of Examples 1 to 4 was significantly high, making these rubber compositions more suitable for use in the tread rubber layer of white cushion tires. On the other hand, when the blending amount of cellulose fiber was small, cut resistance did not improve (Comparative Example 3), and when the blending amount of cellulose fiber was large, abrasion resistance decreased compared to Comparative Example 1 (Comparative Example 4). Furthermore, even when the blending amount of silica was increased without blending cellulose fiber, both cut resistance and abrasion resistance decreased compared to Comparative Example 1 (Comparative Example 2).

Claims

1. The composite material includes a diene rubber, silica, titanium oxide, and cellulose fibers, The rubber composition contains 2 to 20 parts by mass of the cellulose fiber per 100 parts by mass of the diene rubber.

2. The cellulose fibers are nanocellulose having an average fiber diameter of 1 to 1000 nm and an average fiber length of 5 μm or less, and / or powdered cellulose having an average fiber diameter of 5 to 50 μm and an average fiber length of 500 μm or less. The rubber composition according to claim 1.

3. The rubber composition according to claim 1 or 2, further comprising at least one selected from the group consisting of a fatty acid, a resin acid, a mixture of a fatty acid and a resin acid, and crude tall oil.

4. The rubber composition according to claim 3, comprising 1 to 10 parts by mass of the fatty acid, resin acid, mixture of fatty acid and resin acid, and crude tall oil in total relative to 100 parts by mass of the diene rubber.

5. 3. The rubber composition according to claim 1, wherein the cellulose fibers are surface-treated with at least one selected from the group consisting of fatty acids, resin acids, mixtures of fatty acids and resin acids, crude tall oil, and resole-type and / or novolac-type resorcinol-formaldehyde precondensates.

6. 3. The rubber composition according to claim 1, comprising 20 to 70 parts by mass of said silica and 15 to 45 parts by mass of said titanium oxide per 100 parts by mass of said diene rubber.

7. A white cushion tire using the rubber composition according to claim 1 or 2 in a tread rubber layer.

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