Rubber composition

Abstract

To provide a rubber composition which is superior in wear resistance on an oil surface while maintaining adhesiveness to a base rubber.SOLUTION: The rubber composition contains a diene rubber, carbon black, a process oil, and cellulose fibers. The rubber composition contains 10 pts.mass or more in total of an oil component containing the process oil and 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 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, in scrap yards and the like, due to the need to work on oily surfaces, oil resistance (wear resistance on oily surfaces) may be required for the tread rubber layer of cushion tires used on forklifts and the like. However, if a rubber composition composed of a rubber component with high oil resistance (such as acrylonitrile-butadiene copolymer rubber (NBR)) is used in the tread rubber layer of a cushion tire, adhesion to the base rubber layer (a rubber composition composed mainly of natural rubber (NR)) decreases, and the durability of the cushion tire is likely to decrease. This creates a problem: the cushion tire needs to have a special structure, such as a structure in which the sidewall rubber embraces both the tread rubber and the base rubber. In other words, there is generally a trade-off between the adhesion of the tread rubber (the rubber composition used in the tread rubber layer) of a cushion tire to the base rubber and wear resistance on oily surfaces, and there is room for improvement in terms of achieving both.

[0006] Therefore, an object of the present invention is to provide a rubber composition that maintains adhesion to a base rubber and has superior abrasion resistance on oily surfaces. [Means for solving the problem]

[0007] In order to solve the above problems, the present inventors have conducted extensive research and have found that a rubber composition comprising a diene rubber, carbon black, process oil, and cellulose fibers, in which the total amount of oil components including the process oil is 10 parts by mass or more and the cellulose fibers are 2 to 20 parts by mass per 100 parts by mass of the diene rubber, maintains adhesion to the base rubber while providing superior abrasion resistance on oily surfaces, thereby completing the present invention.

[0008] That is, the present invention provides the following: <1> ~ <8> This includes embodiments of the present invention. <1> The rubber composition includes a diene rubber, carbon black, process oil, and cellulose fibers, The rubber composition contains 10 parts by mass or more of oil components including the process oil in total, and 2 to 20 parts by mass of the cellulose fibers, relative to 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 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> ~ <3> The rubber composition according to any one of the above. <5> The diene rubber is a diene rubber having an acrylonitrile-butadiene copolymer rubber (NBR) content of 10% by mass or less. <1> ~ <4> The rubber composition according to any one of the above. <6> the ratio of the total content of the oil components to the content of the carbon black (total content of the oil components / carbon black content) is 0.2 or more; <1> ~ <5> The rubber composition according to any one of the above. <7> The rubber composition contains 30 to 70 parts by mass of the carbon black and 10 to 20 parts by mass of the oil component in total relative to 100 parts by mass of the diene rubber. <1> ~ <6> The rubber composition according to any one of the above. <8> <1> ~ <7> 1. A cushion tire using the rubber composition according to any one of the above items in a tread rubber layer. [Effects of the Invention]

[0009] According to the present invention, a rubber composition can be obtained that maintains adhesion to a base rubber and has excellent abrasion resistance on oily surfaces. By using this rubber composition in a tread rubber layer, a cushion tire with excellent abrasion resistance on oily surfaces can be obtained. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a partial cross-sectional schematic view of a tire showing an example of an embodiment of a cushion tire. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will now be described. The present invention provides a rubber composition comprising a diene rubber, carbon black, process oil, and cellulose fibers, the rubber composition comprising 10 parts by mass or more of oil components including the process oil, and 2 to 20 parts by mass of the cellulose fibers, per 100 parts by mass of the diene rubber. Hereinafter, this rubber composition 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] The components and materials contained in the rubber composition of the present invention, their contents, etc. will be described in detail below, some with reference to the drawings. Note that the dimensional ratios (length, thickness, etc.) and orientations of the components shown in the drawings may differ from the actual dimensional ratios and orientations in order to facilitate understanding of the invention.

[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. 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. The rubber composition of the present invention can exhibit the above-mentioned effects even if the diene rubber contains a small amount of oil-resistant acrylonitrile-butadiene copolymer rubber (NBR). One of the features of the rubber composition of the present invention is that sufficient effects can be obtained even if the diene rubber contains 10% by mass or less, or even 5% by mass or less, of acrylonitrile-butadiene copolymer rubber (NBR). 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 made into a rubber latex. In particular, it is more preferable that the diene rubber contains 90% by mass or more of NR and / or IR, and even more preferable that the diene rubber contains 95% by mass or more of NR and / or IR.

[0015] 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.

[0016] 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).

[0017] [Carbon black] The carbon black contained in the rubber composition of the present invention is not particularly limited, and any known carbon black used in 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, FEF, GPF, SRF, FT, and MT. One type of carbon black may be used alone, or two or more types may be used in combination. The nitrogen adsorption specific surface area (N2SA) of this carbon black is preferably 70 to 145 m, as this facilitates improving wear resistance on oily surfaces. 2 / g, and 80 to 130m 2 / g is more preferred.

[0018] 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 the amount of nitrogen adsorbed to the carbon black surface, measured according to JIS K6217-2:2001, "Part 2: Determination of specific surface area - Nitrogen adsorption method - Single point method." When a single carbon black is used, this value is the nitrogen adsorption specific surface area 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 of ​​each carbon black by its respective usage ratio and adding the results together. In this calculation, the sum of the usage ratios of each carbon black is assumed to be 1.0.

[0019] The rubber composition of the present invention preferably contains 30 to 70 parts by mass of the carbon black per 100 parts by mass of the diene rubber. The lower limit of the carbon black content is more preferably 40 parts by mass or more, and even more preferably 45 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 55 parts by mass or less. Here, the carbon black content in the present invention means the total content of all carbon blacks when multiple types of carbon black are contained.

[0020] [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.

[0021] <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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] <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.

[0027] 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.

[0028] 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 )).

[0029] In order to fully achieve the effects of the present invention (so that the desired effects can be fully achieved even in a composition with a relatively high oil component content), 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 cellulose fiber content is less than 2 parts by mass per 100 parts by mass of diene rubber, the abrasion resistance on oily surfaces may be insufficient, whereas if the cellulose fiber content is more than 20 parts by mass per 100 parts by mass of diene rubber, both the abrasion resistance on oily surfaces and the adhesion to the base rubber may be reduced.

[0030] [Process oil] The process oil contained in the rubber composition of the present invention may be a process oil that is commonly used in rubber compositions for tires, etc., such as aromatic (aroma oil), paraffin (paraffin oil, paraffin wax), naphthenic (naphthenic oil), etc. In particular, a process oil that is liquid at room temperature (10 to 40°C) is more preferred.

[0031] The rubber composition of the present invention contains a total of 10 parts by mass or more of oil components including this process oil (oil-related components, and in addition to process oil, for example, crude tall oil described below) per 100 parts by mass of the diene rubber. In other words, the rubber composition contains a total of 10 parts by mass or more of oil components. In an embodiment in which only process oil is contained as the oil component, the content of the process oil is set to be within the above range. Such a total content of oil components makes it difficult for oil to penetrate, resulting in better wear resistance on oily surfaces. The lower limit is more preferably 12 parts by mass or more. The upper limit is even more preferably 20 parts by mass or less, and even more preferably 18 parts by mass or less. The rubber composition of the present invention is also characterized by a relatively high ratio of the total content of the oil components to the content of the carbon black, and the effects of the present invention are fully exhibited even in this configuration. The ratio of the total content of the oil components to the content of the carbon black (mass ratio, total content of oil components / carbon black content) is more preferably 0.2 or more, and even more preferably 0.25 or more. The upper limit may be 1.0 or less, or may be 0.5 or less.

[0032] [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. This is because the dispersibility of cellulose fibers is further improved, making it easier to achieve the effects of the present invention. In the present invention, the fatty acids, resin acids, mixtures of fatty acids and resin acids, and crude tall oil are all included in the above-mentioned "oil component."

[0033] 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.

[0034] 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.

[0035] 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 while satisfying the above-mentioned range for the total oil component content. 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 while satisfying the above-mentioned range for the total oil component content, 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 an embodiment in which only one of these is contained, the content of that component 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.

[0036] 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 tends to improve abrasion resistance on oily surfaces.

[0037] 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.

[0038] 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 0.8 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.

[0039] [ka]

[0040] [ka]

[0041] 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. The amounts of fatty acids, resin acids, mixtures of fatty acids and resin acids, and crude tall oil used as surface treatment components are preferably 0.1 to 1 part by mass per 1 part by mass of cellulose fibers. Furthermore, the total amount of oil components, including the amount blended separately from the surface treatment components, is preferably within the aforementioned ranges per 100 parts by mass of diene rubber. The total amount, including the amount blended separately from the surface treatment components, is also preferably within the aforementioned ranges per 1 part by mass of cellulose fibers. Additionally, the amount of RF resin used as a surface treatment component is preferably 0.1 to 1 part by mass per 1 part by mass of cellulose fibers. When RF resin and other surface treatment components are used in combination, the total amount of the surface treatment components is preferably 0.1 to 1 part by mass per 1 part by mass of cellulose fibers. Here, since this RF resin is not included in the oil component of the present invention, the total content of the oil components does not need to be considered separately. 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.

[0042] [Other ingredients] The rubber composition of the present invention may further contain various additives that are commonly used in rubber compositions, such as inorganic fillers other than carbon black (e.g., silica, clay, mica, talc, alumina, calcium carbonate, magnesium carbonate, aluminum hydroxide, titanium oxide, calcium sulfate, barium sulfate, etc.), organic fillers (organic fillers, e.g., lecithin, etc.), zinc oxide (zinc white), resin components other than RF resin, stearic acid, antioxidants, plasticizers, curing agents, vulcanizing agents (e.g., sulfur, etc.), vulcanization accelerators, and vulcanization acceleration aids, within the range that does not affect the effects of the present invention, and these additives can be kneaded together to form a rubber composition. Here, "silica" refers to a particulate material made of silicon dioxide (SiO2) or containing silicon dioxide as the main component (e.g., containing 80% by mass or more, or even 90% by mass or more). 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 may also be used.

[0043] For example, the content of each of stearic acid, zinc oxide, and antioxidant in the rubber composition of the present invention is preferably 1 to 5 parts by mass per 100 parts by mass of the diene rubber. 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. 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.

[0044] Furthermore, when the rubber composition of the present invention contains silica, it may further contain a silane coupling agent to further enhance the dispersibility of the 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 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.

[0045] 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.

[0046] 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.

[0047] [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, carbon black, process oil, 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).

[0048] The rubber composition of the present invention obtained as described above is a rubber composition that maintains adhesion to the base rubber and has excellent abrasion resistance on oily surfaces.

[0049] By using the rubber composition of the present invention in at least the tread rubber layer (reference numeral 11 in the embodiment of FIG. 1), a cushion tire with excellent wear resistance on oily surfaces can be obtained. Even if the base rubber layer of this cushion tire (reference numeral 21 in the embodiment of FIG. 1) is made of a rubber composition with a higher hardness in consideration of the fit with the rim, the adhesion of the tread rubber layer to this base rubber layer is sufficiently maintained. Note that the rubber composition of the present invention may be used partially in parts of this cushion tire other than the tread rubber layer.

[0050] 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]

[0051] (Preparation and Evaluation of Rubber Compositions) Rubber compositions having the formulations shown in Table 1 below were prepared.

[0052] Specifically, the components (excluding the vulcanization accelerator and sulfur) in the amounts shown in the upper part of Table 1 below were mixed in a 1.7-liter internal Banbury mixer at a temperature of approximately 150°C for 5 minutes, 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 in advance 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. Subsequently, the predetermined amounts of vulcanization accelerator and sulfur were mixed and kneaded using the Banbury mixer. The mixture was formed into a sheet using a two-roll mill and then press-vulcanized in a predetermined mold at 170°C for 10 minutes to produce the rubber compositions (vulcanized rubber test pieces) of Reference Example 1, Comparative Examples 1 to 4, and Examples 1 to 5.

[0053] The resulting rubber compositions (vulcanized rubber test pieces) of Reference Example 1, Comparative Examples 1 to 4, and Examples 1 to 5 were evaluated for 100% modulus, adhesion to base rubber, and abrasion resistance as follows.

[0054] <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.

[0055] <Adhesion to base rubber> The adhesion of each vulcanized rubber specimen to the base rubber was evaluated by a peel strength test in accordance with JIS K6854-3:1999, with failure due to cracks running through the reference rubber and / or the base rubber being evaluated as ◯, and peeling at the interface between the reference rubber and the base rubber being evaluated as ×. The results are also shown in the upper bottom row of Table 1 below.

[0056] <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.

[0057] <Wear resistance on oily surfaces> The wear resistance on an oily surface of the completed tire was also evaluated. Specifically, a 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 100-hour running test was carried out while the tire of the vehicle was slipping on an oily surface (a concrete floor surface reproduced by applying automobile engine oil to the surface of an oily floor), after which the groove depth at a predetermined position 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.

[0058] [Table 1]

[0059] 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. NBR: Acrylonitrile-butadiene copolymer rubber (Nancar 3345, manufactured by Nantei Chemical Industry Co., Ltd., acrylonitrile content 34% by mass, Mooney viscosity (ML1+4, 100°C) 45) 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) Carbon black: Show Black N339 (Nitrogen adsorption specific surface area (N2SA): 88m 2 / g, manufactured by Gabot Japan) 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. 4S (TDAE (aroma oil), manufactured by 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)

[0060] These results demonstrate that rubber compositions containing predetermined amounts of natural rubber, carbon black, process oil, and cellulose fiber maintain adhesion to the base rubber while providing excellent abrasion resistance, including abrasion resistance on oily surfaces (Examples 1 to 5). These rubber compositions are particularly suitable for use in the tread rubber layer of cushion tires for work vehicles used on oily surfaces. On the other hand, when the amount of cellulose fiber blended was small, the abrasion resistance did not improve (Comparative Example 3), and when the amount of cellulose fiber blended was large, the adhesion to the base rubber decreased (Comparative Example 4).Furthermore, even when the amount of carbon black was increased without blending cellulose fiber, the abrasion resistance did not improve (Comparative Example 2). [Explanation of symbols]

[0061] 100 cushion tires 11 Tread rubber layer 21 Base rubber layer 31 Bead section

Claims

1. The rubber composition includes a diene rubber, carbon black, process oil, and cellulose fibers, The rubber composition contains 10 parts by mass or more of oil components including the process oil in total, and 2 to 20 parts by mass of the cellulose fibers, relative to 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. 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.

5. 3. The rubber composition according to claim 1, wherein the diene rubber contains 10% by mass or less of acrylonitrile-butadiene copolymer rubber (NBR).

6. The rubber composition according to claim 1 or 2, wherein a ratio of the total content of the oil components to the content of the carbon black (total content of oil components / carbon black content) is 0.2 or more.

7. 3. The rubber composition according to claim 1, further comprising 30 to 70 parts by mass of the carbon black and 10 to 20 parts by mass of the oil component in total, relative to 100 parts by mass of the diene rubber.

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

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