Method for producing a cellulose nanofiber-containing rubber composition

Abstract

To provide a method capable of efficiently producing a rubber composition which has cellulose nanofibers uniformly dispersed therein and has suitable physical characteristics.SOLUTION: The method for producing a cellulose nanofiber-containing rubber composition includes a step of kneading a rubber component containing an ethylene-propylene-diene rubber, and an unmodified cellulose nanofiber dispersion in the presence of a water-soluble organic solvent having a boiling point of 150°C or higher and 220°C or lower and an SP value of 8.5-11.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing a rubber composition containing cellulose nanofibers.

Background Art

[0002] In rubber compositions, it is known that the physical properties of the resulting rubber can be improved by containing cellulose fibers as a filler incorporated into the rubber component (Patent Document 1). Such cellulose fibers include microfibrillated cellulose. However, generally, microfibrillated cellulose is used with wood pulp from which lignin has been chemically removed for the purpose of bleaching, reducing the binding force between microfibril units, and enhancing the fibrillation efficiency into microfibril units. Microfibrillated cellulose produced from wood pulp with lignin removed mainly has hydrophilicity derived from cellulose, so it has poor compatibility with the hydrophobic rubber component. Therefore, when trying to produce fiber-reinforced rubber by blending microfibrillated cellulose directly into the rubber component, there is a problem that the dispersibility of the fibers deteriorates, suppressing the improvement of the physical properties of the resulting rubber.

[0003] For example, Patent Document 1 describes a masterbatch of rubber / cellulose-based fibers obtained by stirring and mixing cellulose-based fibers with an average fiber diameter of less than 0.5 μm and rubber latex. As its production method, a dispersion liquid in which cellulose-based fibers with an average fiber diameter of less than 0.5 μm are fibrillated in water, rubber latex, and are mixed and dried to produce a masterbatch of rubber / cellulose-based fibers in which the cellulose-based fibers are uniformly dispersed in the rubber. However, unlike diene-based rubbers synthesized by emulsion polymerization, ethylene propylene diene rubber is synthesized in a hydrocarbon-based solvent, so the latex aqueous dispersion of ethylene propylene diene rubber hardly circulates in the market, and the above production method cannot be used.

[0004] Furthermore, Patent Document 2 describes a method of preparing a cellulose microfiber / EPDM masterbatch by mixing a dispersion of cellulose microfibers produced by mechanical defibration in toluene with a solution of ethylene propylene diene rubber (EPDM) dissolved in toluene, vaporizing the toluene, then kneading the EPDM and adding the masterbatch to the mixture to finally produce an uncrosslinked rubber composition (Example 3-1). However, when using water-insoluble organic solvents such as toluene, if toluene is not used from the time of cellulose nanofiber manufacturing, the cellulose nanofibers will generally not disperse in the toluene solvent and will aggregate. Mechanical defibrillation, such as disc milling or high-pressure dispersion, generates heat during cellulose defibrillation, making it extremely dangerous when using organic solvents with low flash points like toluene.

[0005] Furthermore, although cellulose nanofibers are marketed as aqueous dispersions, the cellulose nanofibers form hydrogen bonds and aggregate during the drying process to remove water from the dispersion. As a result, during the composite process with rubber and resin components, the cellulose nanofibers cannot exist in a highly defibrated state, and the composite material cannot be sufficiently reinforced by the cellulose nanofibers. Therefore, a method has been proposed in which a cellulose nanofiber aqueous dispersion is mixed with rubber latex or resin emulsion (Patent Documents 3 and 4). However, composite materials produced using these methods were sometimes affected by the properties of the rubber latex or resin emulsion. Furthermore, they could not be applied to rubbers or resins that were not commercially available as rubber latex or resin emulsions. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2006-206864 [Patent Document 2] Japanese Patent Publication No. 2019-163861 [Patent Document 3] Japanese Patent Publication No. 2015-98576 [Patent Document 4] Japanese Patent Publication No. 2016-29169 [Overview of the project] [Problems that the invention aims to solve]

[0007] Therefore, the object of the present invention is to provide a method for efficiently producing a rubber composition in which cellulose nanofibers are uniformly dispersed and which has suitable physical properties. [Means for solving the problem]

[0008] The present inventors diligently conducted research with the aim of developing a technology to sufficiently disperse unmodified cellulose nanofibers in a rubber composition using a rubber component containing ethylene propylene diene rubber (EPDM). As a result, they discovered that by using a water-soluble organic solvent with a boiling point of 150°C to 220°C and an SP value of 8.5 to 11 as the solvent, cellulose nanofibers can be dispersed very uniformly and efficiently in the rubber composition, and the resulting rubber composition has desirable physical properties. This led to the completion of the present invention. Furthermore, we have discovered that by using a mixed solvent comprising a water-soluble organic solvent with an SP value of 10 or higher and a non-water-soluble organic solvent with an SP value of 9 or lower, wherein at least one of the water-soluble organic solvent and the non-water-soluble organic solvent has a boiling point of 150°C or higher and 220°C or lower, and the SP value of the mixed solvent is 8.5 to 11, cellulose nanofibers can be dispersed very uniformly and efficiently in the rubber composition, and the resulting rubber composition has desirable physical properties, thus completing the present invention.

[0009] A first embodiment of the present invention is a water-soluble organic solvent having a boiling point of 150°C or higher and 220°C or lower and an SP value of 8.5 to 11, Rubber components including EPDM, The process includes a step of kneading with an unmodified cellulose nanofiber dispersion. This invention relates to a method for producing a rubber composition containing cellulose nanofibers.

[0010] In the first embodiment described above, the process involves swelling a rubber component containing EPDM with a water-soluble organic solvent having a boiling point of 150°C to 220°C and an SP value of 8.5 to 11, and A process of kneading a swollen rubber component with an unmodified cellulose nanofiber dispersion. It may have.

[0011] In the first embodiment described above, a rubber component containing EPDM is swollen with a water-soluble organic solvent having a boiling point of 150°C to 220°C and an SP value of 8.5 to 11, A water-soluble organic solvent having a boiling point of 150°C to 220°C and an SP value of 8.5 to 11, Unmodified cellulose nanofiber dispersion and The process may include a step of kneading the ingredients.

[0012] In the first embodiment described above, the water-soluble organic solvent having a boiling point of 150°C or higher and 220°C or lower and an SP value of 8.5 to 11 may be one or more selected from the group consisting of alcohol-based solvents, ether-based solvents, and ester-based solvents.

[0013] In the first embodiment described above, the unmodified cellulose nanofiber dispersion may be a dispersion of a water-soluble organic solvent having a boiling point of 150°C to 220°C and an SP value of 8.5 to 11.

[0014] Furthermore, a second embodiment of the present invention is a mixed solvent comprising a water-soluble organic solvent with an SP value of 10 or more and a non-water-soluble organic solvent with an SP value of 9 or less, wherein at least one of the water-soluble organic solvent and the non-water-soluble organic solvent has a boiling point of 150°C or more and 220°C or less, and the mixed solvent has an SP value of 8.5 to 11. Rubber components including ethylene propylene diene rubber, The present invention relates to a method for producing a cellulose nanofiber-containing rubber composition, comprising the step of kneading an unmodified cellulose nanofiber dispersion with the rubber composition.

[0015] In the second embodiment, a step of swelling a rubber component containing ethylene propylene diene rubber with the mixed solvent, and a step of kneading the swollen rubber component and an unmodified cellulose nanofiber dispersion may be included.

[0016] In the second embodiment, the rubber component containing ethylene propylene diene rubber swollen with the mixed solvent, the mixed solvent, and an unmodified cellulose nanofiber dispersion may be kneaded.

[0017] In the second embodiment, the water-soluble organic solvent may be N-methylpyrrolidone or 1-methoxy-2-propanol, and the water-insoluble organic solvent may be butyl acetate or methoxybutyl acetate.

[0018] In the second embodiment, the unmodified cellulose nanofiber dispersion may be a dispersion of the mixed solvent.

[0019] In the first or the second embodiment, the average fiber diameter of the unmodified cellulose nanofibers may be 20 to 1000 nm.

[0020] In the first or the second embodiment, a step of removing the water-soluble organic solvent or the mixed solvent so that it becomes 1% by weight or less from the rubber component swollen with the water-soluble organic solvent having a boiling point of 150°C or higher and 220°C or lower and an SP value of 8.5 to 11 or the mixed solvent, and in which unmodified cellulose nanofibers are dispersed may be included.

[0021] In the first or the second embodiment, the solid content concentration of the unmodified cellulose nanofibers in the cellulose nanofiber-containing rubber composition may be 3 to 30 phr.

Advantages of the Invention

[0022] According to the present invention, in either the first or second embodiment, unmodified cellulose nanofibers can be dispersed very uniformly and efficiently in a rubber composition. The resulting rubber molded product obtained by crosslinking the rubber composition has high rubber hardness and elasticity, and therefore possesses desirable physical properties. [Modes for carrying out the invention]

[0023] The following describes embodiments of the method for producing the cellulose nanofiber-containing rubber composition according to the present invention.

[0024] (First embodiment) A method for producing a cellulose nanofiber-containing rubber composition according to the first embodiment of the present invention (hereinafter also referred to as the production method according to the first embodiment) is as follows: In the presence of a water-soluble organic solvent with a boiling point between 150°C and 220°C and an SP value of 8.5 to 11, Rubber components including EPDM, The process includes a step of kneading an unmodified cellulose nanofiber dispersion with the mixture.

[0025] In the manufacturing method according to the first embodiment, as described above, by using a water-soluble organic solvent with a boiling point of 150°C to 220°C and an SP value of 8.5 to 11 as the solvent, unmodified cellulose nanofibers can be dispersed very uniformly and efficiently in the rubber composition. The resulting rubber molded product obtained by crosslinking the rubber composition has high rubber hardness and elasticity, thus possessing desirable physical properties.

[0026] The water-soluble organic solvent used in the manufacturing method according to the first embodiment, having a boiling point of 150°C to 220°C and an SP value of 8.5 to 11, has a boiling point of 150°C or higher, which makes it less likely to vaporize even when mixing the rubber component and the unmodified cellulose nanofibers, thus facilitating sufficient dispersion of the unmodified cellulose nanofibers within the rubber component. Furthermore, the water-soluble nature of the organic solvent suppresses aggregation of the unmodified cellulose nanofibers, and its SP value of 8.5 to 11 facilitates swelling of the rubber component containing EPDM, making it easier for the unmodified cellulose nanofibers to disperse within the rubber component. Furthermore, if the organic solvent used deviates from the following physical properties: boiling point between 150°C and 220°C, SP value between 8.5 and 11, or water solubility, then, as described in the comparative examples below, the rubber hardness may decrease, the dispersibility of unmodified cellulose nanofibers in the rubber component may worsen, the rubber composition may become difficult to knead, and productivity may suffer. Therefore, in the manufacturing method according to the first embodiment, it is necessary to use a water-soluble organic solvent having the boiling point and SP value within the specified range to obtain a rubber composition having predetermined physical properties (hereinafter referred to as the first rubber composition).

[0027] The aforementioned SP value refers to the Solubility Parameter, and in this invention, the value calculated using HSPiP ver.5.2.06 is used.

[0028] Examples of water-soluble organic solvents with a boiling point between 150°C and 220°C and an SP value of 8.5 to 11 include alcohol-based solvents, ether-based solvents, and ester-based solvents. Examples of the aforementioned alcohol-based solvents include 3-methoxybutanol, 3-methoxy-3-methyl-1-butanol, and diacetone alcohol. Examples of the ether-based solvents include diethylene glycol dimethyl ether, diethylene glycol ethyl methyl ether, ethylene glycol monobutyl ether, ethylene glycol monotertiary butyl ether, dipropylene glycol methyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, propylene glycol n-propyl ether, triethylene glycol dimethyl ether, and the like. Examples of the ester-based solvents include diethylene glycol monoethyl ether acetate and ethyl lactate. The aforementioned water-soluble organic solvents may be used individually or in combination of two or more. There are no particular limitations on the type of water-soluble organic solvent, but 3-methoxy-3-methyl-1-butanol can be manufactured safely because its flash point disappears when the water content is 20% or more.

[0029] Furthermore, in the manufacturing method according to the first embodiment, other water-soluble organic solvents other than the water-soluble organic solvent having a boiling point of 150°C or higher and 220°C or lower and an SP value of 8.5 to 11 may be used in combination.

[0030] Examples of other water-soluble organic solvents include N-methylpyrrolidone (boiling point 202°C, SP value 11.5), 1-methoxy-2-propanol (boiling point 120°C, SP value 10.2), propylene glycol (boiling point 188°C, SP value 14.5), pyridine (boiling point 115°C, SP value 15.1), acetonitrile (boiling point 82°C, SP value 12.2), isopropyl alcohol (boiling point 82°C, SP value 13.3), ethyl alcohol (boiling point 78°C, SP value 13.3), and methyl alcohol (boiling point 65°C, SP value 14.7).

[0031] When using the aforementioned water-soluble organic solvent having a boiling point of 150°C to 220°C and an SP value of 8.5 to 11 in combination with another water-soluble organic solvent, it is sufficient that the SP value of the resulting mixed solvent falls within the range of 8.5 to 10.1, and there are no particular limitations on the ratio of the organic solvents to be mixed.

[0032] In this invention, swelling refers to a state in which the force exerted by the water-soluble organic solvent to expand the intermolecular space between the polymer molecules of the rubber component is balanced by the elasticity of the cross-linked network. Swelling depends on the affinity between the water-soluble organic solvent and the polymer of the rubber component; the better the affinity between the two, the greater the swelling.

[0033] The rubber component used in the manufacturing method according to the first embodiment is the main component of the first rubber composition and contains solid EPDM, which cannot be used as latex rubber, like diene rubber.

[0034] The rubber components that can be used with EPDM are not particularly limited, but any solid rubber that swells in a water-soluble organic solvent with an SP value of 8.5 to 11 can be used. Examples include natural rubber, synthetic diene rubber, mixtures of natural rubber and synthetic diene rubber, and other non-diene rubbers.

[0035] Examples of natural rubber include natural rubber latex, technically graded rubber (TSR), smoked sheet (RSS), gutta-percha, natural rubber derived from Eucommia ulmoides, natural rubber derived from guayule, natural rubber derived from Russian dandelion, and resin component fermented rubber. Modified natural rubbers such as epoxidized natural rubber, methacrylic acid modified natural rubber, and styrene modified natural rubber, obtained by modifying these natural rubbers, are also included in the natural rubber of this invention.

[0036] Examples of synthetic diene rubbers include styrene-butadiene copolymer rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), nitrile rubber (NBR), chloroprene rubber (CR), styrene-isoprene-styrene block copolymer (SIS), styrene-butadiene-styrene block copolymer (SBS), ethylene-α-olefin copolymer rubber (SPO), ethylene-α-olefin-diene copolymer rubber, and modified synthetic diene rubbers thereof. Modified synthetic diene rubbers include diene rubbers modified by modification methods such as main chain modification, one-end modification, and both-end modification. Here, examples of modified functional groups in modified synthetic diene rubbers include epoxy groups, amino groups, alkoxy groups, hydroxyl groups, alkoxysilyl groups, polyether groups, and carboxyl groups, and one or more of these functional groups may be included in the modified synthetic diene rubber.

[0037] There are no particular limitations on the method for producing synthetic diene rubber, and examples include emulsion polymerization, solution polymerization, radical polymerization, anionic polymerization, and cationic polymerization. Furthermore, there are no particular limitations on the glass transition temperature of the synthetic diene rubber.

[0038] The cellulose nanofiber dispersion used in the manufacturing method according to the first embodiment is a liquid in which unmodified cellulose nanofibers are dispersed.

[0039] The aforementioned unmodified cellulose nanofibers refer to cellulose nanofibers obtained from raw plant materials that have not undergone any modification treatment for improvement. Cellulose nanofibers are fibrous materials derived from cellulose, which is composed of the skeletal components of plant cell walls obtained by finely breaking down plant fibers. Examples of plant materials used as raw materials for cellulose nanofibers include wood, bamboo, rice, potatoes, sugarcane, aquatic plants, and seaweed. Furthermore, cellulose nanofibers may consist solely of cellulose, or they may be lignocellulose nanofibers containing lignin. These unmodified cellulose nanofibers may be used in a mixture of two or more types.

[0040] The unmodified cellulose nanofibers may have an average fiber diameter of 1000 nm or less, but are preferably 50 to 500 nm in size, from the viewpoint of easy dispersion in the first rubber composition and easy acquisition of suitable strength and elasticity. Furthermore, the fiber length of the unmodified cellulose nanofiber is preferably 1 to 1000 μm, from the viewpoint of easy dispersion in the first rubber composition and easy acquisition of suitable strength and elasticity. The average fiber diameter and fiber length in this invention can be measured by a scanning electron microscope or an atomic force microscope.

[0041] In the manufacturing method according to the first embodiment, the cellulose nanofiber dispersion may be a dispersion of a water-soluble organic solvent having a boiling point of 150°C or higher and 220°C or lower and an SP value of 8.5 to 11. There are no particular limitations on the content of unmodified cellulose nanofibers in the cellulose nanofiber dispersion, but it is sufficient if it is adjusted to 1 to 30% by weight.

[0042] Any known method is acceptable for dispersing cellulose nanofibers in a water-soluble organic solvent having a boiling point between 150°C and 220°C and an SP value of 8.5 to 11; there are no particular limitations. Alternatively, a cellulose nanofiber dispersion may be prepared by dispersing cellulose nanofibers in water, and then replacing the water with a water-soluble organic solvent having a boiling point of 150°C to 220°C and an SP value of 8.5 to 11.

[0043] In the manufacturing method according to the first embodiment, a method for dispersing unmodified cellulose nanofibers by kneading a rubber component containing EPDM swollen with a water-soluble organic solvent with a cellulose nanofiber dispersion is, for example, 1-1) A method comprising the step of kneading a rubber component containing EPDM with a cellulose nanofiber dispersion dispersed in a water-soluble organic solvent having a boiling point of 150°C to 220°C and an SP value of 8.5 to 11. 2-1) A step of swelling a rubber component containing EPDM with a water-soluble organic solvent having a boiling point of 150°C to 220°C and an SP value of 8.5 to 11, and A method comprising the step of kneading a swollen rubber component with a cellulose nanofiber dispersion,

[0044] Specifically, method 1-1) involves adding a cellulose nanofiber dispersion dispersed in a water-soluble organic solvent having a boiling point of 150°C to 220°C and an SP value of 8.5 to 11 to a rubber component containing EPDM that is being kneaded in a kneader, and then vaporizing the water-soluble organic solvent while kneading the mixture. Another method, as described in 2-1), involves adding a water-soluble organic solvent with a boiling point of 150°C to 220°C and an SP value of 8.5 to 11 to a rubber component containing EPDM that is being kneaded in a kneader, kneading them to swell the rubber component, and then adding a cellulose nanofiber dispersion dispersed in the water-soluble organic solvent with a boiling point of 150°C to 220°C and an SP value of 8.5 to 11, and kneading them to vaporize the water-soluble organic solvent. Furthermore, in method 2-1), depending on the type of kneading equipment and the type of water-soluble organic solvent, the step of adding a water-soluble organic solvent with a boiling point of 150°C to 220°C and an SP value of 8.5 to 11, and kneading them while swelling the rubber components, can be omitted. Furthermore, the water-soluble organic solvent used to knead the rubber component and the water-soluble organic solvent used in the cellulose nanofiber dispersion may be of the same type or different types.

[0045] Examples of the aforementioned mixing machines include closed-type mixers (Banbury mixers, Shaw mixers, kneader mixers, etc.), rolls, and extruders (Gordon plasticators, transfer mixers, cavity transfer mixers, pin-type mixers, twin-screw type extruders, etc.).

[0046] The temperature conditions for swelling the rubber component can be any temperature at which the rubber component does not crosslink, and can be adjusted as appropriate depending on the type of rubber component. There are no particular limitations, but 80 to 130°C is preferred. Furthermore, there are no particular limitations on the kneading time for swelling the rubber component.

[0047] The temperature conditions for vaporizing the water-soluble organic solvent while kneading are not particularly limited, as long as the temperature does not cause crosslinking of the rubber components, but 100 to 150°C is preferred. Furthermore, the kneading process may be continued until no water-soluble organic solvent can be detected around the first rubber composition. There are no specific time limitations, but 1 to 3 hours is acceptable. Furthermore, by using a mixing machine and an organic solvent recovery system in combination, water-soluble organic solvents can be recovered and recycled, making it environmentally friendly and leading to cost reductions.

[0048] (Second Embodiment) A method for producing a cellulose nanofiber-containing rubber composition according to a second embodiment of the present invention (hereinafter also referred to as the production method according to the second embodiment) is as follows: A mixed solvent comprising a water-soluble organic solvent with an SP value of 10 or more and a water-insoluble organic solvent with an SP value of 9 or less (hereinafter also referred to as the mixed solvent of the second embodiment), wherein at least one of the water-soluble organic solvent and the water-insoluble organic solvent has a boiling point of 150°C or more and 220°C or less, and the mixed solvent has an SP value of 8.5 to 11. Rubber components including ethylene propylene diene rubber, The process includes a step of kneading an unmodified cellulose nanofiber dispersion with the mixture.

[0049] In the manufacturing method according to the second embodiment, a water-soluble organic solvent having the specific physical properties described above is mixed with a non-water-soluble organic solvent having the specific physical properties, and the SP value of the resulting mixed solvent is adjusted to 8.5 to 11. This makes it difficult for the solvent to vaporize even when kneading the rubber component and the unmodified cellulose nanofibers, allowing the unmodified cellulose nanofibers to disperse sufficiently in the rubber component, suppressing aggregation of the unmodified cellulose nanofibers, making it easier to swell the rubber component containing EPDM, and facilitating the dispersion of the unmodified cellulose nanofibers in the rubber component. Therefore, similar to the first embodiment, the rubber molded product obtained by crosslinking the rubber composition obtained by the manufacturing method according to the second embodiment (hereinafter referred to as the second rubber composition) has high rubber hardness and elasticity, thus possessing desirable physical properties. In the manufacturing method according to the second embodiment, the upper limit of the SP value of the water-soluble organic solvent and the lower limit of the SP value of the non-water-soluble organic solvent are not particularly limited, as long as the SP value of the mixed solvent in the second embodiment can be adjusted to a specific range.

[0050] Examples of water-soluble organic solvents with an SP value of 10 or higher include N-methylpyrrolidone (boiling point 202°C), 1-methoxy-2-propanol (boiling point 120°C), propylene glycol (boiling point 188°C), pyridine (boiling point 115°C), acetonitrile (boiling point 82°C), isopropyl alcohol (boiling point 82°C), ethyl alcohol (boiling point 78°C), and methyl alcohol (boiling point 65°C). Examples of non-water-soluble organic solvents with an SP value of 9 or less include butyl acetate (boiling point 126°C), methoxybutyl acetate (boiling point 172°C), xylene (boiling point 140°C), toluene (boiling point 110°C), and mineral spirits (boiling point 130-230°C). In the manufacturing method according to the second embodiment, the boiling point of at least one of the water-soluble organic solvents with an SP value of 10 or more and the water-insoluble organic solvent with an SP value of 9 or less is 150°C or more and 220°C or less, and the water-soluble organic solvents and water-insoluble organic solvents should be selected such that the SP value of the mixed solvent in the second embodiment is 8.5 to 11. In particular, from the viewpoint of excellent dispersibility of the mixed solvent of the second embodiment, it is preferable to use N-methylpyrrolidone or 1-methoxy-2-propanol as the water-soluble organic solvent and butyl acetate or methoxybutyl acetate as the non-water-soluble organic solvent.

[0051] The mixing ratio of the water-soluble organic solvent and the water-insoluble organic solvent in the mixed solvent of the second embodiment is not particularly limited, as long as it is a mixing ratio that can adjust the SP value of the resulting mixed solvent of the second embodiment to a range of 8.5 to 11.

[0052] The rubber component used in the manufacturing method according to the second embodiment is the main component of the second rubber composition. Specifically, any rubber component that can be used in the manufacturing method according to the first embodiment is acceptable. A detailed explanation of the rubber component is omitted.

[0053] The cellulose nanofiber dispersion used in the manufacturing method according to the second embodiment is a liquid in which unmodified cellulose nanofibers are dispersed. Specifically, any cellulose nanofiber that can be used in the manufacturing method according to the first embodiment is acceptable. A detailed explanation of cellulose nanofibers is omitted.

[0054] In the manufacturing method according to the second embodiment, the cellulose nanofiber dispersion may be a dispersion of a mixed solvent (the mixed solvent of the second embodiment) of the water-soluble organic solvent and the non-water-soluble organic solvent. There are no particular limitations on the content of unmodified cellulose nanofibers in the cellulose nanofiber dispersion, but it is sufficient if it is adjusted to 1 to 30% by weight.

[0055] Any known method can be used to disperse the cellulose nanofibers in the mixed solvent of the second embodiment, and there are no particular limitations. Alternatively, a cellulose nanofiber dispersion may be prepared by dispersing cellulose nanofibers in water, then mixing in the mixed solvent of the second embodiment to replace the water with the mixed solvent.

[0056] In the manufacturing method according to the second embodiment, a method for dispersing unmodified cellulose nanofibers by kneading a rubber component containing EPDM swollen with the mixed solvent of the second embodiment with a cellulose nanofiber dispersion is, for example, 1-2) A method comprising the step of kneading a rubber component containing EPDM with a cellulose nanofiber dispersion dispersed in the mixed solvent of the second embodiment, 2-2) A step of swelling the rubber component containing EPDM with the mixed solvent of the second embodiment, and A method comprising the step of kneading a swollen rubber component with a cellulose nanofiber dispersion.

[0057] Specifically, method 1-2) involves adding a cellulose nanofiber dispersion dispersed in the mixed solvent of the second embodiment to a rubber component containing EPDM that is being kneaded in a kneader, and then vaporizing the mixed solvent of the second embodiment while kneading them together. Another method, as described in 2-2), involves adding the mixed solvent of the second embodiment to a rubber component containing EPDM that is being kneaded in a kneader, kneading them to swell the rubber component, then adding a cellulose nanofiber dispersion dispersed in the mixed solvent of the second embodiment, and kneading them to vaporize the water-soluble organic solvent. Furthermore, in method 2-2), depending on the type of kneading equipment and the type of organic solvent, the step of adding the mixed solvent of the second embodiment and kneading them while swelling the rubber components can be omitted. Furthermore, the water-soluble organic solvent used for mixing with the rubber component and the water-soluble and non-water-soluble organic solvents used in the cellulose nanofiber dispersion may be of the same type or different types.

[0058] The aforementioned kneading machine can be any device that can be used in the manufacturing method of the first embodiment, and is not particularly limited.

[0059] The temperature conditions for swelling the rubber component can be any temperature at which the rubber component does not crosslink, and can be adjusted as appropriate depending on the type of rubber component. There are no particular limitations, but 80 to 130°C is preferred. Furthermore, there are no particular limitations on the kneading time for swelling the rubber component.

[0060] The temperature conditions for vaporizing the mixed solvent of the second embodiment while kneading are not particularly limited, as long as the temperature does not cause crosslinking of the rubber components, but 100 to 150°C is preferred. Furthermore, the kneading process may be continued until the mixed solvent of the second embodiment can no longer be observed around the second rubber composition. There are no specific time limitations, but 1 to 3 hours is acceptable. Furthermore, by using a compounding machine and an organic solvent recovery device in combination, the mixed solvent of the second embodiment can be recovered and recycled, which is environmentally friendly and leads to cost reduction.

[0061] Furthermore, in the manufacturing method of the first or second embodiment described above, optional components such as carbon black, colorants, fillers, oils, plasticizers, surfactants, and processing aids may be added to the obtained first or second rubber composition. There are no particular limitations on the timing of adding these optional components, but in the case of method 1-1) or 1-2) above, it is acceptable to add them during the step of kneading the swollen rubber component with the cellulose nanofiber dispersion, and in the case of method 2-1) or 2-2) above, it is acceptable to add them during the step of kneading the rubber component with the water-soluble organic solvent or the mixed solvent of the second embodiment with the cellulose nanofiber dispersion.

[0062] In the manufacturing method of the first or second embodiment, the water-soluble organic solvent or the mixed solvent of the second embodiment may be removed from the rubber component that has been swollen with the water-soluble organic solvent or the mixed solvent of the second embodiment and in which unmodified cellulose nanofibers are dispersed, so that the amount is 1% by weight or less. Methods for removing the water-soluble organic solvent or the mixed solvent of the second embodiment from the rubber component include continuing to knead while adjusting the temperature to a high level in the kneader, and vacuum reduced-pressure drying. By removing the water-soluble organic solvent or the mixed solvent of the second embodiment in this way, a so-called masterbatch can be prepared.

[0063] In the manufacturing method of the present invention, the dispersibility of unmodified cellulose nanofibers in the first or second rubber composition is excellent, and the solid content concentration of unmodified cellulose nanofibers is adjusted to 3 to 30 phr (per hundred rubber). As a result, the rubber molded product obtained by crosslinking the resulting first or second rubber composition has high rubber hardness and elasticity, thus possessing desirable physical properties.

[0064] The first or second rubber composition obtained by the manufacturing method of the present invention can be used in applications such as power transmission belts, weatherstrips, vibration-damping rubber, hoses, wire insulation, and gaskets.

[0065] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. [Examples]

[0066] [Examples of Cellulose Nanofiber Dispersion Production] 30 parts by weight of kraft pulp was mixed with 970 parts by weight of purified water. Dispersion was carried out using a 6-inch muscoloider (stone mill type grinder manufactured by Masuko Sangyo) while gradually decreasing the contact clearance from the disk contact clearance. The process was terminated when the contact clearance was reduced by 120 μm. A cellulose nanofiber aqueous dispersion was then prepared by filtration and concentration using a Buchner funnel until the cellulose nanofiber dispersion reached 7.5% by weight (solid content concentration 7.5% by weight, average fiber diameter 80-200 nm, fiber length 100 μm).

[0067] To 400 parts by weight of the cellulose nanofiber aqueous dispersion with a solid content of 7.5% by weight obtained as described above, 900 parts by weight of diethylene glycol dimethyl ether (manufactured by Toho Chemical Co., Ltd.: a water-soluble organic solvent with a boiling point of 162°C and an SP value of 9.0) was added and the mixture was stirred. The cellulose nanofiber dispersion was filtered and concentrated using a Buchner funnel until it reached 400 parts by weight. Then, 900 parts by weight of diethylene glycol dimethyl ether was added and stirred, and the mixture was filtered and concentrated again using a Buchner funnel until it reached 400 parts by weight. The moisture content of the obtained cellulose nanofiber dispersion was 10% or less. This cellulose nanofiber dispersion was used in the following examples.

[0068] [Example 1] 300 parts by weight of EPDM "EPT-4021H" (manufactured by Mitsui Chemicals) was being kneaded in a kneader (S-type double-arm kneader manufactured by Nippon Spindle Manufacturing Co., Ltd. (mixing capacity 1L)), to which 60 parts by weight of diethylene glycol dimethyl ether (boiling point 162°C, SP value 9.0) was added, and the rubber components were swelled while kneading at 100°C. Next, while continuing to knead, 500 parts by weight of a diethylene glycol dimethyl ether dispersion containing 6% by weight of pre-prepared unmodified cellulose nanofibers (CNF) was added in stages. Next, the mixture was kneaded while heating at 100-120°C, and the diethylene glycol dimethyl ether was removed until its content was 1% by weight or less, to obtain a rubber composition (solid content concentration of unmodified cellulose nanofibers, 10 phr).

[0069] [Examples 2-6] A rubber composition was obtained in the same manner as in Example 1, except that the organic solvent used for kneading with EPDM and the organic solvent used for the cellulose nanofiber dispersion were replaced with those listed in Table 1 below. In the table, substances that are water-soluble in organic solvents are indicated by "∞".

[0070] [Comparative Examples 1-13] A rubber composition was obtained in the same manner as in Example 1, except that the organic solvent used for kneading with EPDM and the organic solvent used for the cellulose nanofiber dispersion were replaced with those listed in Tables 2 and 3 below.

[0071] (Test Example 1) The rubber hardness and dispersibility of unmodified cellulose nanofibers of the rubber compositions obtained in Examples 1-6 and Comparative Examples 1-13 were evaluated using the following procedure.

[0072] [Rubber hardness] 1) 110 parts by weight of each rubber composition, 7.5 parts by weight of peroxide crosslinking agent (DCP-40 (manufactured by NOF Corporation)), 5 parts by weight of zinc oxide, and 1 part by weight of stearic acid were mixed in a two-roll mixer and kneaded at 70-80°C for 10 minutes. Next, the two rolls were operated to produce sheets with a thickness of 2.2 to 2.6 mm. Next, a 2mm thick test specimen was obtained by hot pressing using a 2mm thick metal frame at 170°C for 20 minutes to perform a cross-linking treatment. 2) Three of the obtained test pieces were stacked to a thickness of 6 mm, and five random points were measured using a Teclock digital durometer "GSD-719J-R (Type A)," with the median value being used as the rubber hardness.

[0073] [Dispersibility] The presence or absence of coarse grains on the surface of the molded rubber was visually inspected and judged according to the following criteria. "〇" indicates products with almost no coarse grains. "△" indicates coarse grains. Items with many coarse particles that can be identified with an "×"

[0074] [comprehensive evaluation] To evaluate production efficiency, mixing time was added and the following criteria were used for a comprehensive assessment. "〇" Dispersibility is "〇", rubber hardness is 75 or higher, and the mixing time is less than 3 hours. "△" Dispersibility is "〇", and one or two of the following conditions are met: rubber hardness is 75 or higher, and mixing time is less than 3 hours. Items with "×" variability

[0075] The results obtained are shown in Table 4. As shown in Table 4, the rubber molded articles of Examples 1 to 6 had high rubber hardness and no coarse grains of unmodified cellulose nanofiber were observed in the rubber molded articles, whereas the rubber molded articles of Comparative Examples 1 to 13 had lower rubber hardness than Examples 1 to 6, and most of the dispersibility evaluations were "△" or "×". Furthermore, upon palpation of the molded rubber products, it was found that the molded rubber products of Examples 1-6 were less prone to deformation and had a clearly higher elastic modulus compared to Comparative Examples 1-4, 7, and 13, which received a "×" rating for dispersibility. From the above, it can be seen that the rubber compositions obtained in Examples 1 to 6 can be suitably used in applications such as friction transmission belts, weatherstrips, vibration-damping rubber, hoses, wire insulation, and packing.

[0076] Regarding the solvent types listed in Table 4, "Digrim" is diethylene glycol dimethyl ether. "EDM" stands for diethylene glycol ethyl methyl ether. "EDGAC" is ethyl diglycol acetate, "Butyl cellosolve" is ethylene glycol n-butyl ether, "Metobuta" is 3-methoxybutanol, "Solfit" contains 3-methoxy-3-methyl-1-butanol. "Metoacetate" is methoxybutyl acetate, "PMA" stands for propylene glycol monomethyl ether acetate. "Cerosolve acetate" is ethylene glycol monoethyl ether acetate. "BDG" is diethylene glycol monobutyl ether. "PM" stands for propylene glycol monomethyl ether. "NMP" stands for N-methyl-2-pyrrolidone. "DMF" stands for dimethylformamide. "PG" stands for propylene glycol. "EG" stands for ethylene glycol This indicates.

[0077] [Table 1]

[0078] [Table 2]

[0079] [Table 3]

[0080] [Table 4]

[0081] [Example 7] When butyl acetate and N-methyl-2-pyrrolidone were mixed in a 1:1 volume ratio, the SP value of the resulting mixed solvent was confirmed to be 10.1. A rubber composition (solid content concentration of unmodified cellulose nanofibers 10 phr) was obtained in the same manner as in Example 1, except that the above mixed solvent was used as the solvent.

[0082] [Examples 8, 9, Comparative Examples 14-17] A rubber composition (solid content of unmodified cellulose nanofibers at 10 phr) was obtained in the same manner as in Example 7, except that a mixed solvent using the organic solvents shown in Table 5 was used.

[0083] The rubber hardness and dispersibility of unmodified cellulose nanofibers of the rubber compositions obtained in Examples 7-9 and Comparative Examples 14-17 were evaluated using the same procedure as in Example 1. The results obtained are shown in Table 5. As shown in Table 5, the rubber molded articles of Examples 7-9 had high rubber hardness and no coarse grains of unmodified cellulose nanofiber were observed in the rubber molded articles, whereas the rubber molded articles of Comparative Examples 14-17 had lower rubber hardness than Examples 1-6 and their dispersibility was rated as "△". Furthermore, upon palpation of the molded rubber products, it was found that the molded rubber products of Examples 7-9, like the molded rubber product of Example 1, were resistant to deformation and had a high modulus of elasticity. From the above, it can be seen that the rubber compositions obtained in Examples 7 to 9 can be suitably used in applications such as friction transmission belts, weatherstrips, vibration-damping rubber, hoses, wire insulation, and packing.

[0084] [Table 5]

[0085] [Reference example] The reference rubber composition was obtained by following the same procedure as in Example 3, except that EPDM was replaced with styrene-butadiene rubber (product name JSR 1502, manufactured by JSR). Next, 110 parts by weight of the reference rubber composition, 1.5 parts by weight of sulfur, 5 parts by weight of zinc oxide, 1 part by weight of stearic acid, 1 part by weight of thiraum-based vulcanization accelerator TMTD (Noxellar TT-P (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)), and 0.5 parts by weight of thiazole-based vulcanization accelerator MBT (Noxellar MP (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)) were mixed in a two-roll mixer and kneaded at 70-80°C for 10 minutes. Next, the two rolls were operated to produce sheets with a thickness of 2.2 to 2.6 mm. Next, a 2mm thick test specimen was obtained by hot pressing using a 2mm thick metal frame at 150°C for 20 minutes to perform a cross-linking treatment. The rubber hardness, dispersibility, mixing time, and overall evaluation of the obtained test specimens were performed based on Test Example 1. The results are shown in Table 6. As shown in Table 6, the reference example rubber molded product had high rubber hardness and no coarse grains of unmodified cellulose nanofiber were observed in the rubber molded product. Furthermore, when the reference example rubber molded product was examined by touch, it was difficult to deform and clearly had a high modulus of elasticity. Therefore, it can be concluded that the rubber composition obtained in the reference example can be suitably used in applications such as friction transmission belts, weatherstrips, vibration-damping rubber, hoses, wire insulation, and gaskets.

[0086] Table 6

Claims

1. In the presence of a water-soluble organic solvent with a boiling point between 150°C and 220°C and an SP value of 8.5 to 11, Rubber components including ethylene propylene diene rubber, A method for producing a cellulose nanofiber-containing rubber composition, comprising the step of kneading an unmodified cellulose nanofiber dispersion with the rubber composition.

2. A process of swelling a rubber component containing ethylene propylene diene rubber with a water-soluble organic solvent having a boiling point of 150°C to 220°C and an SP value of 8.5 to 11, and A process of kneading a swollen rubber component with an unmodified cellulose nanofiber dispersion. A manufacturing method according to claim 1, comprising:

3. A rubber component containing ethylene propylene diene rubber, which has been swollen with a water-soluble organic solvent having a boiling point of 150°C to 220°C and an SP value of 8.5 to 11, A water-soluble organic solvent having a boiling point of 150°C to 220°C and an SP value of 8.5 to 11, Unmodified cellulose nanofiber dispersion and The manufacturing method according to claim 1, comprising the step of kneading.

4. The manufacturing method according to any one of claims 1 to 3, wherein the water-soluble organic solvent having a boiling point of 150°C or higher and an SP value of 8.5 to 11 is one or more selected from the group consisting of alcohol-based solvents, ether-based solvents, and ester-based solvents.

5. The method for producing the product according to any one of claims 1 to 4, wherein the unmodified cellulose nanofiber dispersion is a dispersion of a water-soluble organic solvent having a boiling point of 150°C or higher and 220°C or lower and an SP value of 8.5 to 11.

6. A mixed solvent comprising a water-soluble organic solvent with an SP value of 10 or more and a non-water-soluble organic solvent with an SP value of 9 or less, wherein at least one of the water-soluble organic solvent and the non-water-soluble organic solvent has a boiling point of 150°C or more and 220°C or less, and the mixed solvent has an SP value of 8.5 to 11. Rubber components including ethylene propylene diene rubber, A method for producing a cellulose nanofiber-containing rubber composition, comprising the step of kneading an unmodified cellulose nanofiber dispersion with the rubber composition.

7. A step of swelling a rubber component containing ethylene propylene diene rubber with the mixed solvent, and A process of kneading a swollen rubber component with an unmodified cellulose nanofiber dispersion. The manufacturing method according to claim 6, comprising:

8. A rubber component containing ethylene propylene diene rubber, which has been swollen with the aforementioned mixed solvent, The aforementioned mixed solvent, Unmodified cellulose nanofiber dispersion and The manufacturing method according to claim 6, comprising the step of kneading.

9. The manufacturing method according to any one of claims 6 to 8, wherein the water-soluble organic solvent is N-methylpyrrolidone or 1-methoxy-2-propanol, and the non-water-soluble organic solvent is butyl acetate or methoxybutyl acetate.

10. The manufacturing method according to any one of claims 6 to 9, wherein the unmodified cellulose nanofiber dispersion is a dispersion of the mixed solvent.

11. The manufacturing method according to any one of claims 1 to 10, wherein the average fiber diameter of the unmodified cellulose nanofibers is 20 to 1000 nm.

12. The manufacturing method according to any one of claims 1 to 5, comprising the step of removing the water-soluble organic solvent from a rubber component that has been swollen with a water-soluble organic solvent having a boiling point of 150°C or higher and an SP value of 8.5 to 11, and in which unmodified cellulose nanofibers are dispersed, to a degree of 1% by weight or less.

13. The manufacturing method according to any one of claims 6 to 10, comprising the step of removing the mixed solvent from a rubber component that has been swollen with the mixed solvent and in which unmodified cellulose nanofibers are dispersed, so that the amount of the mixed solvent is 1% by weight or less.

14. The manufacturing method according to any one of claims 1 to 13, wherein the solid content concentration of unmodified cellulose nanofibers in the cellulose nanofiber-containing rubber composition is 3 to 30 phr.

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