JP2013018918A - Rubber composition, and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition having high hardness and tensile strength, having good processability, and excellent in the balance of physical properties, and to provide a method for manufacturing the same.SOLUTION: [1] The rubber composition is prepared by blending a cellulose fiber in a rubber, wherein the average fiber diameter of the cellulose fiber is 1 to 200 nm, and a cellulose constituting the cellulose fiber has a carboxyl group. [2] The method for manufacturing the rubber composition of [1] includes: a step (1) of mixing a rubber latex with a water dispersion of a cellulose fiber, and thereafter removing at least a part of water to thereby obtain a cellulose fiber/rubber composite; and a step (2) of mixing the obtained composite with a rubber.

Description

  The present invention relates to a rubber composition having an excellent balance between mechanical strength and processability, and a method for producing the same.

Although rubber compositions are widely used for industrial applications, the use conditions of molded products using rubber compositions are becoming more severe, and the development of high-performance rubber materials is an urgent need.
For example, in a rubber composition used in a pneumatic tire such as an automobile, a carbon black compounded product is widely used in order to increase strength, wear resistance, and the like. However, there is a limit to the reinforcing property, and when a rubber composition containing a large amount of carbon black is used for a tire, the durability decreases due to heat generation and the workability decreases due to an increase in the viscosity of the rubber composition. There's a problem. Attempts have also been made to replace part or all of the carbon black with silica-based fillers, but silica-based fillers have no affinity for organic rubber and are difficult to disperse uniformly. There is a problem that it tends to cause a decrease, and the viscosity of the unvulcanized rubber is also increased, so that the processability is deteriorated.
As described above, it has been difficult to obtain a rubber composition having excellent processability by lowering the viscosity of the unvulcanized rubber while further increasing the strength of the vulcanized rubber composition.

On the other hand, the rubber composition (patent document 1) which mix | blended the cellulose short fiber masterbatch with rubber | gum is also proposed. However, a composite of hydrophobic rubber and hydrophilic cellulose has poor dispersibility of the reinforcing material in the rubber and cannot exhibit sufficient durability and rigidity. Further, the reinforcing property of the cellulose fiber / rubber interface is not sufficient. For this reason, when the rubber is subjected to mechanical stress, the cellulose fiber is detached or peeled off, and sufficient strength and durability cannot be obtained. Even if attempts are made to improve the reinforcing properties by increasing the interface by refining the cellulose, sufficient strength and durability are not obtained even if the most refined microfibril cellulose is blended.
In view of this, various proposals have been made to further improve the affinity between the cellulose surface and rubber to enhance the reinforcement. For example, a rubber composition containing cellulose nanofibers and a dispersant (Patent Document 2), a rubber composition containing cellulose nanofibers and a silane coupling agent (Patent Document 3), and a rubber component containing —OH groups of cellulose fibers. In order to inhibit hydrogen bonding, a rubber composition containing cellulose nanofibers in which part or all of the —OH groups are masked with a masking agent (Patent Document 4), a rubber composition containing modified cellulose fibers (Patent Document 5) A vulcanized rubber composition (Patent Document 6) containing a rubber component and chemically modified microfibril cellulose has been proposed.

JP 2006-206864 A JP 2009-191197 A JP 2009-191198 A JP 2009-249449 A JP 2010-254925 A JP 2009-084564 A

However, the rubber compositions disclosed in Patent Documents 1 to 6 do not provide a rubber composition in which higher hardness / tensile strength and good workability, which have been required in recent years, are highly balanced.
An object of the present invention is to provide a rubber composition having high hardness and tensile strength and excellent workability and having a good balance of physical properties, and a method for producing the same.

The present inventors have found that by blending specific cellulose fibers with rubber, the hardness and tensile strength can be improved without degrading workability.
That is, the present invention provides the following [1] and [2].
[1] A rubber composition obtained by blending cellulose fibers with rubber, wherein the cellulose fibers have an average fiber diameter of 1 to 200 nm, and the cellulose constituting the cellulose fibers has a carboxy group. Composition.
[2] The method for producing a rubber composition according to the above [1], comprising the following steps (1) and (2).
Step (1): Step of mixing a rubber latex and an aqueous dispersion of cellulose fibers and then removing at least a portion of water to obtain a cellulose fiber / rubber composite Step (2): obtained in the step (1) Of mixing the obtained composite and rubber

  ADVANTAGE OF THE INVENTION According to this invention, it can provide the rubber composition which has high hardness and tensile strength, and has the outstanding physical property balance which has favorable workability, and its manufacturing method.

[Rubber composition]
The rubber composition of the present invention is a rubber composition obtained by blending cellulose fibers with rubber, and the average fiber diameter of the cellulose fibers is 1 to 200 nm, and the cellulose constituting the cellulose fibers has a carboxy group. It is characterized by that.
Hereinafter, the manufacturing method of rubber | gum, a cellulose fiber, and a rubber composition is demonstrated.

[Rubber]
The rubber used in the present invention is not particularly limited, but diene rubber is preferable from the viewpoint of reinforcement.
Diene rubbers include natural rubber (NR), polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), butyl rubber (IIR), butadiene-acrylonitrile copolymer rubber (NBR). ), And modified natural rubber. Examples of the modified natural rubber include epoxidized natural rubber and hydrogenated natural rubber.
Among these, natural rubber (NR), polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-butadiene copolymer rubber (from the viewpoint of achieving both good processability and high impact resilience of the rubber composition ( One or more selected from SBR) is preferable, and one or more selected from natural rubber (NR), styrene-butadiene copolymer rubber (SBR) and modified natural rubber is more preferable.
The diene rubbers can be used alone or in combination of two or more.

[Cellulose fiber]
The cellulose fiber used in the present invention has an average fiber diameter of 1 to 200 nm, and the cellulose constituting the cellulose fiber has a carboxy group.
The cellulose fibers used in the present invention are preferably those obtained by separating natural cellulose fibers into their constituent units, microfibrils (crystallinity of about 50 to 95%, consisting of 30 to 100 cellulose molecules). The cellulose fibers are not necessarily separated into units of microfibrils.
The shape of the microfibril varies depending on the raw material, but many natural cellulose fibers have a rectangular cross-sectional structure in which dozens of cellulose molecular chains are collected and crystallized. For example, microfibrils in the cell walls of higher plants have a square cross-sectional structure in which 6 × 6 cellulose molecular chains are gathered. For the fiber diameter of the cellulose fiber used in the present invention, the height of the cellulose fiber obtained by the atomic force microscope image described in the examples is used as the fiber diameter for convenience.

The average fiber diameter of the cellulose fiber used by this invention is 1-200 nm, Preferably it is 1-100 nm, More preferably, it is 1-50 nm, More preferably, it is 1-20 nm, More preferably, it is 1-10 nm. By using cellulose fibers having such an average fiber diameter, the tensile strength and hardness of rubber can be effectively increased.
The length of the cellulose fiber is preferably 10 to 1000, more preferably 10 to 500, and still more preferably 100 to 350 when the fiber length is represented by an average aspect ratio (fiber length / fiber diameter).
A specific method for measuring the average fiber diameter and the average aspect ratio is based on the method described in the examples.

The cellulose fiber is preferably obtained by subjecting natural cellulose to an oxidation reaction using an N-oxyl compound as a catalyst. The cellulose which comprises a cellulose fiber has a carboxy group, The carboxy group content becomes like this. Preferably it is 0.1-3.0 mmol / g, More preferably, it is 0.4-2 mmol / g, More preferably It is 0.6-1.8 mmol / g, More preferably, it is 0.6-1.6 mmol / g. By using such cellulose fibers, the above-mentioned fine fiber diameter can be achieved more easily, and the hardness and tensile strength can be increased while maintaining the processability of rubber.
The carboxy group content is measured by the method described in the examples.

  In addition, the cellulose fiber derivative obtained by subjecting the cellulose fiber to a modification treatment is also included in the cellulose fiber of the present invention as long as the cellulose has a carboxy group. In the cellulose fiber derivative, since the cellulose has a carboxy group, a fine fiber diameter can be easily achieved. In addition, either the cellulose fiber obtained by making natural cellulose make an oxidation reaction using N-oxyl compound as a catalyst, and the derivative | guide_body of this cellulose fiber can also be used, and both can also be used together.

<Manufacture of cellulose fiber>
In the process of biosynthesis of natural cellulose, normally, nanofibers called microfibrils are first formed, and these form a multi-bundle to construct a higher-order solid structure. The cellulose fiber used in the present invention is preferably oxidized using an N-oxyl compound as a catalyst in order to weaken the hydrogen bond between the surfaces, which is the driving force of strong cohesive force between microfibrils in the naturally derived cellulose solid raw material. By making it react, it can obtain by oxidizing a part of hydroxyl group on the surface of microfibril and converting it into a carboxy group.
Therefore, the one where there is much sum total (carboxy group content) of the amount of carboxy groups which exists in a cellulose can exist stably as a finer fiber diameter. Further, in water, an electric repulsive force is generated, so that the tendency of the microfibrils to break apart without maintaining aggregation is increased, and the dispersion stability of the nanofibers is further increased.

The cellulose fibers used in the present invention can be efficiently produced according to the methods of JP 2008-1728 A and International Publication No. 2009/069641 Pamphlet.
Step (i): Step of oxidizing natural cellulose fibers to obtain reactant fibers in a reaction solution containing an N-oxyl compound and an oxidizing agent (oxidation step)
Step (ii): Dispersing the obtained reactant fiber in a medium and refining (Refining step)

(Process (i): Oxidation process)
In step (i), first, a slurry in which natural cellulose fibers are dispersed in water is prepared. The slurry is obtained by adding about 10 to 1000 times (mass basis) of water to the natural cellulose fiber (absolute dry basis) as a raw material, and processing with a mixer or the like.
Examples of natural cellulose fibers include wood pulp such as softwood pulp and hardwood pulp; cotton pulp such as cotton linter and cotton lint; non-wood pulp such as straw pulp and bagasse pulp; and bacterial cellulose. These can be used alone or in combination of two or more.
The natural cellulose fiber may be subjected to a treatment for increasing the surface area such as beating.
The average fiber diameter of the natural cellulose fiber is not particularly limited, but is preferably 5 to 100 μm and more preferably 10 to 50 μm from the viewpoint of the reactivity of the N-oxyl compound. The natural cellulose fiber average fiber diameter can be adjusted using a sieve or the like.

An N-oxyl compound is used as the oxidation catalyst in step (i).
The N-oxyl compound is a compound having at least one N-oxyl structure in the molecule, and is preferably an N-oxide compound of piperidines.
Preferable examples of the N-oxyl compound include 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO), 4-acetamido-TEMPO, 4-carboxy-TEMPO, 4-phosphonooxy- TEMPO, 4-hydroxy-TEMPO, 4-alkoxy-TEMPO and the like can be mentioned, but TEMPO and 4-acetamido-TEMPO are more preferable.
The N-oxyl compound may be added in a catalytic amount, and is usually 0.1 to 10% by mass, preferably 0.2 to 5% by mass, more preferably based on natural cellulose fiber (absolute dry basis) used as a raw material. Is 0.3-3 mass%.

In step (i), an oxidizing agent is used. Examples of the oxidizing agent include hypohalous acid such as hypochlorous acid and hypobromite, or salts such as alkali metal salts thereof, halous acid or salts thereof, perhalogen acids or salts thereof, hydrogen peroxide, peroxygen salts, and the like. Organic acids and the like are preferred.
The amount of the oxidizing agent used is usually in the range of preferably 1 to 100% by mass with respect to the natural cellulose fiber (absolute dry standard) used as a raw material.
A co-oxidant (for example, an alkali metal bromide such as sodium bromide) can be used in combination. The amount of the co-oxidant used is usually in the range of preferably 1 to 30% by mass with respect to the natural cellulose fiber (absolute dry standard) used as a raw material.

More specifically, hypohalous acid or an alkali metal salt thereof and an alkali metal bromide are reacted as an oxidizing agent in an alkaline reaction solution to oxidize natural cellulose fibers to obtain reactant fibers. In this case, the pH of the reaction solution is preferably 9-12.
Alternatively, the above-described halogenous acid or a salt thereof and hypohalous acid or an alkali metal salt thereof are reacted in a neutral or acidic reaction solution as an oxidizing agent to oxidize natural cellulose fibers to form reactant fibers. obtain. In this case, the pH of the reaction solution is preferably 4-7.
The temperature of the oxidation treatment (temperature of the reaction solution) is preferably 1 to 50 ° C., but the reaction is possible at room temperature, and temperature control is not particularly required. The reaction time is preferably 1 to 240 minutes.

After the completion of the step (i), a purification step is performed before the step (ii), and impurities other than the reactant fibers and water contained in the reaction solution such as unreacted oxidant and various by-products are removed. Can be removed. Since the reaction product fibers are not normally dispersed evenly at the nanofiber unit at this stage, in the purification step, for example, a purification method in which water washing and filtration are repeated can be performed. The purification apparatus used in that case is not particularly limited.
The purified reaction product fiber thus obtained is usually sent to step (ii) in a state of being impregnated with an appropriate amount of water. However, if necessary, it may be dried to form a fiber or powder.

(Process (ii): Refinement process)
In step (ii), the reaction product fiber obtained in step (i) is dispersed in a medium and refined. By performing this refinement treatment, cellulose fibers having an average fiber diameter and an average aspect ratio in the above ranges can be obtained.
In step (ii), water is usually preferable as the dispersion medium. However, in addition to water, alcohols such as ethanol that are soluble in water, ethers, ketones, and other organic solvents or mixtures thereof, depending on the purpose. Can also be used.
Examples of the disperser used for the refining treatment include a disaggregator, a beater, a low pressure homogenizer, a high pressure homogenizer, a grinder, a cutter mill, a ball mill, a jet mill, a single screw extruder, a twin screw extruder, an ultrasonic stirrer, and a household. Juicer mixer for use. The solid content concentration of the reactant fiber in the miniaturization treatment is preferably 50% by mass or less.

  The cellulose fiber obtained in the step (ii) is adjusted to a solid content concentration as necessary, and is in a dispersed liquid form (a visually colorless transparent or opaque liquid) or a dried powder form (however, It is a powder form in which cellulose fibers are aggregated and does not mean cellulose particles). When the dispersion liquid is used, only water may be used as a dispersion medium, or a mixed solvent of water and the above organic solvent, surfactant, acid, base, or the like may be used.

Through the above steps (i) and (ii), the hydroxyl group at the C6 position of the cellulose structural unit is selectively oxidized to the carboxy group via the aldehyde group by oxidation of the N-oxyl compound, and the carboxy group content is preferable. Consists of 0.1-3.0 mmol / g cellulose, and it is possible to easily obtain refined highly crystalline cellulose fibers having an average fiber diameter of 1-200 nm.
This highly crystalline cellulose fiber preferably has a cellulose I-type crystal structure. This means that the cellulose fiber used in the present invention is a fiber that is refined by surface oxidation of a naturally-derived cellulose raw material having an I-type crystal structure. In other words, natural cellulose fiber has a high-order solid structure formed by multi-bundles of microfibrils produced in the process of biosynthesis, and strong cohesion between the microfibrils (hydrogen bonding between surfaces). Is weakened by the introduction of an aldehyde group or a carboxy group by the oxidation treatment in the step (i), and further by the refinement treatment in the step (ii), it is preferably separated into one microfibril. Cellulose fibers can be obtained.
And by adjusting the oxidation treatment conditions in the step (i), the polarity can be changed by adjusting the carboxy group content within a predetermined range. The fiber diameter, average fiber length, average aspect ratio, etc. can be controlled.

(Modification treatment of cellulose fiber)
The cellulose fibers thus obtained can be modified as necessary. Cellulose fiber modification treatment includes esterification or amidation of carboxy group of cellulose fiber, acylation of hydroxyl group, urethanization, etherification, reaction of silyl group, oxirane group, oxetane group, thiirane group, thietane group, etc. And a method of obtaining a cellulose fiber derivative by reacting a compound having a functional group with a hydroxyl group. For the purpose of improving the affinity with rubber, modification with a diene polymer or modification with a sulfide silane coupling agent can also be performed.
The esterification or amidation of the carboxy group of the cellulose fiber can be performed by reacting with an alcohol or amide having an alkyl group. Here, as the alkyl group, methyl group, ethyl group, propyl group, 2-propyl group, butyl group, 2-butyl group, tert-butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, Examples include decyl group, undecyl group, dodecyl group, myristyl group, palmityl group, stearyl group and the like.

The acylation, urethanization or etherification of the hydroxyl group of the cellulose fiber can be performed by reacting with an acid or halide having an acyl group, a compound having an isocyanate group, or an alcohol having an alkyl group.
Here, as the acyl group, acetyl group, acryloyl group, methacryloyl group, propionyl group, propioyl group, butyryl group, 2-butyryl group, pentanoyl group, hexanoyl group, heptanoyl group, octanoyl group, nonanoyl group, decanoyl group, undecanoyl Group, dodecanoyl group, myristoyl group, palmitoyl group, stearoyl group, pivaloyl group, benzoyl group, naphthoyl group, nicotinoyl group, isonicotinoyl group, furoyl group, cinnamoyl group and the like.
In addition, examples of the isocyanate group include isocyanate groups such as a 2-methacryloyloxyethyl isocyanoyl group, and examples of the alkyl group include those described above.
The cellulose fiber derivative obtained by such various modification treatments may be improved in dispersibility in the rubber composition due to the change in hydrophilicity / hydrophobicity with respect to the unmodified cellulose fiber, It can be arbitrarily selected depending on the rubber composition to be used.

[Rubber composition]
The rubber composition of the present invention is formed by blending the cellulose fiber with at least the rubber. Although there is no restriction | limiting in particular in the compounding quantity of a cellulose fiber, It is preferable to mix | blend a cellulose fiber 0.1-100 mass parts with respect to 100 mass parts of rubber | gum from a viewpoint of hardness, tensile strength, and workability, 0.5 More preferably, 80 parts by mass is added, and 1-60 parts by mass is more preferable. If the blending amount of the cellulose fiber is 0.1 parts by mass or more with respect to 100 parts by mass of the rubber, the strength, hardness and tensile strength of the rubber composition can be efficiently improved. It is easy to disperse cellulose fibers in the rubber composition and maintain the processability of the rubber composition.
The content of the cellulose fiber in the rubber composition of the present invention is preferably 0.02 to 50% by mass, more preferably 0.05 to 20% by mass, from the viewpoints of hardness, tensile strength and processability. 1-10 mass% is more preferable.
Moreover, the content of the rubber in the rubber composition of the present invention is preferably 25 to 90% by mass, more preferably 30 to 80% by mass, and 35 to 75% by mass from the viewpoints of hardness, tensile strength, and processability. Further preferred.
In addition, the rubber composition of this invention can mix | blend the additive mentioned later.

[Method for producing rubber composition]
Although there is no restriction | limiting in particular in the manufacturing method of the rubber composition of this invention, According to the method which has the following process (1) and (2), it can manufacture efficiently.
Step (1): Step of mixing a rubber latex and an aqueous dispersion of cellulose fibers and then removing at least a portion of water to obtain a cellulose fiber / rubber composite Step (2): obtained in the step (1) Of mixing the obtained composite and rubber

Although there is no restriction | limiting in particular as rubber latex in a process (1), Diene type rubber latex, such as the said rubber | gum in a latex form, especially natural rubber latex, BR latex, SBR latex, NBR latex, these modified latex, etc. is used suitably. . From the viewpoint of not affecting the physical properties of the rubber composition to be obtained, a latex having the same rubber component as the rubber type used in the step (2) is preferable, and a copolymer type rubber latex is used in the step (2). Those having the same mass composition ratio as the rubber component are preferred.
The mixing mass ratio (dry mass ratio) of cellulose fiber and rubber latex is preferably 10 to 500 parts by mass of rubber latex and more preferably 20 to 300 parts by mass with respect to 100 parts by mass of cellulose fiber. preferable.
As a mixing method, a mixing method using a homogenizer is preferable from the viewpoint of promoting dispersion by applying a high shearing force and pressure, but a method such as a propeller type stirring device, a rotary stirring device, and an electromagnetic stirring device can also be used.
Next, the obtained rubber mixture is dried, and at least a part of water is removed to obtain a cellulose fiber / rubber composite (complex latex). Drying does not need to be performed until the water is completely removed, and may contain water as long as the object of the present invention is not impaired. As a drying method, a method of removing water with a water squeeze roll and then drying in a heating oven, a method of drying by a shock wave by pulse combustion, a freeze drying method, a spray drying method, or the like can be employed.

In step (2), the composite (composite latex) obtained in step (1) and rubber are mixed. The temperature in that case is 10-300 degreeC normally, Preferably it is 20-200 degreeC.
As the mixing method in step (2), the same method as the mixing method in step (1) can be used.
The mixed mass ratio (dry mass ratio) of the composite obtained in the step (1) and the rubber is preferably 0.1 to 100 parts by mass, more preferably 0.1 to 100 parts by mass with respect to 100 parts by mass of the rubber. It is 5-80 mass parts, More preferably, it is 1-60 mass parts.
It is preferable to use 0.2 to 200 parts by mass, more preferably 1 to 160 parts by mass, and still more preferably 2 to 120 parts by mass of the cellulose fiber / rubber composite with respect to 100 parts by mass of rubber.
In step (2), an additive described later is dispersed in advance in the composite obtained in step (1), and then mixed with rubber.

<Additive of rubber composition>
The rubber composition of the present invention includes, in addition to the cellulose fibers, reinforcing fillers such as carbon black and silica that are usually used in the rubber industry, various chemicals, as long as the object of the present invention is not impaired. , For example, vulcanizing agents, vulcanization accelerators, anti-aging agents, scorch preventing agents, zinc white, stearic acid, process oil, vegetable oils and fats, plasticizers, and other additives added to general rubber Can be blended in conventional conventional amounts.

(Reinforcing filler)
Carbon black that can be used is not particularly limited, but from the viewpoint of achieving both mechanical strength and high resilience of the resulting rubber composition, the nitrogen adsorption specific surface area (N ₂ SA; measured in accordance with JIS K6217) is 20 to is preferably a 90m ² / g, it is more preferred 25~90m ² / g. Examples of such carbon black include HAF, FEF, GPF, SRF, N339, IISAF-HS (N285), and the like. The compounding amount of carbon black is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, and still more preferably 70 parts by mass or less with respect to 100 parts by mass of rubber, particularly diene rubber.
The silica that can be used is not particularly limited, and examples thereof include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, and the like. Is preferred. The amount of silka added is preferably 80 parts by mass or less, more preferably 60 parts by mass or less, and still more preferably 50 parts by mass or less with respect to 100 parts by mass of rubber, particularly diene rubber.

(Silane coupling agent)
In the rubber composition of the present invention, when silica is used as the reinforcing filler, a silane coupling agent can be blended for the purpose of further improving the reinforcing property. The silane coupling agent that can be used is not particularly limited, and examples thereof include sulfide, mercapto, vinyl, amino, glycidoxy, nitro, and chloro silane coupling agents. Of these, sulfide-based silane coupling agents are more preferred.
Specific examples of the sulfide-based silane coupling agent include bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (4-triethoxysilylbutyl) tetrasulfide, 3- Trimethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropylbenzothiazole tetrasulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, 3-octanoylthio-1-propyltri Examples include methoxysilane and 3-octanoylthio-1-propyltriethoxysilane.
Although the compounding quantity of a silane coupling agent changes with kinds etc. of a silane coupling agent, Preferably it is 1-20 mass% with respect to a silica, More preferably, it selects in the range of 5-15 mass%.

(Vulcanizing agent, vulcanization accelerator)
As the vulcanizing agent, organic peroxides and sulfur vulcanizing agents can be used. Examples of the organic peroxide include dicumyl peroxide, t-butylperoxybenzene, di-t-butylperoxy-diisopropylbenzene, and examples of the sulfur-based vulcanizing agent include sulfur and morpholine disulfide. .
Among these, a sulfur-based vulcanizing agent is preferable, and sulfur is particularly preferable. As for the amount used, from the viewpoint of ensuring impact resilience and mechanical strength, the sulfur content (the total amount of sulfur and sulfur donors in the sulfur donor) with respect to 100 parts by mass of rubber, particularly diene rubber, is preferably 0.00. 1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, is preferably blended.
Examples of the vulcanization accelerator that can be used include thiazoles such as 2-mercaptobenzothiazole (MTB), di-2-dibenzothiazyl disulfide (MBTS), and N-cyclohexyl-2-benzothiazylsulfenamide (CBS). System; N-cyclohexyl-2-benzothiazylsulfenamide (CBS), N-tert-butyl-2-benzothiazylsulfenamide (TBBS), N-oxydiethylene-2-benzothiazolesulfenamide, etc. Sulfenamide-based; guanidine-based vulcanization accelerators such as diphenylguanidine (DPG).
The amount of use is preferably 0.1 to 5.0 parts by mass, more preferably 0.2 to 3.0 parts by mass with respect to 100 parts by mass of rubber, particularly diene rubber.

(Other additives)
Process oils used as softeners include, for example, paraffinic, naphthenic, aromatic, etc. For applications that emphasize tensile strength and wear resistance, aromatics emphasize hysteresis loss and low-temperature characteristics. For such applications, naphthenic or paraffinic are used. The amount of use is preferably 0 to 100 parts by weight, more preferably 80 parts by weight or less, and still more preferably 50 parts by weight with respect to 100 parts by weight of rubber, particularly diene rubber, from the viewpoint of tensile strength and low heat build-up. It is below mass parts.
Antiaging agents that can be used include, for example, N-isopropyl-N′-phenyl-p-phenylenediamine, N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine, and 6-ethoxy-2. 2,4-trimethyl-1,2-dihydroquinoline, high-temperature condensate of diphenylamine and acetone, and the like. The amount used is preferably 0.1 to 6.0 parts by mass, and more preferably 0.3 to 5.0 parts by mass with respect to 100 parts by mass of rubber, particularly diene rubber.

  In addition, the rubber composition of the present invention can be used by kneading by a known method to obtain a composition and vulcanizing or crosslinking. For example, it can be kneaded using a kneader such as an open kneader such as a roll or a closed kneader such as a Banbury mixer, vulcanized after molding, and applied to various rubber products. For example, it can be used for tire applications, anti-vibration rubber, fenders, belts, hoses and other industrial products, but especially as a tread rubber for fuel-efficient tires, large tires, and high-performance tires. Preferably used.

Hereinafter, in Examples and Comparative Examples, measurement and evaluation of each physical property were performed by the following methods.
<Measurement of average fiber diameter of cellulose fiber>
An aqueous dispersion of cellulose fibers having a solid content concentration of 0.001% by mass is prepared. An observation sample is obtained by dripping this dispersion liquid onto mica (mica) and drying it. The fiber height of the cellulose fiber in the observation sample is measured using an atomic force microscope (SII Nano Technology Co., Ltd., NanoNaVi IIe, SPA400, probe uses SI-DF40Al manufactured by the same company). In a microscopic image in which cellulose fibers can be confirmed, 50 cellulose fibers are extracted, and an average fiber diameter is calculated from their fiber heights.

<Measurement of average aspect ratio of cellulose fiber>
It calculates from the viscosity of the dispersion liquid (The density | concentration of a cellulose fiber 0.005-0.04 mass%) prepared by adding water to a cellulose fiber. The viscosity of the dispersion is measured at 20 ° C. using a rheometer (MCR, DG42 (double cylinder), manufactured by PHYSICA).
From the relationship between the mass concentration of the cellulose fibers in the dispersion and the specific viscosity of the dispersion with respect to water, the aspect ratio of the cellulose fibers is calculated back using the following formula (1) to obtain the average aspect ratio. Formula (1) is the viscosity formula (8.138) of the rigid rod-like molecule described in The Theory of Polymer Dynamics, M.DOI and DFEDWARDS, CLARENDON PRESS · OXFORD, 1986, p312 and Lb ² × ρ = M / N relationship wherein the _a, L is the fiber length, b is the fiber width (cellulose fiber cross-section is a square), [rho is the cellulose fiber concentration (kg / m ^3), M is the molecular weight, N _a is Avogadro's number Derived from]. In the viscosity formula (8.138), rigid rod-like molecule = cellulose fiber. In Formula (1), η _SP is the specific viscosity, π is the circumference ratio, ln is the natural logarithm, P is the aspect ratio (L / b), γ = 0.8, ρ _S is the density of the dispersion medium (kg / M ³ ), ρ ₀ represents the density of cellulose crystals (kg / m ³ ), and C represents the mass concentration of cellulose (C = ρ / ρ _S ).

<Measurement of carboxy group content of cellulose fiber>
Take a cellulose fiber with a dry mass of 0.5 g in a 100 ml beaker, add ion-exchanged water to make a total of 55 ml, add 5 ml of 0.01 M sodium chloride aqueous solution to prepare a dispersion, and until the cellulose fibers are sufficiently dispersed The dispersion is stirred. 0.1 M hydrochloric acid is added to this dispersion to adjust the pH to 2.5-3. Using an automatic titrator (AUT-50, manufactured by Toa DKK Co., Ltd.), 0.05M aqueous sodium hydroxide solution is dropped into the dispersion under a condition of a waiting time of 60 seconds. The conductivity and pH values are measured every minute, and the measurement is continued until the pH is about 11 to obtain a conductivity curve. From this conductivity curve, the sodium hydroxide titration amount is obtained, and the carboxy group content of the cellulose fiber is calculated by the following formula.
Carboxy group content (mmol / g) = sodium hydroxide titration (ml) × concentration of aqueous sodium hydroxide (0.05M) / mass of cellulose fiber (0.5 g)

<Measurement of Mooney viscosity>
Based on JIS K6300-1994, it measured using the measuring apparatus made by Ueshima Seisakusho.
Using a L-shaped rotor and a square groove die, the kneaded unvulcanized rubber sample was preheated at 100 ° C. for 1 minute, and then the rotation of the rotor was started. The value after 4 minutes was defined as ML _{1 + 4} . The ML _{1 + 4} value is shown as an index relative to the control (Comparative Example 1). The result was expressed as an index with the value of Comparative Example 1 as 100. It shows that it is excellent in workability, so that this value is small.
<Measurement of hardness>
In accordance with JIS K-6301, the hardness was measured using a JIS A type hardness tester. It shows that it is so hard that this value is large.
<Measurement of tensile stress>
In accordance with JIS-6301, a rubber sheet is punched into a predetermined dumbbell shape, and a vulcanized rubber tensile test is performed. The tensile stress at 50%, 100%, and 300% elongation is 50% modulus, 100% modulus, and 300% modulus. Was measured respectively. The measured values of Example 1 and Comparative Examples 2 and 3 were set to 100 for Comparative Example 1, Example 2 and Comparative Examples 5 and 6 were set to 100 for Comparative Example 4, and Example 3 and Comparative Example 8 9 shows the value of Comparative Example 7 as 100, and the value of each Example as its index display. The larger this value, the stronger the tensile stress.

Production Example 1 (Production of Cellulose Fiber / SBR Composite)
(1) Production of cellulose fiber First, the following raw materials were prepared.
Natural fiber: Bleached kraft pulp of conifers (Fletcher Challenge Canada, trade name “Machenzie”, CSF 650 ml)
TEMPO: Commercial product (ALDRICH, Free radical, 98% by mass)
Sodium hypochlorite: Commercial product (manufactured by Wako Pure Chemical Industries, Ltd., Cl: 5%)
Sodium bromide: Commercial product (Wako Pure Chemical Industries, Ltd.)
Next, after 100 g of bleached kraft pulp was sufficiently stirred with 9900 g of ion-exchanged water, TEMPO 1.25 wt%, sodium bromide 12.5 wt%, sodium hypochlorite 28 4% by weight was added in this order at 20 ° C. Using a pH stat, 0.5M sodium hydroxide was added dropwise to maintain the pH at 10.5, and an oxidation reaction was performed. After performing the oxidation reaction for 120 minutes, dropping was stopped to obtain oxidized pulp. The oxidized pulp was thoroughly washed with ion-exchanged water and then dehydrated. Thereafter, the oxidized pulp was adjusted to 1% by mass with ion-exchanged water, and refined twice at 245 MPa using a high-pressure homogenizer (Starburst Lab HJP-25005, manufactured by Sugino Machine Co., Ltd.). An aqueous dispersion of fibers was obtained. The solid content concentration of the dispersion was 1% by mass.
The average fiber diameter of the obtained cellulose fibers was 3.3 nm, the average aspect ratio was 225, and the carboxy group content was 1.2 mmol / g.

(2) Preparation of Cellulose Fiber / SBR Composite SBR latex (manufactured by Zeon Corporation, trade name: Nipol LX119) was prepared. The resin concentration of SBR latex was 50% by mass, the shape of the resin particles was spherical, and the average particle size was 50 nm.
3000 g of the cellulose fiber dispersion obtained in the above (1) and 60 g of the SBR latex prepared above are poured into a 5000 ml polyethylene container, and 3000 rpm, using a disperser (laboratory, manufactured by Primix Co., Ltd.). The composite latex was obtained by mixing for 60 minutes.
This composite latex was poured into polypropylene trays (inner dimensions 280 × 190 × 34 mm) in 800 g increments and allowed to air dry in a 23 ° C., 50% RH environment for 1 week to obtain a cellulose fiber / SBR composite. The blending amount of the cellulose fiber calculated from the charged amount at the time of preparing the composite latex was 50% by mass.

Production Example 2 (Production of microfibril cellulose / SBR composite)
In place of the aqueous dispersion of cellulose fibers obtained in Production Example 1, microfibril cellulose (trade name: Celish FD-200L, manufactured by Daicel Chemical Industries, Ltd.) was adjusted to a solid content of 1% by mass with ion-exchanged water. A microfibril cellulose / SBR composite was obtained in the same manner as in Production Example 1 except that the dispersion was used.
Production Example 3 (Production of dried SBR latex)
A dried SBR latex containing no cellulose fibers was obtained by the same method as in Production Example 1 (2) except that (1) was omitted in Production Example 1 and the cellulose fiber dispersion of (2) was removed.

Examples 1-3 and Comparative Examples 1-9
A rubber composition was produced using the cellulose / SBR composite obtained in Production Example 1 or 2.
In the compounding composition shown in Table 1, the components other than the vulcanization accelerator and sulfur are kneaded for 3 to 5 minutes with a 1.7 liter closed mixer and released when the temperature reaches 165 ° C. to give a rubber composition. Obtained. Again, the rubber composition was similarly mixed in the same mixer and released when the temperature reached 165 ° C. Finally, a vulcanization accelerator and sulfur were added to the rubber composition and kneaded to obtain an unvulcanized rubber composition.
The obtained unvulcanized rubber composition was vulcanized at 160 ° C. for 16 minutes in a 15 × 15 × 0.2 cm mold to prepare a vulcanized rubber sheet, and its physical properties were evaluated. The results are shown in Table 1.

The details of each component shown in Table 1 are as follows.
* 1: Solution-polymerized styrene-butadiene rubber, manufactured by Asahi Kasei Chemicals Corporation, trade name: Toughden 2830, Oil Exhibition 37.5%
* 2: Cellulose fiber composite obtained in Production Example 1 * 3: Microfibril cellulose composite obtained in Production Example 2 * 4: Dry SBR latex obtained in Production Example 3 * 5: Tokai Carbon Co., Ltd. Product name: Seest 3
* 6: Tosoh Silica Co., Ltd., precipitated silica (white carbon), product name: Nip Seal AQ
* 7: Degussa, product name: Si69, bis (3-triethoxysilylpropyl) tetrasulfide * 8: Kao Corporation, product name: LUNAC S-70V
* 9: Zodo Chemical Industry Co., Ltd., 3 types of zinc oxide * 10: Ouchi Shinsei Chemical Industry Co., Ltd., guanidine vulcanization accelerator, Product Name: Noxeller D, 1,3-diphenylguanidine (DPG)
* 11: Ouchi Shinsei Chemical Co., Ltd., thiazole vulcanization accelerator, product name: Noxeller DM, di-2-benzothiazyl disulfide (MBTS)
* 12: Sanshin Chemical Industry Co., Ltd., sulfenamide vulcanization accelerator, trade name: Sunseller NS, N-tert-butyl-2-benzothiazylsulfenamide (TBBS)
* 13: Tsurumi Chemical Industries, Ltd.

From Table 1, it can be seen that the rubber compositions of Examples 1 to 3 have higher hardness and tensile strength, lower Mooney viscosity and excellent workability than the rubber compositions of Comparative Examples 1 to 9.
Comparison using Example 1 and Comparative Examples 2 and 3, Example 2 and Comparative Examples 5 and 6, and Example 3 and Comparative Examples 8 and 99 using conventional carbon black and microfibril cellulose composites It can be seen that the rubber compositions of Examples 1 to 3 have significantly higher hardness and tensile strength than the rubber compositions of Examples.

The rubber composition of the present invention has high hardness and tensile strength, and is excellent in a physical property balance having good processability. Therefore, the rubber composition of the present invention is, for example, as a rubber composition for pneumatic tires, particularly for tire treads, base treads, carcass coats, sidewalls, belt coats, beat fillers, inner liners, etc. Useful as. In addition, it is useful as a rubber member that requires high hardness and strength, such as a seismic isolation rubber.
In particular, a pneumatic tire using the rubber composition of the present invention for a tread has excellent resilience, low rolling resistance and excellent fuel efficiency.

Claims (8)

  A rubber composition obtained by blending cellulose fibers with rubber, wherein the cellulose fibers have an average fiber diameter of 1 to 200 nm, and the cellulose constituting the cellulose fibers has a carboxy group.   The rubber composition according to claim 1, wherein a content of carboxy group of cellulose constituting the cellulose fiber is 0.1 to 3.0 mmol / g.   The rubber composition according to claim 1 or 2, wherein the cellulose fiber is obtained by subjecting natural cellulose to an oxidation reaction using an N-oxyl compound as a catalyst.   The rubber composition according to any one of claims 1 to 3, wherein the rubber is a diene rubber.   The rubber composition according to any one of claims 1 to 4, wherein 0.1 to 100 parts by mass of cellulose fiber is blended with 100 parts by mass of rubber.   Furthermore, the rubber composition in any one of Claims 1-5 containing an inorganic filler.   Furthermore, the rubber composition in any one of Claims 1-6 containing a silane coupling agent. The manufacturing method of the rubber composition in any one of Claims 1-7 which has the following process (1) and (2).
Step (1): Step of mixing a rubber latex and an aqueous dispersion of cellulose fibers and then removing at least a portion of water to obtain a cellulose fiber / rubber composite Step (2): obtained in the step (1) Of mixing the obtained composite and rubber