JP7044300B2 - Rubber composition and method for producing rubber composition - Google Patents

Description

The present invention relates to a rubber composition using cellulose nanofibers and a method for producing a rubber composition using cellulose nanofibers.

In recent years, attention has been paid to cellulose nanofibers obtained by defibrating natural cellulose fibers into nano-sized fibers. Natural cellulose fiber is a biomass made from pulp such as wood, and it is expected that the environmental load will be reduced by effectively using it.

A rubber composition containing cellulose nanofibers in a defibrated state and a method for producing the rubber composition have been proposed (Patent Document 1). The rubber composition is reinforced by dispersing cellulose nanofibers in a defibrated state, and is excellent in rigidity, strength, and fatigue resistance.

Japanese Unexamined Patent Publication No. 2015-98576

An object of the present invention is to provide a rubber composition containing cellulose nanofibers in a defibrated state, and in particular, to provide a rubber composition having improved tensile strength. Another object of the present invention is to provide a method for producing a rubber composition in which cellulose nanofibers are deflated, and in particular, a method for producing a rubber composition having improved tensile strength.

The present invention has been made to solve at least a part of the above-mentioned problems, and can be realized as the following aspects or application examples.

[Application example 1]
The method for producing the rubber composition according to this application example is as follows.
A mixing step of mixing an aqueous dispersion containing cellulose nanofibers having an average fiber length of 200 nm to 310 nm and an average fiber width of 2 nm to 5 nm with a rubber latex to obtain a first mixture.
A drying step of drying the first mixture to obtain a second mixture, and
A dispersion step of thinly passing the second mixture through an open roll to obtain a rubber composition, and a dispersion step.
Including
The aqueous dispersion contains 0.1% by mass to 10% by mass of cellulose nanofibers.
The aqueous dispersion has a viscosity of 1 mPa · s to 100 mPa · s measured at 20 ° C. and 60 rpm using a B-type viscometer .
The rubber latex includes natural rubber latex, styrene-butadiene rubber latex, butadiene rubber latex, methylmethacrylate-butadiene rubber latex, 2-vinylpyridine-styrene-butadiene rubber latex, acrylonitrile-butadiene rubber latex, and chloroprene rubber latex. , Silicone rubber latex, one or more of fluororubber latex,
In the dispersion step, a second mixture containing 0.1 part by mass to 60 parts by mass of cellulose nanofibers is set to a roll interval of 0 mm to 0.5 mm and a roll temperature of 0 ° C. to 50 ° C. with respect to 100 parts by mass of rubber. It is characterized by thinning using an open roll.

According to the method for producing a rubber composition according to this application example, the tensile strength of the rubber composition can be improved by dispersing the cellulose nanofibers having a short fiber length in a defibrated state.

[Application example 2]
In the method for producing a rubber composition according to this application example,
Cellulose nanofibers have an average fiber length of 300 nm to 310 nm .
The aqueous dispersion can have a viscosity of 5 mPa · s to 20 mPa · s.

[Application example 3]
In the method for producing a rubber composition according to this application example,
The mixing step can be performed by using a roll kneading method.

[Application example 4]
In the method for producing a rubber composition according to this application example,
Between the mixing step and the drying step, a coagulation step of coagulating the rubber latex in the first mixture can be further included.

[Application example 5]
The rubber composition according to this application example is a rubber composition in which cellulose nanofibers defibrated in hydrogenated acrylonitrile-butadiene rubber are dispersed.
Cellulose nanofibers have an average fiber length of 200 nm to 310 nm and an average fiber width of 2 nm to 5 nm.
Contains 0.1 to 60 parts by mass of cellulose nanofibers with respect to 100 parts by mass of hydrogenated acrylonitrile-butadiene rubber.
The rate of change in tensile strength of the rubber composition is 15% or more and 150% or less .
The rate of change in tensile strength is the rate of change in the tensile strength (TSa) of the rubber composition with respect to the tensile strength (TSo) of the hydrided acrylonitrile-butadiene rubber having the same composition except that the cellulose nanofibers are removed from the rubber composition. TSa-TSo) / (TSo) × 100 (%)], and the tensile strength is measured at 23 ± 2 ° C. and a tensile speed of 500 mm / min based on the tensile test of JIS K6251 .

According to the rubber composition according to this application example, the tensile strength of the rubber composition can be improved by dispersing the cellulose nanofibers having a short fiber length in a defibrated state.

[Application example 6]
In the rubber composition according to this application example,
Cellulose nanofibers have an average fiber length of 300 nm to 310 nm .
The cellulose nanofibers can be contained in an amount of 0.1 part by mass to 40 parts by mass with respect to 100 parts by mass of the rubber.

[Application 7]
In the rubber composition according to this application example,
It is preferable not to have aggregates having a diameter of 0.1 mm or more containing cellulose nanofibers.

It is a figure which shows typically the dispersion process in the manufacturing method of the rubber composition which concerns on one Embodiment. It is a figure which shows typically the dispersion process in the manufacturing method of the rubber composition which concerns on one Embodiment. It is a figure which shows typically the dispersion process in the manufacturing method of the rubber composition which concerns on one Embodiment. It is an electron micrograph of the rubber composition of Comparative Example 4. 6 is an electron micrograph of the rubber composition of Example 6.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The drawings used in this description are for convenience of explanation. The embodiments described below do not unreasonably limit the content of the present invention described in the claims. Moreover, not all of the configurations described below are essential constituent requirements of the present invention.

In the method for producing a rubber composition according to this application example, an aqueous dispersion containing cellulose nanofibers having an average fiber length of 200 nm to 310 nm and an average fiber width of 2 nm to 5 nm, and a rubber latex are used. A mixing step of mixing to obtain a first mixture, a drying step of drying the first mixture to obtain a second mixture, and a thinning of the second mixture with an open roll to obtain a rubber composition. The aqueous dispersion contains 0.1% by mass to 10% by mass of cellulose nanofibers, and the aqueous dispersion is measured using a B-type viscometer at 20 ° C. and 60 rpm. The rubber latex has a viscosity of 1 mPa · s to 100 mPa · s, and the rubber latex is a natural rubber latex, a styrene-butadiene rubber latex, a butadiene rubber latex, a methyl methacrylate-butadiene rubber latex, a 2-vinylpyridine-styrene-butadiene rubber. It contains one or more of latex, acrylonitrile-butadiene rubber latex, chloroprene rubber latex, silicone rubber latex, and fluororubber latex, and the dispersion step contains 0.1 part by mass of cellulose nanofibers with respect to 100 parts by mass of rubber. The second mixture containing up to 60 parts by mass is thinly passed through an open roll having a roll interval of 0 mm to 0.5 mm and a roll temperature of 0 ° C. to 50 ° C.

The rubber composition according to this application example is a rubber composition in which cellulose nanofibers defibrated in hydrided acrylonitrile-butadiene rubber are dispersed, and the average value of the fiber length of the cellulose nanofibers is 200 nm to 310 nm . Moreover, the average value of the fiber width is 2 nm to 5 nm, and 0.1 part by mass to 60 parts by mass of cellulose nanofibers is contained with respect to 100 parts by mass of hydrided acrylonitrile-butadiene rubber, and the tensile strength of the rubber composition changes. The rate of change in tensile strength is 15% or more and 150% or less, and the rate of change in tensile strength is the rubber composition with respect to the tensile strength (TSo) of the hydrided acrylonitrile-butadiene rubber having the same composition except that the cellulose nanofibers are removed from the rubber composition. The rate of change in tensile strength (TSa) [(TSa-TSo) / (TSo) × 100 (%)], and the tensile strength is 23 ± 2 ° C. and the tensile speed is 500 mm / min. It is characterized by measuring based on a test .

A. Raw material A-1. Water dispersion The water dispersion contains cellulose nanofibers having an average fiber length of 200 nm to 310 nm and an average fiber width of 2 nm to 5 nm.

The aqueous dispersion containing the cellulose nanofibers can be obtained by a production method including, for example, an oxidation step of oxidizing natural cellulose fibers to obtain oxidized cellulose fibers and a miniaturization step of refining the oxidized cellulose fibers.

First, in the oxidation step, water is added to the natural cellulose fiber as a raw material and treated with a mixer or the like to prepare a slurry in which the natural cellulose fiber is dispersed in water.

Here, examples of the natural cellulose fiber include wood pulp, cotton pulp, bacterial cellulose and the like. More specifically, examples of wood pulp include coniferous pulp, hardwood pulp and the like, examples of cotton pulp include cotton linter and cotton lint, and examples of non-wood pulp include cotton linter and cotton lint. Straw pulp, bagus pulp and the like can be mentioned. At least one of these can be used as the natural cellulose fiber.

The natural cellulose fiber has a structure composed of a cellulose microfibril bundle and lignin and hemicellulose filling the space between the bundles. That is, it is presumed that hemicellulose covers the cellulose microfibrils and / or the cellulose microfibril bundles, and lignin covers them. Cellulose microfibrils and / or cellulose microfibril bundles are firmly adhered to each other by lignin to form plant fibers. Therefore, it is preferable that the lignin in the plant fiber is removed in advance from the viewpoint that the aggregation of the cellulose fiber in the plant fiber can be prevented. Specifically, the lignin content in the plant fiber-containing material is usually about 40% by mass or less, preferably about 10% by mass or less. Further, the lower limit of the removal rate of lignin is not particularly limited, and it is preferable that it is close to 0% by mass. The lignin content can be measured by the Klason method.

As the cellulose microfibrils, cellulose microfibrils having a width of about 2 to 4 nm exist as the smallest unit, and these can be called single cellulose nanofibers. In the present invention, the "cellulose nanofiber" is a natural cellulose fiber and / or an oxidized cellulose fiber unraveled to a nanosize level, and in particular, the average value of the fiber width can be 2 nm to 5 nm. That is, the cellulose nanofibers can include a single cellulose nanofiber alone or a bundle of a plurality of single cellulose nanofibers. Here, "2 nm to 5 nm" is a range of 2 nm or more and 5 nm or less, and the numerical range indicated by "-" in the present specification includes an upper limit and a lower limit.

The average value of the fiber length of the cellulose nanofibers is 200 nm to 310 nm . By dispersing short cellulose nanofibers having a fiber length of 200 nm to 310 nm in a defibrated state, the tensile strength of the rubber composition can be improved. Further, the average value of the fiber length of the cellulose nanofibers can be 300 nm to 310 nm .

The average value of the fiber width and fiber length of the cellulose nanofibers is, for example, prepared a 0.001% by mass aqueous dispersion of cellulose nanofibers, spread the diluted dispersion thinly on a mica sample table, and at 50 ° C. By heating and drying to prepare an observation sample and measuring the cross-sectional height of the shape image observed with an atomic force microscope (AFM), it can be calculated as an arithmetic mean value as a number average fiber width or fiber length. can.

Next, as an oxidation step, natural cellulose fibers are oxidized in water using an N-oxyl compound as an oxidation catalyst to obtain oxidized cellulose fibers. Examples of the N-oxyl compound that can be used as an oxidation catalyst for cellulose include 2,2,6,6-tetramethyl-1-piperidin-N-oxyl (hereinafter, also referred to as TEMPO), 4-acetamide-TEMPO, and the like. 4-carboxy-TEMPO, 4-phosphonooxy-TEMPO and the like can be used.

After the oxidation step, for example, a purification step of repeating washing and filtration can be carried out to remove impurities other than the oxidized cellulose fibers contained in the slurry, such as unreacted oxidizing agents and various by-products. The solvent containing the cellulose oxide fiber is, for example, impregnated with water, and at this stage, the cellulose oxide fiber is not defibrated to the unit of the cellulose nanofiber. Water can be used as the solvent, but for example, an organic solvent (alcohols, ethers, ketones, etc.) soluble in water can be used in addition to water depending on the purpose.

The oxidized cellulose fiber has a carboxyl group by modifying a part of the hydroxyl group of the cellulose nanofiber with a substituent having a carboxyl group.

The average value of the fiber width of the oxidized cellulose fiber can be 10 μm to 30 μm. The average value of the fiber width of the cellulose oxide fiber is an arithmetic mean value measured for at least 50 or more of the cellulose oxide fibers in the field of view of the electron microscope.

Oxidized cellulose fibers can be bundles of cellulose microfibrils. Oxidized cellulose fibers do not need to be defibrated to the unit of cellulose nanofibers in the mixing step and the drying step described later. Oxidized cellulose fibers can be defibrated into cellulose nanofibers in the miniaturization step.

In the miniaturization step, the cellulose oxide fibers can be agitated in a solvent such as water, and cellulose nanofibers can be obtained.

In the miniaturization step, the solvent as the dispersion medium can be water. Further, as a solvent other than water, an organic solvent soluble in water, for example, alcohols, ethers, ketones and the like can be used alone or in combination.

The stirring process in the miniaturization process includes, for example, a breaker, a beater, a low-pressure homogenizer, a high-pressure homogenizer, a grinder, a cutter mill, a ball mill, a jet mill, a short-screw extruder, a twin-screw extruder, an ultrasonic stirrer, and a household juicer mixer. Etc. can be used.

Further, the solid content concentration of the solvent containing the oxidized cellulose fiber in the miniaturization treatment can be, for example, 50% by mass or less. If the solid content concentration exceeds 50% by mass, high energy is required for dispersion.

An aqueous dispersion containing cellulose nanofibers can be obtained by the miniaturization step. An aqueous dispersion containing cellulose nanofibers having an average fiber length of 200 nm to 310 nm and an average fiber width of 2 nm to 5 nm contains 0.1% by mass to 10% by mass of cellulose nanofibers and has a viscosity. Is 1 mPa · s to 100 mPa · s. The viscosity of the aqueous dispersion is lower by including the short cellulose nanofibers than by containing the long cellulose nanofibers. Since the average value of the fiber length of the cellulose nanofibers is shorter than 310 nm , the tensile strength can be improved. Any aqueous dispersion containing cellulose nanofibers having an average fiber length of more than 200 nm can be produced. As the fiber length of the cellulose nanofibers becomes longer, the viscosity of the aqueous dispersion tends to increase. As a method for measuring the viscosity of the aqueous dispersion, a B-type viscometer TV-10 viscometer (Toki Sangyo Co., Ltd.) was used to apply 1% by mass of the carboxylated cellulose nanofiber aqueous dispersion at 20 ° C. and 60 rpm. Measure under conditions.

The cellulose nanofibers in the aqueous dispersion can have an average fiber length of 300 nm to 310 nm , and the viscosity of the aqueous dispersion can be 5 mPa · s to 20 mPa · s. The tensile strength can be further improved by using cellulose nanofibers having a shorter average fiber length.

The aqueous dispersion containing the cellulose nanofibers can be a colorless transparent or translucent suspension. In the suspension, cellulose nanofibers, which are fibers that have been surface-oxidized and defibrated to be finely divided, are dispersed in water. That is, in this aqueous dispersion, the strong cohesive force between microfibrils (hydrogen bonds between surfaces) is weakened by the introduction of carboxyl groups in the oxidation step, and further through the micronization step, cellulose nanofibers can be obtained. .. Then, by adjusting the conditions of the oxidation step, the carboxyl group content, polarity, average fiber width, average fiber length, average aspect ratio and the like can be controlled.

(Staple treatment)
The staple treatment is a treatment for hydrolyzing oxidized cellulose in an alkaline solution or an acidic solution. The reaction medium for the hydrolysis treatment is preferably water from the viewpoint of suppressing side reactions. By hydrolyzing in an alkaline solution, the viscosity of the dispersion of carboxylated cellulose nanofibers can be reduced. The reason for this is inferred as follows. Carboxyl groups are scattered in the amorphous region of cellulose oxide oxidized using the N-oxyl compound, and the hydrogen at the C5 position adjacent to the carboxyl group is attracted by the carboxyl group. It is in a state of lack of charge. Therefore, under alkaline conditions of pH 8 to 14, the hydrogen is easily extracted by hydroxide ions, and the β-elimination reaction causes cleavage of the glucosidic bond. As a result, since the oxidized cellulose is shortened, the proportion of the carboxylated cellulose nanofibers having a short fiber length is also increased, and the viscosity of the dispersion liquid of the carboxylated cellulose nanofibers can be lowered.

When hydrolyzing in an alkaline solution, the pH value of the reaction solution in the reaction is preferably 8 to 14, more preferably 9 to 13, and even more preferably 10 to 12. When the pH value is less than 8, sufficient hydrolysis does not occur, and the shortening of the oxidized cellulose may be insufficient. On the other hand, when the pH value is more than 14, hydrolysis proceeds, but the oxidized cellulose after hydrolysis is colored, and the obtained cellulose nanofibers are also colored, so that the transparency is lowered and the application technique is limited. May occur. The alkali used for adjusting the pH value may be water-soluble, and sodium hydroxide is preferable from the viewpoint of production cost.

Hydrolysis of cellulose oxide in an alkaline solution may cause the cellulose oxide to turn yellow due to the formation of double bonds during β-desorption. Therefore, the obtained cellulose nanofibers are also colored and the transparency is lowered, which may limit the application technique. Therefore, the hydrolysis step is preferably carried out using an oxidizing agent or a reducing agent as an auxiliary agent in order to suppress the formation of double bonds. When an oxidizing agent or a reducing agent is used during the hydrolysis treatment in an alkaline solution having a pH value of 8 to 14, the oxidized cellulose can be shortened while oxidizing or reducing the double bond. As the oxidizing agent or reducing agent, those having activity in the alkaline region can be used.

From the viewpoint of reaction efficiency, the amount of the auxiliary agent added is preferably 0.1% by mass to 10% by mass, more preferably 0.3% by mass to 5% by mass, and 0.5% by mass with respect to the absolutely dried cellulose oxide. % To 2% by mass is more preferable.

Examples of the oxidizing agent include oxygen, ozone, hydrogen peroxide, and hypochlorite. Among them, as the oxidizing agent, oxygen, hydrogen peroxide and hypochlorite, which are less likely to generate radicals, are preferable, and hydrogen peroxide is more preferable. The oxidizing agent may be used alone or in combination of two or more.

Examples of the reducing agent include sodium borohydride, hydrosulfite, and sulfites. The reducing agent may be used alone or in combination of two or more.

The reaction temperature for hydrolysis is preferably 40 ° C. to 120 ° C., more preferably 50 ° C. to 100 ° C., and even more preferably 60 ° C. to 90 ° C. from the viewpoint of reaction efficiency. When the temperature is low, sufficient hydrolysis does not occur, and the shortening of cellulose oxide or carboxylated cellulose nanofibers may be insufficient. On the other hand, when the temperature is high, hydrolysis proceeds, but the oxidized cellulose may be colored after hydrolysis.

The reaction time for hydrolysis is preferably 0.5 hours to 24 hours, more preferably 1 hour to 10 hours, and even more preferably 2 hours to 6 hours.

From the viewpoint of reaction efficiency, the concentration of cellulose oxide in the alkaline solution is preferably 1% by mass to 20% by mass, more preferably 3% by mass to 15% by mass, still more preferably 5% by mass to 10% by mass.

The aqueous dispersion thus obtained can be, for example, an aqueous dispersion diluted to 1% by mass of the solid content of the cellulose nanofibers. Further, the aqueous dispersion can have a light transmittance of 40% or more, and can have a light transmittance of 60% or more, particularly 80% or more. The transmittance of the aqueous dispersion can be measured as the transmittance at a wavelength of 660 nm using an ultraviolet-visible spectrophotometer.

A-2. Rubber Latex As the rubber latex, a natural rubber latex solution and a synthetic rubber latex solution can be used.

The natural rubber latex solution is a natural product due to the metabolic action of plants, and in particular, a natural rubber / aqueous solution in which the dispersion solvent is water can be used. Examples of the synthetic rubber latex solution include styrene-butadiene rubber, butadiene rubber, methylmethacrylate-butadiene rubber, 2-vinylpyridine-styrene-butadiene rubber, acrylonitrile-butadiene rubber, chloroprene rubber, silicone rubber, and fluororubber. Can be used as produced by emulsification polymerization. In particular, among the acrylonitrile-butadiene rubber latex, hydrogenated acrylonitrile-butadiene rubber (H-NBR) latex can be used. In the synthetic rubber latex solution, a large number of rubber fine particles are dispersed in an aqueous dispersion solvent.

B. Method for Producing Rubber Composition FIGS. 1 to 3 are diagrams schematically showing a method for producing a rubber composition according to an embodiment.

The first method for producing a rubber composition is to mix an aqueous dispersion containing cellulose nanofibers having an average fiber length of 200 nm to 310 nm and an average fiber width of 2 nm to 5 nm, and a rubber latex. A mixing step of obtaining the mixture, a drying step of drying the first mixture to obtain a second mixture, and a dispersion step of diluting the second mixture with an open roll to obtain a rubber composition. include.

B-1. Mixing Step In the mixing step, an aqueous dispersion containing cellulose nanofibers and a rubber latex are mixed to obtain a first mixture. As the mixing step, for example, a roll kneading method using a roll kneading device, a stirring operation using a propeller type stirring device, a homogenizer, a rotary stirring device, and an electromagnetic stirring device, or a manual stirring operation can be used. In particular, a roll kneading method can be used for the mixing step.

As the roll kneading device used in the roll kneading method, for example, an open roll can be used. Further, as the roll kneading device used in the roll kneading method, for example, two rolls or three rolls can be used.

The mixture of the aqueous dispersion and the rubber latex is gradually added to the roll kneading device in which the distance between the rolls is set at a predetermined interval. The distance between the rolls can be set so that the mixture of the aqueous dispersion and the rubber latex wraps around the rolls and the mixture does not fall from between the rolls. The mixture charged into the roll kneading device gradually increases in viscosity by being kneaded. When the viscosity of the mixture becomes high, the mixture can be taken out from the roll kneading device, the distance between the rolls can be set narrower, and the mixture can be put into the roll kneading device again. This step can be performed a plurality of times.

By carrying out the mixing step, it can be expected that the cellulose nanofibers will enter the rubber fine particles while passing between the rolls. In particular, by using the roll kneading method, the reinforcing effect of the fibers can be further improved as compared with other stirring operations.

The first mixture obtained in the mixing step can contain 0.1 part by mass to 60 parts by mass of cellulose nanofibers with respect to 100 parts by mass of the rubber solid component in a mass ratio after the drying step, and further 0. It can be 1 part by mass to 40 parts by mass, and particularly 5 parts by mass to 20 parts by mass in the case of the first mixture containing cellulose nanofibers having an average value of fiber length of more than 310 nm and not more than 330 nm. It can be 5 parts by mass or more and less than 20 parts by mass, and 5 parts by mass to 20 parts by mass in the case of the first mixture containing cellulose nanofibers having an average value of fiber lengths of 300 nm to 310 nm. Can be a department. If the amount of cellulose nanofibers is 0.1 parts by mass or more, a reinforcing effect can be obtained, and if it is 60 parts by mass or less, processing after the drying step is possible.

B-2. Drying step The drying step is a step of drying the first mixture obtained in the mixing step to obtain a second mixture. For example, since the first mixture contains water, common methods for removing water can be adopted. For example, as the drying step, known drying methods such as natural drying, oven drying, freeze drying, blast drying, and pulse combustion can be adopted.

The drying step can be carried out at a temperature at which rubber and cellulose nanofibers do not thermally decompose, and can be dried by heating at, for example, 100 ° C.

The second mixture contains a rubber component and cellulose nanofibers. The second mixture contains 0.1 part by mass to 60 parts by mass of cellulose nanofibers with respect to 100 parts by mass of rubber. Further, the second mixture can contain 1 part by mass to 50 parts by mass of cellulose nanofibers, and in particular, 5 parts by mass to 40 parts by mass. When 0.1 part by mass or more of cellulose nanofibers is contained in the second mixture, the reinforcing effect of the rubber composition can be obtained, and when 60 parts by mass or less of cellulose nanofibers is contained in the solvent, it can be easily processed. ..

B-3. Dispersion Step In the dispersion step, a second mixture containing cellulose nanofibers can be thinly passed through an open roll to obtain a rubber composition. In the dispersion step, a second mixture containing 0.1 part by mass to 60 parts by mass of cellulose nanofibers is set to a roll interval of 0 mm to 0.5 mm and a roll temperature of 0 ° C. to 50 ° C. with respect to 100 parts by mass of rubber. Thinly through using an open roll.

First, prior to thinning, as shown in FIG. 1, the second mixture 30 wound around the first roll 10 can be kneaded to moderately squeeze the rubber molecular chains in the second mixture. Cleaves to generate free radicals. The rubber free radicals generated by kneading are in a state where they can easily bind to the cellulose nanofibers.

Next, as shown in FIG. 2, the compounding agent 80 is appropriately added to the bank 34 of the second mixture 30 wound around the first roll 10 and kneaded to obtain the intermediate mixture 36 (shown in FIG. 3). The resulting kneading step can be performed. Here, the compounding agent 80 is, for example, a cross-linking agent, a vulcanizing agent, a vulcanization accelerator, a vulcanization delaying agent, a softening agent, a plasticizer, a curing agent, a reinforcing agent, a filler, an antiaging agent, a coloring agent, and an acid receiving acid. Agents and the like can be mentioned. These formulations can be added to the rubber at the appropriate time during the mixing process.

The step of obtaining the intermediate mixture 36 (shown in FIG. 3) of FIGS. 1 to 2 is not limited to the open roll method, and for example, a closed kneading method or a multi-screw extrusion kneading method can also be used.

Further, as shown in FIG. 3, thinning can be performed. In the thinning step, an open roll 2 having a roll interval of 0 to 0.5 mm is used, and thinning is performed at a roll temperature of 0 ° C. to 50 ° C. to obtain an uncrosslinked rubber composition 50. In this step, the first roll 10 and the second roll
The roll interval d with the roll 20 is set to an interval of 0 mm to 0.5 mm, and the intermediate mixture 36 obtained by the kneading described in FIG. 2 is put into the open roll 2 and thinly threaded once or multiple times. Can be done. The number of thinnings can be, for example, about 1 to 10 times. Assuming that the surface speed of the first roll 10 is V1 and the surface speed of the second roll 20 is V2, the surface speed ratio (V1 / V2) of both in thinning is 1.05 to 3.00. It can be 1.05 to 1.2. By using such a surface velocity ratio, a desired shearing force can be obtained.

The rubber composition 50 extruded from such a narrow roll is greatly deformed as shown in FIG. 3 by the restoring force due to the elasticity of the rubber, and at that time, the cellulose nanofibers move greatly together with the rubber. The rubber composition 50 obtained by thinly rolling is rolled with a roll and dispensed into a sheet having a predetermined thickness, for example, 100 μm to 500 μm.

In this thinning step, in order to obtain the highest possible shearing force, the roll temperature can be set to 0 ° C. to 50 ° C., and further set to a relatively low temperature of 5 ° C. to 30 ° C. The measured temperature of the rubber composition can also be adjusted to 0 ° C to 50 ° C, and further can be adjusted to 5 ° C to 30 ° C.

By adjusting to such a temperature range, cellulose nanofibers can be defibrated by utilizing the elasticity of rubber, and the deflated cellulose nanofibers can be dispersed in the rubber composition.

Due to the high shearing force in this thinning process, a high shearing force acts on the rubber, and the aggregated cellulose nanofibers are separated from each other so as to be pulled out one by one to the rubber molecules and dispersed in the rubber. .. In particular, since rubber has elasticity and viscosity, cellulose nanofibers can be defibrated and dispersed. Then, it is possible to obtain a rubber composition 50 having excellent dispersibility and dispersion stability of the cellulose nanofibers (the cellulose nanofibers are less likely to reaggregate).

More specifically, when the rubber and the cellulose nanofibers are mixed with an open roll, the viscous rubber penetrates into each other of the cellulose nanofibers. If the surface of the cellulose nanofibers is moderately active, for example, by oxidation treatment, it can be particularly easily bonded to rubber molecules. Next, when a strong shearing force acts on the rubber, the cellulose nanofibers also move with the movement of the rubber molecules, and the agglomerated cellulose nanofibers are separated by the restoring force of the rubber due to the elasticity after shearing. , Will be dispersed in the rubber. In particular, the open roll method is preferable because it can measure and control the actual temperature of the mixture as well as control the roll temperature.

B-4. Coagulation Step Between the mixing step and the drying step, a coagulation step of coagulating the rubber latex in the first mixture can be further included.

Since the first mixture obtained in the mixing step in B-1 contains a large amount of water as it is, it takes a long time to remove the water in the drying step in B-2. Therefore, in the coagulation step, a predetermined amount of a known coagulant that coagulates the rubber latex is added to the first mixture which is an aqueous dispersion, and the mixture is stirred and mixed. The rubber component in the first mixture is coagulated by the coagulant. The coagulation step can include dehydration and washing of the coagulated product. Dehydration and washing can be repeated multiple times.

In the dehydration in this step, it is sufficient to remove enough water to shorten the drying time in the drying step, and the solidified rubber component and the water are separated to some extent. Dehydration can be performed using, for example, a general rotary dehydrator (centrifugation), a rubber film roll, a press machine, or the like. Further, the washing in this step can be performed with, for example, water.

As the coagulant, a known latex coagulant can be appropriately adopted depending on the type of rubber latex in the first mixture. As the coagulant, for example, a known acid or salt can be used, and the polymer flocculant may be used in place of the salt or in combination with the salt. As the acid used for the coagulant, formic acid, acetic acid, propionic acid, citric acid, oxalic acid, sulfuric acid, hydrochloric acid, carbonic acid and the like can be used. As the salt used as the coagulant, for example, sodium chloride, aluminum sulfate, calcium nitrate and the like can be used. As the polymer flocculant, any of anionic type, cationic type and nonionic type polymer flocculants can be used.

Since a large amount of water can be removed from the first mixture in the coagulation step, the heating time in the drying step performed after the coagulation step can be shortened, and the work efficiency is improved.

C. Rubber Composition The rubber composition can be obtained by the method for producing the rubber composition using hydrogenated acrylonitrile-butadiene rubber as the rubber latex.

The rubber composition is a rubber composition in which cellulose nanofibers defibrated in hydrided acrylonitrile-butadiene rubber are dispersed. Cellulose nanofibers have an average fiber length of 200 nm to 310 nm and a fiber width. The average value is 2 nm to 5 nm, and 0.1 part by mass to 60 parts by mass of cellulose nanofibers is contained with respect to 100 parts by mass of hydrided acrylonitrile-butadiene rubber. When the rubber composition contains cellulose nanofibers having a short fiber length of 310 nm or less in a defibrated state, the tensile strength of the rubber composition can be improved. The rate of change in tensile strength of the rubber composition is 15% or more and 150% or less. The rate of change in tensile strength is the rate of change in the tensile strength (TSa) of the rubber composition with respect to the tensile strength (TSo) of the raw rubber having the same composition except that the cellulose nanofibers are removed from the rubber composition [(TSa-TSo). / (TSo) x 100 (%)]. The tensile strength is measured by performing a tensile test based on JIS K6251 at 23 ± 2 ° C. and a tensile speed of 500 mm / min with a test piece punched into a JIS No. 6 dumbbell shape.

An aggregate containing cellulose nanofibers is a mass in which a large number of cellulose nanofibers are gathered together.

According to the rubber composition in the present embodiment, it is desirable that the rubber composition does not have aggregates, and the cellulose nanofibers are reinforced by being dispersed in a defibrated state, and are excellent in rigidity, strength, and fatigue resistance. In particular, according to the rubber composition, the tensile strength can be improved. In particular, in the rubber composition having an agglomerate, the agglomerate becomes a fracture starting point in the tensile test, which causes a decrease in the tensile strength. From the viewpoint of improving the tensile strength, it is desirable that the rubber composition is sufficiently deflated with cellulose nanofibers and does not contain aggregates of 0.1 mm or more.

Further, the rubber composition can contain 0.1 part by mass to 40 parts by mass of cellulose nanofibers with respect to 100 parts by mass of rubber, and in particular, cellulose nanofibers having an average fiber length of more than 310 nm and not more than 330 nm. In the case of the first mixture containing, it can be 5 parts by mass to 20 parts by mass, further can be 5 parts by mass or more and less than 20 parts by mass, and the average value of the fiber length is 300 nm to 310 nm. In the case of the first mixture containing cellulose nanofibers, it can be 5 parts by mass to 20 parts by mass.

In the method for producing a rubber composition described here, a compounding agent usually used in rubber processing can be added. A known compounding agent can be used.

As described above, the embodiments of the present invention have been described in detail, but those skilled in the art can easily understand that many modifications that do not substantially deviate from the new matters and effects of the present invention are possible. Therefore, all such modifications are included in the scope of the present invention.

Hereinafter, examples of the present invention will be described, but the present invention is not limited thereto.

(1-1) Preparation of Samples of Reference Examples 1 to 3 Step of obtaining an aqueous dispersion:
Specifically, after sufficiently stirring the bleached kraft pulp of softwood with ion-exchanged water, TEMPO 1.25% by mass, sodium bromide 12.5% by mass, and sodium hypochlorite 28.4 with respect to 100 g of pulp mass. %% By mass was added in this order at 20 ° C. Sodium hydroxide was added dropwise to maintain the pH at 10.5, and an oxidation reaction was carried out. After the oxidation reaction was carried out for 120 minutes, the dropping was stopped to obtain an aqueous dispersion containing 10% by mass of TEMPO-oxidized cellulose oxide fibers. The oxidized cellulose fibers had a fiber width of 10 μm to 30 μm and a fiber length of 1 mm to 5 mm, which were similar to those of the original pulp.

Further, the oxidized cellulose fibers were thoroughly washed with ion-exchanged water, and then dehydrated. Then, 1% (w / v) of hydrogen peroxide was added to the 5% (w / v) slurry of cellulose oxide with respect to the cellulose oxide, and the pH was adjusted to 11.3 with 1 M sodium hydroxide. This slurry was hydrolyzed at 80 ° C. for 2 hours. Then, it was filtered with a glass filter and washed thoroughly with water. Then, the hydrolyzed cellulose oxide fiber was adjusted to a solid content of 5% by mass with ion-exchanged water, and subjected to a micronization treatment using a high-pressure homogenizer to obtain an aqueous dispersion containing 1% by mass of cellulose nanofibers. The average value of the fiber width of the cellulose nanofibers used in Reference Examples 1 to 3 was 3.3 nm, and the average value of the fiber length was 320 nm.

The aqueous dispersion had a viscosity of 23 mPa · s. The viscosity of the aqueous dispersion is B-type viscosity (mPa · s), and B of the aqueous dispersion of 1% by mass of carboxylated cellulose nanofibers using a TV-10 viscometer (Toki Sangyo Co., Ltd.). The mold viscosity was measured under the conditions of 20 ° C. and 60 rpm.

Mixing process:
Hydrogenated nitrile rubber (hereinafter referred to as "H-NBR") latex (ZLx-B manufactured by Nippon Zeon Corporation: an aqueous dispersion having a solid content concentration of 40% by mass) is added to the aqueous dispersion containing 1% by mass of the cellulose nanofibers. Then, the mixture was mixed at a rotation speed of 10000 rpm using a juicer mixer to obtain a first mixture. Further, after mixing the mixer, the mixture was passed through a three-roll (M-50) manufactured by EXAKT with a nip set to 10 μm at a rotation speed of 200 rpm for additional mixing to obtain a first mixture.

Drying process:
The first mixture was heated and dried in an oven set at 50 ° C. for 4 days to give a second mixture. The blending amount of the cellulose nanofibers in the second mixture after drying is shown in Table 1. The blending amount in Tables 1 to 3 is parts by mass (phr), and the blending amount of H-NBR latex is the weight of the dried body.

Dispersion process:
The second mixture is kneaded at a roll interval of 1.5 mm, an antiaging agent and a cross-linking aid are added and mixed, and the mixture is placed in an open roll having a roll gap of 0.3 mm and thinly passed at 10 ° C to 30 ° C. A rubber composition sample was obtained. At this time, the surface velocity ratio of the two rolls was set to 1.1. The thinning was repeated 5 times.

Vulcanization process:
A sheet-like crosslinked rubber composition sample having a thickness of 1 mm was compression-molded at 165 ° C. for 30 minutes by adding 8 parts by mass of peroxide as a cross-linking agent to the rubber composition sample obtained by thinly passing through. Got

(1-2) Preparation of Samples of Examples 4 to 6 Cellulose nanofibers were added to 1 in the same manner as in the step of obtaining the aqueous dispersion of (1-1) above, except that the pH was adjusted to 12 with 1M sodium hydroxide. An aqueous dispersion containing% by mass was obtained. The average value of the fiber width of the cellulose nanofibers used in Examples 4 to 6 was 3.3 nm, and the average value of the fiber length was 310 nm. The viscosity of the aqueous dispersion was 6.5 mPa · s.

Using this aqueous dispersion, the above-mentioned (1-1) "mixing step", "drying step", "dispersion step", and "vulcanization step" are carried out to form a sheet-shaped crosslinked rubber having a thickness of 1 mm. A composition sample was obtained. The blending amount of the cellulose nanofibers in the second mixture after drying is shown in Table 2.

(1-3) Preparation of Samples of Comparative Examples 1 to 4 Comparative Example 1 was obtained by heating and drying H-NBR latex (ZLx-B manufactured by Zeon Corporation) in an oven set at 50 ° C. for several days. It was a pure rubber compound. A cross-linking agent, an anti-aging agent and a cross-linking auxiliary were blended, and a vulcanization step was carried out in the same manner as in (1-1) above to obtain a sheet-shaped cross-linked rubber composition sample having a thickness of 1 mm.

In Comparative Examples 2 to 4, an aqueous dispersion containing 10% by mass of TEMPO-oxidized cellulose oxide fibers was obtained in the same manner as in Reference Examples 1 to 3 of (1-1) above, and the cellulose oxide was not subjected to hydrolysis treatment. The fibers were adjusted to a solid content of 5% by mass with ion-exchanged water and subjected to micronization treatment using a high-pressure homogenizer to obtain an aqueous dispersion containing 1% by mass of cellulose nanofibers. The average value of the fiber width of the cellulose nanofibers used in Comparative Examples 2 to 4 was 3.3 nm, and the average value of the fiber length was 510 nm. The viscosity of the aqueous dispersion was 1250 mPa · s.

Using this aqueous dispersion, the above-mentioned (1-1) "mixing step", "drying step", "dispersion step", and "vulcanization step" are carried out to form a sheet-shaped crosslinked rubber having a thickness of 1 mm. A composition sample was obtained. The blending amount of the cellulose nanofibers in the second mixture after drying is shown in Table 3.

(2-1) Basic property test The rubber hardness (Hs (JIS A)) of the rubber composition sample was measured based on the JIS K6253 test.

Tensile strength (TS (MPa)), elongation at break (Eb (%)), stress at 50% deformation (σ50 (MPa)) and stress at 100% deformation (σ100 (MPa)) for rubber composition samples. Was measured by performing a tensile test based on JIS K6251 at 23 ± 2 ° C. and a tensile speed of 500 mm / min using a tensile tester manufactured by Shimadzu Corporation with a test piece punched into a JIS No. 6 dumbbell shape.

In Tables 1 to 3, the "TS change rate" is the rate of change in tensile strength, and each Example 4 to 6 and Reference Examples 1 to 3 and comparisons with respect to the tensile strength (TS) of Comparative Example 1 The rate of change in Examples 2 to 4 was determined by TS change rate (%) = (TSa-TSo) / (TSo) × 100. Here, TSa is the TS value of Examples 4 to 6 , Reference Examples 1 to 3 and Comparative Examples 2 to 4, and TSo is the TS value of Comparative Example 1 (33.0 MPa).

From the results in Table 1, the rubber compositions of Reference Examples 1 to 3 are reinforced with cellulose nanofibers, and have tensile strength, stress at 50% deformation, and 100% deformation as compared with the pure rubber of Comparative Example 1. Stress has improved. In particular, the rubber compositions of Reference Examples 1 to 3 were larger than the TS change rates of Comparative Examples 2 to 4, which had the same amount of cellulose nanofibers, and the tensile strength was improved.

From the results in Table 2, the rubber compositions of Examples 4 to 6 were reinforced with cellulose nanofibers, and had tensile strength, stress at 50% deformation, and 100% deformation as compared with the pure rubber of Comparative Example 1. Stress has improved. In particular, the rubber compositions of Examples 4 to 6 were larger than the rate of change of each TS of Comparative Examples 2 to 4, which had the same amount of cellulose nanofibers, and the tensile strength was improved.

(2-2) Electron Microscope Observation Scanning electron microscope (SEM) observation was performed on the fracture surface of the rubber composition samples of Examples 4 to 6 , Reference Examples 1 to 3 and Comparative Examples 2 to 4 after the tensile test. The presence or absence of aggregates of cellulose nanofibers was confirmed.

FIG. 4 is an SEM photograph of the rubber composition of Comparative Example 4, and FIG. 5 is an SEM photograph of the rubber composition of Example 6. The samples of the rubber compositions of Examples 4 to 6 , Reference Examples 1 to 3 and Comparative Examples 2 to 4 had a smooth fracture surface and an aggregate of 0.1 mm or more (if there is an aggregate, the fracture surface is from the aggregate). (It looks like a sea-island with scattered particle shapes) could not be confirmed.

The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, the present invention includes substantially the same configurations as those described in the embodiments (eg, configurations with the same function, method, and result, or configurations with the same purpose and effect). The present invention also includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. Further, the present invention includes a configuration having the same action and effect as the configuration described in the embodiment or a configuration capable of achieving the same object. Further, the present invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

2 ... open roll, 10 ... first roll, 20 ... second roll, 30 ... second mixture, 34 ... bank, 36 ... intermediate mixture, 50 ... rubber composition, 80 ... compounding agent, V1, V2 ... Rotational speed

Claims (7)

A mixing step of mixing an aqueous dispersion containing cellulose nanofibers having an average fiber length of 200 nm to 310 nm and an average fiber width of 2 nm to 5 nm with a rubber latex to obtain a first mixture.
A drying step of drying the first mixture to obtain a second mixture, and
A dispersion step of thinly passing the second mixture through an open roll to obtain a rubber composition, and a dispersion step.
Including
The aqueous dispersion contains 0.1% by mass to 10% by mass of cellulose nanofibers.
The aqueous dispersion has a viscosity of 1 mPa · s to 100 mPa · s measured at 20 ° C. and 60 rpm using a B-type viscometer .
The rubber latex includes natural rubber latex, styrene-butadiene rubber latex, butadiene rubber latex, methylmethacrylate-butadiene rubber latex, 2-vinylpyridine-styrene-butadiene rubber latex, acrylonitrile-butadiene rubber latex, and chloroprene rubber latex. , Silicone rubber latex, one or more of fluororubber latex,
In the dispersion step, a second mixture containing 0.1 part by mass to 60 parts by mass of cellulose nanofibers is set to a roll interval of 0 mm to 0.5 mm and a roll temperature of 0 ° C. to 50 ° C. with respect to 100 parts by mass of rubber. A method for producing a rubber composition, which is thinly passed through an open roll. In claim 1,
Cellulose nanofibers have an average fiber length of 300 nm to 310 nm .
The method for producing a rubber composition, wherein the aqueous dispersion has a viscosity of 5 mPa · s to 20 mPa · s. In claim 1 or 2,
The mixing step is a method for producing a rubber composition, which is carried out by using a roll kneading method. In any one of claims 1 to 3,
A method for producing a rubber composition, further comprising a coagulation step of coagulating the rubber latex in the first mixture between the mixing step and the drying step. A rubber composition in which cellulose nanofibers defibrated in hydrogenated acrylonitrile-butadiene rubber are dispersed.
Cellulose nanofibers have an average fiber length of 200 nm to 310 nm and an average fiber width of 2 nm to 5 nm.
Contains 0.1 to 60 parts by mass of cellulose nanofibers with respect to 100 parts by mass of hydrogenated acrylonitrile-butadiene rubber.
The rate of change in tensile strength of the rubber composition is 15% or more and 150% or less .
The rate of change in tensile strength is the rate of change in the tensile strength (TSa) of the rubber composition with respect to the tensile strength (TSo) of the hydrided acrylonitrile-butadiene rubber having the same composition except that the cellulose nanofibers are removed from the rubber composition. TSa-TSo) / (TSo) × 100 (%)], the rubber composition measured based on the tensile test of JIS K6251 at a tensile strength of 23 ± 2 ° C. and a tensile speed of 500 mm / min . In claim 5,
Cellulose nanofibers have an average fiber length of 300 nm to 310 nm .
A rubber composition containing 0.1 part by mass to 40 parts by mass of cellulose nanofibers with respect to 100 parts by mass of rubber. In claim 5 or 6,
A rubber composition containing cellulose nanofibers and having no aggregate having a diameter of 0.1 mm or more.

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