JP6874411B2 - Method for manufacturing rubber composition - Google Patents

Description

The present invention relates to a method for producing a rubber composition.

In recent years, there has been known a technique for improving various strengths in a rubber composition such as tensile strength by incorporating a material called cellulose nanofiber, which is produced by finely loosening plant fibers to the nano level, into the rubber composition. ..

For example, Patent Document 1 discloses a master batch of rubber / short fibers obtained by stirring and mixing short fibers of cellulose having an average diameter of less than 0.5 μm and rubber latex. According to this document, short fibers having an average fiber diameter of less than 0.5 μm are fibrillated in water in advance to prepare a dispersion liquid, which is mixed with rubber latex and dried to make the short fibers uniform in the rubber. It can be dispersed, and it is said that a rubber composition having a good balance between rubber reinforcing property and fatigue resistance can be obtained by using this rubber / short fiber master batch.

However, in this method, since the solid content concentration of the cellulose nanofiber aqueous dispersion is as low as several% or less, when this is added to the rubber latex, the solid content concentration of the entire mixture becomes low and it is difficult to handle.

On the other hand, a solid substance obtained by drying cellulose nanofibers dispersed in water is known. However, once dried cellulose nanofibers are not sufficiently redispersed even if they are tried to be dispersed in water again. As a means for redispersing the dried solids of cellulose nanofibers in water, freeze-drying method, critical point drying method, or organic In addition to a method of replacing with a solvent and then drying, a method of mixing with a water-soluble polymer and then drying (Patent Document 2) has been proposed. Not listed.

Japanese Unexamined Patent Publication No. 2006-206864 International Publication No. 2015/107995

Therefore, an object of the present invention is to provide a method for producing a rubber composition having sufficiently improved reinforcing properties by containing a dry solid of cellulose nanofibers having an acetyl group at a relatively high solid content concentration. And.

[1] A method for producing a rubber composition containing cellulose nanofibers having an acetyl group, wherein a dry solid containing cellulose nanofibers having an acetyl group and an aqueous dispersion containing a rubber component are mixed. A method for producing a rubber composition, which comprises.
[2] The method for producing a rubber composition according to [1], further comprising a step of removing a dispersion medium from a dispersion of cellulose nanofibers having an acetyl group to prepare the dry solid.
[3] The dry solid containing the cellulose nanofibers having an acetyl group contains 5 to 50% by weight of a water-soluble polymer with respect to the absolute dry solid content of the cellulose nanofibers having an acetyl group [1]. The method for producing a rubber composition according to.
[4] The dry solid containing cellulose nanofibers having an acetyl group is obtained by removing a dispersion medium from a dispersion containing cellulose nanofibers having an acetyl group and a water-soluble polymer with a drum dryer. The method for producing a rubber composition according to [1] or [3].
[5] The dry solid containing the cellulose nanofibers having an acetyl group adjusts the pH of the dispersion liquid containing the cellulose nanofibers having an acetyl group and the water-soluble polymer to 9 to 11, and then uses the dispersion medium. The method for producing a rubber composition according to any one of [1], [3] or [4], which is obtained by removing the rubber composition.
[6] The solution according to [2], wherein the dispersion of cellulose nanofibers having an acetyl group contains 5 to 50% by weight of a water-soluble polymer with respect to the absolute dry solid content of the cellulose nanofibers having an acetyl group. Method for producing rubber composition.
[7] The dispersion liquid of the cellulose nanofibers having an acetyl group contains a water-soluble polymer, and in the preparation step, a dispersion medium is drummed from the dispersion liquid containing the cellulose nanofibers having the acetyl group and the water-soluble polymer. The method for producing a rubber composition according to [2] or [6], which is removed by a dryer.
[8] The dispersion liquid of the cellulose nanofibers having an acetyl group contains a water-soluble polymer, and in the preparation step, the pH of the dispersion liquid containing the cellulose nanofibers having the acetyl group and the water-soluble polymer is 9 to 9. The method for producing a rubber composition according to any one of [2], [6] or [7], wherein the dispersion medium is removed after the adjustment to 11.
[9] The method for producing a rubber composition according to any one of [3] to [8], wherein the water-soluble polymer is carboxymethyl cellulose or a salt thereof.

According to the present invention, it is possible to provide a method for producing a rubber composition having improved dispersibility of dry solids of cellulose nanofibers having an acetyl group and improved tensile strength at a relatively high solid content concentration. ..

In the present invention, "X to Y" includes the fractional values X and Y. "X or Y" means either X or Y, or both.

<Cellulose nanofibers with acetyl group>
In the present invention, the cellulose nanofiber having an acetyl group is a fine fiber having an average fiber diameter of 2 to 500 nm, preferably 2 to 50 nm, and an average aspect ratio of 10 or more, and is a cellulose raw material chemically modified by a compound having an acetyl group. Can be obtained by defibrating.

The average fiber diameter and average fiber length of cellulose nanofibers having an acetyl group can be determined by observing each fiber using an atomic force microscope (AFM) or a transmission electron microscope (TEM). The aspect ratio can be calculated by the following formula:
Aspect ratio = average fiber length / average fiber diameter

In the present invention, a part of the hydroxyl group of cellulose is chemically modified to an acetyl group by a compound having an acetyl group. As a result, the binding force between the cellulose fibers is weakened, and the defibration property is improved.

<Cellulose raw material>
In the present invention, as the cellulose raw material, plants (for example, wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, pulp (conifer unbleached kraft pulp (NUKP), conifer bleached kraft pulp (NBKP), broadleaf tree unbleached Bleached kraft pulp (LUKP), broadleaf bleached kraft pulp (LBKP), coniferous unbleached sulphite pulp (NUSP), coniferous bleached sulphite pulp (NBSP) thermomechanical pulp (TMP), recycled pulp, waste paper, etc.), animals (eg Those originating from squirrels), algae, microorganisms (for example, acetic acid bacteria (acetactor)), microbial products, etc. are known, and any of them can be used in the present invention. Pulpose fibers derived from plants or microorganisms are preferable. It is more preferably a plant-derived cellulose fiber.

The fiber diameter of the cellulose fiber raw material used in the present invention is not particularly limited, and the number average fiber diameter is 1 μm to 1 mm. The one that has undergone general purification is about 50 μm. For example, when a chip or the like having a size of several cm is purified, it is preferable to perform mechanical treatment with a dissociator such as a refiner or a beater to make it about 50 μm. The dispersion liquid of the cellulose raw material is preferably water.

<Treatment with a compound having an acetyl group>
In the treatment with a compound having an acetyl group, a part of the hydroxyl groups of cellulose is chemically modified into an acetyl group by the compound having an acetyl group. As a result, the binding force between the cellulose fibers is weakened and the defibration property is improved. Examples of the compound having an acetyl group include acetic anhydride and acetic acid. These may be used alone or in combination of two or more. Of the compounds having an acetyl group, acetic anhydride is preferable.

The mass ratio of the compound having an acetyl group to the cellulose suspension is not particularly limited, but is preferably 0.01 times or more, more preferably 0.05 times or more, based on the number of moles of hydroxyl groups of cellulose. , 100 times or less is preferable, and 50 times or less is more preferable. When the mass ratio of the compound having an acetyl group is within the above range, the effect of improving the yield of fine fibrous cellulose in the defibration step becomes higher.

As the solvent, it is preferable to use a water-soluble organic solvent that does not inhibit acetylation. Examples of the water-soluble organic solvent include organic solvents such as acetone and pyridine, and organic acids such as formic acid, acetic acid and oxalic acid, and organic acids such as acetic acid are particularly preferable. By using an organic acid such as acetic acid, chemical modification proceeds uniformly to cellulose, which facilitates defibration, which will be described later, and it is considered that the obtained composite exhibits high heat resistance and high productivity. Further, a solvent other than the above solvent may be used in combination.

The amount of the solvent used is not particularly limited, but is usually 0.5 times or more, more preferably 1 time or more, preferably 200 times or less, and more preferably 100 times or less with respect to the weight of cellulose. As the catalyst, it is preferable to use a basic catalyst such as pyridine, triethylamine, sodium hydroxide and sodium acetate, and an acidic catalyst such as acetic acid, sulfuric acid and perchloric acid. The amount of the catalyst is not particularly limited and varies depending on the type, but is usually preferably 0.01 times or more, more preferably 0.05 times or more, and preferably 100 times or less, based on the number of moles of hydroxyl groups of cellulose. 50 times or less is more preferable.

The temperature condition is not particularly limited, but if it is too high, there is a concern about yellowing of cellulose and a decrease in the degree of polymerization, and if it is too low, the reaction rate decreases. Therefore, 10 to 130 ° C. is preferable. The reaction time is not particularly limited, and it is several minutes to several tens of hours depending on the chemical modification agent and the chemical modification rate. After the chemical modification in this way, it is preferable to thoroughly wash with an organic solvent or water in order to terminate the reaction. If an unreacted chemical modifier remains, it may cause coloring later or cause a problem when it is compounded with a resin, which is not preferable.

In the present invention, the amount of the substituent introduced into the acetyl group is not particularly limited, but is preferably 1 mol% or more, more preferably 5 mol% or more, and particularly preferably 10 mol% or more, based on the total hydroxyl groups of the cellulose. preferable. Further, 65 mol% or less is preferable, 50 mol% or less is more preferable, and 40 mol% or less is further preferable. Within the above range, a rubber composition having sufficiently improved reinforcing properties can be produced at a relatively high solid content concentration by containing a dry solid of cellulose nanofibers having an acetyl group.

<Defibration>
In the present invention, the device for defibrating is not particularly limited, but a strong shearing force is applied to the aqueous dispersion using a device such as a high-speed rotary type, a colloid mill type, a high-pressure type, a roll mill type, or an ultrasonic type. Is preferable. In particular, in order to efficiently defibrate, it is preferable to use a wet high-pressure or ultra-high pressure homogenizer capable of applying a pressure of 50 MPa or more to the aqueous dispersion and applying a strong shearing force. The pressure is more preferably 100 MPa or more, still more preferably 140 MPa or more. Further, prior to the defibration and dispersion treatment with a high-pressure homogenizer, if necessary, a known mixing, stirring, emulsifying, and dispersing device such as a high-speed shear mixer is used to prepare the cellulose nanofibers having the above acetyl group. It is also possible to apply processing.

When defibrated by the above treatment, the solid content concentration as a cellulose fiber raw material is 0.1% by weight or more, preferably 0.2% by weight or more, particularly 0.3% by weight or more, and 10% by weight or less, particularly 6. It is preferably% by weight or less. If the solid content concentration is too low, the amount of liquid becomes too large with respect to the amount of the cellulose fiber raw material to be treated, resulting in poor efficiency, and if the solid content concentration is too high, the fluidity deteriorates.

<Water-soluble polymer>
In the present invention, the water-soluble polymer means a polymer compound that dissolves in water, for example, cellulose derivatives (carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, ethyl cellulose), xanthan gum, xyloglucan, dextrin, dextran, carrageenan, locust bean. Gum, alginic acid, alginate, purulan, starch, shavings, scraps, positive starch, phosphorylated starch, corn starch, arabic gum, locust bean gum, gellan gum, gellan gum, polydextrose, pectin, chitin, water-soluble chitin, chitosan, casein , Albumin, soybean protein lysate, peptone, polyvinyl alcohol, polyacrylamide, sodium polyacrylic acid, polyvinylpyrrolidone, vinyl acetate, polyamino acid, polylactic acid, polyapple acid, polyglycerin, latex, rosin-based sizing agent, petroleum resin-based Sizing agent, urea resin, melamine resin, epoxy resin, polyamide resin, polyamide / polyamine resin, polyethyleneimine, polyamine, vegetable gum, polyethylene oxide, hydrophilic cross-linked polymer, polyacrylic acid salt, starch polyacrylic acid copolymer, tamarind Gum, gellan gum, starch, guar gum and colloidal silica and one or more mixtures thereof. Among these, it is preferable to use carboxymethyl cellulose or a salt thereof from the viewpoint of affinity. Carboxymethyl cellulose as a water-soluble polymer is different from cellulose nanofibers having an acetyl group into which a carboxymethyl group has been introduced.

<Dry solids>
In the present invention, the dry solid material refers to a solid material obtained by removing the dispersion medium from a dispersion liquid of cellulose nanofibers having an acetyl group. In the present invention, the dry solid material refers to a material in an absolutely dry state or a wet state, and means a solid material in which a dispersion medium is present in an amount of 12% by weight or less. Specifically, from cellulose nanofibers having an acetyl group or a dry solid composed of a dispersion medium of the same amount or less, or a cellulose nanofiber having an acetyl group and a water-soluble polymer, or a dispersion medium of these and the amount or less. Dry solids such as Examples of the dispersion medium include water and an aqueous organic solvent, but water is preferable. Removing the dispersion medium means removing the dispersion medium by dehydrating (dedispersing medium) or drying the dispersion liquid.

In the present invention, a solid or liquid water-soluble polymer may be dissolved or dispersed in the aqueous dispersion. Further, by adjusting the pH of the dispersion to 9 to 11 and then dehydrating or drying, a dry solid having a good affinity between the rubber composition and the cellulose nanofiber having an acetyl group can be obtained. In the present invention, the dispersion liquid of cellulose nanofibers having an acetyl group means a liquid in which cellulose nanofibers having an acetyl group are dispersed in a dispersion medium.

In the present invention, the blending amount of the water-soluble polymer in the dry solid containing the cellulose nanofiber having an acetyl group and the water-soluble polymer is 5 with respect to the absolute dry solid content of the cellulose nanofiber having an acetyl group. It is preferably ~ 50% by weight. If it is less than 5% by weight, a sufficient redispersibility effect is unlikely to be exhibited. On the other hand, if it exceeds 50% by weight, problems such as deterioration of viscosity characteristics and dispersion stability, which are characteristics of cellulose nanofibers having an acetyl group, may occur. Further, although it is not clear why the dry solid containing the cellulose nanofiber having an acetyl group and the water-soluble polymer has a high affinity (dispersibility) with the rubber component, the cellulose nanofiber having the rubber component and the acetyl group is not clear. When mixing, the water-soluble polymer dissolves in the rubber component and the viscosity increases. As a result, it is presumed that the cellulose nanofibers having an acetyl group can be uniformly dispersed in the rubber component by applying a high shear stress during stirring.

The method for dehydrating or drying the dispersion or the mixture may be any conventionally known method, and examples thereof include spray drying, squeezing, air drying, hot air drying, and vacuum drying. Examples of the drying apparatus specifically used in the method of the present invention are as follows. That is, continuous tunnel drying device, band drying device, vertical drying device, vertical turbo drying device, multi-stage disk drying device, aeration drying device, rotary drying device, air flow drying device, spray dryer drying device, spray drying device. , Cylindrical drying device, drum drying device, screw conveyor drying device, rotary drying device with heating tube, vibration transport drying device, batch type box drying device, aeration drying device, vacuum box type drying device, stirring drying device, etc. Can be used alone or in combination of two or more. Among these, it is preferable to use a drum drying device from the viewpoint of energy efficiency because heat energy is directly supplied to the object to be dried uniformly. In addition, the drum drying device is preferable from the viewpoint that the dried product can be recovered immediately without applying heat more than necessary.

<Rubber component>
The rubber component is a raw material for rubber that is crosslinked to become rubber. There are a rubber component for natural rubber and a rubber component for synthetic rubber, but in the present invention, either of them may be used, or both may be combined. For convenience, a rubber component for natural rubber or the like is referred to as a "natural rubber polymer" or the like.

Natural rubber (NR) polymers include natural rubber polymers in the narrow sense that are not chemically modified; chemically modified natural rubber polymers such as chlorinated natural rubber polymers, chlorosulfonated natural rubber polymers, and epoxidized natural rubber polymers; hydrogenated natural Rubber polymer; Examples thereof include deproteinized natural rubber polymer. Examples of the synthetic rubber polymer include butadiene rubber (BR) polymer, styrene-butadiene copolymer rubber (SBR) polymer, isoprene rubber (IR) polymer, acrylonitrile-butadiene rubber (NBR) polymer, chloroprene rubber polymer, and styrene-isoprene. Diene-based rubber polymers such as polymer rubber polymer, styrene-isoprene-butadiene copolymer rubber polymer, isoprene-butadiene copolymer rubber polymer; butyl rubber (IIR) polymer, ethylene-propylene rubber (EPM, EPDM) polymer, acrylic rubber Non-diene type such as (ACM) polymer, epichlorohydrin rubber (CO, ECO) polymer, fluororubber (FKM) polymer, silicone rubber (Q) polymer, urethane rubber (U) polymer, chlorosulfonated polyethylene (CSM) polymer, etc. Examples include rubber polymers. Only one kind of these rubber polymers may be used, or a plurality of kinds thereof may be used in combination. Of these, diene-based rubber is preferable. These may be used alone or in combination of two or more.

In the present invention, the rubber component is preferably used as an aqueous dispersion (latex) of the rubber component. Here, the aqueous dispersion (latex) containing a rubber component is a system (emulsion) in which fine particles of the rubber component are stably dispersed in the water solution, and the solid content concentration of the rubber component is usually 30 to 70. It is about%. Further, the pH of the aqueous dispersion of the rubber component is preferably 7 to 12.

When the cellulose nanofiber having an acetyl group and the dry solid containing a water-soluble polymer are mixed in the rubber component, the weight ratio of the cellulose nanofiber having the acetyl group to the absolute dry solid content of the rubber component is It is preferably 1 to 50% by weight. If the ratio is less than 1% by weight, a sufficient effect of improving the tensile strength will not be exhibited when the crosslinked rubber composition is obtained. On the other hand, if the ratio exceeds 50% by weight, the processability of the rubber composition is lowered.

The lower limit of the total solid content concentration of the mixture obtained in this step is preferably 10% by weight or more, more preferably 15% by weight or more, still more preferably 20% by weight or more. The upper limit of the concentration is preferably 100% by weight or less, more preferably 90% by weight or less, and further preferably 80% by weight or less. In the production method of the present invention, a dry solid obtained by removing a dispersion medium from a dispersion containing cellulose nanofibers having an acetyl group, which has not been studied conventionally, is subjected to mixing with a rubber component to increase the solid content concentration. Prepare a high mixture. Therefore, the production method of the present invention is excellent in work efficiency and productivity. Further, by dispersing at a high solid content concentration, sufficient shear stress is applied to the cellulose nanofibers having an acetyl group, and the redispersibility is improved, so that a rubber composition having excellent mechanical strength can be produced with high work efficiency and high work efficiency. Achieved to be productive.

<Rubber composition>
The rubber composition of the present invention is produced by removing water or the like derived from latex or the dry solid from a mixture of the rubber component and the dry solid. When the dry solid contains a dispersion medium other than water, water and the dispersion medium are removed from the mixture of the rubber component and the dry solid. In the present invention, water or a dispersion medium is also referred to as a "liquid medium". The method for removing the liquid medium is not particularly limited, and the mixture may be dried as it is in an oven, or may be coagulated and then dehydrated or dried. At this time, the pH may be adjusted to 2 to 6.

In the present invention, the above rubber composition and other necessary rubbers and compounding agents are mixed by a conventionally known method using, for example, a rubber kneader, and crosslinked by a conventionally known method (when sulfur is used, " It can also be called "vulcanization"). In the present invention, the rubber composition includes a composition before cross-linking and a cross-linked composition, but the composition before cross-linking is also referred to as an "uncross-linked rubber composition" and the composition after cross-linking is also referred to as a "cross-linked rubber composition". Say.

In addition to the above-mentioned components, the rubber composition of the present invention includes, for example, a reinforcing agent, a silane coupling agent, a vulcanizing agent, stearic acid, a vulcanization accelerator, and other compounding agents conventionally used in the rubber industry. Vulcanization accelerators, oils, hardened resins, waxes, anti-aging agents, deliquescent agents, colorants, pH adjusters, etc. can be blended.

As the reinforcing agent, any of those used for tire applications can be preferably used, but it is particularly preferable to use at least one of carbon black and silica.

The vulcanized rubber composition of the present invention is not particularly limited in its use, but is suitable for tires due to its characteristics. For example, it can be used as a pneumatic tire for passenger cars, trucks, buses, heavy vehicles, and the like.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

<Manufacture of cellulose nanofibers having an acetyl group>
The bleached unbeaten kraft pulp (whiteness 85%) derived from softwood was dispersed in acetic acid and filtered three times, and the water in the cellulose fiber raw material was replaced with acetic acid. These were mixed at a ratio of 20 ml of acetic acid and 10 ml of acetic anhydride with respect to 1 g (dry weight) of the cellulose fiber, and the acetic acid-substituted cellulose fiber raw material was added thereto. Then, the cellulose fibers were acetylated by reacting at 115 ° C. for 5 hours with stirring. After the reaction, the reaction solution was filtered and washed in the order of methanol and desalinated water to obtain a cellulose fiber raw material having an acetyl group.
Ion-exchanged water was added to the pulp obtained after washing and then stirred to obtain a 0.5% (w / v) slurry. This pulp slurry was treated three times with an ultra-high pressure homogenizer (20 ° C., 150 MPa) to obtain a cellulose nanofiber dispersion having an acetyl group.

<Example 1>
Carboxymethyl cellulose (trade name: F350HC-4) was added to the 0.5% by weight aqueous dispersion of the above-mentioned cellulose nanofibers having an acetyl group in an amount of 30% by weight based on the cellulose nanofibers having an acetyl group, and a TK homomixer was added. The mixture was stirred at (12,000 rpm) for 60 minutes. 0.5% by weight of an aqueous sodium hydroxide solution was added to this aqueous dispersion to adjust the pH to 9, and then the vapor pressure was 0.5 MPa. G, dried in a drum dryer D0405 (Katsuragi Kogyo) having a drum rotation speed of 2 rpm to obtain a mixed dry solid of cellulose nanofibers having an acetyl group having a water content of 5% by weight and carboxymethyl cellulose. The mixed dry solid is mixed in an amount of 5% by weight equivalent to absolute dryness with 100 g of an absolute dry solid content of rubber latex (trade name: HA Latex, Reditex Co., Ltd., solid content concentration 65% by weight), and TK homomixer (8000 rpm). ) Was stirred for 60 minutes to obtain a mixture. The mixture had a very high total solid content concentration of 68.25% by weight. The mixture was dried in a heating oven at 70 ° C. for 15 hours to obtain a masterbatch.

Zinc oxide and stearic acid were mixed in an open roll (manufactured by Kansai Roll Co., Ltd.) with 6% by weight and 0.5% by weight of the rubber components in the masterbatch, respectively, with respect to the masterbatch obtained by the above method. A kneaded product was obtained by kneading at 30 ° C. for 10 minutes. Sulfur and vulcanization accelerators (BBS, Nt-butyl-2-benzothiazolesulfenamide) were added to the kneaded product in an amount of 3.5% by weight and 0.7% by weight, respectively, based on the rubber components in the kneaded product. % And kneaded at 30 ° C. for 10 minutes using an open roll (manufactured by Kansai Roll Co., Ltd.) to obtain a sheet of an unvulcanized rubber composition. The obtained sheet of the unvulcanized rubber composition was sandwiched between molds and press-vulcanized at 150 ° C. for 10 minutes to obtain a vulcanized rubber sheet having a thickness of 2 mm. The obtained vulcanized rubber sheet is cut into test pieces having a predetermined shape, and according to JIS K6251 "Vulcanized rubber and thermoplastic rubber-How to obtain tensile properties", it is assumed that the tensile strength is shown at 100% strain. The stress and breaking strength at the time of 300% strain were measured. The larger each value is, the better the vulcanized rubber composition is reinforced, and the more excellent the mechanical strength is.

In this example, the vulcanized rubber composition was produced using a mixture having a very high total solid content concentration of 68.25% by weight, but the dispersion of cellulose nanofibers having an acetyl group in the rubber matrix was good. , Excellent mechanical properties were obtained as shown in Table 1.

<Example 2>
When the aqueous dispersion of cellulose nanofibers having an acetyl group was dried, it was carried out in the same manner as in Example 1 except that the cellulose nanofibers having an acetyl group were dried alone without mixing carboxymethyl cellulose.

<Comparative example 1>
In Example 1, a masterbatch was obtained in the same manner as in Example 1 except that a mixed dry solid of cellulose nanofibers having an acetyl group and carboxymethyl cellulose was not added.

<Comparative example 2>
The same procedure as in Example 2 was carried out except that an aqueous dispersion of cellulose nanofibers having an acetyl group (solid content concentration: 0.5% by weight) was used instead of the dry solids of cellulose nanofibers having an acetyl group. .. The amount of cellulose nanofibers having an acetyl group with respect to the rubber component was the same as in Example 2.

From the above results, in Example 1 using a mixed dry solid of cellulose nanofibers having an acetyl group and a water-soluble polymer, and in Example 2 using a dry solid of cellulose nanofibers having an acetyl group, an acetyl group was used. Compared with Comparative Example 1 in which the cellulose nanofibers having the above-mentioned were not used and Comparative Example 2 in which the cellulose nanofiber aqueous dispersion having an undried acetyl group was used, the stress at 100% and 300% strains was clearly larger. It can be seen that the vulgarized rubber composition is well reinforced and has excellent mechanical strength. This is because the solid content concentration is high in the mixture of the rubber component and the cellulose nanofibers having an acetyl group, so that sufficient shear stress is generated during stirring to improve the dispersibility of the cellulose nanofibers having an acetyl group. It is presumed that it was a result. Further, it is clear that the present invention is excellent in productivity and workability because the vulcanized rubber composition can be obtained from the mixture having a high solid content concentration.

Claims (9)

A method for producing a rubber composition containing cellulose nanofibers having an acetyl group, which is a dry solid product containing cellulose nanofibers having an acetyl group of 1 mol% or more and 65 mol% or less with respect to all hydroxyl groups of cellulose. A method for producing a rubber composition, which comprises a step of mixing an aqueous dispersion containing a rubber component. The method for producing a rubber composition according to claim 1, further comprising a step of removing a dispersion medium from a dispersion of cellulose nanofibers having an acetyl group to prepare the dry solid. The first aspect of claim 1, wherein the dry solid containing the cellulose nanofibers having an acetyl group contains 5 to 50% by weight of a water-soluble polymer with respect to the absolute dry solid content of the cellulose nanofibers having an acetyl group. Method for producing rubber composition. The dry solid containing cellulose nanofibers having an acetyl group is obtained by removing a dispersion medium from a dispersion liquid containing cellulose nanofibers having an acetyl group and a water-soluble polymer with a drum dryer. Or the method for producing a rubber composition according to 3. The dry solid containing the cellulose nanofibers having an acetyl group adjusts the pH of the dispersion liquid containing the cellulose nanofibers having an acetyl group and the water-soluble polymer to 9 to 11, and then removes the dispersion medium. The method for producing a rubber composition according to any one of claims 1, 3 or 4, which is obtained. The rubber composition according to claim 2, wherein the dispersion liquid of the cellulose nanofibers having an acetyl group contains 5 to 50% by weight of a water-soluble polymer with respect to the absolute dry solid content of the cellulose nanofibers having an acetyl group. Manufacturing method. The dispersion liquid of the cellulose nanofibers having an acetyl group contains a water-soluble polymer, and in the preparation step, a dispersion medium is prepared from the dispersion liquid containing the cellulose nanofibers having an acetyl group and the water-soluble polymer by a drum dryer. The method for producing a rubber composition according to claim 2 or 6, which is removed. The dispersion liquid of the cellulose nanofibers having an acetyl group contains a water-soluble polymer, and in the preparation step, the pH of the dispersion liquid containing the cellulose nanofibers having an acetyl group and the water-soluble polymer is adjusted to 9 to 11. The method for producing a rubber composition according to any one of claims 2, 6 or 7, wherein the dispersion medium is removed after the process. The method for producing a rubber composition according to any one of claims 3 to 8, wherein the water-soluble polymer is carboxymethyl cellulose or a salt thereof.