JP2015025141A - Rubber composition and method for producing rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition that allows a microfibrillated vegetable fiber to be favorably dispersed in a rubber component and has improved fracture characteristics, to provide a method for producing a rubber composition allowing a microfibrillated vegetable fiber to be favorably dispersed in a rubber component and to provide a tire using the rubber composition that can improve fracture characteristics without deteriorating fuel consumption.SOLUTION: The rubber composition includes (A) a rubber component and (B) a microfibrillated vegetable fiber having an average value of fiber length of 1-20 μm, an average value of fiber diameter of 10 μm or less and an aspect ratio of 2-1,000.

Description

  The present invention relates to a rubber composition containing a rubber component and specific microfibrillated plant fibers, a tire using the rubber composition, and a method for producing the rubber composition.

  In rubber compositions, it has been conventionally known that physical properties of rubber are improved by containing cellulose fibers as a filler to be blended in a rubber component (for example, Patent Document 1). Patent Document 1 discloses a master batch obtained by stirring and mixing an aqueous dispersion of cellulose short fibers and rubber latex, and removing water from the mixed solution. However, cellulose fibers are poorly compatible with rubber, and when blended as a rubber composition, sufficient effects cannot be obtained in terms of breaking characteristics and energy loss at the interface, etc. It is difficult to put it into practical use for various purposes. Therefore, in order to improve the compatibility between cellulose fibers and rubber components, it has been proposed to use microfibrillated plant fibers obtained by microfibrillating cellulose (for example, Patent Document 2).

  However, microfibrillated plant fibers have a long fiber length and have a network with a branched structure. Therefore, when fiber reinforced rubber is produced by directly blending microfibrillated plant fibers with rubber, dispersion in the rubber component Due to the occurrence of agglomerates of microfibrillated plant fibers having poor properties, there was a problem that the fracture characteristics of the resulting rubber composition deteriorated.

JP 2006-206864 A

  An object of the present invention is to provide a rubber composition in which microfibrillated plant fibers are well dispersible in a rubber component and have improved breaking characteristics. Another object of the present invention is to provide a method for producing a rubber composition in which microfibrillated plant fibers are well dispersible in a rubber component. It is another object of the present invention to provide a tire using the rubber composition capable of enhancing the fracture characteristics without deteriorating fuel consumption.

  As a result of intensive studies to solve the above problems, the present inventors have a specific average fiber length, average fiber diameter, and aspect ratio as microfibrillated plant fibers dispersed in a rubber component, In particular, by applying a material having a short average fiber length, it can be dispersed well in the rubber component. As a result, in the rubber composition, agglomerates that are the starting point of destruction can be reduced, and the rubber composition is destroyed. It has been found that the characteristics can be improved.

  The present invention has been completed based on such findings.

Item 1. A rubber composition comprising (A) a rubber component, and (B) a microfibrillated plant fiber having an average fiber length of 1 to 20 μm, an average fiber diameter of 10 μm or less, and an aspect ratio of 2 to 1000.

  Item 2. Item 2. The rubber composition according to Item 1, wherein the microfibrillated plant fiber (B) is obtained by mechanically defibrating after treating the pulp with acid.

  Item 3. Item 3. The rubber composition according to Item 1 or 2, wherein the content of the microfibrillated plant fiber (B) is 1 to 100 parts by mass with respect to 100 parts by mass of the rubber component (A).

  Item 4. Item 4. The rubber composition according to Item 2 or 3, wherein the mechanical defibrating treatment is a grinding treatment.

Item 5. (A) a step of treating with pulp and acid,
(B) a step of preparing microfibrillated plant fibers by mechanically defibrating the acid-treated pulp;
(C) The step of mixing the microfibrillated plant fiber obtained in step (b) and the rubber latex to disperse the microfibrillated plant fiber in the rubber latex, and (d) the dispersion obtained in step (c). A method for producing a rubber composition comprising a step of drying a liquid.

  Item 6. Item 6. The method for producing a rubber composition according to Item 5, wherein the acid in the step (a) is at least one selected from the group consisting of hydrochloric acid, sulfuric acid, acetic acid, and formic acid.

  Item 7. Item 7. The method for producing a rubber composition according to Item 5 or 6, wherein the amount of acid added in the step (a) is 5 to 100 parts by mass with respect to 100 parts by mass of the pulp.

  Item 10. Item 10. The method for producing a rubber composition according to any one of Items 5 to 9, further comprising a step of washing with water after the acid treatment in the step (a).

  Item 11. Item 11. The method for producing a rubber composition according to any one of Items 5 to 10, wherein the mechanical defibrating treatment in the step (b) is a grinding treatment.

  Item 12. Item 5. The rubber composition according to any one of Items 1 to 4, which is used for tires.

  Item 13. Item 15. A pneumatic tire using the rubber composition according to any one of Items 1 to 4 and 12.

  Hereinafter, the present invention will be described in detail.

  The rubber composition of the present invention contains (A) a rubber component, and (B) a specific microfibrillated plant fiber.

  Examples of the rubber component (A) include diene rubber components. Specifically, natural rubber (NR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), isoprene rubber (IR) ), Butyl rubber (IIR), acrylonitrile-butadiene rubber (NBR), acrylonitrile-styrene-butadiene copolymer rubber, chloroprene rubber, styrene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, isoprene-butadiene copolymer Examples thereof include polymer rubber, chlorosulfonated polyethylene, modified natural rubber such as epoxidized natural rubber (ENR), hydrogenated natural rubber, deproteinized natural rubber, and the like. Examples of the rubber component other than the diene rubber component include ethylene-propylene copolymer rubber, acrylic rubber, epichlorohydrin rubber, polysulfide rubber, silicone rubber, fluorine rubber, and urethane rubber. These rubber components may be used alone or in combination of two or more. What is necessary is just to mix | blend suitably also in the blend ratio in the case of blending according to various uses.

  The microfibrillated plant fiber (B) used in the present invention has an average fiber length (hereinafter also referred to as an average fiber length) shorter than that of conventional microfibrillated plant fibers, and therefore has a fiber network and entanglement. It is difficult to occur, and when dispersed in the rubber component, aggregation is suppressed and it can be favorably dispersed. The average fiber length of such microfibrillated plant fibers (B) is 1 μm or more, preferably 2 μm or more, and more preferably 5 μm or more. When the average fiber length is less than 1 μm, the rubber reinforcing effect tends not to be remarkably exhibited. The average fiber length of the microfibrillated plant fiber (B) is 20 μm or less, preferably 15 μm or less, and more preferably 10 μm or less. If the average fiber length exceeds 20 μm, the fiber network and entanglement will occur, the dispersibility in the rubber component will deteriorate, and the effect of restraining the rubber will work strongly, resulting in a deterioration in the fracture characteristics of the rubber. Tend to.

  The average fiber diameter (hereinafter also referred to as average fiber diameter) of the microfibrillated plant fiber (B) is 10 μm or less, preferably 1 μm or less, and more preferably 0.2 μm or less. When the average fiber diameter exceeds 10 μm, it tends to agglomerate when dispersed in the rubber component, deteriorating the fracture characteristics of the rubber, and because the fiber itself is large, it becomes the starting point of fracture when the rubber is deformed. As a result, there is a tendency for the fracture characteristics of the rubber to deteriorate. The upper limit of the average fiber diameter is not particularly limited, but is preferably 4 nm or more from the viewpoint of good operability when forming a master batch with rubber in an aqueous system.

  The aspect ratio of the microfibrillated plant fiber (B) is calculated by the ratio of the average fiber diameter to the average fiber length (the average fiber length / average fiber diameter). The aspect ratio is 2 or more, preferably 10 or more, and more preferably 50 or more. When the aspect ratio is less than 2, the rubber reinforcing effect tends to be hardly exhibited. Further, the aspect ratio is 1000 or less, preferably 500 or less, and more preferably 300 or less. When the aspect ratio exceeds 1000, the effect of restraining rubber works strongly, and as a result, the fracture characteristics of rubber tend to deteriorate.

  The method for producing the microfibrillated plant fiber (B) having the specific average fiber length, average fiber diameter, and aspect ratio is not particularly limited. For example, as described in the method for producing a rubber composition described later, pulp After acid treatment, it is obtained by mechanically defibrating.

  From the viewpoint that the content of the microfibrillated plant fiber (B) in the rubber composition can exhibit a rubber reinforcing effect without deteriorating the dispersibility of the microfibrillated plant fiber in the rubber, the rubber component (A) Within the range of 1 to 50 parts by mass with respect to 100 parts by mass, more preferably within the range of 2 to 35 parts by mass, and even more preferably within the range of 3 to 20 parts by mass.

  The present invention includes (a) a step of treating pulp with an acid, (b) a step of preparing microfibrillated plant fibers by mechanically defibrating the acid-treated pulp, (c) step (b) A step of mixing the microfibrillated plant fiber obtained in step 1) and rubber latex, dispersing the microfibrillated plant fiber in the rubber latex, and (d) drying the dispersion obtained in step (c). The present invention also relates to a method for producing the rubber composition.

  The pulp to be acid-treated in the step (a) may be any pulp that has been used in the production of conventional microfibrillated cellulose, and the lignin has not been removed, has been partially removed, or is completely removed. Any of those removed may be used.

  As a plant raw material for supplying pulp used in producing the microfibrillated plant fiber (B), a wide variety of plant raw materials for supplying pulp used in the production of conventional microfibrillated cellulose are used. For example, wood, bamboo, hemp, jute, kenaf, crop waste, cloth, recycled pulp, and waste paper. Preferred are wood, bamboo, hemp, jute, kenaf, and crop residue.

  The method for pulping the plant material is not particularly limited, and is performed by a conventional method. For example, a mechanical pulping method for mechanically pulping plant materials can be applied. Examples of the mechanical pulp (MP) obtained by the mechanical pulping method include groundwood pulp (GP), refiner mechanical pulp (RMP), thermomechanical pulp (TMP), and chemithermomechanical pulp (CTMP).

  Also, chemical pulp (CP) obtained by chemically or mechanically and mechanically pulping plant raw materials by chlorination, alkali treatment, oxygen oxidation treatment, sodium hypochlorite treatment, sulfite treatment, etc. Kraft pulp (KP), sulfite pulp (SP), etc.), semi-chemical pulp (SCP), chemiground pulp (CGP), and chemimechanical pulp (CMP) can also be used. Further, the pulp may be subjected to chemical modification treatment that is commonly used in the pulp field as necessary, and examples thereof include pulp subjected to etherification treatment, pulp treated with an aromatic ring of lignin, and the like. . The etherification treatment mainly includes etherification treatment of hydroxyl groups present in cellulose, hemicellulose, and lignin. Further, the treatment of the lignin aromatic ring includes introducing a desired substituent into the lignin aromatic ring.

  The modification treatment described above chemically modifies the hydroxyl group in the glucose unit of cellulose forming the pulp, and is different from the pulp treatment with acid described later.

  In step (a), the pulp is treated with an acid. Here, “treating the pulp with an acid” means that the glycoside bond of the cellulose portion having low crystallinity in the cellulose fiber forming the pulp is partially hydrolyzed by the acid, and as a result, the pulp Can be partially cut. Therefore, it is possible to obtain microfibrillated plant fibers having a short average fiber length by subjecting the pulp after the treatment with acid to a defibrating treatment described later.

  Examples of the acid used in the step (a) include hydrochloric acid, sulfuric acid, acetic acid, formic acid and the like. Among these, hydrochloric acid is used from the viewpoint that it is excellent in the efficiency and cost of hydrolysis and the efficiency of washing after the reaction. preferable.

  The addition amount of the acid is preferably in the range of 5 to 100 parts by mass, and in the range of 10 to 50 parts by mass, with respect to 100 parts by mass of the pulp, from the viewpoint of good balance between the efficiency of hydrolysis and the cost. More preferably, it is more preferably within the range of 20 to 40 parts by mass.

  Here, in the case of a solution containing an acid, the “addition amount of acid” means the addition amount of the acid component excluding the solution.

  The reaction temperature between the pulp and the acid is preferably in the range of 50 to 100 ° C., more preferably in the range of 70 to 97 ° C., and 80 to 95 ° C. from the viewpoint that the hydrolysis is easily controlled and the efficiency is good. It is further preferable to be within the range.

  The reaction time between the pulp and the acid is preferably in the range of 0.1 to 10 hours, more preferably in the range of 0.5 to 5 hours, from the viewpoint that the fraction that has not been hydrolyzed can be suppressed. More preferably within the time range.

  It is preferable that the acid-treated pulp is further washed with water to remove unreacted acid from the viewpoint of suppressing contamination in subsequent steps and deterioration of the pulp itself.

  In the step (a), the pulp treated with an acid is mechanically defibrated in the step (b), whereby the microfibrillated plant fiber having the above average fiber length, average fiber diameter, and aspect ratio is obtained. Is obtained. The defibrating process is performed in the presence of water. As a method of defibrating treatment, mechanically using a refiner, twin screw kneader (double screw extruder), twin screw kneader, high pressure homogenizer, medium stirring mill, stone mill, grinder, vibration mill, sand grinder, etc. The method of grinding or beating is mentioned. By these methods, the pulp is defibrated or refined into microfibrillated plant fibers. A preferable temperature in the defibrating treatment is 0 to 99 ° C, more preferably 0 to 90 ° C. It is desirable that the pulp that is the raw material for the defibrating process has a shape (for example, a powder form) suitable for such a defibrating process. In addition, it is advantageous in terms of reducing the defibrating energy when the pulp is steamed with steam (for example, heated in a pressure cooker in the presence of moisture) prior to the defibrating treatment.

  A preferable defibrating method is grinding treatment, and it is preferable to use a stone mill type grinding machine or a twin screw kneading extruder. The grinding may be performed until the fiber diameter reaches a desired size.

  The raw pulp is mechanically defibrated without acid treatment, and then the resulting plant fiber is acid-treated to obtain the above-mentioned average fiber length, average fiber diameter, and aspect ratio. Although it is possible to obtain fibrillated plant fibers, in this method, since the viscosity is improved after the acid treatment, the viscosity must be controlled. The washing treatment of the microfibrillated plant fibers after the reaction treatment In the case of carrying out the process, the process tends to be complicated from the viewpoint of poor drainage and greatly deteriorated workability.

  In addition, the lignin contained in the microfibrillated plant fiber (B) may be further chemically removed or not removed.

  If the lignin is not completely removed chemically, it is presumed that the matrix portion composed of lignin and hemicellulose filling the space between the microfibrillated cellulose is broken and microfibrillated (microfibrillated). Therefore, the microfibrillated plant fiber (B) obtained by mechanical fibrillation treatment is composed of cellulose, hemicellulose and protolignin (lignin in a state existing in the plant tissue) inherent in the plant material. It is presumed that this structure is retained. A structure in which hemicellulose and / or lignin is coated partly or entirely around cellulose microfibrils and / or cellulose microfibril bundles, in particular, hemicellulose covers cellulose microfibrils and / or cellulose microfibril bundles, It is presumed to have a structure covered with lignin. However, it is presumed that there will also be a portion where hemicellulose and / or lignin is removed and the hemicellulose or cellulose fiber length is exposed on the surface.

  In JP 2001-342353 A, an acetone solution of a phenol derivative is added to a defatted wood powder obtained by degreasing wood powder (ethanol: benzene = 1: 2 solution) to sorb the phenol derivative, and phosphoric acid is added. Although a composition obtained by treatment is described, this composition is different from the microfibrillated plant fiber (B) used in the present invention in that it is not microfibrillated.

  In the step (c), the microfibrillated plant fiber obtained in the step (b) and the rubber latex are mixed, and the microfibrillated plant fiber is dispersed in the rubber latex.

The solid content concentration of the microfibrillated plant fiber dispersed in the step (c) is preferably 0.1% by mass or more in the dispersion from the viewpoint that the yield of each material during solidification is good. More preferably, it is more preferably 0.5% by mass or more. The solid content concentration of the microfibrillated plant fiber is preferably 10% by mass or less, more preferably 5% by mass or less, and 2% by mass in the dispersion from the viewpoint of good mixing efficiency with the rubber component (A). The following is more preferable.

  The solid content concentration of the rubber component dispersed in the step (c) is preferably 0.5% by mass or more, preferably 1.0% by mass or more in the dispersion, from the viewpoint that the yield of each material during solidification is good. Is more preferable, and 1.5 mass% or more is still more preferable. The solid content concentration of the rubber component is preferably 30% by mass or less, more preferably 20% by mass or less, and further preferably 10% by mass or less in the dispersion from the viewpoint of good mixing efficiency with the microfibrillated plant fiber. preferable.

  The amount of the microfibrillated plant fiber added does not deteriorate the dispersibility of the microfibrillated plant fiber in the rubber at the time of coagulation, and from the viewpoint that the rubber reinforcing effect can finally be exhibited, the rubber contained in the dispersion liquid The range of 1-50 mass parts is preferable with respect to 100 parts by mass of the component, more preferably within the range of 2-35 mass parts, and even more preferably within the range of 3-20 mass parts.

  The dispersion obtained in step (c) is coagulated with an acid and then dried.

  Examples of the acid for solidifying the solid content in the dispersion include formic acid, acetic acid, hydrochloric acid, and sulfuric acid.

  The rubber composition (masterbatch) obtained by the above method further comprises reinforcing fillers such as carbon black and silica; silane compounds such as silane coupling agents; process oils; waxes; anti-aging agents; sulfur and vulcanization. Vulcanizing agents such as accelerators; vulcanizing aids such as zinc oxide and stearic acid can be appropriately blended.

  In the rubber composition of the present invention, since the acid-treated microfibrillated plant fiber (B) has a particularly short average fiber length, a network is formed like conventional microfibrillated plant fibers. The entanglement is less likely to occur and is well dispersed in the rubber component (A). Therefore, aggregates that are the starting point of destruction can be reduced, and the fracture characteristics can be improved. Therefore, it is suitably used for tires, and when used for tires, it is possible to improve durability and improve steering stability without deteriorating low fuel consumption characteristics.

  When the rubber composition of the present invention is used for tires, it is a microfibrillated plant having a specific average fiber length, average fiber diameter, and aspect ratio as described above using a Banbury mixer, a kneader, an open roll or the like. The rubber composition containing the fiber (B) can be further applied as a tire rubber composition by kneading a desired additive.

  The present invention also relates to a pneumatic tire using the rubber composition. A pneumatic tire is manufactured by a normal method using the rubber composition of the present invention. That is, the rubber composition of the present invention is further mixed with a desired compounding agent and kneaded, and the resulting kneaded product is extruded in accordance with the shape of various members of the tire at an unvulcanized stage. An unvulcanized tire is formed by molding in the usual manner. A tire can be obtained by heating and pressurizing this unvulcanized tire in a vulcanizer.

  In the rubber composition of the present invention, since the microfibrillated plant fiber (B) treated with an acid has a particularly short average fiber length, it is well dispersed in the rubber component (A). Therefore, aggregates that are the starting point of destruction can be reduced, and the fracture characteristics can be improved. Therefore, when used for tires, the durability can be improved without deteriorating fuel consumption.

  Furthermore, by the method for producing a rubber composition of the present invention, a microfibrillated plant fiber (B) having a short average fiber length can be produced and can be well dispersed in the rubber component (A).

  The present invention will be described more specifically with reference to the following examples and comparative examples. In addition, this invention is not limited to the following embodiment.

-Example 1, Comparative example 1, and Reference example 1
<Preparation of microfibrillated plant fiber 1>
Bleached kraft pulp from softwood was diluted with water to a solid content concentration of 2.0% by mass. Thereafter, hydrochloric acid was added so that the hydrochloric acid concentration in the batch was 0.6%, and the mixture was stirred at 90 ° C. for 2 hours. The obtained mixture was repeatedly washed with water until the pH reached about 7.0, and then dehydrated so that the solid concentration was 30% by mass. Next, microfibrillated plant fiber 1 was prepared by treating the obtained hydrous pulp with a twin-screw kneader / extruder having an operating condition of 400 rpm and 0 ° C.

  The average fiber length of the obtained microfibrillated plant fiber 1 was about 8 μm, the average fiber diameter was about 40 nm, and the aspect ratio was about 200, as a result of observation by an electron microscope.

<Preparation of microfibrillated plant fiber 2>
The same softwood-derived bleached kraft pulp as in <Preparation of microfibrillated plant fiber 1> is treated with a twin-screw kneading extruder under an operating condition of 400 rpm and 0 ° C. at a solid content concentration of 30% by mass without acid treatment. Thus, microfibrillated plant fiber 2 was prepared.

  The average fiber length of the obtained microfibrillated plant fiber 1 was about 200 μm, the average fiber diameter was about 100 nm, and the aspect ratio was about 2000, as a result of observation by an electron microscope.

<Preparation of master batch>
Preparation of Masterbatch 1 Microfibrillated plant fiber 1 (solid content concentration: 30% by mass) described in Table 1 was added to a high speed homogenizer (IKA batch homogenizer T25 Ultra Turrax (Ultraturrax) in the amount of water described in Table 1. Using T25)), the mixture is stirred and dispersed at 24,000 rpm for 1 hour, and then the amount of natural rubber latex described in Table 1 (Golden Hope Plantations, HYTEX-HA, solid content concentration 60 mass%) is added. The mixture was further stirred and dispersed for 30 minutes. The obtained mixed solution was further coagulated with a 5% aqueous formic acid solution, washed with water, and dried in a heating oven at 40 ° C. to obtain a master batch 1.

Preparation of masterbatch 2 A masterbatch 2 was prepared in the same manner as the preparation of masterbatch 1 except that microfibrillated plant fiber 2 was used.

Preparation of masterbatch 3 Without using microfibrillated plant fibers, 250 g of a natural rubber latex having a solid content of 60% by mass used in the preparation of masterbatch 1 was coagulated with a 5% aqueous formic acid solution, washed with water, and heated at 40 ° C. Masterbatch 3 was obtained by drying in an oven.

  The compounding quantity of the microfibrillated plant fiber in the said masterbatch 1-3, water, and natural rubber latex is shown.

<Preparation of vulcanized rubber composition>
According to the composition of Table 2, various master batches and compounding agents were kneaded for 5 minutes with a 6-inch open roll at 60 ° C. and 24 rpm, and then press-heated at 150 ° C., Example 1, Comparative Example 1, and Reference Example A vulcanized rubber composition corresponding to 1 was obtained.

  The detail of each compounding component used when preparing a vulcanized rubber composition is shown below.

Anti-aging agent: NOCRACK 6C (Ouchi Shinsei Chemical Co., Ltd.)
Stearic acid: Bead stearic acid Tsubaki (manufactured by NOF Corporation)
Zinc oxide: 2 types of zinc oxide (Mitsui Metal Mining Co., Ltd.)
Sulfur: Powdered sulfur (manufactured by Tsurumi Chemical Co., Ltd.)
Vulcanization accelerator: Noxeller DM (Ouchi Shinsei Chemical Co., Ltd.)

<Physical property evaluation>
The following evaluation was performed using the vulcanized rubber composition produced by the above method. Note that the tensile strength index, breaking elongation index, breaking energy index, and rolling resistance index in the characteristic data shown in Table 3 were calculated by the following formula using Reference Example 1 as a reference composition.

(Tensile test)
The breaking stress and breaking elongation were measured according to JIS K6251 “Vulcanized rubber and thermoplastic rubber—How to obtain tensile properties”. The following formula:
Tensile strength index = (breaking stress of each compound) ÷ (breaking stress of standard compound) × 100
Breaking elongation index = (breaking elongation of each compound) ÷ (breaking elongation of the standard compound) × 100
Fracture energy index = (breaking stress of each formulation x breaking elongation ÷ 2) ÷ (breaking stress of standard formulation x breaking elongation ÷ 2) x 100
Was used to calculate the tensile strength index, the breaking elongation index, and the breaking energy index. The larger the index, the better the vulcanized rubber composition is reinforced, and the higher the mechanical strength of the rubber, the better the fracture characteristics.

(Rolling resistance index)
A test specimen for measurement was cut out from a 2 mm rubber slab sheet of the vulcanized rubber composition prepared by the above-described method, and the temperature was 70 ° C. and the initial strain was 10% using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho). E * (complex elastic modulus) and tan δ (loss tangent) of each test specimen were measured under the conditions of dynamic strain 2% and frequency 10 Hz. The following formula:
Rolling resistance index = (tan δ of each formulation) ÷ (tan δ of standard formulation) × 100
The steering stability index and rolling resistance index were calculated.

  A smaller rolling resistance index indicates better rolling resistance characteristics when used as a pneumatic tire.

Claims (9)

(A) a step of treating the pulp with an acid;
(B) By mechanically defibrating the acid-treated pulp, microfibrillation having an average fiber length of 1 to 20 μm, an average fiber diameter of 10 μm or less, and an aspect ratio of 2 to 1000 Preparing plant fibers,
(C) The step of mixing the microfibrillated plant fiber obtained in step (b) and the rubber latex to disperse the microfibrillated plant fiber in the rubber latex, and (d) the dispersion obtained in step (c). A method for producing a rubber composition comprising a step of drying a liquid. The method for producing a rubber composition according to claim 1, wherein the acid in the step (a) is at least one selected from the group consisting of hydrochloric acid, sulfuric acid, acetic acid, and formic acid. The method for producing a rubber composition according to claim 1 or 2, wherein an addition amount of the acid in the step (a) is 5 to 100 parts by mass with respect to 100 parts by mass of the pulp. The manufacturing method of the rubber composition in any one of Claims 1-3 including the process of washing with water after the acid treatment in a process (a). The method for producing a rubber composition according to any one of claims 1 to 4, wherein the mechanical defibrating treatment in the step (b) is a grinding treatment. A rubber composition obtained by the production method according to claim 1,
A rubber composition comprising (A) a rubber component, and (B) a microfibrillated plant fiber having an average fiber length of 1 to 20 μm, an average fiber diameter of 10 μm or less, and an aspect ratio of 2 to 1000. The rubber composition according to claim 6, wherein the content of the microfibrillated plant fiber (B) is 1 to 100 parts by mass with respect to 100 parts by mass of the rubber component (A). The rubber composition according to claim 6 or 7, which is used for tires. A pneumatic tire using the rubber composition according to claim 6.