Method for producing composite material, and composite material

Abstract

To provide a method for producing a composite material and a composite material in which water absorption property can be reduced without hydrophobing nano-cellulose.SOLUTION: A method for producing a composite material according to the present invention includes: a step of mixing rubber latex containing a rubber component, oxidized cellulose and / or nano-cellulose, and unsaturated carboxylic acid salt containing at least any one of aluminum ion, zinc ion and iron ion to obtain a first mixture; a step (S40) of performing ion exchange of the first mixture to obtain a second mixture; a step (S50) of heating the second mixture and reducing moisture content to obtain a third mixture; and a step (S60) of kneading the third mixture to obtain a composite material. The oxidized cellulose and nano-cellulose are derived from an oxide of cellulose-based raw material by hypochlorous acid or a salt thereof, and are not derived from an oxide of cellulose-based raw material by N-oxyl compound.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a composite material containing nanocellulose and the composite material. [Background technology]

[0002] In recent years, plant-derived cellulose nanofibers, which have a low environmental impact as part of the Sustainable Development Goals (SDGs), have been attracting attention. In this context, rubber composite materials using cellulose nanofibers as fiber reinforcement have also been proposed (Patent Document 1).

[0003] However, cellulose nanofibers are generally available commercially as aqueous dispersions, which must be mixed with a rubber component dispersion (latex) and then dried to obtain a solid rubber composite. During this drying process, the cellulose nanofibers bond and aggregate, leaving numerous agglomerates in the rubber composite. These agglomerates are known to affect basic physical properties of rubber products, such as tensile strength and elongation at break.

[0004] Therefore, a method for producing a composite material containing nanocellulose that reduces nanocellulose agglomerates and is easy to apply to rubber products has been proposed (Patent Document 2).

[0005] According to the composite material manufacturing method of Patent Document 2, it is possible to manufacture a composite material with few nanocellulose agglomerates, and by using the composite material as a masterbatch for rubber products, nanocellulose can be easily applied to rubber products.

[0006] On the other hand, a method for producing a composite material has also been proposed in which cellulose nanofibers are hydrophobized by converting the hydrophilic hydroxyl groups into hydrophobic groups, thereby improving compatibility with matrices such as synthetic resins and forming composites (e.g., Non-Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-95611 [Patent Document 2] International Publication No. 2023 / 219077 [Non-patent literature]

[0008] [Non-Patent Document 1] Daisuke Kuroki, "Development Status of Modified Cellulose Nanofibers," Journal of the Imaging Society of Japan, Vol. 55, No. 3, 2016: 369-374 Summary of the Invention [Problem to be solved by the invention]

[0009] However, as in Non-Patent Document 1, if nanocellulose is made hydrophobic, the nanocellulose particles tend to aggregate, making dispersion difficult, and the physical properties of the composite material deteriorate.

[0010] Furthermore, in the presence of moisture, the interaction between the hydrophilic groups in nanocellulose and the rubber molecules is broken, which is thought to affect the composite formation, so it is necessary to suppress the water absorption of composite materials.

[0011] Therefore, the present invention provides a composite material and a method for producing the same that can reduce water absorption without hydrophobizing nanocellulose.The present invention also provides a composite material in which the hybridization of nanocellulose and rubber molecules is not affected even in the presence of water. [Means for solving the problem]

[0012] The present invention has been made to solve at least some of the above-mentioned problems, and can be realized as the following aspects or application examples.

[0013] [1] One aspect of the method for producing a composite material according to the present invention is to A step of mixing rubber latex containing a rubber component, oxidized cellulose and / or nanocellulose, and an unsaturated carboxylate salt containing at least any one of aluminum ions, zinc ions, and iron ions to obtain a first mixture; performing ion exchange of the first mixture to obtain a second mixture; heating the second mixture to reduce the water content to obtain a third mixture; kneading the third mixture to obtain a composite material; Including, The oxidized cellulose and nanocellulose are characterized in that they are derived from the oxidation of a cellulosic raw material with hypochlorous acid or its salt, and are not derived from the oxidation of a cellulosic raw material with an N-oxyl compound.

[0014] [2] One aspect of the method for producing a composite material according to the present invention is to A step of mixing rubber latex containing a rubber component, oxidized cellulose and / or nanocellulose, and an unsaturated carboxylate salt containing at least any one of aluminum ions, zinc ions, and iron ions to obtain a first mixture; performing ion exchange of the first mixture to obtain a second mixture; heating the second mixture to reduce the water content to obtain a third mixture; kneading the third mixture to obtain a composite material; Including, The oxidized cellulose and nanocellulose are characterized by having a structure in which the hydroxyl groups at the second and third positions of the glucopyranose ring are oxidized and carboxyl groups are introduced.

[0015] [3] In any one embodiment of the method for producing a composite material, The step of obtaining the first mixture includes: a step of mixing the rubber latex, the oxidized cellulose and / or the nanocellulose, and the unsaturated carboxylate to obtain a mixed solution; heating the mixture to reduce the water content to obtain a first mixture; may include:

[0016] [4] In any one embodiment of the method for producing a composite material, The rubber component can be natural rubber.

[0017] [5] In any one embodiment of the method for producing a composite material, In the step of obtaining the first mixed liquid, the oxidized cellulose and / or the nanocellulose may be contained in an amount of 10 parts by mass or more and 30 parts by mass or less per 100 parts by mass of the rubber component.

[0018] [6] In any one embodiment of the method for producing a composite material, The unsaturated carboxylate may be contained in an amount of 0.8 to 7.0 times the equivalent of the carboxyl group contained in the oxidized cellulose and / or nanocellulose.

[0019] [7] In any one embodiment of the method for producing a composite material, In the step of obtaining the third mixture, the second mixture can be heated so that the moisture content of the third mixture becomes 3% or less.

[0020] [8] In any one embodiment of the method for producing a composite material, The composite material may have a water absorption rate of 10% or less in a water absorption test in which the composite material is immersed in water at 70°C for 48 hours.

[0021] [9] In any one embodiment of the method for producing a composite material, The composite material may have a rate of change of 20% modulus value in a tensile test based on JIS K6251 after the water absorption test relative to 20% modulus value before the water absorption test within ±20%.

[0022]

[10] One aspect of the composite material according to the present invention is The present invention relates to a rubber composition, a composition for producing a rubber composition, and a composition for producing a rubber composition comprising: a rubber component; nanocellulose; and an unsaturated carboxylate salt containing any one of aluminum ions, zinc ions, and iron ions; A composite material, wherein the nanocellulose is derived from the oxidation of a cellulosic raw material with hypochlorous acid or a salt thereof, and is not derived from the oxidation of a cellulosic raw material with an N-oxyl compound; The composite material is characterized in that the water absorption rate in a water absorption test in which the composite material is immersed in water at 70°C for 48 hours is 10% or less.

[0023]

[11] One aspect of the composite material according to the present invention is The present invention relates to a rubber composition, a composition for producing a rubber composition, and a composition for producing a rubber composition comprising: a rubber component; nanocellulose; and an unsaturated carboxylate salt containing any one of aluminum ions, zinc ions, and iron ions; The nanocellulose has a structure in which the hydroxyl groups at the second and third positions of the glucopyranose ring are oxidized and carboxyl groups are introduced, The composite material is characterized in that the water absorption rate in a water absorption test in which the composite material is immersed in water at 70°C for 48 hours is 10% or less. [Effects of the Invention]

[0024] According to one aspect of the composite material and the manufacturing method of the composite material of the present invention, the composite material has few nanocellulose agglomerates, yet the deterioration of physical properties due to water absorption is small. According to one aspect of the composite material of the present invention, the composite material has few nanocellulose agglomerates, yet the physical properties of the composite material are maintained even in the presence of water. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a flowchart of a method for producing a composite material according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0026] Preferred embodiments of the present invention will be described in detail below with reference to the drawings. Note that the embodiments described below do not unduly limit the content of the present invention as set forth in the claims. Furthermore, not all of the configurations described below are necessarily essential constituent elements of the present invention. Note that "to" indicates that the upper and lower limits are included unless otherwise specified.

[0027] A. Composite materials The composite material according to this embodiment includes a rubber component, nanocellulose, and an unsaturated carboxylate containing at least one of aluminum ions, zinc ions, and iron ions, and the oxidized cellulose is derived from the oxidation of a cellulosic raw material with hypochlorous acid or a salt thereof, but is not derived from the oxidation of a cellulosic raw material with an N-oxyl compound. The composite material according to this embodiment also includes a rubber component, nanocellulose, and an unsaturated carboxylate containing one of aluminum ions, zinc ions, and iron ions, and the nanocellulose has a structure in which the second and third hydroxyl groups of the glucopyranose ring are oxidized to introduce carboxyl groups.

[0028] The composite material may be used as a masterbatch for blending nanocellulose into rubber products. The composite material is moisture-free or low-moisture due to the drying process used to obtain the first mixture (described below). Normally, nanocellulose molecules tend to aggregate due to hydrogen bonding. However, this aggregation is suppressed by the rubber component and the unsaturated carboxylate salt containing at least aluminum ions, zinc ions, and iron ions. Therefore, the composite material does not contain cellulose aggregates that can be identified visually (by visual observation of scanning electron microscope images). Visually identifiable cellulose aggregates can often be identified if they have a maximum width of 10 μm or more, and can be reliably identified if they have a maximum width of 50 μm or more.

[0029] Furthermore, when the composite material is mixed as a masterbatch with an additional rubber component, the nanocellulose in the composite material is easily defibrated and dispersed by the rubber component and at least one of aluminum ions, zinc ions, and iron ions. The additional rubber component preferably does not contain water. Therefore, the composite material has few nanocellulose agglomerates, providing excellent reinforcement for rubber products. The composite material can also be used as a masterbatch for rubber products and diluted with the rubber component. The quality of a composite material is determined by visual observation, but visually observing a portion of the composite material to identify agglomerates is insufficient because it does not determine the overall condition. Therefore, it is preferable to determine the defibration and dispersion of nanocellulose through physical property testing. The physical properties of a composite material can be determined by a significant improvement in the 50% modulus (σ50) measured by tensile testing due to the addition of nanocellulose. Improvements in tensile strength (Tb) can also be used as a criterion for composite material properties. While improving elongation at break (Eb) is also an important factor, increasing the nanocellulose content decreases Eb, so it is preferable to adjust the criterion to match the increase in 50% modulus. In addition, rubber products diluted using the composite material as a masterbatch have improved elongation at break (Eb) compared to the composite material, so there are no problems when using the rubber products. The criteria for judging the quality of a composite material can be the comprehensive evaluation criteria in the examples described later.

[0030] The content of oxidized cellulose and / or nanocellulose in the composite material is 10 parts by mass or more but less than 50 parts by mass, for example, 10 parts by mass or more but less than 30 parts by mass, per 100 parts by mass of the rubber component. To improve physical properties, the content of oxidized cellulose and / or nanocellulose is preferably 10 parts by mass or more, more preferably 20 parts by mass or more. Furthermore, if the content of oxidized cellulose and / or nanocellulose is 50 parts by mass or more, processing becomes difficult, if it is less than 50 parts by mass it is processable, and if it is 30 parts by mass or less it is easier to process.

[0031] The composite material can contain at least one of aluminum ions, zinc ions, and iron ions in an amount of 0.8 to 7.0 times equivalent relative to the carboxyl groups contained in the oxidized cellulose and / or nanocellulose, preferably 1.0 to 6.0 times equivalent, and more preferably 1.5 to 4.5 times equivalent.

[0032] The composite material is less likely to absorb water due to the reduced sodium ions, as described below. The composite material is less likely to absorb water, which can prevent the deterioration of physical properties in a humid environment. For example, the composite material can have a water absorption rate of 10% or less, and even 6% or less, in a water absorption test in which the composite material is immersed in water at 70°C for 48 hours.

[0033] The composite material shows little deterioration in its physical properties before and after water absorption. This is presumably because the hydrophobic interaction between the nanocellulose and rubber molecules in the composite material is maintained even after water absorption. For example, the composite material shows a decrease in the water absorption rate compared to the 20% modulus value in a tensile test based on JIS K6251 before the water absorption test. The rate of change in the 20% modulus value in the tensile test after the test preferably does not exceed -20%, and is preferably within ±20% in terms of the stability of physical properties. For example, in the case of a composite material, the rate of change in the 50% modulus value in the tensile test based on JIS K6251 after the water absorption test relative to the 50% modulus value in the tensile test based on JIS K6251 before the water absorption test preferably does not exceed -12%, and is preferably within ±12%, in terms of the stability of physical properties. For example, in the case of a composite material, the rate of change in the tensile strength value in the tensile test based on JIS K6251 after the water absorption test relative to the tensile strength value in the tensile test based on JIS K6251 before the water absorption test preferably does not exceed -35%, and is preferably within ±35%, in terms of the stability of physical properties. For example, in the case of a composite material, the rate of change in the breaking elongation value in the tensile test based on JIS K6251 after the water absorption test relative to the breaking elongation value in the tensile test based on JIS K6251 before the water absorption test preferably does not exceed -10%, and is preferably within ±10% in terms of the stability of physical properties.

[0034] B. Raw materials Next, each raw material used in the production of the composite material according to this embodiment will be described.

[0035] B-1. Nanocellulose Nanocellulose is a nano-sized version of oxidized cellulose obtained by oxidizing a cellulosic raw material with hypochlorous acid or its salts. Nanocellulose and oxidized cellulose are derived from the oxidation of a cellulosic raw material with hypochlorous acid or its salts, and are not derived from the oxidation of a cellulosic raw material oxidized with an N-oxyl compound. Here, the oxidized cellulose can also be referred to as an oxide of a cellulosic raw material. In other words, nanocellulose includes the oxidation of a cellulosic raw material with hypochlorous acid or its salts. Here, nanocellulose is a general term for cellulose that has been micronized (also called nanoized), and includes cellulose nanofibers, cellulose nanocrystals, etc.

[0036] Nanocellulose can be obtained by oxidizing cellulosic raw materials with hypochlorous acid or its salts, and this oxidation does not require the use of N-oxyl compounds such as TEMPO. Therefore, nanocellulose and oxidized cellulose are substantially free of N-oxyl compounds. Herein, the phrase "substantially free of N-oxyl compounds" means that the nanocellulose and oxidized cellulose each contain no N-oxyl compounds, or that the content of N-oxyl compounds is 2.0 ppm by mass or less, preferably 1.0 ppm by mass or less, relative to the total amount of nanocellulose and oxidized cellulose. Furthermore, "substantially free of N-oxyl compounds" also refers to the increase in the content of N-oxyl compounds from the cellulosic raw materials, preferably 2.0 ppm by mass or less, more preferably 1.0 ppm by mass or less. The content of N-oxyl compounds can be measured using a trace total nitrogen analyzer (e.g., Mitsubishi Chemical Analytical Co., Ltd., Model: TN-2100H).

[0037] Nanocellulose contains carboxyl groups, which may be in the H form (-COOH) or in the salt form (-COO- X + :X + is an anion that forms a salt form), or the carboxy group may be modified by reacting with another compound to form a covalent bond. The type of salt is not particularly limited, but examples include alkali metal salts such as lithium, sodium, and potassium; alkaline earth metal salts such as calcium salts and barium salts; other metal salts such as magnesium salts and aluminum salts; ammonium salts, and organic amine salts. When the carboxy group is modified by a covalent bond, the other compound is not particularly limited as long as it reacts with a carboxylic acid. The carboxy group of nanocellulose is preferably in the salt form, more preferably in the alkali metal form, and even more preferably in the sodium form.

[0038] The cellulosic raw material in the present invention is not particularly limited as long as it is a material mainly composed of cellulose, and examples thereof include pulp, natural cellulose, regenerated cellulose, and cellulose raw materials mechanically produced. Examples of suitable cellulose-based raw materials include fine cellulose depolymerized by processing. Commercially available products such as crystalline cellulose made from pulp can be used as is as the cellulosic raw material. Unused biomass containing a large amount of cellulose components, such as soybean hulls and soybean pulp, can also be used as the raw material. When oxidizing a cellulosic raw material, the cellulosic raw material may be treated with an alkali of an appropriate concentration to facilitate the penetration of the oxidizing agent into the raw pulp. Cellulose is the main component of plants, and bundles of cellulose molecules are called cellulose microfibrils. The cellulose in the cellulosic raw material used in the present invention is also contained in the form of cellulose microfibrils.

[0039] As described above, nanocellulose is derived from oxidized cellulose. Preferably, this oxidized cellulose has a structure in which at least two of the hydroxyl groups on the glucopyranose ring that constitutes the cellulose have been oxidized. More specifically, it is preferable that the hydroxyl groups at the second and third positions on the glucopyranose ring have been oxidized and carboxyl groups have been introduced. Furthermore, it is preferable that the hydroxyl group at the sixth position on the glucopyranose ring in oxidized cellulose is not oxidized and remains as a hydroxyl group. Nanocellulose also preferably has a structure similar to the above-described structure. Therefore, the oxidized cellulose and nanocellulose of the present invention can be referred to as oxidized cellulose having a structure in which the hydroxyl groups at the second and third positions on the glucopyranose ring have been oxidized and carboxyl groups have been introduced, respectively, or nanocellulose having a structure in which the hydroxyl groups at the second and third positions on the glucopyranose ring have been oxidized and carboxyl groups have been introduced. Furthermore, the oxidized cellulose and nanocellulose of the present invention can also be referred to as oxidized cellulose in which the hydroxyl groups at the second and third positions of the glucopyranose ring have been oxidized to introduce carboxyl groups, and a hydroxyl group at the sixth position of the glucopyranose ring, respectively, or nanocellulose in which the hydroxyl groups at the second and third positions of the glucopyranose ring have been oxidized to introduce carboxyl groups, and a hydroxyl group at the sixth position of the glucopyranose ring. Note that the position of the carboxyl group on the glucopyranose ring of oxidized cellulose is determined by the solid 13 It can be analyzed by C-NMR spectroscopy.

[0040] The structure of the glucopyranose ring can also be determined by analysis according to the method described in Sustainable Chem. Eng. 2020, 8, 48, 17800-17806.

[0041] The average fiber length of nanocellulose is preferably 50 to 2000 nm. If the average fiber length exceeds 2000 nm, the slurry containing nanocellulose tends to thicken and become less easy to handle. Furthermore, if the average fiber length is less than 50 nm, the viscosity characteristic of nanocellulose tends to be less pronounced and tends to decrease. Furthermore, an average fiber length of 50 to 2000 nm is preferable because it further improves the reinforcing effect of rubber products, such as rigidity, tensile strength, and elongation at break. The average fiber length is more preferably 100 to 1000 nm, even more preferably 100 to 500 nm, even more preferably 100 to 400 nm, and even more preferably 100 to 250 nm.

[0042] The average fiber width of nanocellulose is not particularly limited, but is preferably 1 to 200 nm. An average fiber width of 1 to 200 nm is preferable because it further improves the reinforcing effect of rubber products, such as rigidity, tensile strength, and elongation at break. The average fiber width is more preferably 1 to 10 nm, and even more preferably 1 to 5 nm.

[0043] In nanocellulose, the aspect ratio (average fiber length / average fiber width), which is the ratio of the average fiber width to the average fiber length, is preferably 20 or more and 200 or less. An aspect ratio of 200 or less is preferable because it further improves the reinforcing effect of rubber products, such as rigidity, tensile strength, and elongation at break. From this perspective, the aspect ratio is more preferably 145 or less, even more preferably 130 or less, and even more preferably 120 or less. It is preferably 20 or more, more preferably 30 or more, even more preferably 100 or less. On the other hand, if the aspect ratio is too low, that is, if the shape of the nanocellulose is thick rod-like rather than elongated fiber-like, aggregation occurs due to uneven distribution, and dispersibility tends to decrease. Therefore, the aspect ratio is preferably 20 or more, more preferably 30 or more, even more preferably 35 or more, and even more preferably 40 or more.

[0044] The average fiber width and average fiber length were calculated by mixing nanocellulose with water to a nanocellulose concentration of approximately 1 to 10 ppm, air-drying the resulting diluted cellulose aqueous dispersion on a mica substrate, and then randomly selecting a number of fibers from the resulting image. The cross-sectional height of the nanocellulose was calculated as the fiber width, and the perimeter divided by 2 was calculated as the fiber length. Image processing software can be used to calculate these average fiber widths and lengths. While the image processing conditions are arbitrary, differences in the calculated values ​​may occur even for the same image. The range of difference between the values ​​under different conditions is preferably within ±100 nm for the average fiber length. The range of difference between the values ​​under different conditions is preferably within ±10 nm for the average fiber width. The average fiber length can be calculated by binarizing and analyzing the resulting images using the image processing software "Image J." The number-average fiber length can be calculated for 100 fibers by dividing the fiber length by perimeter by 2. The software included with the MFP-3D infinity can be used to calculate the number-average fiber width [nm] for 50 or more fibers, where the cross-sectional height of the shape image is equal to the fiber width.

[0045] The amount of carboxy groups in nanocellulose is preferably 0.20 to 2.0 mmol / g. A carboxy group amount of 0.20 mmol / g or more can impart sufficient defibration properties to oxidized cellulose. This allows for dispersion-stabilized nanocellulose to be obtained even when defibration treatment is performed under mild conditions. On the other hand, a carboxy group amount of 2.0 mmol / g or less allows for the production of nanocellulose with a low proportion of particulate cellulose and uniform quality. This improves the dispersibility of nanocellulose, and tends to further improve the reinforcing effect of rubber products, such as rigidity, tensile strength, and elongation at break. From this perspective, the amount of carboxy groups in nanocellulose is more preferably 0.35 mmol / g or more, even more preferably 0.40 mmol / g or more, even more preferably 0.42 mmol / g or more, even more preferably 0.50 mmol / g or more, even more preferably greater than 0.50 mmol / g, and even more preferably 0.55 mmol / g or more. The upper limit of the carboxyl group content may be 1.5 mmol / g or less, 1.2 mmol / g or less, 1.0 mmol / g or less, or 0.9 mmol / g or less. A preferred range of the carboxyl group content can be determined by appropriately combining the above-mentioned upper and lower limits. The carboxyl group content of nanocellulose is more preferably 0.35 to 2.0 mmol / g, even more preferably 0.35 to 1.5 mmol / g, even more preferably 0.40 to 1.5 mmol / g, even more preferably 0.50 to 1.2 mmol / g, even more preferably more than 0.50 to 1.2 mmol / g, and even more preferably 0.55 to 1.0 mmol / g. In one embodiment, the carboxyl group content of nanocellulose is preferably 0.50 mmol / g to 0.90 mmol / g.

[0046] The amount of carboxyl groups (mmol / g) was calculated using the following formula from the amount of sodium hydroxide (a) consumed in the neutralization stage of weak acids, where the change in electrical conductivity is gradual, after adding 0.1 M hydrochloric acid to an aqueous solution of oxidized cellulose or nanocellulose mixed with water to adjust the pH to 2.5, and then adding 0.05 N sodium hydroxide dropwise.

[0047] Amount of carboxyl group = a (ml) x 0.05 / mass of oxidized cellulose or nanocellulose (g) The amount of carboxyl groups can be adjusted by changing the reaction time, reaction temperature, pH of the reaction solution, etc. of the oxidation reaction.

[0048] The composite material of the present invention contains nanocellulose, but oxidized cellulose can also be used to prepare the composite material. The oxidized cellulose of the present invention can be easily defibrated, and at least a portion of the oxidized cellulose can be defibrated into nanocellulose during the process of mixing / stirring with the components that make up the composite material. Oxidized cellulose and nanocellulose are commercially available, or may be produced by oxidizing a cellulose-based raw material with hypochlorous acid or a salt thereof. A suitable commercially available product is Aronfibro (registered trademark), an oxidized cellulose and nanocellulose manufactured by Toagosei Co., Ltd.

[0049] Oxidized cellulose and nanocellulose are available as aqueous dispersions or dried products. From the viewpoint of workability when producing the composite material of the present invention, oxidized cellulose and nanocellulose are preferably in the form of aqueous dispersions. The nanocellulose solids content of aqueous dispersions of oxidized cellulose and nanocellulose is generally 0.01% to 10% by mass, but may also be 0.01% to 5% by mass, or 0.1% to 2% by mass. If the nanocellulose solids content in the aqueous dispersion is less than 0.01% by mass, the drying step described below will take a long time. If it exceeds 10% by mass, uniform processing will be impossible and nanocellulose aggregates will likely form.

[0050] Nanocellulose can be produced, for example, by a method comprising step A, in which a cellulosic raw material is oxidized with hypochlorous acid or a salt thereof to obtain oxidized cellulose, and step B, in which the oxidized cellulose is defibrated. A composite material may be produced using the oxidized cellulose obtained in step A, or a composite material may be produced using the nanocellulose obtained in step B. Oxidized cellulose and nanocellulose can be produced with reference to, for example, International Publication Nos. WO2022 / 009979 and WO2022 / 009980.

[0051] B-2. Rubber component The rubber component of the composite material is provided as a rubber latex containing the rubber component. The rubber component is preferably natural rubber (NR), carboxy-modified nitrile rubber (X-NBR), or carboxystyrene butadiene rubber (X-SBR), and can be natural rubber. The rubber latex preferably contains ammonia. By including ammonia in the rubber latex, sodium ions contained in the first mixture can be substituted with ammonium ions in the step of obtaining a second mixture, which will be described later. The ammonia content in the rubber latex is 0.01% or more, preferably 0.1% to 0.7%. The rubber latex can be natural rubber latex containing 0.01% or more, preferably 0.1% to 0.7% ammonia. The weight-average molecular weight of the rubber component is preferably 50,000 to 3,000,000, and more preferably 100,000 to 2,000,000. In the present invention, the "weight average molecular weight" refers to a value measured in terms of standard polystyrene by gel permeation chromatography (GPC) using tetrahydrofuran as a solvent.

[0052] Carboxy-modified nitrile rubber (carboxy-modified acrylonitrile butadiene rubber) or carboxy-modified styrene butadiene rubber is a modified diene rubber that has been functionalized with carboxy groups. The carboxy groups in carboxy-modified nitrile rubber or carboxy-modified styrene butadiene rubber can increase the affinity with nanocellulose that has phosphorus oxo acid groups, and when kneaded, the carboxy groups bond with the nanocellulose, thereby enhancing the fiber-defibrating ability. In addition, natural rubber It is thought that the defibration ability is enhanced by the interaction between the free radicals generated by mastication and nanocellulose.

[0053] The composite material may also contain known fillers that are commonly compounded in rubber compositions. Examples of fillers include carbon black, silica, clay, aluminum hydroxide, calcium carbonate, mica, talc, aluminum hydroxide, aluminum oxide, titanium oxide, barium sulfate, and lecithin. The composite material may also contain a crosslinking agent. The crosslinked body and / or rubber product of this embodiment can be suitably obtained by including a crosslinking agent in the composite material. These fillers and crosslinking agents may be added, for example, at the stage of obtaining the first mixture, the second mixture, or the third mixture, or when the third mixture is kneaded to obtain the composite material.

[0054] B-3. ​​Unsaturated carboxylic acid salts Unsaturated carboxylates containing at least aluminum ions, zinc ions, or iron ions are used in the production of composite materials. Therefore, the unsaturated carboxylates are water-soluble. Examples of unsaturated carboxylates include (meth)acrylic acid, maleic acid (anhydride), fumaric acid, itaconic acid (anhydride), crotonic acid, and their salts. By mixing the water-soluble unsaturated carboxylates with oxidized cellulose and latex, the carboxyl and carbonyl groups form hydrogen bonds with the carbonyl or hydroxyl groups of the nanocellulose, thereby forming pseudo-crosslinks between the nanocelluloses. Metals that form these salts include aluminum, zinc, and iron. The unsaturated carboxylates can be at least one selected from aluminum acrylate, zinc acrylate, iron acrylate, aluminum methacrylate, zinc methacrylate, and iron methacrylate. When forming the unsaturated carboxylate compounds, one or more of the above metals can be used to form metal salt compounds. The content of the unsaturated carboxylates is explained in "C. Method for Manufacturing Composite Materials." The unsaturated carboxylate is preferably water-soluble so that it can be mixed with rubber latex. If the unsaturated carboxylate is not water-soluble, it may be dissolved in water using a cationic surfactant such as dodecylmethylammonium chloride.

[0055] C. Composite Material Manufacturing Methods Next, a method for producing a composite material will be described. Fig. 1 is a flowchart of a method for producing a composite material according to one embodiment. The method for producing a composite material can use the raw materials described in B above. The method for producing a composite material can produce the composite material described in A above.

[0056] 1, the method for producing a composite material includes a step of obtaining a first mixture, a step of obtaining a second mixture (S40), a step of obtaining a third mixture (S50), and a step of obtaining a composite material (S60). The step of obtaining the first mixture can include a step of obtaining a mixed solution (S10) and a step of obtaining the first mixture (S30). In this embodiment, an example will be described in which a kneading step (S20) is further included after S10.

[0057] S10: The step of obtaining a mixed solution is a step of obtaining a mixed solution by mixing rubber latex containing a rubber component, oxidized cellulose and / or nanocellulose, and an unsaturated carboxylate containing at least any one of aluminum ions, zinc ions, and iron ions. The oxidized cellulose and nanocellulose are derived from the oxidation of a cellulosic raw material with hypochlorous acid or its salts, and are not derived from the oxidation of a cellulosic raw material with an N-oxyl compound. The oxidized cellulose and nanocellulose have a structure in which the hydroxyl groups at the second and third positions of the glucopyranose ring are oxidized to introduce carboxyl groups. The rubber latex, oxidized cellulose, and unsaturated carboxylate are all provided in an aqueous solvent and can be mixed using a known mixer. If the unsaturated carboxylate is not water-soluble, it can be dissolved in water using a surfactant. The rubber latex may be mixed with the mixture from the above-mentioned mixture. As the stirrer, for example, a magnetic stirrer, a propeller stirrer, or the like can be used.

[0058] In the step (S10) of obtaining a mixed solution, the amount of oxidized cellulose and / or nanocellulose can be 10 parts by mass or more but less than 50 parts by mass, and preferably 10 parts by mass or more but less than 30 parts by mass, per 100 parts by mass of the rubber component. When the amount of oxidized cellulose and / or nanocellulose in the step of obtaining a mixed solution is 10 parts by mass or more per 100 parts by mass of the rubber component, composite materials containing high concentrations of oxidized cellulose and / or nanocellulose can be provided to the market, and it is more preferable that the amount be 20 parts by mass or more. Furthermore, if the amount is less than 50 parts by mass, stirring and kneading are possible, and in consideration of workability, it is more preferable that the amount be 30 parts by mass or less. The rubber component is not limited as long as it can be used as a rubber latex, but natural rubber, carboxy-modified nitrile rubber, or carboxy-modified styrene-butadiene rubber is preferred.

[0059] The amount of unsaturated carboxylate can be adjusted appropriately depending on the salt type and the purpose of blending. The mixed solution is blended so that it contains 0.8 to 7.0 equivalents of unsaturated carboxylate containing at least one of aluminum ions, zinc ions, and iron ions relative to the carboxy groups contained in the oxidized cellulose and / or nanocellulose. While 1 equivalent is theoretically appropriate, depending on the type of latex and the required properties of the rubber product, less than 1 equivalent may be blended. Furthermore, more than 1 equivalent may be blended due to uneven distribution of additives or incompatibility of local structure. As mentioned above, an amount of 0.8 equivalents or more is preferred because it inhibits aggregation of oxidized cellulose and / or nanocellulose through the development of a pseudo-crosslinked structure. An amount of 7.0 equivalents or less is preferred because the impact of aggregation of excess unsaturated carboxylate on the rubber product is relatively small. Furthermore, from the viewpoint of suppressing aggregation of oxidized cellulose and / or nanocellulose and aggregation of excess material, it is more preferable that the amount of aluminum ions, zinc ions, and iron ions is 1.5 to 4.5 equivalents relative to the carboxyl groups of oxidized cellulose and / or nanocellulose.

[0060] Here, the amounts of aluminum ions, zinc ions, and iron ions can be calculated according to the molar amount of carboxy groups contained in the nanocellulose. For example, if the total amount of anions derived from the carboxy groups of the nanocellulose used in S10 is 0.7 mmol / g, the amount of unsaturated carboxylate can be calculated so that it is 0.8 to 7.0 times the molar amount.

[0061] For example, if the carboxyl group of nanocellulose is 0.7 mmol / g, then 20 g (20 parts by mass) of nanocellulose will be 14 mmol, and to this, for example, 1.6 g of zinc methacrylate should be added in an amount equivalent to 1, or 3.3 g in an amount equivalent to 2.

[0062] S20: Kneading the Mixed Liquid is a step of kneading the mixed liquid obtained in S10. In the kneading step, the viscosity of the mixed liquid at 25°C measured using a vibration viscometer in accordance with JIS Z8803 (2011) is preferably 100 mPa·s to 1000 mPa·s. A tuning fork vibration rheometer, for example, can be used as the vibration viscometer. If the viscosity of the mixed liquid is within the above range, kneading can be performed by utilizing the restoring force due to the elasticity of the mixed liquid. The region in which the mixed liquid exhibits elasticity is determined by a stress-strain curve obtained using a dynamic viscoelasticity test, and is a range in which the elastic modulus is constant regardless of stress and in which stress and strain are proportional. Such an elastic region can also be estimated from the viscosity of the mixed liquid. Kneading can be performed using a device capable of applying a certain degree of shear force to the mixed liquid, such as a planetary mixer, a three-roll mill, or a two-roll mill. S10 can be performed until the viscosity of the mixed liquid becomes nonlinear (i.e., resembles a non-Newtonian fluid).

[0063] S30: The step of obtaining a first mixture is a step of heating the mixed liquid after the kneading step of S20 to reduce the water content and obtain a first mixture. In the step of obtaining a first mixture, the mixed liquid may be heated to evaporate the water. The mixed liquid is heated, for example, in an oven at 40 to 60°C for 1 to 24 hours. The first mixture preferably has a water content of 15% or less. Reducing the water content of the first mixture improves the workability in the next step. The water content can be measured using a heat-dry moisture meter. Alternatively, the water content may be calculated from the blend amounts by measuring the masses before and after drying. For the drying step of S30, any known method can be used as long as it can efficiently remove the aqueous solvent from the mixed liquid. For example, degassing while heating may be used. In addition, although the water content of the mixed liquid is reduced in this embodiment, this is not limited thereto. If washing is possible in S40, the mixed liquid obtained in S20 may be used as the first mixture as is.

[0064] S40: The step of obtaining a second mixture is a step of performing ion exchange on the first mixture obtained in S30 to obtain a second mixture. The ion exchange process involves washing the first mixture to reduce the sodium ions in the first mixture and obtain a second mixture. The step of obtaining a second mixture can also be performed by placing the first mixture in water. Because the sodium ions in the first mixture flow out into the water, it is preferable to use running water. In the washing step, other components may be added to the water as long as the sodium ions can migrate from the first mixture into the running water. As the sodium ions in the first mixture decrease, the water absorption capacity of the composite material decreases. The sodium ions in the first mixture are replaced by ammonium ions contained in, for example, rubber latex. The reduction in sodium in the second mixture can be confirmed by X-ray fluorescence analysis.

[0065] S50: The step of obtaining a third mixture involves heating the second mixture to reduce the moisture content and obtain a third mixture. In the step of obtaining a third mixture, the moisture content in the second mixture is evaporated and reduced by heating. The second mixture is heated, for example, in an oven at 40°C to 160°C for 1 hour to 24 hours. If the moisture content of the third mixture is 3% or less, kneading in S60 is possible, which is preferable. The moisture content can be measured by the method described above.

[0066] S60: The process for obtaining a composite material involves kneading the third mixture to obtain a composite material. The third mixture contains numerous aggregates of nanocellulose due to the reduction in moisture caused by S50. It is presumed that the presence of the rubber component, aluminum ions, and unsaturated carboxylate salts in the mixture inhibits bonding of nanocellulose particles together. Kneading the mixture in this state by applying high shear force improves the dispersion of nanocellulose in the rubber component, which is preferable. Kneading in S60 can be carried out by compressing the third mixture and then using the elastic recovery of the rubber component to significantly move the nanocellulose.

[0067] The process for obtaining the S60 composite material is not particularly limited, but for example, an open roll method, an internal kneading method, or a multi-screw extrusion kneading method can be used, of which the open roll method is preferred.

[0068] When kneading using the open-roll method, the third mixture is wrapped around one of the rolls and kneaded to appropriately sever the molecular chains of the rubber component and generate free radicals. Because these free radicals easily bond with nanocellulose, it is preferable to include this step in the manufacturing method of the composite material. In the manufacturing method of the composite material of the present invention, it is preferable to further include a thin-threading step after this kneading.

[0069] The roll gap in the thinning step is preferably more than 0 mm and not more than 1 mm, more preferably more than 0 mm and not more than 0.5 mm, and even more preferably 0.1 mm or more and not more than 0.5 mm.

[0070] The roll surface temperature in the thin-threading process is preferably 0°C or higher and 50°C or lower. It is more preferable that the temperature is between 0°C and 30°C.

[0071] The number of times of treatment in the thin-threading step is preferably from 1 to 10 times, and more preferably from 1 to 5 times.

[0072] The surface speed ratio of the two rolls in the thinning process is preferably 1.05 or more and 3.00 or less, more preferably 1.05 or more and 2.00 or less, even more preferably 1.05 or more and 1.5 or less, and particularly preferably 1.05 or more and 1.20 or less.

[0073] By setting the roll gap, roll surface temperature, number of treatments, and roll surface speed ratio in the thin-passing process as described above, the temperature of the composite material itself can be adjusted to between 0°C and 70°C, more preferably between 0°C and 50°C, and even more preferably between 5°C and 30°C. By adjusting the temperature to within this range and kneading, the elasticity of the rubber component can be used to defibrate the nanocellulose, and the defibrated nanocellulose can be dispersed in the composite material.

[0074] The composite material may be removed from the kneader as a masterbatch (intermediate), and then re-introduced into the kneader, after which additional rubber components may be added and kneaded. In this case, it is preferable from the viewpoint of processability that the additional rubber components be solid components that do not contain moisture. Antioxidants, crosslinking agents, etc. may be added to the composite material and further kneaded.

[0075] Uncrosslinked composite materials can be further vulcanized to form crosslinked materials. Despite containing nanocellulose, vulcanized composite materials exhibit low water absorption. For example, a water absorption test in which the composite material is immersed in 70°C water for 48 hours shows a water absorption rate of 10% or less. The physical properties of vulcanized composite materials change little before and after water absorption. This is presumably because the hydrophobic interaction between nanocellulose and rubber molecules is maintained even after water absorption. Furthermore, it is presumed that ammonia volatilizes during vulcanization, causing carboxyl groups, phosphorus oxoacid groups, and substituents derived from phosphorus oxoacid groups to become hydrophobic. Therefore, nanocellulose has a high affinity with rubber molecules, and its physical properties are less likely to deteriorate even after water absorption.

[0076] The composite material does not contain any visible nanocellulose agglomerates. Such agglomerates have a maximum width of 10 μm or more. The composite material obtained in this manner may be used as a masterbatch. Because the composite material does not contain agglomerates that are likely to become fracture initiation points, crosslinked bodies and / or rubber products with excellent mechanical properties can be produced.

[0077] As used in this specification and claims, "at least one of A, B, and C" or "one or more of A, B, and C," in connection with a listing of one or more elements, is intended to include A only, B only, C only, the pair of A and B, the pair of A and C, the pair of B and C, the pair of A, B, and C, etc.

[0078] In the present invention, some configurations may be omitted or various embodiments and modifications may be combined within the scope of the features and effects described in this application.

[0079] The present invention includes configurations that are substantially the same as those described in the embodiments (configurations with the same functions, methods, and results, or configurations with the same purpose and effects). The present invention also includes configurations that replace non-essential parts of the configurations described in the embodiments. The present invention also includes configurations that achieve the same effects or purposes as the configurations described in the embodiments. The present invention also includes configurations that add publicly known technology to the configurations described in the embodiments. [Example]

[0080] Examples of the present invention will be described below, but the present invention is not limited to these.

[0081] (1) Sample preparation (1-1) Examples 1 to 6 Rubber latex and a 40% aqueous solution of zinc methacrylate were added to an aqueous dispersion (solvent: water) of oxidized cellulose (10% to 20% concentration shown in Tables 1 and 2, which may be diluted to 0.4% to 0.7%), and mixed using a Tornado mixer (PM-204, manufactured by AS ONE Corporation) to obtain a mixture (S10), which was then further kneaded using a planetary mixer (planetary mixer, manufactured by THINKY Corporation) (S20). The aqueous solution of zinc methacrylate was prepared by stirring at room temperature with an aqueous solution of surfactant dissolved in pure water in advance.

[0082] Next, the mixed liquid was poured into a tray and dried in an oven at 40°C for about 24 hours to reduce the amount of aqueous solvent, thereby obtaining a first mixture (S30). The moisture content of the first mixture obtained by drying was 15% or less for all first mixtures.

[0083] Next, the first mixture was washed in running water at 80°C for 24 hours to obtain a second mixture (S40).

[0084] Next, the second mixture was dried in an oven at 40°C for 24 hours to reduce the amount of the aqueous solvent, thereby obtaining a third mixture (S50). The moisture content of the third mixture was 3% or less.

[0085] Next, the third mixture was wrapped around an open roll (two rolls, Yasuda Seiki Co., Ltd., 191-TH test mixing roll) and kneaded, and then the third mixture was thin-spun (roll temperature: room temperature, roll gap: 0.7 mm, roll speed ratio: 26 / 30) to obtain a composite material (S60). In Examples 2, 3, and 8, the third mixture was kneaded to obtain a masterbatch, and the third mixture was added to the diluted natural rubber (solid) that had been wrapped around an open roll and kneaded, and further kneaded and thin-spun to obtain a composite material with an adjusted nanocellulose content.

[0086] Furthermore, the composite material was wound around the open roll again, and the antioxidant and crosslinking agent were added and mixed. The separated sheet was pressure-molded at 165°C for 20 minutes to obtain a sheet-shaped crosslinked sample of each example having a thickness of 1 mm.

[0087] where: "NR (Latex)": Natural rubber latex, manufactured by Regitex, ULACOL, total solids 61%, ammonia 0.1%, "NR (Diluted Rubber)": Natural rubber, RSS#3, "Oxidized cellulose": T-OP100 (manufactured by Toagosei Co., Ltd.), carboxyl group amount 0.70 mmol / g (note that the nanocellulose obtained under the <defibration conditions> below had an average fiber width of 2 nm to 4 nm and an average fiber length of 100 nm to 160 nm). "MAZn": Zinc methacrylate (manufactured by Asada Chemical Industry Co., Ltd., product name M-CP, purity 96.9%, CAS No. 13189-00-9), "Surfactant": dodecyltrimethylammonium chloride, Although not listed in the table, each example contained 2 phr of peroxide (Percumyl D, 98% or higher purity, manufactured by Nippon Oil & Fats Co., Ltd.), 3 phr of zinc oxide (99.5% purity, manufactured by Seido Chemical Co., Ltd.), 1.5 phr of antioxidant MB (secondary antioxidant, manufactured by Kawaguchi Chemical Co., Ltd.), and 1.5 phr of antioxidant RD (primary antioxidant (amines)) as crosslinking agents.

[0088] <Defibrillation conditions> 200 mL of a 5% by mass aqueous dispersion of oxidized cellulose was mixed with a homogenizer (PRIMIX, Lab. The mixture is treated with a fusion machine (registered trademark) at 10,000 rpm for 10 minutes.

[0089] (1-2) Comparative Examples 1 to 3 Crosslinked samples of Comparative Examples 1 to 3 were obtained with the formulations shown in Table 2. In Comparative Example 1, a crosslinked sample was obtained by carrying out the same treatment as in Example 1, except that the unsaturated carboxylate and surfactant were not added and the ion exchange treatment (S40) was not performed. In Comparative Example 2, a crosslinked sample was obtained by carrying out the same treatment as in Example 1, but that the unsaturated carboxylate and surfactant were not added. In Comparative Example 3, a crosslinked sample was obtained by carrying out the same treatment as in Example 1, except that the ion exchange treatment (S40) was not performed.

[0090] (1-3) Comparative Example 4 and Examples 7 and 8 Crosslinked samples of Comparative Example 4 and Examples 7 and 8 were obtained using the formulations shown in Table 3. In Comparative Example 4, aluminum acrylate was added instead of zinc methacrylate and a surfactant, and a crosslinked sample was obtained by carrying out the same treatment as in Example 1, except that the ion exchange treatment (S40) was not carried out. In Example 7, aluminum acrylate was added instead of zinc methacrylate and a surfactant, and a crosslinked sample was obtained by carrying out the same treatment as in Example 1. In Example 8, a crosslinked sample was obtained by adding aluminum acrylate instead of zinc methacrylate and a surfactant, and a crosslinked sample was obtained by carrying out the same treatment as in Example 2.

[0091] where: "AAAl": Aluminum acrylate (manufactured by Asada Chemical Industry Co., Ltd., product name AAL7, purity 23%) Formulated with:

[0092] (2) Evaluation method and evaluation (2-1) Water absorption evaluation Crosslinked samples (test pieces punched into a dumbbell shape (dumbbell No. 6) as defined in JIS K 6251:2017) of the Examples and Comparative Examples were immersed in water at 70°C for 48 hours, and the water absorption (%) was measured from the change in mass of the sample before and after the test, and the results are shown in Tables 1 to 3. The mass (g) and water absorption (%) are shown in Tables 1 to 3, with the samples before the test referred to as pre-water absorption samples and the samples after the test referred to as post-water absorption samples.

[0093] (2-2) Tensile test For each sheet-shaped cross-linked sample, the JIS Test pieces punched into a dumbbell shape (dumbbell No. 6) as specified in K 6251:2017 were subjected to a tensile test using a tensile tester (Shimadzu Corporation, Autograph AG-X) according to JIS Tensile tests were conducted in accordance with K6251:2017 at 23±2°C with a gauge length of 20 mm and a tensile speed of 500 mm / min. Tables 1 to 3 show the measured values ​​for the 20% modulus (σ20 (MPa)), 50% modulus (σ50 (MPa)), tensile strength (Tb (MPa)), and elongation at break (Eb (%)). The percent change in the 20% modulus (σ20 (MPa)), 50% modulus (σ50 (MPa)), tensile strength (Tb (MPa)), and elongation at break (Eb (%)) of the specimen after water absorption compared to the specimen before water absorption was calculated and is shown in Tables 1 to 3.

[0094] [Table 1]

[0095] [Table 2]

[0096] [Table 3]

[0097] (2-3) Coagulation evaluation The fracture surfaces of each crosslinked sample after tensile testing were visually inspected using a scanning electron microscope to confirm the presence of agglomerates. Agglomerates are areas where nanocellulose is insufficiently dispersed, and visible agglomerates have a maximum width of 10 μm or more.

[0098] In the crosslinked samples of Examples 1 to 8, no aggregates of 10 μm or more were visually observed.

[0099] (2-4) Overall rating The crosslinked samples of Examples 1 to 8 had lower water absorption rates than the crosslinked samples of Comparative Examples 1 to 6. The crosslinked samples of Examples 1 to 3, 7, and 8 had water absorption rates of 5% or less, and the crosslinked samples of Examples 4 to 6 had water absorption rates of 5% to 7%. The crosslinked samples of Comparative Examples 1, 3, and 4 had water absorption rates of 24.9% or more.

[0100] The crosslinked samples of Examples 1, 3, 5, 7, and 8 had a change rate of 20% modulus (σ20) of less than ±10%. The crosslinked samples of Examples 2 and 4 had a change rate of 20% modulus (σ20) of less than ±20%. The crosslinked samples of Examples 1 to 4, 7, and 8 had a change rate of 50% modulus (σ50) of less than ±10%. The crosslinked samples of Examples 5 and 6 had a change rate of 50% modulus (σ50) of less than ±12%. The crosslinked samples of Examples 1 to 3 and 7 had a change rate of tensile strength (Tb) of less than ±35% and a change rate of elongation at break (Eb) of less than ±10%. The crosslinked samples of Examples 4 to 6 and 8 had a change rate of tensile strength (Tb) of less than ±43% and a change rate of elongation at break (Eb) of less than ±20%.

Claims

1. A step of mixing rubber latex containing a rubber component, oxidized cellulose and / or nanocellulose, and an unsaturated carboxylate salt containing at least any one of aluminum ions, zinc ions, and iron ions to obtain a first mixture; performing ion exchange of the first mixture to obtain a second mixture; heating the second mixture to reduce the water content to obtain a third mixture; kneading the third mixture to obtain a composite material; Including, A method for producing a composite material, wherein the oxidized cellulose and the nanocellulose are derived from an oxidation of a cellulosic raw material with hypochlorous acid or a salt thereof, and are not derived from an oxidation of a cellulosic raw material with an N-oxyl compound.

2. A step of mixing rubber latex containing a rubber component, oxidized cellulose and / or nanocellulose, and an unsaturated carboxylate salt containing at least any one of aluminum ions, zinc ions, and iron ions to obtain a first mixture; performing ion exchange of the first mixture to obtain a second mixture; heating the second mixture to reduce the water content to obtain a third mixture; kneading the third mixture to obtain a composite material; Including, A method for producing a composite material, wherein the oxidized cellulose and the nanocellulose have a structure in which the hydroxyl groups at the second and third positions of the glucopyranose ring are oxidized and carboxyl groups are introduced.

3. The step of obtaining the first mixture includes: A step of mixing the rubber latex, the oxidized cellulose and / or the nanocellulose, and the unsaturated carboxylate to obtain a mixed solution; heating the mixture to reduce the water content to obtain a first mixture; A method for producing the composite material according to claim 1 or 2, comprising:

4. The method for producing a composite material according to claim 1 or 2, wherein the rubber component is natural rubber.

5. 3. The method for producing a composite material according to claim 1 or 2, wherein in the step of obtaining the first mixed solution, the oxidized cellulose and / or the nanocellulose is present in an amount of 10 parts by mass or more and 30 parts by mass or less per 100 parts by mass of the rubber component.

6. The method for producing a composite material according to claim 1 or 2, comprising: the unsaturated carboxylate in an amount of 0.8 to 7.0 times the equivalent of the carboxyl group contained in the oxidized cellulose and / or the nanocellulose.

7. The method for producing a composite material according to claim 1 or 2, wherein in the step of obtaining the third mixture, the second mixture is heated so that the moisture content of the third mixture is 3% or less.

8. The method for producing a composite material according to claim 1 or 2, wherein the composite material has a water absorption rate of 10% or less in a water absorption test in which the composite material is immersed in water at 70°C for 48 hours.

9. 9. The method for producing a composite material according to claim 8, wherein a rate of change in a 20% modulus value of the composite material, measured in a tensile test based on JIS K6251 after the water absorption test, relative to a 20% modulus value before the water absorption test, is within ±20%.

10. A rubber component, nanocellulose, and aluminum ions, zinc ions, or iron ions. and an unsaturated carboxylic acid salt containing any one of the above, A composite material, wherein the nanocellulose is derived from an oxidation of a cellulosic raw material with hypochlorous acid or a salt thereof, and is not derived from an oxidation of a cellulosic raw material with an N-oxyl compound, A composite material having a water absorption rate of 10% or less in a water absorption test in which the composite material is immersed in water at 70°C for 48 hours.

11. The present invention relates to a rubber composition, a composition for producing a rubber composition, and a composition for producing a rubber composition comprising: a rubber component; nanocellulose; and an unsaturated carboxylate salt containing any one of aluminum ions, zinc ions, and iron ions; The nanocellulose has a structure in which the hydroxyl groups at the second and third positions of the glucopyranose ring are oxidized and carboxyl groups are introduced, A composite material having a water absorption rate of 10% or less in a water absorption test in which the composite material is immersed in water at 70°C for 48 hours.

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