Rubber compositions and rubber additives

Abstract

To provide an additive for forming a rubber composition that achieves both shape retention and processability. [Solution] A rubber additive containing nanocellulose, wherein the average fiber length of the nanocellulose is 50 to 500 nm, and the Mooney viscosity (ML(1+4)80°C) of the rubber component to which the additive is added at 80°C is 5 to 120.

Description

Technical Field

[0001] The present invention relates to a rubber composition and an additive for rubber.

Background Art

[0002] In recent years, as a material that is lightweight and has excellent strength, rubber blended with a reinforcing material to enhance strength has been widely used, and research on using plant fibers as a reinforcing material for resin has been underway. Plant fibers are not artificially synthesized but are used after loosening plant-derived fibers. Since plant fibers hardly remain as ash during combustion, problems such as ash treatment in incinerators and landfill treatment do not occur. For this reason, research on using plant fibers as a reinforcing material for resin has been underway, and in particular, the use of nanocellulose obtained by defibrating plant fibers to the nanolevel has been studied.

[0003] As a type of nanocellulose, nanocellulose derived from an oxide obtained by oxidizing raw cellulose with hypochlorous acid or its salt is known. For example, Patent Document 1 describes a method for producing nanocellulose having a step of oxidizing a cellulose-based raw material using hypochlorous acid or its salt having an available chlorine concentration of 14 to 43% by mass to produce oxidized cellulose, and a step of defibrating the oxidized cellulose to make it nanoscale. Further, Patent Document 2 describes a method for producing nanocellulose having a step of subjecting a cellulose-based raw material to an oxidation reaction while adjusting the pH to a range of 5.0 to 14.0 using hypochlorous acid or its salt having an available chlorine concentration of 6% by mass to 14% by mass, and defibrating the oxidized cellulose to make it nanoscale.

[0004] Furthermore, Patent Document 3 describes that by using nanocellulose derived from an oxide obtained by oxidizing raw cellulose with hypochlorous acid or its salt as a rubber material, the strength of the rubber, particularly the tensile strength, can be improved.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] International Publication No. 2018 / 230354 [Patent Document 2] International Publication No. 2020 / 027307 [Patent Document 3] International Publication No. 2023 / 219076 [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention aims to provide a rubber composition that achieves both shape retention and processability, and an additive for forming the rubber composition. [Means for solving the problem]

[0007] By using nanocellulose having a predetermined average fiber length, it is possible to achieve both shape retention and processability in the rubber composition.

[0008] The present invention includes the following embodiments. [A1] A rubber composition comprising nanocellulose and a rubber component, The average fiber length of the nanocellulose is 50 to 500 nm. The Mooney viscosity (ML(1+4)80℃) of the aforementioned rubber component at 80℃ is 5 to 120. Rubber composition. [A2] A rubber composition comprising nanocellulose and a rubber component, The average fiber length of the nanocellulose is 50 to 500 nm. The CF change rate, expressed by the following formula, is -1% or less. CF change rate = [(Target CF value - Control CF value) / Control CF value] × 100 [The target CF value is the cold flow value of the target rubber sample formed from the rubber composition, The control CF value is the cold flow value of a control rubber sample formed from a control rubber composition obtained by removing the nanocellulose from the aforementioned rubber composition. Rubber composition. [A3] The rubber composition according to [A1] or [A2], wherein the nanocellulose comprises a structure in which the hydroxyl groups at the 2nd and 3rd positions of the glucopyranose ring are oxidized and dicarboxyl groups are introduced. [A4] The rubber composition according to any one of [A1] to [A3], wherein the nanocellulose contains an oxide of a cellulosic raw material due to hypochlorous acid or a salt thereof, and substantially does not contain an N-oxyl compound. [A5] The rubber composition according to any one of [A1] to [A4], wherein the amount of nanocellulose is 0.01 to 5.0 parts by mass per 100 parts by mass of the rubber component. [A6] The rubber composition according to any one of [A1] to [A5], wherein the rubber component comprises at least one selected from the group consisting of ethylene propylene diene rubber, butyl rubber, natural rubber, and polyisoprene rubber. [A7] A rubber composition according to any one of [A1] to [A6], further comprising carbon black. [A8] The rubber composition according to any one of [A1] to [A7], wherein the Mooney viscosity (ML(1+4)80℃) of the rubber composition at 80℃ is 5 to 120. [A9] The rubber composition according to any one of [A1] to [A8], wherein the ratio of the Mooney viscosity (ML(1+4)80°C) of the rubber composition at 80°C to the Mooney viscosity (ML(1+4)80°C) of a control rubber composition obtained by removing the nanocellulose from the rubber composition is 0.80 to 1.3. [A10] The rubber composition according to any one of [A1] to [A9], wherein the rubber composition is a molded article. [B1] A rubber additive containing nanocellulose, The average fiber length of the nanocellulose is 50 to 500 nm, the Mooney viscosity (ML(1+4)80°C) of the rubber component to which the additive is added at 80°C is 5 to 120, Additive for rubber. [B2] The rubber additive according to [B1], wherein the nanocellulose has a structure in which the hydroxyl groups at the 2nd and 3rd positions of the glucopyranose ring are oxidized and a dicarboxy group is introduced. [B3] The rubber additive according to [B1] or [B2], wherein the nanocellulose contains an oxide of a cellulose-based raw material by hypochlorous acid or a salt thereof and substantially does not contain an N-oxyl compound. [B4] The rubber additive according to any one of [B1] to [B3] for improving the shape retention of the rubber component. [B5] The rubber additive according to any one of [B1] to [B4], wherein the rubber component contains at least one selected from the group consisting of ethylene propylene diene rubber, butyl rubber, natural rubber and polyisoprene rubber. [B6] The rubber additive according to any one of [B1] to [B5] added to the rubber for coating an electric wire.

Advantages of the Invention

[0009] The present invention can provide a rubber composition in which shape retention and processability are compatible, and an additive for forming the rubber composition.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be specifically described, but the present invention is not limited thereto, and various modifications are possible without departing from the gist thereof.

[0011] <<Rubber Composition>> One embodiment of the present invention relates to a rubber composition comprising nanocellulose and a rubber component, wherein the average fiber length of the nanocellulose is 50 to 500 nm, and the Mooney viscosity (ML(1+4)80°C) of the rubber component at 80°C is 5 to 120.

[0012] One embodiment of the present invention is a rubber composition comprising nanocellulose and a rubber component, wherein the average fiber length of the nanocellulose is 50 to 500 nm, and the CF change rate, expressed by the following formula, is -1% or less. CF change rate = [(Target CF value - Control CF value) / Control CF value] × 100 [The target CF value is the cold flow value of the target rubber sample formed from the rubber composition, The control CF value is the cold flow value of a control rubber sample formed from a control rubber composition obtained by removing the nanocellulose from the aforementioned rubber composition. This relates to rubber compositions.

[0013] Hereinafter, the rubber compositions according to the two embodiments described above will be collectively referred to as the rubber compositions according to this embodiment.

[0014] The rubber composition according to this embodiment can achieve both shape retention and processability by including short-fiber nanocellulose. Specifically, it is possible to improve shape retention while maintaining the processability of the rubber component (in other words, while suppressing the increase in Mooney viscosity of the rubber component).

[0015] In this specification, "shape retention" means the property of a molded article of a rubber composition to maintain its shape. When shape retention is high, for example, when an external force is applied to the molded article, it is difficult for the article to deform, or even if it is deformed, it easily returns to its original shape when the external force is removed.

[0016] Because nanocellulose, with its short fiber length, has high dispersibility, it is presumed that the uniform dispersion of nanocellulose in the rubber component is the reason for the improved shape retention. However, the present invention is not limited in any way by the reasons stated above. Generally speaking, improving shape retention tends to increase the Mooney viscosity of a rubber composition, leading to a decrease in processability. In other words, there is a trade-off between shape retention and processability. However, surprisingly, the rubber composition according to this embodiment can improve shape retention while suppressing the increase in Mooney viscosity (i.e., while maintaining processability).

[0017] [Cold flow rate change] The CF change rate of the rubber composition according to this embodiment, represented by the following formula, is preferably -1% or less, more preferably -5% or less, and even more preferably -10% or less. A lower CF change rate indicates improved shape retention. Since a lower CF change rate is preferable, there is no particular lower limit, but for example, -40%, -30%, or -20% may be set as the lower limit. CF change rate = [(Target CF value - Control CF value) / Control CF value] × 100 [The target CF value is the cold flow value of the target rubber sample formed from the target rubber composition according to this embodiment.] The control CF value is the cold flow value of a control rubber sample formed from a control rubber composition obtained by removing nanocellulose from the target rubber composition according to this embodiment.

[0018] The control rubber composition may be prepared by mixing the same types and amounts of components as the target rubber composition, except that nanocellulose is not used.

[0019] The methods for forming the target rubber sample and the control rubber sample are as follows. Using an 8-inch roll, a 3 mm thick sheet of rubber is obtained from the rubber composition. From the sheet of rubber, a dumbbell-shaped sample (Type 1) is cut out as described in JIS K6251, and markings are made at 40 mm intervals to obtain a rubber sample. The rubber sample is cut so that the length of the dumbbell is perpendicular to the roll direction (flow direction) of the sheet of rubber.

[0020] The method for measuring the cold flow values ​​of the target rubber sample and the control rubber sample is as follows. The rubber sample is left suspended vertically at 50°C for 16 hours, and the cold flow value (distance between the markings on the dumbbell) is measured.

[0021] The specific methods for forming the target rubber sample and the control rubber sample, as well as the method for measuring the cold flow value, are as described in the examples below.

[0022] The CF change rate can be adjusted, for example, by changing the amount of nanocellulose or the type of rubber component. For instance, increasing the amount of nanocellulose or using a rubber component with poor shape retention tends to lower the CF change rate.

[0023] [Mooney viscosity ratio] The viscosity ratio (target viscosity / control viscosity) of the target rubber composition at 80°C (ML(1+4)80°C) (hereinafter referred to as "target viscosity") to the Mooney viscosity at 80°C (ML(1+4)80°C) (hereinafter referred to as "control viscosity") of the control rubber composition obtained by removing nanocellulose from the target rubber composition is preferably 0.70 to 1.5, more preferably 0.80 to 1.3, and even more preferably 0.90 to 1.1. The closer the viscosity ratio is to 1, the more effectively the decrease in processability of the rubber component due to the addition of nanocellulose can be suppressed.

[0024] The target viscosity is preferably 5 to 70, more preferably 5 to 60, and even more preferably 5 to 50.

[0025] Mooney viscosity can be measured using a Mooney viscometer. The specific measurement conditions are as described in the examples below.

[0026] [Form of composition] The rubber composition according to this embodiment may be a raw material mixture before molding, or a molded article of the raw material mixture. The raw material mixture may be a masterbatch (i.e., a rubber component containing a high concentration of nanocellulose for use in combination with other rubber components).

[0027] <Nanocellulose> The rubber composition according to this embodiment contains nanocellulose. By using nanocellulose, both shape retention and processability can be achieved.

[0028] The average fiber length of nanocellulose is preferably 50 to 500 nm, more preferably 60 to 300 nm, and even more preferably 70 to 200 nm.

[0029] The amount of nanocellulose is preferably 0.01 to 5.0 parts by mass, more preferably 0.05 to 3.0 parts by mass, and even more preferably 0.1 to 1.0 parts by mass, per 100 parts by mass of the rubber component.

[0030] Nanocellulose is cellulose that has been nano-sized. Nanocellulose may be oxidized. Oxidized nanocellulose can be obtained, for example, by oxidation and nano-sizing of a cellulosic raw material. The order of oxidation and nano-sizing is not particularly limited, but it is preferable to oxidize the cellulosic raw material first and then nano-sizing it. Performing the oxidation of the cellulosic raw material first tends to facilitate nano-sizing.

[0031] Examples of oxidizing agents for oxidizing cellulosic raw materials include hypochlorous acid or its salts, and N-oxyl compounds. An example of an N-oxyl compound is 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO).

[0032] From the viewpoint of achieving both shape retention and processability, it is preferable to use hypochlorous acid or a salt thereof as the oxidizing agent. In other words, it is preferable that nanocellulose is obtained by oxidizing a cellulosic raw material with hypochlorous acid or a salt thereof (without using an N-oxyl compound), and then nano-processing the resulting oxidized cellulose.

[0033] The following explanation will focus on oxides of cellulosic raw materials produced by hypochlorous acid or its salts, but nanocellulose is not limited to nanocellulose produced by hypochlorous acid or its salts.

[0034] [Oxidized Cellulose] Unless otherwise specified, "oxidized cellulose" in this column refers to the oxide of cellulosic raw materials with hypochlorous acid or its salts, before fibrillation.

[0035] Examples of hypochlorous acid or its salts include hypochlorous acid water, sodium hypochlorite, potassium hypochlorite, calcium hypochlorite, and ammonium hypochlorite.

[0036] The amount of hypochlorous acid or its salt used is not particularly limited, but it is preferable to use it so that the effective chlorine concentration of the reaction system is 6 to 43% by mass. The effective chlorine concentration may be a low concentration of 6 to 14% by mass, or a high concentration of 14 to 43% by mass.

[0037] The definition of the effective chlorine concentration of hypochlorous acid or its salts is as described in International Publication No. 2022 / 009979.

[0038] Cellulosic raw materials are not particularly limited as long as they are primarily composed of cellulose, and examples include pulp, natural cellulose, and fine cellulose obtained by depolymerizing cellulose through mechanical treatment. It is preferable that the cellulosic raw material has a type I crystalline structure. Commercially available products such as crystalline cellulose made from pulp can be used as the cellulosic raw material. Other unused biomass containing large amounts of cellulose, such as okara (soy pulp) or soybean hulls, may also be used as raw materials. Furthermore, the cellulosic raw material may be pre-treated. For example, the cellulosic raw material may be pre-treated with an appropriate concentration of alkali to facilitate the penetration of the oxidizing agent into the raw material pulp. The main component of plants is cellulose, and bundles of cellulose molecules are called cellulose microfibrils. Cellulose in cellulosic raw materials is also contained in the form of cellulose microfibrils.

[0039] (N-oxyl compound) It is preferable that oxidized cellulose is substantially free of N-oxyl compounds. By substantially free of N-oxyl compounds, the impact on the environment and human health is sufficiently reduced, resulting in high safety. An example of an N-oxyl compound is 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO).

[0040] In this specification, "substantially free of N-oxyl compounds" means that N-oxyl compounds are not used in the production of oxidized cellulose, that N-oxyl compounds are not contained in the oxidized cellulose at all, 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 oxidized cellulose. Furthermore, if the N-oxyl compound content is preferably 2.0 ppm by mass or less, and more preferably 1.0 ppm by mass or less, as an increase from the cellulosic raw material, it is also considered to be "substantially free of N-oxyl compounds."

[0041] The content of N-oxyl compounds can be measured by known means. Known means include using a trace total nitrogen analyzer (for example, the TN-2100H manufactured by Nitto Seiko Analytech Co., Ltd.).

[0042] (Carboxylate group amount) The amount of carboxyl groups in oxidized cellulose is preferably 0.1 to 3.0 mmol / g, more preferably 0.2 to 2.0 mmol / g, even more preferably 0.3 to 1.5 mmol / g, particularly preferably 0.4 to 1.2 mmol / g, and most preferably 0.5 to 0.9 mmol / g.

[0043] The amount of carboxyl groups in oxidized cellulose can be measured by the method described in International Publication No. 2022 / 009979.

[0044] Oxidized cellulose preferably has a structure in which at least two of the hydroxyl groups of the glucopyranose ring constituting cellulose are oxidized, and more specifically, it is preferable that the hydroxyl groups at positions 2 and 3 of the glucopyranose ring are oxidized and a dicarboxyl group is introduced. Furthermore, it is preferable that the hydroxyl group at position 6 of the glucopyranose ring is not oxidized and remains as a hydroxyl group. Note that the position of the carboxyl group in the glucopyranose ring is solid. 13 This can be analyzed using 1C-NMR spectroscopy.

[0045] Rayon has the same chemical structure as cellulose, and its oxide (rayon oxide) is water-soluble. When rayon oxide is dissolved in heavy water, a one-dimensional solution is formed. 13 1C-NMR measurements reveal a peak at 165–185 ppm attributed to the carboxyl group. In one embodiment of the cellulose-based raw material oxide by hypochlorous acid or its salt, two signals appear within this chemical shift range. Furthermore, two-dimensional solution NMR measurements can determine that the carboxyl group is introduced at positions 2 and 3.

[0046] Solid oxide of cellulose-based raw materials using hypochlorous acid or its salts 13 In 1C-NMR, when a large amount of carboxyl groups are introduced, two signals appear at 165-185 ppm, while when a small amount of carboxyl groups are introduced, a very broad signal may appear. As can be seen from the results for rayon oxide, the signals of carboxyl group carbons introduced at positions 2 and 3 are close together, and the solid has low resolution. 13 In 1C-NMR, the separation of the two signals is insufficient. Therefore, when the amount of carboxyl group introduced is small, it is observed as a broad signal. In other words, solid 13 In the 1C-NMR spectrum, the introduction of carboxyl groups at positions 2 and 3 can be confirmed by evaluating the broadening of the peak appearing at 165–185 ppm.

[0047] In other words, solid 13 A baseline is drawn over the peaks in the 165 ppm to 185 ppm range in the 1C-NMR spectrum to determine the total area value. Then, the area value is vertically divided at the peak top to obtain the ratio of the two resulting peak area values ​​(larger area value / smaller area value). If this ratio is 1.2 or greater, the peak can be considered broad. Furthermore, the presence or absence of the broad peak can be determined by the ratio of the baseline length L in the range of 165 ppm to 185 ppm to the length L' of the perpendicular from the peak top to the baseline. That is, if the ratio L' / L is 0.1 or greater, it can be determined that a broad peak exists. The ratio L' / L may also be 0.2 or greater, 0.3 or greater, 0.4 or greater, or 0.5 or greater. There is no particular upper limit to the ratio L' / L, but it is usually sufficient if it is 3.0 or less, 2.0 or less, or 1.0 or less.

[0048] The structure of the glucopyranose ring described above can also be determined by analysis according to the method described in Sustainable Chem. Eng. 2020, 8, 48, 17800-17806.

[0049] (Viscosity average degree of polymerization) The viscosity-average degree of polymerization of oxidized cellulose is preferably 30 to 500, more preferably 60 to 300, even more preferably 70 to 150, and particularly preferably 80 to 130.

[0050] Viscosity-average degree of polymerization is the average degree of polymerization measured by the viscosity method. Viscosity-average degree of polymerization can be measured by the method described in International Publication No. 2022 / 009979.

[0051] [Method for producing oxidized cellulose] Oxidized cellulose can be produced by oxidizing cellulosic raw materials with hypochlorous acid or its salts. Specific production methods include, for example, those described in International Publication No. 2022 / 009979 and International Publication No. 2022 / 009980. Oxidized cellulose is also available commercially, such as Aronfibro® manufactured by Toagosei Co., Ltd.

[0052] [Nanocellulose] Unless otherwise specified, "nanocellulose" in this column refers to an oxide of a cellulosic raw material using hypochlorous acid or a salt thereof, after defibration.

[0053] Nanocellulose is a general term for cellulose that has been finely processed, and includes fine cellulose fibers and cellulose nanocrystals. Fine cellulose fibers are also called cellulose nanofibers (also written as CNF).

[0054] Nanocellulose preferably has a carboxyl group. The carboxyl group may be H-type (-COOH) or salt type. The type of salt is not particularly limited, but examples include alkali metal salts such as lithium salts, sodium salts, and potassium salts; alkaline earth metal salts such as calcium salts and barium salts; other metal salts such as magnesium salts and aluminum salts; ammonium salts, organic amine salts, etc.

[0055] Nanocellulose is an aggregate of individual fibers. When nanocellulose contains carboxylated nanocellulose, it is sufficient that it contains at least one carboxylated nanocellulose fiber, and it is preferable that carboxylated nanocellulose is the main component. Here, carboxylated nanocellulose being the main component means that the proportion of carboxylated nanocellulose in the total amount of nanocellulose exceeds 50% by mass, preferably exceeds 70% by mass, and more preferably exceeds 80% by mass. The upper limit of the above proportion is 100% by mass, but it may also be 98% by mass or 95% by mass.

[0056] (N-oxyl compound) It is preferable that nanocellulose is substantially free of N-oxyl compounds. The meaning of "substantially free of N-oxyl compounds" for nanocellulose, and the method for measuring the content of N-oxyl compounds, shall be as described in the (N-oxyl compounds) column of [Oxidized Cellulose] above.

[0057] (Carboxylate group amount) The amount of carboxyl groups in nanocellulose, the method of measuring it, and the position of introduction of the carboxyl groups shall be in accordance with the description in the (Carboxyl Group Amount) column of [Oxidized Cellulose] above.

[0058] (Average fiber length) The average fiber length of nanocellulose is preferably 50 to 500 nm, more preferably 60 to 300 nm, and even more preferably 70 to 200 nm.

[0059] (Average fiber width) The average fiber width of nanocellulose is preferably 1 to 20 nm, more preferably 1 to 15 nm, even more preferably 1 to 10 nm, and particularly preferably 1 to 5 nm.

[0060] The average fiber length and average fiber width of nanocellulose can be measured by the method described in International Publication No. 2022 / 009980.

[0061] (Aspect ratio) The aspect ratio (average fiber length / average fiber width) of nanocellulose is preferably 20 to 1000, more preferably 20 to 200, even more preferably 30 to 190, and particularly preferably 40 to 180.

[0062] (Zeta potential) The zeta potential of nanocellulose is preferably -30mV or less, more preferably -90mV to -30mV, even more preferably -80mV to -30mV, even more preferably -70mV to -30mV, and particularly preferably -65mV to -35mV.

[0063] Zeta potential can be measured by the method described in International Publication No. 2022 / 009980.

[0064] (Degree of crystallinity) The degree of crystallinity of nanocellulose is preferably 10-70%, more preferably 20-70%, even more preferably 30-65%, particularly preferably 40-60%, and most preferably 50-55%.

[0065] The degree of crystallinity can be measured by the method described in International Publication No. 2022 / 138759.

[0066] [Method for producing nanocellulose] Nanocellulose can be produced by defibrating the oxidized cellulose described above. Specific production methods include, for example, those described in International Publication No. 2022 / 009979 and International Publication No. 2022 / 009980. Nanocellulose can also be obtained by defibrating commercially available oxidized cellulose (for example, Aronfibro® manufactured by Toagosei Co., Ltd.).

[0067] <Rubber components> The rubber composition according to this embodiment contains a rubber component. When the rubber component is mixed with nanocellulose, its shape retention is improved while maintaining processability.

[0068] Examples of rubber components include natural rubber components and synthetic rubber components.

[0069] Examples of natural rubber components include unmodified natural rubber, chemically modified natural rubber (e.g., chlorinated natural rubber, chlorosulfonated natural rubber, and epoxidized natural rubber), hydrogenated natural rubber, and deproteinized natural rubber.

[0070] Examples of synthetic rubber components include diene-based rubber and non-diene-based rubber. Examples of diene rubbers include butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), polyisoprene rubber (IR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, and isoprene-butadiene copolymer rubber. Examples of non-diene rubbers include butyl rubber (IIR), ethylene propylene rubber (EPM), ethylene propylene diene rubber (EPDM), acrylic rubber (ACM), epichlorohydrin rubber (CO, ECO), fluororubber (FKM), silicone rubber (Q), urethane rubber (U), and chlorosulfonated polyethylene (CSM).

[0071] The Mooney viscosity (ML(1+4)80°C) of the rubber component at 80°C is preferably 5 to 120. Rubber components with this viscosity tend to have poor shape retention, so the effect of nanocellulose is particularly easily exhibited. The Mooney viscosity of the rubber component is more preferably 10 to 110, and even more preferably 15 to 100.

[0072] The Mooney viscosity of the above rubber component is preferably 5 to 120. To achieve a Mooney viscosity of 5 to 120, the type of rubber component with a viscosity of 5 to 120 can be appropriately selected. Furthermore, the Mooney viscosity can be adjusted by the structure of the rubber (type, molecular weight distribution), the type and amount of filler added, the type and amount of softener added, the type and amount of other auxiliary materials added, and the processing method (mixing method).

[0073] Examples of rubber components for which improved shape retention is particularly required include ethylene propylene diene rubber, butyl rubber, natural rubber, and polyisoprene rubber.

[0074] The rubber component may be in a solid state, a dispersion (latex) obtained by dispersing the rubber component in a dispersion medium, or a solution obtained by dissolving it in a solvent. Examples of the dispersion medium and solvent include water and organic solvents. The amounts of the dispersion medium and solvent may be 10 to 1000 parts by mass each per 100 parts by weight of the rubber component.

[0075] <Optional ingredients> The rubber composition according to this embodiment may contain other optional components. Examples of optional components include fillers, softeners, and crosslinking agents.

[0076] Examples of fillers include carbon black, silica, talc, mica, clay, and calcium carbonate.

[0077] Examples of softening agents include mineral oils (e.g., paraffinic mineral oils, naphthenic mineral oils, and aromatic mineral oils) and vegetable oils. Since the presence of softening agents tends to reduce shape retention, the effects of nanocellulose are particularly pronounced.

[0078] Examples of crosslinking agents include sulfur, metal oxides, resin crosslinking agents, organic peroxides, and triazine derivatives.

[0079] Examples of sulfur include powdered sulfur, finely powdered sulfur, precipitated sulfur, colloidal sulfur, and sulfur chloride.

[0080] Examples of metal oxides include magnesium oxide, calcium oxide, zinc oxide, and copper oxide.

[0081] Examples of resin crosslinking agents include alkylphenol formaldehyde resins such as alkylphenol formaldehyde resins, heat-reactive phenol resins, phenol dialcohol-based resins, bisphenol resins, and heat-reactive bromomethylalkylated phenol resins.

[0082] Examples of organic peroxides include alkyl peroxides, aryl peroxides, acyl peroxides, ketone peroxides, peroxyketals, peroxycarbonates, peroxyesters, and hydroperoxides.

[0083] Examples of triazine derivatives include 2,4,6-trimercapto-s-triazine, 2-methylamino-4,6-dimercapto-s-triazine, 2-(n-butylamino)-4,6-dimercapto-s-triazine, 2-octylamino-4,6-dimercapto-s-triazine, 2-propylamino-4,6-dimercapto-s-triazine, 2-diallylamino-4,6-dimercapto-s-triazine, 2-dimethylamino-4,6-dimercapto-s-triazine, and 2-dibutylamino-4,6-dimercapto-s-triazine. Examples include capto-s-triazine, 2-di(iso-butylamino)-4,6-dimercapto-s-triazine, 2-dipropylamino-4,6-dimercapto-s-triazine, 2-di(2-ethylhexyl)amino-4,6-dimercapto-s-triazine, 2-dioleylamino-4,6-dimercapto-s-triazine, 2-laurylamino-4,6-dimercapto-s-triazine, or 2-anilino-4,6-dimercapto-s-triazine, or their sodium or disodium salts.

[0084] <Method for manufacturing rubber composition> The rubber composition according to this embodiment can be manufactured by mixing nanocellulose and a rubber component using a known method.

[0085] There are no particular limitations on the method for producing the rubber composition, but for example, a method using an open roll can be used, and for specifics, please refer to Japanese Patent Application Publication No. 2015-98576.

[0086] For example, the rubber composition according to this embodiment can be produced by a manufacturing method that includes the steps of: mixing nanocellulose and a rubber component to obtain a mixture; and dispersing the mixture by passing it through an open roll to obtain a rubber composition. In the dispersion step, nanocellulose can be dispersed in the rubber composition.

[0087] The rubber composition according to this embodiment can also be produced by melt-kneading a mixture of nanocellulose and rubber components.

[0088] For example, the rubber composition according to this embodiment can also be produced by a manufacturing method that includes the steps of: mixing nanocellulose and a rubber component to obtain a first mixture; drying the first mixture; and melt-kneading the dried first mixture.

[0089] If the rubber composition is a molded article, it may be further molded by known methods.

[0090] <<Rubber additive>> One embodiment of the present invention relates to a rubber additive containing nanocellulose, wherein the average fiber length of the nanocellulose is 50 to 500 nm, and the Mooney viscosity (ML(1+4)80°C) of the rubber component to which the additive is added at 80°C is 5 to 120.

[0091] Details of the nanocellulose and rubber components are as described in the section above under "Rubber Composition".

[0092] The additive according to this embodiment can be used to improve the shape retention of rubber components. Although not particularly limited, the additive is preferably added to the rubber covering the electric wire. [Examples]

[0093] The present invention will be described in more detail below using examples and comparative examples, but the technical scope of the present invention is not limited thereto.

[0094] The various values ​​in the examples may be preferred lower or upper limits in the embodiments of the present invention. Alternatively, two similar values ​​in the examples may be combined as appropriate to form a preferred numerical range.

[0095] In the following, unless otherwise specified, "parts" and "%" refer to "parts by mass" and "percent mass," respectively. phr (parts per hundred rubber) refers to parts by weight relative to 100 parts by weight of rubber component.

[0096] (Raw materials used) The components used in the examples and comparative examples are as follows: • Nanocellulose: Prepared according to Production Example 1 described below. • Rubber component: Ethylene propylene diene rubber (EPDM) (manufactured by ENEOS Material Co., Ltd., EP33, Mooney viscosity (ML(1+4)80℃): 90.3 (measured value, measured by the method described in <Mooney viscosity> below)) • Carbon Black: FEF Carbon Black (manufactured by Tokai Carbon Co., Ltd., Seast SO) and SRF Carbon Black (manufactured by Asahi Carbon Co., Ltd., #50) • Paraffin-based mineral oil (manufactured by Nippon SUN Oil Co., Ltd., SUNPAR115) • Zinc oxide (manufactured by Sakai Chemical Industry Co., Ltd., 2 types of zinc oxide) • Stearic acid (manufactured by Kao Corporation, Lunac S-30) • Sulfur (manufactured by Tsurumi Chemical Industries, Ltd., SULFAX200S) • Vulcanization accelerator (Manufactured by Kawaguchi Chemical Industry Co., Ltd., Accel EM55) I used it.

[0097] [Manufacturing Example 1: Manufacturing of Nanocellulose] Pulp (KC Floc W100GK, Nippon Paper Industries) was used as a cellulose-based raw material. 350 g of sodium hypochlorite pentahydrate crystals with an effective chlorine concentration of 42% by mass was placed in a beaker, and pure water was added and stirred to obtain a sodium hypochlorite aqueous solution with an effective chlorine concentration of 21% by mass. 35% by mass hydrochloric acid was then added and stirred to adjust the pH to 11.0. This sodium hypochlorite aqueous solution was heated to 30°C in a constant temperature water bath while being stirred at 200 rpm using a propeller-type stirring blade in a stirrer (Three One Motor, BL600) manufactured by Shinto Kagaku Co., Ltd., and then 50 g of the above pulp was added. After adding the cellulose-based raw material, the reaction pH was maintained at 11.0 while the mixture was kept warm at 30°C in the same constant-temperature water bath, and a 48% by mass sodium hydroxide aqueous solution was added. The mixture was stirred at 200 rpm using a propeller-type stirring blade, and the oxidation reaction was carried out for 4 hours (pH maintenance was continued). After the reaction is complete, use the filter cloth (manufactured by Nakao Filter Co., Ltd., KE022, air permeability 0.3 cc / cm²). 2 The product was separated into solid and liquid by pressure filtration using a pressure of 0.7 / sec, and the resulting oxidized cellulose solid was washed with pure water. The amount of carboxyl groups in the oxidized cellulose was 0.7 mmol / g. The amount of carboxyl groups was measured by the method described below.

[0098] An aqueous dispersion of oxidized cellulose (solid content 7.5%) was treated with a homomixer (Primix, Robomix) at 10,000 rpm with a liquid volume of 300 mL for 46 minutes to defibrillate the oxidized cellulose into nanocellulose, obtaining an aqueous dispersion of nanocellulose. The average fiber width was 3.7 nm and the average fiber length was 150 nm.

[0099] (Measurement of carboxyl group content) To 60 ml of an aqueous dispersion of oxidized cellulose, adjusted to a concentration of 0.5% by mass, a 0.1 M hydrochloric acid solution was added to bring the pH to 2.5. Then, a 0.05 N sodium hydroxide solution was added dropwise, and the electrical conductivity was measured until the pH reached 11.0. The amount of sodium hydroxide consumed during the neutralization stage of the weak acid, where the change in electrical conductivity was gradual (a), was used to calculate the amount of carboxyl groups (mmol / g) using the following formula. Amount of carboxyl groups = a (ml) × 0.05 / Mass of oxidized cellulose (g)

[0100] (Measurement of available chlorine concentration in sodium hypochlorite aqueous solution) 0.582 g of an aqueous solution of sodium hypochlorite pentahydrate crystals added to pure water was precisely weighed, 50 mL of pure water was added, 2 g of potassium iodide and 10 mL of acetic acid were added, and the container was immediately sealed and left in the dark for 15 minutes. After 15 minutes, the liberated iodine was titrated with a 0.1 mol / L sodium thiosulfate solution (solution factor 1.000) (indicator: starch solution), and the titration volume was 34.55 mL. A blank test was performed separately and corrected, and since 1 mL of 0.1 mol / L sodium thiosulfate solution corresponds to 3.545 mg Cl, the effective chlorine concentration in the sodium hypochlorite aqueous solution was 21% by mass.

[0101] [Example 1] 100 phr of EPDM as solids, a nanocellulose aqueous dispersion obtained in Production Example 1 with 0.5 phr of solids (7.5 wt%), 50 phr of FEF carbon black and 50 phr of SRF carbon black, 75 phr of paraffinic mineral oil, 5 phr of zinc oxide, and 1 phr of stearic acid were mixed using a 1.7 L Banbury mixer at 103 rpm for 3 minutes, and then mixed further at 100°C for 3 minutes. Next, 1.5 phr of sulfur and 4.0 phr of vulcanization accelerator (EM55) were added using an 8-inch roll, and the mixture was further kneaded to obtain a rubber composition. The obtained rubber composition was subjected to the cold flow test and Mooney viscosity test described later in its unvulcanized state.

[0102] [Comparative Example 1] A rubber composition was obtained in the same manner as in Example 1, except that a nanocellulose aqueous dispersion was not used.

[0103] (Measurement method) <Cold Flow Test> A 3 mm thick sheet of rubber was obtained from the rubber compositions obtained in the examples and comparative examples using an 8-inch roll. From this 3 mm thick sheet of rubber, a dumbbell-shaped sample of type 1 as described in JIS K6251 was cut, and markings were made at a distance of 40 mm between the gauge marks to obtain a test sample. Two types of test samples were prepared: Sample 1, cut so that the length of the dumbbell was perpendicular to the roll direction (flow direction) of the sheet of rubber, and Sample 2, cut so that the length of the dumbbell was parallel to the roll direction (flow direction). Next, the test samples were left suspended vertically at room temperature (25°C) or 50°C for 16 hours, and the cold flow state (distance between the gauge marks on the dumbbell after suspension) was measured.

[0104] <Moony viscosity> The Mooney viscosity of the rubber compositions obtained in the examples and comparative examples was measured according to the Mooney viscosity test of the unvulcanized rubber testing method specified in JIS K6300. A Mooney viscometer manufactured by Toyo Seikikai Seisakusho was used for the measurements.

[0105] Table 1 shows the results of the cold flow test and Mooney viscosity measurement.

[0106] [Table 1]

Claims

1. A rubber additive containing nanocellulose, The average fiber length of the nanocellulose is 50 to 500 nm. The Mooney viscosity (ML(1+4)80°C) of the rubber component to which the aforementioned additive is added is 5 to 120. Rubber additive.

2. The nanocellulose includes a structure in which the hydroxyl groups at the 2nd and 3rd positions of the glucopyranose ring are oxidized and dicarboxyl groups are introduced. The rubber additive according to claim 1.

3. The nanocellulose contains an oxide of a cellulosic raw material with hypochlorous acid or a salt thereof, and is substantially free of N-oxyl compounds. The rubber additive according to claim 1.

4. To improve the shape retention of the aforementioned rubber component, The rubber additive according to claim 1.

5. The rubber component includes at least one selected from the group consisting of ethylene propylene diene rubber, butyl rubber, natural rubber, and polyisoprene rubber. The rubber additive according to claim 1.

6. It is added to the rubber that covers the electric wires. The rubber additive according to claim 1.

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