Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L9/00—Compositions of homopolymers or copolymers of conjugated diene hydrocarbons
  • C08L9/02—Copolymers with acrylonitrile
  • C08L9/04—Latex
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J3/00—Processes of treating or compounding macromolecular substances
  • C08J3/20—Compounding polymers with additives, e.g. colouring
  • C08J3/22—Compounding polymers with additives, e.g. colouring using masterbatch techniques
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/04—Reinforcing macromolecular compounds with loose or coherent fibrous material
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L1/00—Compositions of cellulose, modified cellulose or cellulose derivatives
  • C08L1/02—Cellulose; Modified cellulose
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L21/00—Compositions of unspecified rubbers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2310/00—Masterbatches
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2312/00—Crosslinking

Definitions

• the present invention relates to a rubber composition and a rubber.
• Patent Document 1 describes a method for producing nanocellulose, which includes a step of producing oxidized cellulose by oxidizing a cellulose-based raw material using hypochlorous acid or its salts with an effective chlorine concentration of 14 to 43% by mass, and a step of defibrating the oxidized cellulose to produce nanocellulose.
• Patent Document 2 describes a method for producing nanocellulose, which includes a step of oxidizing a cellulose-based raw material using hypochlorous acid or its salts with an effective chlorine concentration of 6 to 14% by mass while adjusting the pH to the range of 5.0 to 14.0, and defibrating the oxidized cellulose to produce nanocellulose.
• Cellulosic fibers are sometimes used as reinforcing materials to increase the strength of rubber, but when cellulosic fibers are used as rubber reinforcing materials, there is a problem that the reinforcing material has poor affinity and dispersibility with the rubber, and is unable to fully exhibit the properties of the rubber, as it is made by combining hydrophilic cellulose with hydrophobic rubber.
• Patent Document 3 aims to provide a rubber composition for tires that improves mechanical properties beyond conventional levels, and describes a rubber composition for tires that is "characterized in that 100 parts by mass of diene rubber containing 5% by mass or more of modified diene rubber having 0.1 mol% or more of polar groups is blended with 1 to 50 parts by mass of oxidized cellulose nanofibers.”
• Patent Document 4 aims to provide a composite material in which a rubber component is reinforced with cellulose nanofibers, and describes a composite material comprising: "a rubber component, a cationic surfactant, cellulose nanofibers, and a silicon-containing hydrophobizing agent, the silicon-containing hydrophobizing agent being at least one selected from organosilane compounds and organosilazane compounds each consisting of a silane compound having two or more hydroxyl groups or alkoxy groups in one molecule and/or a partial hydrolysis condensate thereof, as represented by the following formula (1), the cellulose nanofiber is blended in an amount of 5.0 parts by mass to 40.0 parts by mass per 100 parts by mass of the rubber component, the cationic surfactant is blended in an amount of 0.1 parts by mass to 2.5 parts by mass per 1 part by mass of the cellulose nanofiber, and the silicon-containing hydrophobizing agent is blended in an amount of 0.05 parts by mass or more per 1 part by mass of the cellulose nanofiber and 30.0 parts by mass or less
• R 2 m Si(OR 1 ) 4-m (1)
• R 1 is a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms
• R 2 is an unsubstituted or substituted hydrocarbon group having 1 to 10 carbon atoms
• m is 0, 1 or 2.
• the oxidized cellulose nanofibers or cellulose nanofibers used are specifically those obtained by oxidation using 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO).
• TEMPO 2,2,6,6-tetramethylpiperidine-1-oxyl
• the objective of the present invention is to provide a rubber composition that can form rubber with excellent tensile strength while maintaining breaking elongation.
• nanocellulose which is made by defibrating the oxide of cellulose-based raw materials using hypochlorous acid or its salts, it is possible to form rubber that has excellent tensile strength while maintaining breaking elongation.
• a rubber composition comprising nanocellulose and a rubber component,
• the nanocellulose comprises an oxide of a cellulosic raw material with hypochlorous acid or a salt thereof, and is substantially free of N-oxyl compounds;
• the ratio of the breaking elongation value of the rubber formed from the rubber composition to the breaking elongation value of a control rubber formed from a control rubber composition in which the nanocellulose is excluded from the rubber composition is 0.90 or more and less than 1.15; Rubber composition.
• [1-2] The rubber composition according to [1] or [1-1], wherein the ratio of the breaking elongation value of the rubber to the breaking elongation value of the control rubber is 0.95 or more and 1.10 or less.
• [1-3] The rubber composition according to any one of [1] to [1-2], wherein the ratio of the breaking elongation value of the rubber to the breaking elongation value of the control rubber is 1.00 or more and 1.05 or less.
• [2] The rubber composition according to any one of [1] to [1-3], wherein the content of the nanocellulose is 0.5 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the rubber component.
• [3] The rubber composition according to any one of [1] to [2], which is used as a masterbatch.
• a rubber formed from a rubber composition The rubber composition includes nanocellulose and a rubber component, The nanocellulose comprises an oxide of a cellulosic raw material with hypochlorous acid or a salt thereof, and is substantially free of N-oxyl compounds;
• the ratio of the breaking elongation value of the rubber to the breaking elongation value of a control rubber formed from a control rubber composition in which the nanocellulose is excluded from the rubber composition is 0.90 or more and less than 1.15; Rubber.
• the present invention provides a rubber composition that can form rubber with excellent tensile strength while maintaining breaking elongation.
• FIG. 1 shows the stress-strain curves when only nitrile butadiene rubber (NBR) is used, and when nanocellulose oxidized with hypochlorous acid and NBR are used.
• NBR nitrile butadiene rubber
• One embodiment of the present invention relates to a rubber composition comprising nanocellulose and a rubber component, wherein the nanocellulose comprises an oxide of a cellulose-based raw material with hypochlorous acid or a salt thereof, and is substantially free of N-oxyl compounds, and the ratio of the breaking elongation value of the rubber formed from the rubber composition to the breaking elongation value of a control rubber formed from a control rubber composition obtained by excluding the nanocellulose from the rubber composition is 0.90 or more and less than 1.15.
• the rubber composition according to this embodiment can form a rubber with excellent tensile strength while maintaining breaking elongation.
• the tensile strength improves but the breaking elongation decreases.
• nanocellulose oxidized with hypochlorous acid or a salt thereof it is surprising that the tensile strength improves while maintaining the breaking elongation.
• the reason why the breaking elongation is maintained is assumed to be, for example, due to the interaction between the rubber component and the carboxyl group of the nanocellulose oxidized with hypochlorous acid or a salt thereof, but the present invention is not limited in any way by the assumed reason.
• the ratio of the breaking elongation value of the rubber formed from the rubber composition to the breaking elongation value of the control rubber formed from the control rubber composition is preferably 0.90 or more, more preferably 0.95 or more, and even more preferably 1.00 or more.
• the upper limit of the breaking elongation ratio is not particularly limited, but may be, for example, less than 1.15, 1.10 or less, or 1.05 or less.
• the range of the breaking elongation ratio can be determined by appropriately combining the above-mentioned upper and lower limits.
• the range of the breaking elongation ratio may be, for example, 0.90 or more and less than 1.15, 0.95 or more and 1.10 or less, or 1.00 or more and 1.05 or less.
• the elongation at break ratio can be adjusted, for example, by changing the amount of nanocellulose, the type of rubber component, or the method of mixing the nanocellulose and rubber components. For example, increasing the amount of nanocellulose tends to increase the elongation at break ratio.
• the method for measuring the breaking elongation of the rubber formed from the rubber composition according to the present embodiment and the control rubber formed from the control rubber composition is as follows. (1) A dumbbell-shaped No. 6 measurement sample (thickness: 1.1 to 1.2 mm) as specified in JIS K6251 is cut out from a sheet of rubber or a control rubber. (2) A tensile test is performed on the measurement sample using a tensile tester (e.g., INSTRON 5566A manufactured by INSTRON) under conditions of 23 ⁇ 2° C., a gauge length of 20 mm, and a tensile speed of 500 mm/min based on JIS K6251.
• a tensile tester e.g., INSTRON 5566A manufactured by INSTRON
• a control rubber composition obtained by removing nanocellulose from the rubber composition according to this embodiment can be prepared by mixing the same types and amounts of components as those in the rubber composition, except that nanocellulose is not used.
• the rubber composition according to this embodiment may be used as a master batch.
• the rubber composition according to this embodiment may be mixed with other rubber components and used.
• Oxidized cellulose refers to an oxide of a cellulose-based raw material with hypochlorous acid or a salt thereof before defibration.
• hypochlorous acid or its salts examples include hypochlorous acid water, sodium hypochlorite, potassium hypochlorite, calcium hypochlorite, and ammonium hypochlorite.
• hypochlorous acid is a weak acid that exists as an aqueous solution
• hypochlorite is a compound in which hydrogen of hypochlorous acid is replaced by other cations.
• sodium hypochlorite which is a hypochlorite, exists in a solvent (preferably in an aqueous solution), so the concentration is measured as the effective chlorine amount in the solution, not the concentration of sodium hypochlorite.
• the amount of carboxy groups in the oxidized cellulose in this embodiment is preferably 0.20 to 2.0 mmol/g.
• amount of carboxy groups is 0.20 mmol/g or more, sufficient easy defibration properties can be imparted to the oxidized cellulose. This makes it possible to obtain a nanocellulose-containing slurry of uniform quality even when defibration processing is performed under mild conditions, and improves the viscosity stability and handleability of the slurry.
• the amount of carboxy groups is 2.0 mmol/g or less, excessive decomposition of cellulose during defibration processing can be suppressed, and nanocellulose with a low ratio of particulate cellulose and uniform quality can be obtained. This is thought to improve dispersibility.
• Rayon has the same chemical structure as cellulose, and its oxide (oxidized rayon) is water-soluble.
• oxidized rayon is dissolved in heavy water and solution one-dimensional 13 C-NMR measurement is performed, a carbon peak attributable to a carboxy group is observed at 165 to 185 ppm.
• the oxide of a cellulose-based raw material with hypochlorous acid or its salt two signals appear in this chemical shift range. Furthermore, it can be determined by solution two-dimensional NMR measurement that the carboxy groups are introduced at the 2- and 3-positions.
• a baseline is drawn around a peak in the range of 165 ppm to 185 ppm in a solid-state 13C -NMR spectrum to determine the total area, and then the area is vertically divided at the peak top to determine the ratio of the two peak area values (larger area value/smaller area value). If the ratio of the peak area values is 1.2 or more, the peak can be said to be broad.
• the presence or absence of the broad peak can be determined by the ratio of the length L of the baseline in the range of 165 ppm to 185 ppm to the length L' of the perpendicular line from the peak top to the baseline. That is, if the ratio L'/L is 0.1 or more, it can be determined that a broad peak is present.
• the ratio L'/L may be 0.2 or more, 0.3 or more, 0.4 or more, or 0.5 or more.
• the upper limit of the ratio L'/L is not particularly limited, but is usually 3.0 or less, 2.0 or less, or 1.0 or less.
• the degree of polymerization of the oxidized cellulose is preferably 600 or less.
• the energy required for defibration decreases, and defibration tends to be easier.
• the amount of oxidized cellulose that is insufficiently defibrated decreases, and dispersibility tends to improve.
• the size of the obtained nanocellulose becomes uniform, and the viscosity of the slurry containing the nanocellulose tends to be low.
• the degree of polymerization of the oxidized cellulose is more preferably 580 or less, even more preferably 560 or less, still more preferably 550 or less, even more preferably 500 or less, even more preferably 450 or less, and even more preferably 400 or less.
• the degree of polymerization of the oxidized cellulose is more preferably 60 or more, even more preferably 70 or more, still more preferably 80 or more, even more preferably 90 or more, even more preferably 100 or more, still more preferably 110 or more, and particularly preferably 120 or more.
• the preferred range of the degree of polymerization of oxidized cellulose can be determined by appropriately combining the above upper and lower limits.
• the degree of polymerization of oxidized cellulose is more preferably 60 to 600, even more preferably 70 to 600, even more preferably 80 to 600, even more preferably 80 to 550, even more preferably 80 to 500, even more preferably 80 to 450, and particularly preferably 80 to 400.
• the degree of polymerization of oxidized cellulose can be adjusted by changing the reaction time, reaction temperature, pH, and effective chlorine concentration of hypochlorous acid or its salt during the oxidation reaction. Specifically, since the degree of polymerization tends to decrease as the degree of oxidation increases, methods for decreasing the degree of polymerization include, for example, increasing the reaction time and/or reaction temperature of the oxidation. As another method, the degree of polymerization of oxidized cellulose can be adjusted by the stirring conditions of the reaction system during the oxidation reaction. For example, under conditions in which the reaction system is sufficiently homogenized using a stirring blade or the like, the oxidation reaction proceeds smoothly and the degree of polymerization tends to decrease.
• Nanocellulose is a general term for finely divided cellulose, including fine cellulose fibers and cellulose nanocrystals. Fine cellulose fibers are also called cellulose nanofibers (also written as CNF).
• Image processing software can be used to calculate such average fiber width and average fiber length.
• the image processing conditions are arbitrary, but the calculated values may differ depending on the conditions, even for the same image.
• the range of difference in values depending on the conditions is preferably within ⁇ 100 nm for the average fiber length.
• the range of difference in values depending on the conditions is preferably within ⁇ 10 nm for the average fiber width.
• the zeta potential of nanocellulose is preferably ⁇ 35 mV or less, more preferably ⁇ 40 mV or less, and even more preferably ⁇ 50 mV or less.
• the zeta potential of the nanocellulose is preferably -90 mV or more, more preferably -85 mV or more, even more preferably -80 mV or more, even more preferably -77 mV or more, even more preferably -70 mV or more, and even more preferably -65 mV or more.
• Nanocellulose can be produced by defibrating the above-mentioned oxidized cellulose. 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 products (for example, Aronfibro (registered trademark) manufactured by Toagosei Co., Ltd.).
• the rubber composition according to the present embodiment contains a rubber component in addition to the nanocellulose described above.
• the rubber component include a natural rubber component and a synthetic rubber component.
• the rubber component may be in a solid form, a dispersion liquid (latex) in which the rubber component is dispersed in a dispersion medium, or a solution in which the rubber component is dissolved in a solvent.
• a dispersion liquid latex
• a solution in which the rubber component is dissolved in a solvent examples include water and organic solvents.
• the amount of the dispersion medium and the solvent may each be 10 to 1000 parts by mass per 100 parts by weight of the rubber component.
• the rubber composition according to the present embodiment can be produced by appropriately mixing the nanocellulose according to the present embodiment with a rubber component.
• the rubber composition according to the present embodiment may be produced by mixing the nanocellulose according to the present embodiment with a rubber component by a known method.
• the method for producing a rubber composition containing nanocellulose is not particularly limited, but it can be produced, for example, by a method using an open roll. For example, see JP 2015-98576 A.
• One embodiment of the present invention relates to a method for producing a rubber composition according to the present embodiment, which includes a step of mixing the nanocellulose according to the present embodiment with a rubber component to obtain a mixture, and a dispersion step of thinly passing the mixture through an open roll to obtain a rubber composition.
• the nanocellulose can be dispersed in the rubber composition.
• the rubber composition according to the present embodiment can also be produced by melt-kneading a mixture of the nanocellulose according to the present embodiment and a rubber component. This allows the breaking elongation ratio according to the present embodiment to be adjusted to be higher.
• the rubber composition according to this embodiment can also be produced by a production method including a step of mixing the nanocellulose and the rubber component according to this embodiment to obtain a first mixture, a step of drying the first mixture, and a step of melt-kneading the dried first mixture.
• a stirrer such as a homomixer or a planetary stirrer.
• An embodiment of the present invention relates to a rubber formed from the above-mentioned rubber composition.
• the rubber according to this embodiment can also be expressed as a cross-linked product of the rubber composition.
• One embodiment of the present invention relates to a rubber formed from a rubber composition, the rubber composition comprising nanocellulose and a rubber component, the nanocellulose comprising an oxide of a cellulose-based raw material produced by hypochlorous acid or a salt thereof, and substantially free of N-oxyl compounds, the ratio of the breaking elongation value of the rubber to the breaking elongation value of a control rubber formed from a control rubber composition obtained by removing the nanocellulose from the rubber composition being 0.90 or more and less than 1.15.
• Details of the rubber composition, the control rubber composition, the breaking elongation ratio, etc. are as described in the section ⁇ Rubber composition> above.
• the rubber according to this embodiment can be obtained, for example, by heating the rubber composition and/or by reacting the rubber composition with a crosslinking agent.
• sulfur examples include powdered sulfur, finely divided sulfur, precipitated sulfur, colloidal sulfur, and sulfur chloride.
• metal oxides examples include magnesium oxide, calcium oxide, zinc oxide, and copper oxide.
• organic peroxides examples include alkyl peroxides, aryl peroxides, acyl peroxides, ketone peroxides, peroxyketals, peroxycarbonates, peroxyesters, and hydroperoxides.
• dicumyl peroxide is a suitable organic peroxide.
• triazine derivatives examples 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, 2-dibutylamino-4,6-dimercapto-s-triazine, Examples of the mercapto-s-triazine include 2-di(iso-butylamino)-4,6-dimercapto-s-triazine, 2-dipropylamino-4,6-dimercap
• the amount of crosslinking agent added can be adjusted as appropriate, and is usually 0.01 to 15 parts by mass, preferably 0.1 to 10 parts by mass, and more preferably 0.1 to 5 parts by mass, per 100 parts by mass of the rubber component.
• the temperature during crosslinking can be adjusted as appropriate, but is usually within the range of 20 to 200°C.
• parts and % mean parts by mass and % by mass unless otherwise specified.
• phr parts per hundred rubber
• Pulp (KC Flock W100GK, Nippon Paper Industries Co., Ltd.) was used as the cellulosic raw material. Put 350g of sodium hypochlorite pentahydrate crystals with effective chlorine concentration of 42% by mass into a beaker, add pure water and stir to obtain an aqueous solution of sodium hypochlorite with effective chlorine concentration of 21% by mass.Add 35% by mass hydrochloric acid thereto and stir to make pH 11.0.This aqueous solution of sodium hypochlorite is heated to 30°C in a thermostatic water bath while stirring at 200 rpm using a propeller-type stirring blade in a stirrer (Three-one motor, BL600) manufactured by Shinto Scientific Co., Ltd., and then add 50g of the above-mentioned pulp.
• aqueous solution of sodium hypochlorite is heated to 30°C in a thermostatic water bath while stirring at 200 rpm using a propeller-type stirring blade in a stirrer (Thre
• the pH during the reaction was maintained at 11.0 while adding a 48% by mass aqueous sodium hydroxide solution in the same thermostatic water bath while keeping the temperature at 30° C.
• a propeller-type stirring blade was used to stir at 200 rpm, and the oxidation reaction was carried out for 4 hours (pH maintenance was continued).
• the product was subjected to solid-liquid separation by pressure filtration using a filter cloth (KE022, manufactured by Nakao Filter Co., Ltd., air permeability 0.3 cc/ cm2 /sec), and the obtained oxidized cellulose solid was washed with pure water.
• the amount of carboxy groups in the oxidized cellulose was 0.7 mmol/g.
• the available chlorine concentration in the aqueous sodium hypochlorite solution was measured by the following method. (Measurement of available chlorine concentration in sodium hypochlorite aqueous solution) 0.582g of the aqueous solution of sodium hypochlorite pentahydrate crystals added to pure water was precisely measured, 50mL of pure water was added, 2g of potassium iodide and 10mL of acetic acid were added, and the solution was immediately sealed and left in the dark for 15 minutes. After leaving the solution for 15 minutes, the liberated iodine was titrated with 0.1mol/L sodium thiosulfate solution (solution factor 1.000) (indicator starch test solution), and the titration amount was 34.55mL.
• Production Example 2 Production of nanocellulose
• the aqueous dispersion of oxidized cellulose (solid content 7.5%) obtained in Production Example 1 was treated for 46 minutes with a homomixer (Primix, Robomix) at 10,000 rpm and 300 mL of liquid to defibrate the oxidized cellulose into nanocellulose, obtaining an aqueous nanocellulose dispersion.
• the average fiber width was 3.7 nm and the average fiber length was 150 nm.
• Example 1 A nitrile butadiene rubber latex (Nipol LX513, manufactured by Nippon Zeon Co., Ltd., concentration 45 wt%; hereinafter, the rubber is referred to as "NBR") having a solid content of 100 phr and a nanocellulose aqueous dispersion (solid content 7.5 wt%) obtained in Production Example 2 having a solid content of 20 phr were mixed, treated with a homomixer (Robomix, manufactured by Primix) at 3,000 rpm for 1 minute, and dispersed with a planetary mixer (Awatori Rentaro ARE310, manufactured by THINKY) at Mix 2,000 rpm for 30 seconds and Defoam 2,200 rpm for 30 seconds to obtain a rubber composition.
• NBR nitrile butadiene rubber latex
• Example 1 The rubber alone was mixed and evaluated. That is, the NBR latex was cast on a plastic tray and dried at 50° C. for 3 days. After that, the same mixing and testing as in Example 1 were carried out.
• Example 2 A mixture was obtained by kneading a carboxy-modified NBR latex (Nipol 1571C2, manufactured by Zeon Corporation, solid content 45% by mass, hereinafter, this rubber will be referred to as "X-NBR") and the oxidized cellulose aqueous dispersion obtained in Production Example 2 with a planetary centrifugal mixer (Planary centrifugal mixer, manufactured by Thinky Corporation). Next, the mixture was poured into a vat and dried in an oven at 40 to 50°C for about 24 hours to remove the aqueous solvent, thereby obtaining a mixture. The moisture content of the obtained mixture was 5% or less.
• X-NBR carboxy-modified NBR latex
• the mixture was wound around an open roll (two rolls, Yasuda Seiki Co., Ltd., 191-TH test mixing roll) and kneaded, and then the mixture was thin-passed (roll temperature 10° C. to 30° C., roll gap 0.3 mm or less, roll speed ratio 1.1) to obtain an intermediate. Furthermore, the intermediate product was wound around the open roll again, and zinc oxide and an antioxidant were mixed therein. Then, a crosslinking agent (DCP) was further added and mixed, and the separated sheet was pressure-molded at 165°C for 30 minutes to obtain a sheet-like crosslinked product sample having a thickness of 1 mm.
• DCP crosslinking agent
• Example 2 The rubber alone was mixed and evaluated. That is, the latex of X-NBR was cast on a plastic tray and dried at 50° C. for 3 days. After that, the same mixing and testing as in Example 2 were carried out.
• the strength was evaluated by the following tensile test.
• a sample (thickness: 1.1 to 1.2 mm) was obtained by cutting out the sheet rubber into a dumbbell-shaped No. 6 shape as described in JIS K6251.
• a tensile test was carried out based on JIS K6251 using a tensile tester (INSTRON 5566A, manufactured by INSTRON) at 23 ⁇ 2° C., a gauge length of 20 mm, and a tensile speed of 500 mm/min using the tensile tester.
• the tensile test was carried out to measure the 50% modulus ( ⁇ 50 (MPa)), 100% modulus ( ⁇ 50 (MPa)), 300% modulus ( ⁇ 300 (MPa)), tensile strength (TS (MPa)), elongation at break (Eb (%)), and elastic modulus.
• Example 1 The results of the strength evaluation of each rubber are shown in Table 1.
• the results of Example 1 and Comparative Example 1 are shown in Figure 1.
• the breaking elongation ratio of Example 1 was based on Comparative Example 1.
• the breaking elongation ratio of Example 2 was based on Comparative Example 2.

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