Rubber composition

Abstract

[Problem] To provide: a rubber composition comprising a natural nanopolymer that has good interfacial adhesion to rubber and has high dispersibility in rubber; and a method for producing the rubber composition. The solution of the present invention is a rubber composition containing (A) a rubber component, (B-1) a molten mixture containing a natural nanopolymer, and (C) a silane coupling agent having a mercapto group and a silane coupling agent having an amino group. The rubber composition according to the present invention provides: a molten mixture comprising a natural nanopolymer having good interfacial adhesion to rubber and high dispersibility in rubber; and a rubber product obtained by crosslinking the natural nanopolymer.

Description

Technical Field

[0001] The present invention relates to a rubber composition and a method for manufacturing the same, and the rubber composition contains a molten mixture of cellulose fibers or nano natural polymers. Background Art

[0002] Generally, rubber refers to a material with a high elastic limit and a low elastic modulus, such as natural rubber or synthetic rubber, which has an organic polymer as the main component, that is, elastic rubber. Compositions containing rubber (rubber compositions) are widely used in industrial applications such as tires, sealing materials, and anti-vibration and shock-absorbing materials. Moreover, in order to exhibit the properties of rubber and obtain more excellent performance, various components are used as additives for rubber compositions.

[0003] For example, Patent Document 1 discloses a technique related to a rubber / short fiber masterbatch, which is obtained by stirring and mixing an aqueous dispersion of short fibers with an average diameter of less than 0.5 μm and a rubber latex, and then spraying the mixed liquid in an atmosphere of a shock wave of pulse combustion and drying it.

[0004] Moreover, Patent Document 2 discloses a technique related to a rubber composition and a method for manufacturing the same, which improves the dispersibility and adhesion of a reinforcing material composed of cellulose-based fibers to a rubber component and exhibits sufficient durability and rigidity.

[0005] These patent documents indicate that cellulose-based fibers are useful as additives for rubber compositions.

[0006] However, there is still room for improvement in enhancing the adhesion at the interface between rubber and cellulose-based fibers and improving the dispersion of cellulose-based fibers in rubber.

[0007] Moreover, there is still room for improvement in improving the crosslinking characteristics, processability, mechanical strength, etc. of rubber compositions or rubber products crosslinked therefrom.

[0008] Prior Art Documents

[0009] Patent Documents

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 2006-206864

[0011] Patent Document 2: Japanese Patent Application Laid-Open No. 2009-191198

[0012] Non-Patent Documents

[0013] Non-Patent Document 1: Method for Measuring Powder Flowability, Journal of the Japan Society for Imaging Science and Technology, Vol. 46, No. 6, pp. 472-477 Summary of the Invention

[0014] Problems to be Solved by the Invention

[0015] In view of the above problems in the prior art, the present invention aims to provide a rubber composition and a method for manufacturing the same, wherein the rubber composition has a high dispersibility of a molten mixture containing a nano natural polymer or cellulose fibers in the rubber, and good interfacial adhesion between the rubber and the molten mixture containing the nano natural polymer or cellulose fibers.

[0016] The inventors of the present invention have intensively studied to achieve the above object, and as a result, have found a rubber composition that can solve the above problems, which is obtained by mixing a molten mixture and a silane coupling agent or by mixing cellulose fibers having a specific bulk specific gravity and average particle diameter with rubber, and the molten mixture is obtained by melt-mixing a mixture including a nano natural polymer and a solvent with an aqueous dispersion of a polyolefin resin including at least polyolefin and water or a styrene-based polymer having a weight average molecular weight in a specific range.

[0017] Technical solution for solving the problem

[0018] That is, the rubber composition of the present invention contains: (A) a rubber component; (B-1) a molten mixture containing a nano natural polymer; and (C) a silane coupling agent having a mercapto group.

[0019] Effect of the invention

[0020] By the present invention, there is provided a rubber composition and a method for manufacturing the same, wherein the rubber composition has a high dispersibility of a molten mixture containing a nano natural polymer or cellulose fibers in the rubber, and good interfacial adhesion between the rubber and the molten mixture containing the nano natural polymer or cellulose fibers. Description of the drawings

[0021] Figure 1 is a conceptual diagram of a CNF manufacturing (defibrillation treatment) apparatus. Detailed description of the invention

[0022] Hereinafter, the present invention will be described in more detail based on examples. In addition, the present invention is not limited to the following examples.

[0023] (Definition of terms)

[0024] In the present invention, the molten mixture refers to a mixture obtained by heating and powdering a mixture composed of at least a nano natural polymer and an aqueous dispersion of a polyolefin resin or a mixture including a nano natural polymer and a styrene-based polymer having a weight average molecular weight in a specific range.

[0025] In the present invention, the paper powder refers to a product obtained after subjecting paper to a treatment of pulverizing it very finely.

[0026] ​In the present invention, the so-called rubber composition refers to a composition obtained by incorporating at least the above-mentioned molten mixture into rubber.

[0027] The present invention relates to a rubber composition comprising: (A) 100 parts by mass of rubber; (B-1) 1 to 100 parts by mass of a molten mixture containing nano-natural polymer relative to 100 parts by mass of rubber; and (C) 5 to 60% by mass of a silane coupling agent relative to the (B-1) molten mixture containing nano-natural polymer.

[0028] Moreover, the present invention relates to a rubber composition comprising: (A) 100 parts by mass of rubber; (B-2) 1 to 100 parts by mass of cellulose fiber relative to 100 parts by mass of rubber; and (C) 5 to 60% by mass of a silane coupling agent relative to the (B-2) cellulose fiber.

[0029] [(A) Rubber]

[0030] The rubber used in the present invention is not particularly limited, and examples thereof include natural rubber, chloroprene rubber, ethylene-propylene-non-conjugated diene copolymer rubber, ethylene-1-butene copolymer rubber, ethylene-hexene copolymer rubber, ethylene-octene copolymer rubber, polybutadiene, styrene-butadiene block copolymer rubber, styrene-butadiene copolymer rubber, partially hydrogenated styrene-butadiene-styrene block copolymer rubber, styrene-butadiene-acrylonitrile copolymer rubber, styrene-isoprene block copolymer rubber, partially hydrogenated styrene-isoprene block copolymer rubber, polyurethane rubber, styrene-grafted ethylene-propylene-non-conjugated diene copolymer rubber, styrene-grafted ethylene-propylene copolymer rubber, styrene / acrylonitrile-grafted ethylene-propylene-non-conjugated diene copolymer rubber, styrene / acrylonitrile-grafted ethylene-propylene copolymer rubber, chlorosulfonated polyethylene rubber, silicone rubber, ethylene-vinyl acetate rubber, epichlorohydrin rubber, polysulfide rubber, etc. In addition, these rubbers can be used alone or in combination of two or more.

[0031] [(B-1) Molten mixture]

[0032] The molten mixture used in the present invention is obtained by heating at least an aqueous dispersion of (a) nano-natural polymer and (b-1) polyolefin resin or a mixture of (b-2) a polymer mainly composed of a vinyl aromatic compound in a specific molecular weight range, and then pulverizing.

[0033] [(a) Nano-natural polymer]

[0034] The nano-natural polymer used in the molten mixture of the present invention is a fibrous material with a diameter of less than 1 to 1000 nm, a natural polymer nanofiber with a length of more than 100 times the diameter, or a natural polymer nanocrystal in the form of a rod or spindle with a diameter of 10 to 50 nm and a length of 100 to 500 nm or less.

[0035] The natural polymer used in the present invention is not particularly limited, but examples thereof include polysaccharides such as cellulose, chitin, and chitosan, and proteins such as collagen, silk, and gelatin.

[0036] In the present invention, a nano-natural polymer with a crystallinity in the range of 50% or more is preferably used. This is because when using a nano-natural polymer with a relatively high crystallinity, the ability to carry the resin is poor due to the decrease in the specific surface area of the nano-natural polymer, and the ability and operability of the resin molded product (fluidity of the resin, shape retention of the resin molded product) are poor due to the decrease in strength, elasticity, and touchability. And if the crystallinity is low, it also becomes prone to spoilage.

[0037] In the present invention, a nano-natural polymer with an average degree of polymerization in the range of 400 to 900 is preferably used. This is because when the degree of polymerization is higher than 900 of the average degree of polymerization, the nano-natural polymer becomes prone to entanglement or distortion, so it is difficult to exert the function as a fiber and it is easy to become a foreign substance (aggregate) inside the resin, and since it cannot exert the function as a straight fiber, the effect of reinforcing the resin is poor. When the average degree of polymerization is less than 400, the straightness of the natural fiber is lost, so it is difficult to produce a reinforcing effect.

[0038] Next, a method for preparing an aqueous solution of cellulose nanofibers (hereinafter also referred to as "CNF") using cellulose as a natural polymer will be described. In the present invention, examples of CNF include CNF derived from natural plants such as wood fibers, broad-leaved trees, coniferous trees, bamboo fibers, sugarcane fibers, seed hair fibers, leaf fibers, seaweeds, etc., and polysaccharide-derived CNF such as the pellicle derived from acetic acid bacteria. Further, it may also be produced from crop residues such as bagasse, rice straw, rice husk, tea residue, and residue of fruit juice, which are derived from leaves, flowers, stems, fruits, roots, and outer skins of plants. These CNFs may be used alone or in combination of two or more. As the polysaccharide, pulp having an α-cellulose content of 60% to 99% by mass is preferably used. When the α-cellulose content is 60% by mass or more, the fiber diameter and fiber length are easily adjusted, entanglement between fibers can be suppressed, and compared with the case of using pulp having an α-cellulose content of less than 60%, the thermal stability during melting is higher. In addition to not causing a decrease in impact strength, the inhibitory effect on coloring caused by thermal decomposition of hemicellulose is good, and the effects of the present invention can be made more excellent. On the other hand, when the content is 99% or more, it is difficult to defibrate the fibers to the nano level and the energy cost increases, and the fiber diameter and fiber length become difficult to adjust.

[0039] The CNF in the present invention is obtained, for example, by performing the following defibrillation treatment to obtain a CNF dispersion (hereinafter sometimes also referred to as CNF in an aqueous state).

[0040] The defibrillation treatment is performed using Figure 1 the water counter-jet method shown below (hereinafter sometimes also referred to as the ACC method). This is a method of introducing pulp suspended in water into two opposing nozzles ( Figure 1 : 107) in a chamber and spraying and impinging from these nozzles toward a single point. Figure 1 : 108a, 108b). Figure 1 The device shown below is a liquid circulation type and includes a hopper ( Figure 1 : 109), a plunger ( Figure 1 : 110), two opposing nozzles ( Figure 1 : 108a, 108b), and, if necessary, a heat exchanger ( Figure 1 : 111). Fine particles dispersed in water are introduced into the two nozzles and sprayed and impinge against each other under a high pressure of about 50 to 400 MPa from the two opposing nozzles ( Figure 1 : 108a, 108b).

[0041] Furthermore, the degree of defibrillation from pulp fibers to CNF can be evaluated by the viscosity value of the CNF dispersion.

[0042] Moreover, since the ratio of the fiber length to the fiber diameter (aspect ratio) after fibrillation varies depending on the source of the pulp raw material, the viscosity values of the CNF dispersions are different from each other.

[0043] Furthermore, for example, by combining pulp fibers from different raw material sources or by controlling the degree of fibrillation, the B-type viscosity value in a 1 wt% CNF aqueous dispersion can be adjusted to a range of approximately 300 to 10,000 mPa·s.

[0044] The CNF obtained in the above manner preferentially undergoes nano-finement by cleaving the interactions between natural cellulose fibers, so there is no change in the structure of cellulose molecules and it has the structural formula represented by the following Chemical Formula 1 derived from the raw material pulp. In other words, the CNF used in the present invention means that it has six hydroxyl groups within the cellobiose unit in Chemical Formula 1 and is not chemically modified. This can be confirmed by comparing the IR spectrum of cellulose with that of the CNF used in the present invention using FT-IR. By this ACC method, the average fiber diameter of cellulose fibers can be pulverized to less than 1 μm, and as a result, CNF with an average thickness of 3 to 1,000 nm and an average length of 0.1 μm or more is obtained.

[0045] The measurement of the average thickness and average fiber length is carried out by appropriately selecting a scanning electron microscope (SEM), a transmission electron microscope (TEM), a scanning probe microscope (SPM), etc., observing / measuring the CNF, selecting 20 or more from the obtained photographs, and averaging each of them. In the counter-impact treatment, the applied energy is far less than the energy required to break covalent bonds (estimated to be 1 / 300 or less), and it is difficult to cause a decrease in the degree of polymerization of cellulose. The cellulose nanofibers obtained by this ACC method coexist with hydrophilic ends and hydrophobic ends, indicating amphiphilicity.

[0046] [Chemical Formula 1]

[0047]

[0048] In addition, in the present invention, cellulose nanofibers obtained by chemical treatment methods such as TEMPO oxidation catalyst, phosphoric acid esterification treatment, ozone treatment, enzyme treatment, maleic acid treatment, hydrophobic modification with alkenyl succinic anhydride, hydrophobic modification with alkyl ketene dimer, hydrophobic modification by acetylation, etc., which are known as other manufacturing methods of cellulose nanofibers, or cellulose nanofibers obtained by physical methods of thinning cellulose-based fibers by wet pulverization using mechanical action such as a grinder (mortar type crusher), disk refiner, conical refiner, high-pressure homogenizer, ball mill, wet explosion method, ultrasonic fibrillation method, kneading method, freeze pulverization method, etc., can all be used as the CNF dispersion in the present invention. Moreover, cellulose nanofibers obtained by combining chemical treatment and physical treatment methods can also be used as the CNF dispersion.

[0049] The CNF concentration of the CNF dispersion obtained in the above manner is usually in the range of 0.1 to 10%.

[0050] Next, the obtained CNF dispersion is desolvated so that the CNF solid content concentration is in the range of 20 to 50%. When the CNF solid content concentration is less than 20%, the amount of solvent becomes large, resulting in heat energy loss and deterioration of the yield of additives during the manufacture of the molten mixture.

[0051] On the other hand, when the solid content concentration is higher than 50%, since the CNFs are already partially aggregated with each other and the aggregates cannot be redispersed during the manufacture of the molten mixture, it is less preferred. The solvent may contain water, and other solvents such as organic solvents can be used without particular limitation in addition to water.

[0052] [(B-2) Cellulose fiber]

[0053] As the cellulose fiber used in the present invention, as long as the raw material represents a fibrous shape derived from cellulose. In particular, from the viewpoint of easy availability, pulp for papermaking, cellulose nanofibers, pulverized paper powder, etc. can be used without particular limitation.

[0054] In one aspect, fine paper powder obtained by pulverizing paper very finely can be used. The paper used as the raw material can be used without particular limitation. If an example is still to be given, waste paper or defective batches generated in a paper mill can be used. Moreover, the type of paper can be used without particular limitation. If an example is still to be given, in addition to virgin paper including virgin pulp, various types of paper such as waste paper and used paper can also be used. Furthermore, as the raw material pulp, various pulps derived from coniferous trees, broad-leaved trees, bamboo, etc. can also be used. Moreover, the fillers contained in the paper can be used without particular limitation within the range that does not cause adverse effects on the rubber.

[0055] Furthermore, as a method of finely pulverizing paper, there are no particular restrictions, and if examples are still required, a pulverizer, a roll mill, a shredder, a mortar-type pulverizer, etc. can be used alone, or these can be used in combination.

[0056] For example, pulverization by a shredder (Utility Model Registration No. 1904682) can set the gap between the fixed blade and the rotating blade to a minimum of 0.5 mm, and since there is little retention of raw materials and little temperature rise, even thin paper with a paper thickness of 5 μm can be pulverized. The size of the paper powder can be easily adjusted using a round-hole sieve. If the round-hole size of the sieve mesh uses a minimum diameter of 0.5 mm, it becomes ultra-fine paper powder. If 5 mm is used, it becomes larger, and if 10 mm is used, it becomes coarser paper powder. And the pulverization treatment can be carried out only once, or multiple treatments can be combined. In the case of multiple treatments, paper powder of the desired size can be obtained by adjusting the sieve mesh size or the gap.

[0057] In one aspect, the cellulose fiber used in the present invention, in terms of the D90 value obtained by measuring the laser diffraction particle size distribution, is in the range of 10 to 50 μm, preferably in the range of 20 to 40 μm, more preferably in the range of 25 to 35 μm, or the D50 value is in the range of 5 to 100 μm, preferably in the range of 20 to 100 μm, more preferably in the range of 25 to 50 μm. For cellulose fibers with a D90 value less than 10 μm, the manufacturing cost may increase. For those exceeding 50 μm, there is a concern that the paper powder cannot be evenly dispersed in the rubber composition. And there may be drawbacks such as the paper powder forming large lumps in the synthetic resin, and sometimes the fluidity of the composition will be significantly reduced due to the large lumps. The fibrillation of the cellulose fiber can also be adjusted for use.

[0058] Moreover, the water absorption of the cellulose fiber used in the present invention at 23°C, 50% RH, and 48 hours is 0.1% or more and 10% or less, preferably 1% or more and 8% or less, more preferably 2% or more and 6% or less.

[0059] The bulk specific gravity of the cellulose fiber used in the present invention is preferably 0.1 or more and 0.4 or less. If the bulk specific gravity is 0.4 or more, there is a concern about a decrease in dispersibility. On the other hand, if the bulk specific gravity is less than 0.1, there is a concern that the process control becomes difficult.

[0060] In addition, the bulk specific gravity is a value measured in accordance with JIS K7365.

[0061] In the present invention, the angle of repose of the cellulose fiber used is preferably 30° or more and 75° or less, more preferably 30° to 70°. If the angle of repose is 75° or more, the fluidity is small, and there is a concern that it becomes difficult to uniformly blend with rubber. On the other hand, if the angle of repose is less than 30°, the fluidity is high and the processability decreases. In addition, the angle of repose is the average value measured three times by the tilt angle method (starting angle) described in Non-Patent Document 1.

[0062] [(b-1) Aqueous dispersion of polyolefin resin]

[0063] In the present invention, the aqueous dispersion of polyolefin resin refers to a dispersion of polyolefin in water, and can be produced by methods such as dispersing a kneaded product composed of polyolefin and a water-soluble polymer such as polyvinyl alcohol in water, and melting and kneading polyolefin and a polyolefin containing a carboxyl group, and then supplying it to hot water containing a basic substance and applying a shearing force to obtain a dispersion liquid.

[0064] The polyolefin used herein refers to a crystalline or non-crystalline olefin-based polymer. And it may also contain a diene having two or more double bonds.

[0065] And as the olefin constituting the polymer, in addition to ethylene, α-olefins such as propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, etc. can be cited. These can be used alone or in combination of multiple kinds.

[0066] As the diene, there are isoprene, butadiene, dicyclopentadiene, 1,4-pentadiene, 2-methyl-1,4-pentadiene, 1,4-hexadiene, divinylbenzene, methylene norbornene, ethylidene norbornene, etc., and these can be used alone or in combination of multiple kinds. Furthermore, styrene, vinyl acetate, acrylic acid, acrylic esters such as methyl acrylate, methacrylic acid, methacrylic esters such as methyl methacrylate, etc. can also be used.

[0067] Specific examples of the polyolefin include polyethylene, polypropylene, ethylene / propylene copolymer, ethylene / 1-butene copolymer, propylene / 1-butene copolymer, ethylene / propylene / 1,4-hexadiene copolymer, ethylene / propylene / dicyclopentadiene copolymer, ethylene / propylene / 5-ethylidene-2-norbornene copolymer, ethylene / propylene / 5-vinyl-2-norbornene copolymer, ethylene / 1-butene / 5-ethylidene-2-norbornene copolymer, ethylene / 1-butene / dicyclopentadiene copolymer, ethylene / dicyclopentadiene copolymer, ethylene / vinyl acetate copolymer, ethylene / methyl methacrylate copolymer, ethylene / acrylic acid copolymer, ethylene / methacrylic acid copolymer, ethylene / butadiene copolymer, etc.

[0068] The water-soluble polymer mixed with the above polyolefin refers to saponified polyvinyl alcohol or the like, without particular limitation. And the polyolefin containing a carboxyl group refers to those obtained by reacting maleic anhydride, maleic acid, fumaric acid, hypochlorous acid, etc. with the above polyolefin, or those obtained by copolymerizing acrylic acid, methacrylic acid, etc.

[0069] Moreover, when dispersing those mixtures in water to produce a dispersion, an anionic surfactant and / or a nonionic surfactant may be contained in the mixture.

[0070] The solid content concentration of the aqueous dispersion of the polyolefin resin thus produced is usually 10 to 70%, and the average particle diameter of the solid content particles is 0.01 to 20 μm. In addition, the average particle diameter can be measured by either the Coulter counting method or the Microtrack method.

[0071] [(b-2) Polymer having a vinyl aromatic compound in a specific molecular weight range as the main component]

[0072] The polymer having a vinyl aromatic compound in a specific molecular weight range as the main component is a styrene-based polymer having a vinyl aromatic compound as the main component. As the vinyl aromatic compound, styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, vinyldimethylbenzene, etc. can be exemplified, and styrene is preferred. As the styrene-based polymer, polystyrene, rubber-modified polystyrene, acrylonitrile-styrene, acrylonitrile-butadiene-styrene, methyl methacrylate-butadiene-styrene, acrylonitrile-acrylic acid-styrene, styrene-maleic acid copolymer, oligomer of styrene-butadiene-styrene copolymer, its hydride, or those having repeating units derived from monomers having a styrene skeleton are preferred. Among them, from the viewpoints of physical properties and cost, styrene polymer and acrylonitrile-styrene polymer are preferred. In addition, the styrene-based polymer can be used alone or in combination of two or more.

[0073] Moreover, the styrene-based polymer used in the present invention is a styrene polymer obtained by polymerizing styrene monomer under special conditions in an organic solvent in the presence of a Friedel-Crafts type catalyst. Its weight average molecular weight is 2000 or more, preferably 2200 or more and 4000 or less, more preferably 3800 or less. The ratio of weight average molecular weight to number average molecular weight is 1.6 to 2.1, and the ratio of Z average molecular weight to weight average molecular weight is 1.6 to 2.0. The softening point is 60 to 160 °C, preferably 80 to 130 °C, more preferably 95 to 120 °C.

[0074] By having a softening point within such a range, the heating temperature for the powdering means can be lowered, and furthermore, it also helps to reduce the energy cost. In addition, the weight average molecular weight refers to the polystyrene conversion value by gel permeation chromatography (GPC) method.

[0075] Alternatively, it is obtained by polymerizing or copolymerizing a monomer having a styrene skeleton in the presence of a Friedel-Crafts type catalyst, and the weight average molecular weight is 200 or more, preferably 750 or more, more preferably 1000 or more and 5000 or less, preferably 4000 or less, more preferably 3800 or less.

[0076] In addition, as the Friedel-Crafts type catalyst, a commonly used catalyst can be used.

[0077] Styrene polymers are also commercially available. For example, commercially available products such as “ARUFON (registered trademark) UP-1150” manufactured by Toagosei Co., Ltd., “YS Resin SX-100” (weight average molecular weight 2500) manufactured by Yasuhara Chemical Co., Ltd., Piccolastic A5 (polystyrene, softening point 5°C, weight average molecular weight 350), Piccolastic A-75 (polystyrene, softening point 74°C, weight average molecular weight 1300), Picotex 75 (copolymer of vinyltoluene and α-methylstyrene, softening point 75°C, weight average molecular weight 1100), Picotex LC (copolymer of vinyltoluene and α-methylstyrene, softening point 91°C, weight average molecular weight 1350), Kristalex 3070 (poly-α-methylstyrene, softening point 70°C, weight average molecular weight 950), Kristalex 3085 (poly-α-methylstyrene, softening point 85°C, weight average molecular weight 1150), Kristalex 3100 (poly-α-methylstyrene, softening point 100°C, weight average molecular weight 1500), and Kristalex 5140 (poly-α-methylstyrene, softening point 139°C, weight average molecular weight 4900) manufactured by EASTMAN COMPANY, or Hymer-ST-95 (polystyrene, softening point 95°C, weight average molecular weight 4000; manufactured by Sanyo Chemical Industries, Ltd.) can be used.

[0078] [(c-1) (silane coupling agent)]

[0079] The (c-1) silane coupling agent can be further incorporated into the molten mixture of the present invention.

[0080] The so-called silane coupling agent refers to an organosilicon compound having a hydrolyzable group and an organic functional group in one molecule.

[0081] A hydrolyzable group is a substituent that is directly bonded to a silicon atom and can form a siloxane bond through a hydrolysis reaction and / or a condensation reaction. Generally, it represents a hydrogen atom or an alkyl group having 1 or more and 22 or less carbon atoms. The alkyl group can be any of linear, branched, or cyclic. When there are multiple hydrolyzable groups in the molecule of the silane coupling agent, the substituents can be the same or different.

[0082] The organic functional group is generally preferably at least one selected from vinyl, epoxy, styryl, methacryloyl, acryloyl, amino, ureido, mercapto, thioether, isocyanate, isocyanurate, etc. When there are multiple organic functional groups in the molecule of the silane coupling agent, the organic functional groups can be the same or different.

[0083] Examples of such silane coupling agents include vinyltrimethoxysilane, vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, hydrochloride of N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane, 3-ureidopropyltrialkoxysilane, 3-isocyanatopropyltriethoxysilane, tris(trimethoxysilylpropyl)isocyanurate, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, etc.

[0084] [(c-2) (modified polyolefin)]

[0085] (c-2) modified polyolefin can be further incorporated into the molten mixture of the present invention. In addition, (c-1: silane coupling agent) and (c-2: modified polyolefin) can also be incorporated together into the molten mixture of the present invention.

[0086] As the modified polyolefin, as long as the polyolefin is modified to impart polarity, there is no particular limitation. For example, polypropylene modified with (anhydrous) carboxylic acid, epoxide, oxazoline, isocyanate, carbodiimide, etc. can be cited. Preferably, it is maleic anhydride-modified polypropylene, carbodiimide-modified polypropylene, or epoxy-modified polypropylene. A modified polyolefin having a weight average molecular weight of 500,000 or less, preferably 300,000 or less, and more preferably 200,000 or less can be used.

[0087] (Ratio of (a) nano-natural polymer and (b-1) aqueous dispersion of polyolefin resin in (B-1) molten mixture)

[0088] In the (B) molten mixture of the present invention, with respect to 1 part by mass of the (a) nano-natural polymer, the aqueous dispersion of the (b-1) polyolefin resin is preferably 0.05 to 1 part by mass, more preferably 0.1 part by mass to 0.5 part by mass, and still more preferably 0.2 part by mass to 0.3 part by mass in terms of solid content. This is because if the aqueous dispersion of the polyolefin resin is less than 0.05 part by mass, it has no effect on the dispersibility of cellulose nanofibers, and if it is more than 1 part by mass, it acts as a lubricant, no shear is applied, and the water in the molten mixture cannot be removed.

[0089] (Ratio of (a) nano-natural polymer and (b-2) styrene-based polymer having vinyl aromatic compound as the main component in (B-1) molten mixture)

[0090] In the (B-1) molten mixture of the present invention, with respect to 1 part by mass of the (a) nano-natural polymer, the (b-2) styrene-based polymer having vinyl aromatic compound as the main component is preferably 0.05 to 5 parts by mass, more preferably 0.1 part by mass to 1 part by mass, and still more preferably 0.2 part by mass to 0.6 part by mass in terms of solid content. If the styrene-based polymer is less than 0.05 part by mass, it has no effect on the dispersibility of cellulose nanofibers, and if it is more than 5 parts by mass, the strength properties are significantly reduced, and problems on the surface of the molded product occur due to exudation, etc.

[0091] When (c-1: silane coupling agent) is contained in the molten mixture, with respect to 100 parts by mass of the mixture of the (a) nano-natural polymer and the aqueous dispersion of the (b-1) polyolefin resin or the (b-2) styrene-based polymer having vinyl aromatic compound as the main component, the (c-1) silane coupling agent may be blended in an amount of 1 part by mass or more and 10 parts by mass or less.

[0092] Further, when the molten mixture contains (c-2: modified polyolefin), with respect to 100 parts by mass of the mixture of the aqueous dispersion of (a) nano natural polymer and (b-1) polyolefin resin or the styrene-based polymer having vinyl aromatic compound as the main component (b-2), (c-2) (modified polyolefin) may be blended in an amount of 0.05 parts by mass or more and 5 parts by mass or less.

[0093] Moreover, when the molten mixture contains (c-1: silane coupling agent) and (c-2: modified polyolefin), with respect to 100 parts by mass of the mixture of the aqueous dispersion of (a) nano natural polymer and (b-1) polyolefin resin or the styrene-based polymer having vinyl aromatic compound as the main component (b-2), (c-1) silane coupling agent may be blended in an amount of 0.1 parts by mass or more and 10 parts by mass or less, and (c-2) (modified polyolefin) may be blended in an amount of 0.05 parts by mass or more and 5 parts by mass or less.

[0094] (Method for manufacturing molten mixture)

[0095] The method for manufacturing the molten mixture first performs a mixing step of mixing a mixture including (a) nano natural polymer and a solvent with the aqueous dispersion of (b-1) polyolefin resin or the styrene-based polymer having vinyl aromatic compound as the main component (b-2) to obtain a mixture. Here, the reason for using the aqueous dispersion of (b-1) polyolefin resin is that the components of (a) and (b) are in a form where components insoluble in water are dispersed in water, and moreover, the dispersibility of the nano natural polymer and the rubber can be improved by the presence of olefins in the molten mixture.

[0096] And as the device for mixing, a high-speed mixer typified by a drum mixer, a Henschel mixer, a ribbon mixer, a super mixer, etc. can be used.

[0097] Next, a step of heating the obtained mixture and applying a shear force to remove the moisture of the mixture and pulverize it is performed.

[0098] The moisture content of the obtained molten mixture can be 10.0% or less, preferably 8.0% or less, more preferably 6.0% or less. This is because if the moisture content value of the molten mixture is higher than 10.0%, the dispersibility of the nano natural polymer in the rubber composition will deteriorate.

[0099] Moreover, there are no particular limitations on the pulverization method as long as it can be heated and shear force can be applied. Specifically, examples include single-screw extruders, twin-screw extruders, twin-screw kneaders, kneaders, Banbury mixers, reciprocating kneaders, roll kneaders, etc. Here, if a continuous extruder such as a twin-screw kneader is used, since the operation can be continuously carried out until the resin kneading step, it is particularly preferred because of good efficiency. In addition, in order to remove moisture and other volatile components generated in the pulverization step, a degassing device or the like can be used. Also, nitrogen purging can be carried out to suppress deterioration or abnormal decomposition caused by oxidation. Moreover, there are no particular limitations on the heating conditions such as heating time for the nano-natural polymer mixture.

[0100] The particle size of the obtained molten mixture, in terms of the value of the average particle size D50 (median particle size) obtained by measuring the particle size distribution, is 11,000 μm or less, preferably 7,500 μm or less, and more preferably 5,500 μm or less.

[0101] Similarly, in terms of the value of D90, it is 12,000 μm or less, preferably 11,100 μm or less, and more preferably 8,300 μm or less. This is because if the value of the average particle size D50 is higher than 11,000 μm or the value of D90 is higher than 12,000 μm, the dispersibility of the nano-natural polymer in the rubber composition will deteriorate.

[0102] ([(C) Silane coupling agent])

[0103] In the present invention, a silane coupling agent having a mercapto group is used. The mercapto group is a functional group represented by (-SH) and includes thiol group, thioalkyl group, sulfhydryl group, etc. There are no particular limitations on the silane coupling agent having a mercapto group. For example, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, etc. can be cited.

[0104] Moreover, in the rubber composition of the present invention, a silane coupling agent having other functional groups can be used in combination. There are no particular limitations on the silane coupling agent used in combination. Examples include silane coupling agents having vinyl group, epoxy group, styryl group, acrylic group, amino group, ureido group, mercapto group, thioether group, isocyanate group, isocyanurate group, etc. Among these, a silane coupling agent having an amino group is preferably used.

[0105] The blending amount of the silane coupling agent is preferably in the range of 5 to 50% by mass, more preferably 10 to 20% by mass, relative to the molten mixture.

[0106] (Additives, etc. for the rubber composition)

[0107] In the rubber composition of the present invention, as long as it is within the scope of not impairing the object of the present invention, reinforcing fillers such as carbon black or silica commonly used in the rubber industry can be blended in known general amounts as desired, and various drugs such as vulcanizing agents, vulcanization accelerators, antioxidants, scorch inhibitors, zinc white, stearic acid, processing oils, vegetable oils, plasticizers, and other various additives for tires and other general rubber applications can be blended. These various additives can be blended singly or in any combination.

[0108] As the vulcanizing agent, organic peroxides and sulfur-based vulcanizing agents can be used. As the organic peroxides, dicumyl peroxide, tert-butyl peroxybenzoate, di-tert-butyl peroxide diisopropylbenzene, etc. can be cited, and as the sulfur-based vulcanizing agents, sulfur, morpholine disulfide, etc. can be cited.

[0109] As the vulcanization accelerators that can be used, for example, thiazole-based ones such as 2-mercaptobenzothiazole (MTB) and bis(2-benzothiazolyl) disulfide (MBTS); sulfenamide-based ones such as N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N,N'-dioxidodipropylene-2-benzothiazolesulfenamide; and guanidine-based vulcanization accelerators such as diphenylguanidine (DPG) can be cited.

[0110] (Method for manufacturing rubber composition)

[0111] The method for manufacturing the rubber composition of the present invention is not particularly limited, and it can be manufactured by a manufacturing method having the following steps A to D. In addition, the order of the mixing step (step A) and the first kneading step (step B) can be changed before and after.

[0112] Step A: A mixing step of mixing the molten mixture and a mercapto group-containing silane coupling agent, or the molten mixture, a mercapto group-containing silane coupling agent, and an amino group-containing silane coupling agent to obtain a molten mixture / silane coupling agent mixture

[0113] Step B: The first kneading step of kneading the rubber

[0114] Step C: The second kneading step of kneading the mixture obtained in step A in a kneader after the first kneading step

[0115] Step D: The third kneading step of taking out the rubber composition obtained in the second kneading step, putting it into a kneader together with the additives, and processing it into sheets

[0116] (Mixing step)

[0117] The mixing step is a step of mixing a mercapto group-containing silane coupling agent or a mercapto group-containing silane coupling agent and an amino group-containing silane coupling agent into the molten mixture. There is no particular limitation on the mixing method, and known methods can be used. By using the amino group-containing silane coupling agent in combination, the hydrolysis reaction can be promoted by transfer to the base side.

[0118] (First kneading step)

[0119] The first kneading step is a step of kneading rubber (raw rubber). Examples of the kneader used in this step include open or closed kneaders such as a kneading extruder, an open mill, a kneader, a Banbury mixer, a roll, and an internal mixer.

[0120] For example, a rubber polymer is put into an internal mixer at a filling rate of 80% and kneaded for 5 minutes to obtain a kneaded rubber polymer. In addition, the set temperature at this time can be 80°C and the rotation speed can be 30 rpm.

[0121] (Second kneading step)

[0122] The second kneading step is a step of kneading the mixture obtained in the mixing step in a kneader after the first kneading step.

[0123] This step is a necessary step when further incorporating carbon black, antioxidant, stearic acid, wax, zinc oxide, oil, etc. into the rubber composition.

[0124] For example, the kneaded rubber polymer obtained in the first kneading step, the mixture obtained in the mixing step including cellulose fibers, and other blending agents are put into an internal mixer at a filling rate of 80% and kneaded at a rotor rotation speed of 30 rpm for 3 minutes. Then, the rotation speed is adjusted to make the rubber temperature 150°C, and it is held at 150°C for 5 minutes and then released. The set temperature at this time can be 80°C.

[0125] (Third kneading step)

[0126] The third kneading step is a step of taking out the rubber composition obtained in the second kneading step, putting it into a kneader together with additives, and processing it into sheets. This step is a necessary step when further incorporating oil, sulfur, vulcanization accelerator, etc. into the rubber composition obtained in the second kneading step.

[0127] For example, the rubber kneaded in the first and second kneading steps is placed on an open roll, and additives such as sulfur and vulcanization accelerators are further added. The steps of taking out the thin sheet, kneading it into a ball and then putting it back on the roll, taking out the thin sheet, and kneading it into a ball are repeated four times to promote the dispersion of the vulcanization system. Then, it is adjusted to an appropriate thickness and processed into sheets.

[0128] Furthermore, the rubber composition of the present invention can be compounded into a composition by a known method and used after vulcanization or crosslinking. For example, an open mixer such as a roll or a closed mixer such as a Banbury mixer can be used for compounding, and after forming and processing, vulcanization is carried out, which is applicable to various rubber product uses.

[0129] Examples

[0130] The present invention will be described more specifically by the following examples, but the present invention is not limited to these examples. Moreover, the average degree of polymerization described in the examples and comparative examples is measured by the following measurement method.

[0131] (Measurement of CNF Degree of Polymerization)

[0132] Dissolve 0.15 g of CNF solid content in 30 mL of 0.5 M cuprammonium ethylenediamine solution, measure the viscosity η of the CNF / cuprammonium ethylenediamine solution using a Cannon-Fenske kinematic viscosity tube, set the viscosity of the 0.5 M ethylenediamine solution as η0, calculate the limiting viscosity [η] from the following Schulz-Blaschke formula, and calculate the degree of polymerization DP from the following Mark-Houwink-Sakurada formula.

[0133] Specific viscosity ηsp = η / η0 - 1

[0134] Limiting viscosity [η] = ηsp / {c(1 + A×ηsp)}

[0135] η0 is the viscosity of the 0.5 M cuprammonium ethylenediamine solution, c is the CNF concentration (g / mL), A is an inherent value determined by the solution type, and in the case of 0.5 M cuprammonium ethylenediamine solution, A = 0.28.

[0136] Degree of polymerization DP = [η] / Ka

[0137] K and a are inherent values determined by the types of polymer and solvent. In the case of cellulose dissolved in cuprammonium ethylenediamine solution, K = 0.57 and a = 1.

[0138] (Production Example 1: Melt Mixture A1)

[0139] Using Mechano Hybrid (manufactured by Nippon Coke & Engineering Co., Ltd., model: MMH-75B / I), mix the CNF aqueous mixture (CNF solid content 50%, water 50%, average degree of polymerization 810) derived from softwood pulp and the aqueous dispersion of polyolefin resin (manufactured by Mitsui Chemicals, Inc.: Chemipearl 401) at a ratio of 9:1 (1:0.1) to obtain a mixture.

[0140] Next, the obtained mixture was fed into a twin-screw extruder (Japan Steel Works, Ltd., model: TEX25αIII) to obtain a molten mixture. The screw diameter was Φ25 mm, and the average barrel temperature was set at 129 °C.

[0141] (Production Example 2: Molten Mixture A2)

[0142] Using Mechano Hybrid (Nippon Coke & Engineering Co., Ltd., model: MMH-75B / I), the ratio of the CNF aqueous mixture derived from softwood pulp (CNF solid content 30%, water 70%, average degree of polymerization 810) and the aqueous dispersion of polyolefin resin (manufactured by Mitsui Chemicals, Inc.: Chemipearl 401) was set to 9:1 (1:0.1).

[0143] As a silane coupling agent, 3.3 parts by mass of 3-glycidoxypropyltriethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.: KBE-403) was mixed with respect to 100 parts by mass of the mixture to form a mixture.

[0144] It was fed into a twin-screw extruder (Japan Steel Works, Ltd., model: TEX25αIII) to obtain a molten mixture. The screw diameter was Φ25 mm, and the average barrel temperature was set at 118 °C.

[0145] (Production Example 3: Molten Mixture A3)

[0146] Using Mechano Hybrid (Nippon Coke & Engineering Co., Ltd., model: MMH-75B / I), the ratio of the CNF aqueous mixture derived from softwood pulp (CNF solid content 30%, water 70%, average degree of polymerization 810) and the aqueous dispersion of polyolefin resin (manufactured by Mitsui Chemicals, Inc.: Chemipearl 401) was set to 9:1 (1:0.1) and mixed to obtain a mixture.

[0147] Next, the obtained mixture was fed into a twin-screw extruder (Japan Steel Works, Ltd., model: TEX25αIII) to obtain a molten mixture. The screw diameter was Φ25 mm, and the average barrel temperature was set at 106 °C.

[0148] (Production Example 4: Molten Mixture B1)

[0149] Using Mechano Hybrid (Nippon Coke & Engineering Co., Ltd., model: MMH-75B / I), the ratio of the CNF aqueous mixture derived from softwood pulp (CNF solid content 35%, water 65%, average degree of polymerization 810) and the styrene-based polymer (manufactured by Yasuhara Chemical Co., Ltd.: YS Resin SX100) was set to 7:3 (1:0.4) and mixed.

[0150] Next, the obtained CNF and styrene oligomer mixture was fed into a twin-screw extruder (manufactured by Japan Steel Works, Ltd., model: TEX25αIII) to obtain powdery cellulose nanofibers. The screw system was Φ25 mm, and the resin temperature was set at 114°C.

[0151] (Production Example 5: Melt Mixture B2)

[0152] Using Mechano Hybrid (manufactured by Nippon Coke & Engineering Co., Ltd., model: MMH-75B / I), a CNF aqueous mixture derived from softwood pulp (CNF solid content 35%, water 65%, average degree of polymerization 810) and a styrene-based polymer (manufactured by Yasuhara Chemical Co., Ltd.: YS Resin SX100) were mixed at a ratio of 7:3 (1:0.4).

[0153] Next, the obtained CNF and styrene oligomer mixture was fed into a twin-screw extruder (manufactured by Japan Steel Works, Ltd., model: TEX25αIII) to obtain powdery cellulose nanofibers. The screw system was Φ25 mm, and the resin temperature was set at 103°C.

[0154] (Measurement of moisture content and particle size distribution)

[0155] Using an infrared / halogen moisture meter (manufactured by Mettler-Toledo Co., Ltd., model: HC103), the moisture content of the melt mixtures obtained in Production Examples 1 to 5 was measured.

[0156] Moreover, for the melt mixtures obtained in Production Examples 1 to 5, the particle size distribution was measured by the following measurement method.

[0157] The results are shown in Table 1.

[0158] (Measurement of particle size distribution)

[0159] Approximately 5 g of the melt mixture was measured using an image diffraction particle size diameter distribution measuring device (manufactured by Microtrac Inc.: Microtrac PartAn3D). The values of D50 and D90 were used as the measurement results.

[0160] [Table 1]

[0161]

[0162] The following shows the respective components used in the following examples and comparative examples.

[0163] · Natural rubber: "SMR CV60 (trade name)" manufactured by Astlett Rubber Inc.

[0164] · Synthetic rubber: "EP21 (trade name)" manufactured by JSR Corporation

[0165] · Carbon black: "Asahi #60G (trade name)" manufactured by Asahi Carbon Co., Ltd.

[0166] · Paper powder 1 (Example 22)

[0167] Angle of repose: 65°, bulk specific gravity: 0.22, moisture content: 3.3%, D50 (median particle size) 33.6 μm

[0168] · Paper powder 2 (Example 23)

[0169] Angle of repose: 44°, bulk specific gravity: 0.23, moisture content: 3.7%, D50 (median particle size) 35.8 μm

[0170] · Silane coupling agent (C1): "Si-69 (trade name)" (bis(3-triethoxysilylpropyl)tetrasulfide) manufactured by EVONIK

[0171] · Silane coupling agent (C2): "NXT-Z45 (trade name)" (structural formula shown in Chemical Formula 2) manufactured by Momentive

[0172] · Silane coupling agent (C3): "A1891 (trade name)" (3-mercaptopropyltriethoxysilane) manufactured by Momentive

[0173] · Silane coupling agent (C4): "NXT-Silane (trade name)" (3-octanoylthiopropyltriethoxysilane) manufactured by Momentive

[0174] · Silane coupling agent (C5): "A1110" (3-aminopropyltrimethoxysilane) manufactured by Momentive

[0175] · Stearic acid: "Tsubaki (trade name)" manufactured by NOF Corporation

[0176] · Zinc white: "Zinc Oxide Type 3 (trade name)" manufactured by Shoindo Chemical Industry Co., Ltd.

[0177] · Refined mineral oil: "SNH-22 (trade name)" manufactured by Sankyo Yuka Kogyo Co., Ltd.

[0178] · Sulfur: "HK-200-5 (5% oil sulfur) (trade name)" manufactured by Hosoi Chemical Industry Co., Ltd.

[0179] · Vulcanization accelerator 1: "Sanceler CM-G (N-cyclohexyl-2-benzothiazolesulfenamide) (trade name)" manufactured by Sanshin Chemical Industry Co., Ltd.

[0180] ·Vulcanization accelerator 2: "Nocceler NS-P (N-tert-butyl-2-benzothiazolesulfenamide) (trade name)" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0181] [Chemical formula 2]

[0182]

[0183] (Example 1)

[0184] (Manufacture of rubber composition)

[0185] After weighing each of the following components, the molten mixture (A1) and the silane coupling agent (C2) were premixed to form a mixture. Next, the natural rubber was kneaded for 30 seconds using a Banbury mixer (Toyosha Seisakusho Co., Ltd., laboratory kneading extruder), and then the said mixture was put into the Banbury mixer and kneaded for 30 seconds. Next, carbon black was added and kneaded at 110 °C, and the dispersibility was evaluated visually. Next, the following other components were added and kneaded at 110 °C to obtain a rubber composition.

[0186] · Natural rubber: 100 parts by mass

[0187] · Carbon black: 50 parts by mass

[0188] · Molten mixture (A1): 7.8 parts by mass

[0189] · Silane coupling agent (C2): 2.65 parts by mass

[0190] · Stearic acid: 2 parts by mass

[0191] · Zinc oxide: 5 parts by mass

[0192] · Refined mineral oil: 15 parts by mass

[0193] · Sulfur: 2.48 parts by mass

[0194] · Vulcanization accelerator 2: 1 part by mass

[0195] (Dispersibility evaluation)

[0196] Using the following evaluation criteria, the dispersion state of the cellulose fibers in the rubber composition after adding carbon black was visually confirmed.

[0197] 〇: No aggregates were observed and it was uniformly dispersed.

[0198] ×: Aggregates were observed.

[0199] Next, using the obtained rubber composition, the Mooney viscosity was measured by the following method. Next, using the obtained rubber composition, the Mooney viscosity and vulcanization properties as physical property evaluations were measured. Next, the obtained rubber sheet was compression crosslinked and molded to obtain a test piece. After confirming the dispersibility of the cellulose fibers in the test piece, using the obtained rubber crosslinked sheet, the evaluation of the vulcanized rubber was measured by the following method.

[0200] [Physical Property Evaluation]

[0201] (Mooney Viscosity (ML1+10(100℃))

[0202] The Mooney viscosity at 100°C (ML(1+4)125°C) was measured at 100°C using a Mooney viscometer (M&K Co., Ltd., apparatus name: MVM11) in accordance with JIS K6300.

[0203] (Vulcanization Characteristics)

[0204] The vulcanization characteristics were measured using a CURELASTOMETER (registered trademark) (M&K Co., Ltd., apparatus name: Curebase) in accordance with JIS K6300-2.

[0205] The vulcanization curve was measured at a measurement temperature of 160°C for 20 minutes, and the minimum torque ML (kgf·cm), maximum torque MH (kgf·cm), time T10 (minutes) until the torque reached 10% of MH, time T50 (minutes) until the torque reached 50% of MH, and time T90 (minutes) until the torque reached 90% of MH were obtained from the graph with torque on the vertical axis and time on the horizontal axis.

[0206] As a result, T10 was 0.7 minutes, T90 was 1.2 minutes, ML was 3.9 kgf·cm, and MH was 46.7 kgf·cm.

[0207] (Evaluation of Vulcanized Rubber Physical Properties)

[0208] (Tensile Break Point Stress, Tensile Break Point Elongation)

[0209] The tensile break electrical stress and tensile break point elongation of the rubber crosslinked sheet were measured by the following method.

[0210] A punching die is used to cut a crosslinked rubber sheet to prepare dumbbell test pieces described in JIS K 6251. Using these test pieces, a tensile test is conducted under the conditions of a measurement temperature of 23°C, a relative humidity of 50%, and a tensile speed of 500 mm / min in accordance with the method specified in K6251. Measure the tensile stress (25% modulus (M25)), tensile stress at an elongation of 50% (50% modulus (M50)), tensile stress at an elongation of 100% (100% modulus (M100)), tensile stress at an elongation of 200% (200% modulus (M200)), tensile stress at an elongation of 300% (300% modulus (M300)), tensile fracture point stress (TB), and tensile fracture point elongation (EB) when the elongation is 25%.

[0211] (Examples 2 to 18, Comparative Examples 1 to 3)

[0212] In the above "manufacture of rubber composition", except for changing the types and amounts of the components as shown in Table 2, a rubber composition is obtained in the same manner as in Example 1. Then, the same evaluation as in Example 1 is performed using the obtained rubber composition. The results are shown in Tables 2 and 3.

[0213] Moreover, in Comparative Examples 2 and 3, since the evaluation during the dispersibility evaluation was "×", no subsequent treatment was performed.

[0214] [Table 2]

[0215]

[0216] [Table 3]

[0217]

[0218] From Table 3, it is known that in Examples 8, 11, 12, and 13 where the same blending of carbon black and molten mixture is used, the vulcanization characteristics vary depending on the type of silane coupling agent.

[0219] Furthermore, it is also known that under the blending of the molten mixture, the stress in the low strain region of M25, M50, M100, and M200 increases, but the stress and elongation at break decrease.

[0220] (Examples 19 - 21, Comparative Example 4)

[0221] In the above "manufacture of rubber composition", except for changing the types and amounts of the components as shown in Table 4, a rubber composition is obtained in the same manner as in Example 1. The same evaluation as in Example 1 is performed using the obtained rubber composition. Moreover, in addition to the evaluation in Example 1, the loss factor and loss modulus are measured by the following method. The results are shown in Table 4.

[0222] (Measurement of Viscoelasticity)

[0223] Measuring device (Ueshima Seisakusho Co., Ltd.: VR-7130)

[0224] Sample size (4 mm × 40 mm)

[0225] Measuring frequency: 10 Hz, measuring temperature conditions (0°C, 60°C)

[0226] Regarding the strain-temperature dispersion, measurement was carried out with a strain of ±2%. The loss factor and loss modulus are the values at 2% at a frequency of 10 Hz.

[0227] [Table 4]

[0228]

[0229] From Table 4, it is obvious that the value of the loss factor of the rubber composition blended with the molten mixture becomes smaller. And since the value of the loss factor (tanδ) becomes smaller compared with Comparative Example 4, it is considered that low fuel consumption performance can be expected.

[0230] (Examples 22 to 24)

[0231] After weighing each of the following components, paper powder (Examples 22, 23) or molten mixture (Example 24) and silane coupling agents (C2 and C5) were premixed to form a mixture. Next, natural rubber (Example 22) or synthetic rubber (Examples 23 and 24) was kneaded for 30 seconds using a Banbury mixer (Toyo Seiki Seisakusho Co., Ltd., laboratory kneading extruder), and then the said mixture was put into the Banbury mixer and kneaded for 30 seconds. Next, carbon black was added and kneaded under the condition of 110°C, and the dispersibility was evaluated visually. Next, other components were added and kneaded under the condition of 110°C to obtain a rubber composition.

[0232] · Natural rubber: 100 parts by mass

[0233] · Synthetic rubber (EPDM): 100 parts by mass

[0234] · Carbon black: 50 parts by mass

[0235] · Molten mixture (A1): 7.8 parts by mass

[0236] · Paper powder: 9 parts by mass

[0237] · Silane coupling agent (C2): 1 part by mass

[0238] · Silane coupling agent (C5): 0.5 part by mass

[0239] · Stearic acid: 2 parts by mass

[0240] · Zinc white: 5 parts by mass

[0241] · Refined mineral oil: 15 parts by mass

[0242] [Table 5]

[0243]

[0244] Obviously, the rubber compositions of Examples 22 to 24 do not contain agglomerates and are well dispersed.

[0245] According to Comparative Example 1 and Examples 5, 14, and 22, in the case of using the paper powder of microfibers, whether blended or not, the vulcanization characteristics (t90) did not change, and the result did not bring an improvement in productivity. In terms of the tensile strength, the strength until fracture was the same as that of Comparative Example 1, but the stress in the low-strain region was higher than that of Comparative Example 1, but inferior to those of Examples 5 and 14.

[0246] Moreover, according to Examples 23 and 24, it was found that the vulcanization characteristic t10 was lower in Example 24, and the molten mixture was more likely to scorch, but t90, which is an index of productivity, remained unchanged, and the productivity did not change.

[0247] Furthermore, it was found that the breaking tensile strength and the elongation at break were higher in Example 23, and the strength in the low-strain region was higher in Example 24.

[0248] The evaluation of the adhesion can be judged at the initial stage where the elongation rate is small in the tensile strength. According to the results of M25, M50, and M100, it was found that the adhesion was improved.

Claims

1. A rubber composition, characterized in that, it contains: (A) a rubber component; (B-1) a molten mixture containing a nano natural polymer; and (C) a silane coupling agent having a mercapto group and a silane coupling agent having an amino group.

2. The rubber composition according to claim 1, characterized in that, the moisture value of the molten mixture is less than 10.3%, the value of the average particle size D50 of the molten mixture is less than 10,500 μm.

3. A rubber composition, characterized in that, it contains: (A) a rubber component; (B-2) cellulose fibers; and (C) a silane coupling agent having a mercapto group and a silane coupling agent having an amino group.

4. A rubber composition, characterized in that, it contains: (A) a rubber component; (B-1) a molten mixture containing a nano natural polymer and an aqueous dispersion of a polyolefin resin; and (C) a silane coupling agent having a mercapto group.

5. A rubber composition, characterized in that, it contains: (A) a rubber component; (B-1) a molten mixture containing a nano natural polymer and an aqueous dispersion of a polyolefin resin; and (C) a silane coupling agent having a mercapto group and a silane coupling agent having an amino group.

6. A rubber composition, characterized in that, it contains: (A) a rubber component; (B-1) a molten mixture containing a nano natural polymer and a polymer having a vinyl aromatic compound with a weight average molecular weight in the range of 200 or more and 5000 or less as a main component; and (C) a silane coupling agent having a mercapto group and a silane coupling agent having an amino group.

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