Recycled carbon black, mixture of recycled carbon black and liquid polymer, rubber composition, and rubber product

Abstract

The present invention addresses the problem of providing: a recycled carbon black capable of maintaining the physical properties of a rubber composition even when reused in the rubber composition; and a mixture of the recycled carbon black and a liquid polymer. The means for solving the problem is: a recycled carbon black obtained by the decomposition of a crosslinked rubber containing a diene-based rubber and carbon black, the recycled carbon black being characterized in that the organic content remaining in the recycled carbon black after toluene cleaning is 5 mass% or more; and a mixture of the recycled carbon black and a liquid polymer, the mixture being characterized in that the weight average molecular weight of the liquid polymer is 300,000 or less.

Description

Recycled carbon black, mixture of recycled carbon black and liquid polymer, rubber composition, and rubber product

[0001] The present invention relates to recycled carbon black, a mixture of recycled carbon black and a liquid polymer, a rubber composition, and a rubber product.

[0002] Conventionally, rubber products primarily made of cross-linked rubber such as vulcanized rubber have been difficult to reuse, and after the end of their product life, they have often been reused as fuel, particularly in cement factories. However, with the recent rise in environmental concerns, there has been a demand for the development of methods for recycling materials obtained by decomposing rubber products, rather than burning them as fuel. There are various methods for decomposing cross-linked rubber. For example, Patent Document 1 listed below discloses the thermal decomposition of organic materials such as used tires at 550 to 800°C, and further discloses the incorporation of carbon black obtained by thermal decomposition into a rubber mixture as a filler.

[0003] EP 3427975

[0004] Generally, rubber products made of crosslinked rubber use a rubber composition in which a filler such as carbon black is blended with a diene rubber, and therefore, by decomposing the crosslinked rubber, carbon black can be recovered as described in the above-mentioned Patent Document 1. The present inventors have also found that by selecting the decomposition conditions of the crosslinked rubber, constituent monomers and oligomers (liquid polymers) of the diene rubber can be obtained in addition to carbon black.

[0005] However, when recycled carbon black obtained by decomposition of crosslinked rubber is reused in a rubber composition, there is a problem that the physical properties of the resulting rubber composition are deteriorated.

[0006] Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional technology and to provide recycled carbon black that can maintain the physical properties of a rubber composition even when reused in the rubber composition. Another object of the present invention is to provide a mixture of such recycled carbon black and a liquid polymer, as well as a rubber composition and a rubber product containing such recycled carbon black.

[0007] The recycled carbon black, the mixture of recycled carbon black and a liquid polymer, the rubber composition, and the rubber product of the present invention, which solve the above problems, are outlined below.

[0008] [1] Reclaimed carbon black obtained by decomposing a crosslinked rubber containing a diene rubber and carbon black, characterized in that the organic content remaining in the reclaimed carbon black after washing with toluene is 5% by mass or more.

[0009] [2] The recycled carbon black according to [1], which has a maximum DTG temperature (the temperature at which the DTA value associated with the weight loss of the organic component in a thermal gravimetric loss measurement is maximum) of 350°C or higher.

[0010] [3] A mixture of recycled carbon black and a liquid polymer obtained by decomposition of a crosslinked rubber containing a diene rubber and carbon black, wherein the recycled carbon black is the recycled carbon black described in [1] (in other words, recycled carbon black in which the organic content remaining in the recycled carbon black after washing with toluene is 5% by mass or more) or the recycled carbon black described in [2], and the liquid polymer has a weight average molecular weight of 300,000 or less.

[0011] [4] A mixture of recycled carbon black and a liquid polymer obtained by decomposition of a crosslinked rubber containing a diene rubber and carbon black, wherein the recycled carbon black is the recycled carbon black described in [1] (in other words, recycled carbon black in which the organic content remaining in the recycled carbon black after washing with toluene is 5% by mass or more) or the recycled carbon black described in [2], and the liquid polymer contains 30% by mass or less of components with a molecular weight of 15,000 or less.

[0012] [5] A rubber composition comprising a rubber component and the recycled carbon black according to [1] or [2].

[0013] [6] A rubber composition comprising a rubber component and the mixture of recycled carbon black and liquid polymer described in [3].

[0014] [7] A rubber composition comprising a rubber component and the mixture of recycled carbon black and liquid polymer described in [4].

[0015] [8] The rubber composition according to any one of [5] to [7], which is for use in a tire.

[0016] [9] A rubber product comprising a rubber member made of the rubber composition according to any one of [5] to [7].

[0017]

[10] The rubber product according to [9], which is a tire.

[0018] The present invention provides recycled carbon black that can maintain the physical properties of a rubber composition even when reused in the rubber composition. The present invention also provides a mixture of the recycled carbon black and a liquid polymer, as well as a rubber composition and a rubber product that contain the recycled carbon black.

[0019] 1 is a graph showing the relationship between temperature and DTG value [μg / min] for the recycled carbon black used in Example 1 and Comparative Examples 1 and 2, and the recycled carbon black mainly used in Example 2. 1 is a graph showing the relationship between temperature and DTG value (DTG / maximum DTG [%]) for the recycled carbon black used in Example 1 and Comparative Examples 1 and 2, and the recycled carbon black mainly used in Example 2.

[0020] The recycled carbon black, the mixture of recycled carbon black and liquid polymer, the rubber composition, and the rubber product of the present invention will be described in detail below with reference to the following embodiments.

[0021] <Definitions> The compounds described herein may be derived in part or in whole from fossil resources, from biological resources such as plant resources, from recycled resources such as used tires, or from a mixture of two or more of fossil resources, biological resources, and recycled resources.

[0022] <Recycled Carbon Black> The recycled carbon black of this embodiment is recycled carbon black obtained by decomposition of a crosslinked rubber containing a diene rubber and carbon black. The recycled carbon black of this embodiment is characterized in that the organic content remaining in the recycled carbon black after washing with toluene is 5% by mass or more.

[0023] As described above, when conventional recycled carbon black obtained by decomposition of crosslinked rubber is reused in a rubber composition, the physical properties of the resulting rubber composition are degraded. After extensive research, the inventors discovered that while conventional recycled carbon black contains only a small amount of organic content (at most about 4% by mass), recycling recycled carbon black with an organic content of 5% by mass or more in a rubber composition can maintain the physical properties of the resulting rubber composition, such as tensile strength (TB) and elongation at break (EB). While not wishing to be bound by theory, it is believed that the recycled carbon black of the present embodiment, having an organic content of 5% by mass or more, improves dispersibility in the rubber components of the rubber composition, thereby maintaining the physical properties of the rubber composition.

[0024] (Organic Content) The recycled carbon black of this embodiment is obtained by removing the liquid polymer component and low-molecular-weight organic compounds from a mixture containing recycled carbon black and a liquid polymer obtained by decomposition of a crosslinked rubber containing a diene rubber and carbon black using toluene as a washing solvent. The organic content remaining in the recycled carbon black is 5% by mass or more, preferably 10% by mass or more, and preferably 30% by mass or less. If the organic content of the recycled carbon black is less than 5% by mass, the physical properties of the resulting rubber composition will be reduced when the recycled carbon black is reused in a rubber composition. At least 50% by mass of the organic content is diene polymer, preferably 80% by mass or more, and more preferably 90% by mass or more. In this specification, the "organic content" of recycled carbon black refers to the mass (m ) of the sample recycled carbon black measured by thermogravimetric analysis (TGA) when heated to 120°C and maintained for 1 hour. ０ ) and then heated to 550 ° C and held for 2 hours. １ ) and the following formula: Organic content (mass%) = (m０ -m １ ) / m ０ × 100. Therefore, in this specification, the "organic content" of recycled carbon black can also be said to be the difference (weight loss) between the mass of recycled carbon black at 120°C and the mass at 550°C. The organic content is thought to be mainly present on the surface of the recycled carbon black.

[0025] (Maximum DTG Temperature) The recycled carbon black of this embodiment preferably has a maximum DTG temperature (the temperature at which the DTA value associated with the weight loss of the organic component in a thermal weight loss measurement is maximum) of 350°C or higher. A DTG (derivative thermogravimetry) curve is a first-order derivative of a TG (thermogravimetry) curve, and the maximum DTG temperature corresponds to the temperature at which the weight loss of the organic component is most rapid. Recycled carbon black with a maximum DTG temperature of 350°C or higher has a high proportion of organic components remaining at high temperatures of 350°C or higher and is highly dispersible in rubber components. Therefore, even when recycled carbon black is reused in a rubber composition, the physical properties of the resulting rubber composition can be more reliably maintained.

[0026] (Dispersion Stability) The recycled carbon black of this embodiment preferably has a dispersion stability in toluene of 0.5 or more. When the recycled carbon black has a dispersion stability in toluene of 0.5 or more, the physical properties of the resulting rubber composition can be more reliably maintained when the recycled carbon black is reused in a rubber composition. The "dispersion stability in toluene" of the recycled carbon black can be measured using a LUMiSizer (registered trademark)-611 manufactured by LUM Corporation. The sample carbon black or recycled carbon black was dispersed in toluene to a concentration of 5% by weight using an ultrasonic cleaner at 120 W and a frequency of 40 kHz for 30 minutes. The dispersion was then added to a polyamide sample tube with a 2 mm thick transmission section, and the tube was placed in the ultrasonic cleaner at 120 W and a frequency of 38 kHz for 5 minutes. The transmittance was then determined by analyzing the sample using a light source with a wavelength of 865 nm in a 6x sensitization mode. The dispersion stability in toluene is determined by determining the transmittance at an apparatus position of 110 mm to 125 mm at a constant rotation speed, determining the rate of change in transmittance from the change in transmittance over time, and treating the reciprocal of this value as the dispersion stability. The larger the dispersion stability value, the higher the dispersion stability in toluene is judged to be.

[0027] (Agglomerate Proportion) The recycled carbon black of this embodiment preferably has a proportion of agglomerates with a diameter of 5 μm or more, as determined using a particle size distribution analyzer after ultrasonically dispersing the recycled carbon black in a toluene solvent, of 50% by volume or less. When recycled carbon black having a proportion of agglomerates with a diameter of 5 μm or more is 50% by volume or less, the physical properties of the resulting rubber composition can be more reliably maintained when reused in a rubber composition. Furthermore, the recycled carbon black of this embodiment preferably has a proportion of agglomerates with a diameter of 1 μm or less, as determined using a particle size distribution analyzer after ultrasonically dispersing the recycled carbon black in a toluene solvent, of 50% by volume or more. When recycled carbon black having a proportion of agglomerates with a diameter of 1 μm or less is 50% by volume or more, the physical properties of the resulting rubber composition can also be more reliably maintained when reused in a rubber composition. The "proportion of agglomerates with a diameter of 5 μm or more" and the "proportion of agglomerates with a diameter of 1 μm or less" of recycled carbon black can be measured using the following measurement method. A dispersion of the sample recycled carbon black in toluene at an optimal concentration (0.1-5 wt%) was prepared and dispersed for 5-30 minutes using an ultrasonic cleaning device with a power output of 120 W and a frequency of 40 kHz. Then, using a Malvern Panalytical "Mastersizer 3000" and "HydroSV" (trade name), toluene was filled into the "HydroSV" cell at room temperature as the solvent. While stirring at 500-1000 rpm with a stirrer, the toluene dispersion of the sample recycled carbon black was added until the scattering intensity reached a value of 10-20%. The sample recycled carbon black was treated as non-spherical particles with a refractive index of 1.746, and the refractive index of toluene was set to 1.49. The particle size distribution was measured using the resulting particle size distribution profile to determine the percentage of agglomerates of the sample recycled carbon black with a diameter of 5 μm or more and the percentage of agglomerates of 1 μm or less.

[0028] (Sulfur Component and Zinc Component) The recycled carbon black of this embodiment preferably has a sulfur component and a zinc component attached to its surface. Such recycled carbon black can be obtained without washing or surface treating the carbon black. Whether or not the sulfur component and / or zinc component is attached to the surface of the recycled carbon black can be confirmed by transmission electron microscope-energy dispersive X-ray analysis (TEM-EDS), and this confirmation is made without performing treatments to remove inorganic substances by separating, washing, surface treating, etc., the product obtained by pyrolysis.

[0029] (Crosslinked Rubber) The crosslinked rubber that is the raw material for the recycled carbon black of this embodiment contains a diene rubber and carbon black, and may further contain other components. The recycled carbon black of this embodiment is obtained by decomposition of such crosslinked rubber.

[0030] The crosslinked rubber to be used for decomposition may be grouped according to the type of diene rubber previously compounded, and then the decomposition step may be carried out for each group. Alternatively, the crosslinked rubber may be grouped according to the type of filler previously compounded (e.g., type of carbon black, type of silica, mixing ratio of carbon black and silica, etc.), and then the decomposition step may be carried out for each group. Furthermore, the crosslinked rubber may be grouped according to both the type of diene rubber and the type of filler, and then the decomposition step may be carried out for each group. When the decomposition step is carried out for each group in this way, liquid polymers, recycled carbon black, regenerated silica, etc. having more uniform physical properties can be obtained, and therefore, when compounded again into a rubber composition, a rubber composition with better performance can be obtained.

[0031] Furthermore, when the crosslinked rubber used for degradation is derived from tires, the tires may be grouped in advance by type (e.g., for passenger cars, for trucks and buses, for large vehicles such as off-road vehicles, for aircraft, for agricultural vehicles, etc.), and then the decomposition process may be carried out for each group. Alternatively, the tires may be grouped in advance by tire component (e.g., tread rubber, sidewall rubber, bead rubber, steel cord-coated rubber, organic fiber-coated rubber, pad rubber, cushion rubber, etc.), and then the decomposition process may be carried out for each group. Furthermore, the tires may be grouped both by type and by tire component, and then the decomposition process may be carried out for each group. When the decomposition process is carried out for each group in this way, a liquid polymer or recycled carbon black having more uniform physical properties can be obtained, and therefore, when blended again into a rubber composition, a rubber composition with better performance can be obtained.

[0032] The form of the crosslinked rubber is not particularly limited, and may be, for example, powdered rubber. The powdered rubber can be obtained by cutting and pulverizing used rubber products such as scrap tires. The pulverization step may include multiple steps such as a preliminary pulverization step and a fine pulverization step, and the particle size of the powdered rubber to be used may be adjusted by a classification step after the pulverization step.

[0033] The crosslinked rubber may be recycled waste rubber, used rubber products, etc. Waste rubber refers not only to rubber generated from rubber products, but also to all discarded rubber, including unnecessary scraps generated during the production or repair of rubber products. Examples of scraps include buffing powder and peeled rubber. Buffing powder is fine rubber generated during the buffing process of scraping off the tread portion remaining on the base tire, for example, during tire retreading. Peeled rubber is a long piece of rubber, for example, 1 to 2 cm wide, peeled off from the surface of a rubber product such as a tire. Peeled rubber is generated by scraping the surface of a rubber product such as a tire using a U- or V-shaped knife like a peeler. Rubber products include, for example, final products such as tires, rubber hoses, and rubber conveyor belts, as well as rubber parts or components used in the manufacturing process of final products. Used tires may be, for example, tires to be retreaded, or may be tires discarded for some reason, such as waste tires generated as a result of tire replacement or scrapping, or ELTs (End-of-Life Tires) that have reached the end of their life as tires.

[0034] -Diene-Based Rubber- The diene-based rubber is a rubber containing units derived from a diene-based monomer (diene-based units) and may further contain units derived from a copolymerizable comonomer. The units derived from the diene-based monomer enable the diene-based rubber to be crosslinked (vulcanized) and to exhibit rubber-like elongation and strength. Note that, although the diene-based rubber is usually present in a crosslinked state in the crosslinked rubber, a portion of it may not be crosslinked. Specific examples of diene-based monomers (diene-based compounds) include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, etc., and among these, 1,3-butadiene and isoprene are preferred, with isoprene being particularly preferred. On the other hand, examples of the copolymerizable comonomer include aromatic vinyl compounds, etc. Specific examples of the aromatic vinyl compound include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, o,p-dimethylstyrene, o-ethylstyrene, m-ethylstyrene, and p-ethylstyrene.

[0035] Examples of the diene rubber include isoprene-skeleton rubber, styrene-butadiene rubber (SBR), butadiene rubber (BR), and chloroprene rubber (CR). Here, the isoprene-skeleton rubber is a rubber whose main skeleton is an isoprene unit, and specific examples include natural rubber (NR) and synthetic isoprene rubber (IR). Among these, the diene rubber preferably includes at least one selected from the group consisting of isoprene-skeleton rubber, styrene-butadiene rubber, and butadiene rubber, with isoprene-skeleton rubber being particularly preferred. When the diene rubber includes at least one selected from the group consisting of isoprene-skeleton rubber, styrene-butadiene rubber, and butadiene rubber, decomposition of the crosslinked rubber produces a liquid polymer containing easily recyclable diene monomers, such as isoprene or butadiene, in its skeleton, along with recycled carbon black.

[0036] The content of the diene rubber in the crosslinked rubber is not particularly limited, and is preferably, for example, in the range of 10 to 100% by mass, and more preferably in the range of 30 to 100% by mass from the viewpoint of further improving the yield of a liquid polymer containing a diene monomer in the skeleton, as well as butadiene and isoprene.

[0037] -Carbon Black- The carbon black is not particularly limited. Examples of grades of carbon black include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. The carbon black content in the crosslinked rubber is not particularly limited, and is, for example, in the range of 10 to 150 parts by mass, preferably 30 to 120 parts by mass, per 100 parts by mass of the diene rubber. The carbon black content in the crosslinked rubber is preferably 20% by mass or more, more preferably 30% by mass or more, and is preferably 40% by mass or less, and even more preferably 35% by mass or less. When the carbon black content in the crosslinked rubber is 20% by mass or more, a larger amount of carbon black can be recovered.

[0038] -Other Components- In addition to the diene rubber and carbon black described above, the crosslinked rubber may contain various components commonly used in the rubber industry, such as rubber components other than diene rubbers, fillers other than carbon black (silica, calcium carbonate, etc.), silane coupling agents, antioxidants, softeners, processing aids, resins, surfactants, organic acids (stearic acid, etc.), zinc oxide (zinc white), vulcanization accelerators, crosslinking agents (sulfur, peroxides, etc.), etc.

[0039] (Method for Decomposing Crosslinked Rubber) The recycled carbon black of this embodiment can be obtained by decomposing crosslinked rubber, for example, by the following methods: (i) a method for decomposing crosslinked rubber using a metathesis catalyst (first decomposition method); (ii) a method for thermally decomposing crosslinked rubber at 150°C or higher and 400°C or lower (second decomposition method); (iii) a method for decomposing crosslinked rubber in a solvent (third decomposition method); or (iv) a method for decomposing crosslinked rubber using a radical initiator (fourth decomposition method). These first, second, third, and fourth decomposition methods involve decomposition at lower temperatures than conventional high-temperature thermal decomposition of crosslinked rubber, and therefore can leave a large amount of organic components, such as liquid polymers, on the surface of the recycled carbon black. Furthermore, in the first, second, third, and fourth decomposition methods, the organic components of the recycled carbon black can be controlled by appropriately selecting the decomposition conditions. The first, second, third, and fourth decomposition methods are described in detail below.

[0040] -First Decomposition Method (Metathesis Decomposition)- In the first decomposition method, the crosslinked rubber is decomposed using a metathesis catalyst. Here, the metathesis catalyst is a compound represented by the following general formula (1), (2), or (3): The catalysts represented by the general formula (1), (2) or (3) are excellent in promoting metathesis decomposition, and can decompose diene rubbers simply (under mild conditions) and quickly.

[0041] In the above general formulas (1), (2), and (3), M is ruthenium (Ru), titanium (Ti), molybdenum (Mo), or tungsten (W). Among these, ruthenium is preferred as M from the viewpoint of promoting the decomposition reaction of the diene rubber in the crosslinked rubber.

[0042] In the above general formulas (1) and (2), X １ and X ２ Each independently represents a ligand, and is preferably an anionic ligand. １ and X ２ Examples of the X include hydrogen, halogen, pseudohalogen, a linear or branched alkyl group having 1 to 30 carbon atoms, an aryl group having 6 to 24 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, an aryloxy group having 6 to 24 carbon atoms, an alkyldiketonate having 3 to 20 carbon atoms, an aryldiketonate having 6 to 24 carbon atoms, a carboxylate having 1 to 20 carbon atoms, an alkylsulfonate having 1 to 20 carbon atoms, an arylsulfonate having 6 to 24 carbon atoms, an alkylthiol group having 1 to 20 carbon atoms, an arylthiol group having 6 to 24 carbon atoms, an alkylsulfonyl group having 1 to 20 carbon atoms, and an alkylsulfinyl group having 1 to 20 carbon atoms. １ and X ２ may be substituted with one or more further groups, for example, a halogen (preferably fluorine), an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, or an aryl group having 6 to 24 carbon atoms, wherein these groups may also be further substituted with one or more substituents selected from the group consisting of a halogen (preferably fluorine), an alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, and a phenyl group. １ and X ２ are the same or different, and each is a halogen (particularly fluorine, chlorine, bromine or iodine), a benzoate, a carboxylate having 1 to 5 carbon atoms, an alkyl group having 1 to 5 carbon atoms, a phenoxy group, an alkoxy group having 1 to 5 carbon atoms, an alkylthiol group having 1 to 5 carbon atoms, an arylthiol group having 6 to 24 carbon atoms, an aryl group having 6 to 24 carbon atoms, or an alkylsulfonate having 1 to 5 carbon atoms. １ and X ２ are identical and each represents a halogen (especially chlorine), CF ３ COO, CH ３ COO, CFH ２ COO, (CH ３ ) ３ CO, (CF ３ ) ２(CH ３ ) CO, (CF ３ ) (CH ３ ) ２ CO, PhO (phenoxy), MeO (methoxy), EtO (ethoxy), tosylate (p-CH ３ -C ６ H ４ -SO ３ ), mesylate (2,4,6-trimethylphenyl) or CF ３ SO ３ (trifluoromethanesulfonate).

[0043] In the above general formulas (1), (2) and (3), L １ , L ２ and L ３ each independently represents a ligand, preferably a neutral (uncharged) electron donor (also called an "electron-donating neutral ligand"). １ , L ２ and L ３ can be, for example, independently of one another, a phosphine, sulfonated phosphine, phosphate, phosphinite, phosphonit, arsine, stibine, ether, amine, amide, aryloxy, sulfonate, sulfoxide, carboxyl, nitrosyl, pyridine, thioether or imidazolidine ligand. １ , L ２ and L ３are each independently an arylphosphine ligand having 6 to 24 carbon atoms, an alkylphosphine ligand having 1 to 10 carbon atoms or a cycloalkylphosphine ligand having 3 to 20 carbon atoms, a sulfonated arylphosphine ligand having 6 to 24 carbon atoms or a sulfonated alkylphosphine ligand having 1 to 10 carbon atoms, an aryl phosphinite ligand having 6 to 24 carbon atoms or an alkyl phosphinite ligand having 1 to 10 carbon atoms, an arylphosphonite ligand having 6 to 24 carbon atoms or an alkylphosphonite ligand having 1 to 10 carbon atoms, an aryl phosphite ligand having 6 to 24 carbon atoms or an alkyl phosphite ligand having 1 to 10 carbon atoms, an aryl arsine ligand having 6 to 24 carbon atoms or an alkyl phosph ... is preferably an alkylarsine ligand having 1 to 10 carbon atoms, an arylamine ligand having 6 to 24 carbon atoms or an alkylamine ligand having 1 to 10 carbon atoms, a pyridine ligand, an arylsulfoxide ligand having 6 to 24 carbon atoms or an alkylsulfoxide ligand having 1 to 10 carbon atoms, an arylether ligand having 6 to 24 carbon atoms or an alkylether ligand having 1 to 10 carbon atoms, or an arylamide ligand having 6 to 24 carbon atoms or an alkylamide ligand having 1 to 10 carbon atoms, each of which may be substituted with a phenyl group, and the phenyl group may also be optionally further substituted with a halogen, an alkyl group having 1 to 5 carbon atoms or an alkoxy group having 1 to 5 carbon atoms. The term "phosphine" includes, for example, PPh ３ , P(p-Tol) ３ , P(o-Tol) ３ , PPh(CH ３ ) ２ , P(CF ３ ) ３ , P(p-FC ６ H ４ ) ３ , P(p-CF ３ C ６ H ４ ) ３ , P(C ６ H ４ -SO ３ Na) ３ , P(CH ２ C ６ H ４ -SO ３ Na) ３ , P(isopropyl) ３ , P(CHCH ３ (CH２ CH ３ )) ３ , P(cyclopentyl) ３ , P (cyclohexyl) ３ , P (neopentyl) ３ and P(neophenyl) ３ The term "phosphinite" includes, for example, triphenyl phosphinite, tricyclohexyl phosphinite, triisopropyl phosphinite, and methyldiphenyl phosphite. The term "phosphite ester" includes, for example, triphenyl phosphite, tricyclohexyl phosphite, tri-tert-butyl phosphite, triisopropyl phosphite, and methyldiphenyl phosphite. The term "stibine" includes, for example, triphenylstibine, tricyclohexylstibine, and trimethylstibine. The term "aryloxy" includes, for example, 2-tert-butyl-4,5-dimethylphenyloxy. The term "sulfonate" includes, for example, trifluoromethanesulfonate, tosylate, and mesylate. The term "sulfoxide" includes, for example, (CH ３ ) ２ S(=O) and (C ６ H ５ ) ２ The term "thioether" includes, for example, CH ３ SCH ３ , C ６ H ５ SCH ３ , C.H. ３ OCH ２ CH ２ SCH ３and tetrahydrothiophene. The term "pyridine" includes, for example, pyridine, picolines (α-, β-, and γ-picoline), lutidines (2,3-, 2,4-, 2,5-, 2,6-, 3,4-, and 3,5-lutidine), collidine (2,4,6-trimethylpyridine), trifluoromethylpyridine, phenylpyridine, 4-(dimethylamino)pyridine, chloropyridines, bromopyridines, nitropyridines, quinoline, pyrimidine, pyrrole, imidazole, and phenylimidazole. In the imidazolidine ligand, hydrogen atoms bonded to carbon atoms or nitrogen atoms constituting the imidazolidine ring may be substituted with a linear or branched alkyl group having 1 to 30 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an aryl group having 6 to 24 carbon atoms, a carboxylate having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, an alkenyloxy group having 2 to 20 carbon atoms, an alkynyloxy group having 2 to 20 carbon atoms, an aryloxy group having 6 to 20 carbon atoms, an alkoxycarbonyl group having 2 to 20 carbon atoms, an alkylthio group having 1 to 20 carbon atoms, an arylthio group having 6 to 20 carbon atoms, an alkylsulfonyl group having 1 to 20 carbon atoms, an alkylsulfonate having 1 to 20 carbon atoms, an arylsulfonate having 6 to 20 carbon atoms, or an alkylsulfinyl group having 1 to 20 carbon atoms.

[0044] In the above general formulas (1), (2) and (3), R １ , R ２ and R ３each independently represent a hydrogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, an aryl group, an aralkyl group, a carboxylate group, an alkoxy group, an alkenyloxy group, an alkynyloxy group, an aryloxy group, an alkoxycarbonyl group, an alkylamino group, an alkylthio group, an arylthio group, an alkylsulfonyl group, or an alkylsulfinyl group, wherein these groups are optionally substituted with one or more alkyl groups, halogens, alkoxy groups, aryl groups, or heteroaryl groups. Furthermore, the alkyl group is preferably an alkyl group having 1 to 30 carbon atoms, the cycloalkyl group is preferably a cycloalkyl group having 3 to 20 carbon atoms, the alkenyl group is preferably an alkenyl group having 2 to 20 carbon atoms, the alkynyl group is preferably an alkynyl group having 2 to 20 carbon atoms, the aryl group is preferably an aryl group having 6 to 24 carbon atoms, the aralkyl group is preferably an aralkyl group having 7 to 24 carbon atoms, the carboxylate group is preferably a carboxylate group having 1 to 20 carbon atoms, the alkoxy group is preferably an alkoxy group having 1 to 20 carbon atoms, and the alkenyloxy group is preferably an alkenyloxy group having 2 to 20 carbon atoms. As the alkynyloxy group, an alkynyloxy group having 2 to 20 carbon atoms is preferred, as the aryloxy group, an aryloxy group having 6 to 24 carbon atoms is preferred, as the alkoxycarbonyl group, an alkoxycarbonyl group having 2 to 20 carbon atoms is preferred, as the alkylamino group, an alkylamino group having 1 to 30 carbon atoms is preferred, as the alkylthio group, an alkylthio group having 1 to 30 carbon atoms is preferred, as the arylthio group, an arylthio group having 6 to 24 carbon atoms is preferred, as the alkylsulfonyl group, an alkylsulfonyl group having 1 to 20 carbon atoms is preferred, and as the alkylsulfinyl group, an alkylsulfinyl group having 1 to 20 carbon atoms is preferred. In one embodiment, R １ and R ２one of the groups is hydrogen, and the other is alkyl having 1 to 20 carbon atoms, cycloalkyl having 3 to 10 carbon atoms, alkenyl having 2 to 20 carbon atoms, alkynyl having 2 to 20 carbon atoms, aryl having 6 to 24 carbon atoms, aralkyl having 7 to 24 carbon atoms, carboxylate having 1 to 20 carbon atoms, alkoxy having 1 to 20 carbon atoms, alkenyloxy having 2 to 20 carbon atoms, alkynyloxy having 2 to 20 carbon atoms, aryloxy having 6 to 24 carbon atoms, alkoxycarbonyl having 2 to 20 carbon atoms, alkylamino having 1 to 30 carbon atoms, alkylthio having 1 to 30 carbon atoms, arylthio having 6 to 24 carbon atoms, alkylsulfonyl having 1 to 20 carbon atoms, or alkylsulfinyl having 1 to 20 carbon atoms, each of which is optionally substituted with one or more alkyl groups, halogens, alkoxy groups, aryl groups, or heteroaryl groups.

[0045] In the above general formulas (1), (2) and (3), L １ and L ２ may be bonded to each other to form a ring. １ and L ２ The ring formed by the combination of may be aliphatic or aromatic and may be optionally substituted and contain one or more heteroatoms, such as oxygen, sulfur, nitrogen, phosphorus, etc.

[0046] In the above general formulas (1), (2) and (3), R １ and R ２ may be bonded to each other to form a ring. １ and R ２ However, these R １ and R ２ The ring formed together with the common carbon atom to which it is attached may be aliphatic or aromatic and may be optionally substituted and contain one or more heteroatoms.

[0047] In the above general formulas (1), (2) and (3), L １ and R １ may be bonded to each other to form a ring. １ and R １The ring formed by the combination of may be aliphatic or aromatic and may be optionally substituted and contain one or more heteroatoms, such as oxygen, sulfur, nitrogen, phosphorus, etc.

[0048] The catalyst represented by the general formula (1) above includes those represented by the following structural formulas (1-1) to (1-3): [In the formula, Cy represents a cyclohexyl group, and Mes represents a mesityl group (also called a "2,4,6-trimethylphenyl group")]. The catalyst represented by structural formula (1-1) is called a Grubbs first-generation catalyst, the catalyst represented by structural formula (1-2) is called a Grubbs second-generation catalyst, and the catalyst represented by structural formula (1-3) is called a Grubbs-Hoveyda second-generation catalyst. When a catalyst represented by any of structural formulas (1-1) to (1-3) is used, the decomposition reaction (metathesis decomposition) of the diene rubber in the crosslinked rubber proceeds more rapidly.

[0049] The catalyst represented by the general formula (2) above is represented by the following structural formula (2-1): The catalyst represented by structural formula (2-1) is called a Grubbs third generation catalyst. When the catalyst represented by structural formula (2-1) is used, the decomposition reaction (metathesis decomposition) of the diene rubber in the crosslinked rubber proceeds more rapidly.

[0050] The catalyst represented by the general formula (3) above is represented by the following structural formula (3-1): Examples of the catalyst include those represented by the following formula:

[0051] The amount of the catalyst used is preferably 0.1 part by mass or more, more preferably 1 part by mass or more, and is preferably 10 parts by mass or less, and more preferably 8 parts by mass or less, per 100 parts by mass of the diene rubber. If the amount of the catalyst used is 0.1 part by mass or more per 100 parts by mass of the diene rubber, the decomposition reaction of the diene rubber will further proceed, and if the amount of the catalyst used is 10 parts by mass or less per 100 parts by mass of the diene rubber, it is preferable from the standpoint of cost.

[0052] The decomposition by the metathesis catalyst (hereinafter sometimes simply referred to as "metathesis decomposition") is preferably carried out at a temperature of 20°C or higher and 200°C or lower. By carrying out the metathesis decomposition at 20°C or higher, the rate of the decomposition reaction of the diene rubber in the crosslinked rubber is improved, and by carrying out the metathesis decomposition at 200°C or lower, the decomposition of the catalyst (metathesis catalyst) represented by the above general formula (1), (2), or (3) can be suppressed, and after the decomposition, the retention rate (selectivity) of the monomer skeleton of the diene rubber in the crosslinked rubber is improved. From the viewpoint of improving the decomposition reaction rate of the diene rubber, the metathesis decomposition temperature is more preferably 25°C or higher, and from the viewpoint of suppressing the decomposition of the metathesis catalyst and improving the selectivity of the product retaining the monomer skeleton, it is more preferably 100°C or lower.

[0053] The metathesis decomposition can be carried out at any pressure, including reduced pressure, normal pressure, and elevated pressure. For example, the reaction pressure is preferably 1 kPa to 10 MPa, more preferably 10 kPa to 1 MPa, and even more preferably 50 kPa to 500 kPa.

[0054] In the metathesis decomposition, the catalyst represented by the above-mentioned general formula (1), (2), or (3) may be dissolved in a solvent, or the crosslinked rubber may be immersed in the solvent. By allowing the catalyst to act on the crosslinked rubber in a solvent, the decomposition reaction of the diene rubber in the crosslinked rubber can be facilitated. Any solvent that does not inhibit the decomposition reaction can be used as the solvent, and examples thereof include ethers, aliphatic hydrocarbons, alicyclic hydrocarbons, and aromatic hydrocarbons (aromatic solvents). More specifically, the solvent is preferably tetrahydrofuran (THF), hexane, cyclohexane, pentane, cyclopentane, toluene, or xylene, and more preferably toluene or tetrahydrofuran. When the solvent is selected from tetrahydrofuran, hexane, cyclohexane, pentane, cyclopentane, toluene, or xylene, the decomposition reaction of the diene rubber in the crosslinked rubber can be facilitated. The amount of the solvent used is preferably 10 mL or more, more preferably 50 mL or more, and preferably 500 mL or less, more preferably 200 mL or less, per 1 g of the crosslinked rubber. If the amount of the solvent used is 10 mL or more per 1 g of the crosslinked rubber, the decomposition reaction of the diene rubber in the crosslinked rubber will further proceed, and if the amount of the solvent used is 500 mL or less per 1 g of the crosslinked rubber, it is preferable from the standpoint of cost.

[0055] The metathesis degradation may be carried out in the presence of a chain transfer agent (CTA). Examples of the chain transfer agent include cis-1,4-diacetoxy-2-butene and cis-1,4-dibenzyloxy-2-butene. The amount of the chain transfer agent used is preferably in the range of 1 to 100 mol per 1 mol of the catalyst.

[0056] The recycled carbon black obtained by metathesis decomposition contains components derived from the metathesis catalyst, such as ruthenium (Ru), titanium (Ti), molybdenum (Mo), tungsten (W), and phosphorus (P), and the Ru, Ti, Mo, W, P, etc. derived from the metathesis catalyst can be used as a marker. For example, the recycled carbon black obtained by metathesis decomposition can be reused in a rubber composition, and the contents of Ru, Ti, Mo, W, P, etc. in the rubber composition can be measured to calculate the content of recycled carbon black in the rubber composition.

[0057] - Second Decomposition Method (Low-Temperature Pyrolysis) - In the second decomposition method, the crosslinked rubber is thermally decomposed at a temperature of 150°C or higher and 400°C or lower. By carrying out the thermal decomposition at 150°C or higher, the rate of the decomposition reaction of the diene rubber in the crosslinked rubber is improved, and by carrying out the thermal decomposition at 400°C or lower, gasification and aromatization of the decomposition products can be suppressed, and after the decomposition, the retention rate (selectivity) of the monomer skeleton of the diene rubber in the crosslinked rubber is improved. From the viewpoint of improving the decomposition reaction rate of the diene rubber, the thermal decomposition temperature is preferably 175°C or higher, and more preferably 190°C or higher. Furthermore, from the viewpoint of improving the selectivity of products that maintain the monomer skeleton, the thermal decomposition temperature is preferably 350°C or lower, and more preferably 300°C or lower.

[0058] The second decomposition method is preferably carried out under an inert gas atmosphere. By carrying out the thermal decomposition under an inert gas atmosphere, oxidation and reduction of the decomposition products can be suppressed, and in particular, hydrogenation of double bonds in oligomers and monomers in the decomposition products can be suppressed. Furthermore, oxidation of the recycled carbon black can also be suppressed. Examples of inert gases include nitrogen, carbon dioxide, argon, and helium.

[0059] To carry out the pyrolysis under an inert gas atmosphere, for example, when a batch reactor is used, the atmosphere charged into the reactor may be an inert gas, and when a flow reactor is used, the atmosphere circulated through the reactor may be an inert gas. Note that although hydrogen may be generated during pyrolysis, the generated hydrogen is not taken into consideration when determining the pyrolysis atmosphere.

[0060] The thermal decomposition can be carried out at any pressure, whether under reduced pressure, normal pressure, or increased pressure, but is preferably carried out under reduced pressure or normal pressure. For example, the reaction pressure for the thermal decomposition is preferably 1000 kPa to 65 kPa. By carrying out the thermal decomposition under reduced pressure or normal pressure, polymerization (repolymerization) of oligomers and monomers in the decomposition products can be suppressed.

[0061] The reaction time of the thermal decomposition is not particularly limited. For example, the reaction time of the thermal decomposition is preferably 1 minute to 180 minutes, more preferably 3 minutes to 60 minutes, and even more preferably 5 minutes to 30 minutes.

[0062] The thermal decomposition may or may not use a catalyst, but it is preferable not to use a catalyst. Not using a catalyst for thermal decomposition can reduce costs. When a catalyst is used, any catalyst that has the effect of accelerating the decomposition reaction of the crosslinked rubber can be used.

[0063] -Third Decomposition Method (Solvent Decomposition)- In the third decomposition method, the crosslinked rubber is decomposed in a solvent. When the decomposition of the crosslinked rubber is carried out in a solvent, the crosslinked rubber swells due to the solvent. By decomposing the crosslinked rubber under solvent swelling, gasification and aromatization of the decomposition products can be suppressed, and a decomposition product (liquid polymer) can be obtained that retains a higher percentage of the skeletons of the constituent monomers of the diene rubber (isoprene skeleton, butadiene skeleton, etc.) than in normal high-temperature thermal decomposition.

[0064] As the solvent, various solvents that have the effect of swelling the crosslinked rubber can be used, such as aromatic solvents, aliphatic solvents, alicyclic solvents, ester solvents, etc. Examples of aromatic solvents include benzene, toluene, xylene, etc., aliphatic solvents include pentane, hexane, heptane, etc., alicyclic solvents include cyclopentane, cyclohexane, etc., and ester solvents include ethyl acetate, propyl acetate, butyl acetate, etc. Among these, the solvent is preferably at least one selected from the group consisting of toluene, xylene, and cyclohexane, and toluene is particularly preferred. When toluene, xylene, or cyclohexane is used as the solvent, a decomposition product (liquid polymer) can be obtained that has a high retention rate of the skeleton (isoprene skeleton, butadiene skeleton, etc.) of the constituent monomer of the diene rubber.

[0065] The amount of the solvent used is preferably 1 mL or more, more preferably 5 mL or more, and is preferably 500 mL or less, more preferably 200 mL or less, per gram of the crosslinked rubber. If the amount of the solvent used is 10 mL or more per gram of the crosslinked rubber, the decomposition reaction of the diene rubber in the crosslinked rubber will further proceed, and if the amount of the solvent used is 500 mL or less per gram of the crosslinked rubber, this is preferred from the standpoint of cost.

[0066] The temperature for decomposition in the solvent is preferably 150 to 300°C. By carrying out the decomposition in the solvent at 150°C or higher, the rate of the decomposition reaction of the diene rubber in the crosslinked rubber is improved. On the other hand, by carrying out the decomposition in the solvent at 300°C or lower, the carbon black can be recovered and reused as high-quality carbon black. In addition, gasification and aromatization of the decomposition products can be suppressed, and after decomposition, the retention rate (selectivity) of the structural monomer skeleton of the diene rubber in the crosslinked rubber is improved. From the viewpoint of improving the decomposition reaction rate of the crosslinked rubber, the decomposition temperature in the solvent is preferably 180°C or higher, more preferably 200°C or higher. On the other hand, from the viewpoint of improving the selectivity of the product that maintains the monomer skeleton, the temperature is preferably 260°C or lower, more preferably 240°C or lower.

[0067] The decomposition time in the solvent is not particularly limited. As an example, the decomposition time in the solvent is preferably 1 hour to 48 hours, and more preferably 3 hours to 18 hours. By carrying out the decomposition in the solvent for 3 hours or more, the decomposition rate of the crosslinked rubber is improved. On the other hand, if the reaction time is too long, the skeleton (double bond, etc.) of the constituent monomer of the diene rubber is decomposed, and the decomposition products are gasified or aromatized. However, by carrying out the decomposition in the solvent for 18 hours or less, the decomposition of the monomer skeleton and the gasification or aromatization of the decomposition products can be suppressed, and the retention rate (selectivity) of the skeleton of the constituent monomer of the diene rubber in the crosslinked rubber after the decomposition is improved.

[0068] The decomposition in the solvent is preferably carried out under an inert gas atmosphere. By carrying out the decomposition in the solvent under an inert gas atmosphere, the active species (oxygen, hydrogen, etc.) dissolved in the solvent can be reduced, and the oxidation and reduction of the decomposition products can be suppressed, particularly the oxidation of the recycled carbon black can be suppressed, and also the hydrogenation of the double bonds in the oligomers and monomers in the decomposition products can be suppressed. Here, examples of the inert gas include nitrogen, carbon dioxide, argon, and helium.

[0069] To carry out the decomposition in the solvent under an inert gas atmosphere, for example, when a batch reactor is used, the atmosphere charged into the reactor may be an inert gas, and when a flow reactor is used, the atmosphere circulated through the reactor may be an inert gas. Note that, although hydrogen may be generated during the decomposition in the solvent, the generated hydrogen is not taken into consideration when determining the atmosphere for the decomposition in the solvent.

[0070] The decomposition in the solvent can be carried out at any pressure, such as reduced pressure, normal pressure, or increased pressure. For example, the reaction pressure is preferably 1 kPa to 10 MPa, more preferably 10 kPa to 5 MPa, and even more preferably 50 kPa to 2 MPa.

[0071] The decomposition in the solvent may or may not involve the use of a catalyst, but it is preferable not to use a catalyst. Not using a catalyst in the decomposition in the solvent can reduce costs. When a catalyst is used, any catalyst that has the effect of accelerating the decomposition reaction of the crosslinked rubber can be used.

[0072] -Fourth Decomposition Method (Radical Decomposition)- In the fourth decomposition method, a radical initiator is reacted with a crosslinked rubber in an atmosphere containing oxygen gas. The radical initiator is thought to act mainly on crosslinking sites caused by sulfur, severing the crosslinked bonds. Therefore, in the case of diene rubber, it is thought that its main chain structure is basically maintained even after the decomposition reaction.

[0073] As the radical initiator, various known compounds can be used, but from the viewpoint of reaction efficiency, peroxides and azo compounds are preferred, and peroxides are more preferred. Examples of peroxides include acyl peroxide, percarboxylic acid, dialkyl peroxide, and alkyl hydroperoxide. Among these, from the viewpoint of reaction rate, acyl peroxide and percarboxylic acid are preferred, and acyl peroxide is more preferred. Specific examples of acyl peroxides include benzoyl peroxide, toluoyl peroxide, chlorobenzoyl peroxide, dichlorobenzoyl peroxide, methoxybenzoyl peroxide, phthaloyl peroxide, acetyl peroxide, propanoyl peroxide, caprylyl peroxide, decanoyl peroxide, lauroyl peroxide, myristoyl peroxide, and stearoyl peroxide. Among acyl peroxides, benzoyl peroxide, lauroyl peroxide, and acetyl peroxide are preferred from the viewpoints of reaction rate, cost, and availability. From the viewpoints of reaction rate and peroxide stability, lauroyl peroxide is preferred over benzoyl peroxide. Examples of percarboxylic acids include perbenzoic acid, chloroperbenzoic acid, peracetic acid, and perpropionic acid. Examples of dialkyl peroxides include di-tert-butyl peroxide, dicumyl peroxide, and tert-butylcumyl peroxide. Examples of alkyl hydroperoxides include tert-butyl hydroperoxide and cumene hydroperoxide. Examples of azo compounds include azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobiscyclohexanecarbonitrile, and methyl azobisisobutyrate. These radical initiators may be in the form of a hydrate from the viewpoints of safety, availability, and the like. By using a suitable initiator, crosslinked rubber can be efficiently decomposed under mild conditions.

[0074] The amount of the radical initiator used is preferably 0.1 part by mass or more, more preferably 1 part by mass or more, and is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, per 100 parts by mass of the crosslinked rubber. If the amount of the radical initiator used is 0.1 part by mass or more per 100 parts by mass of the crosslinked rubber, the decomposition reaction of the crosslinked rubber proceeds more quickly, and if the amount of the radical initiator used is 30 parts by mass or less per 100 parts by mass of the crosslinked rubber, it is preferable from the standpoint of cost.

[0075] The fourth decomposition method is carried out in an atmosphere containing oxygen gas. The concentration (volume %) of oxygen gas in the reaction atmosphere is typically 1 to 100%, preferably 1 to 80%, and more preferably 5 to 50%, including the atmospheric oxygen concentration of approximately 20%. When the oxygen gas concentration is not 100%, an inert gas such as nitrogen gas can be used as the remaining gas component. The decomposition reaction in the fourth decomposition method is generally more advantageous as the oxygen concentration increases, but because undesirable side reactions are more likely to occur, it is preferable to appropriately control the reaction time, reaction temperature, etc. when the oxygen concentration is high. On the other hand, using atmospheric air with an oxygen concentration of approximately 20% eliminates the need for separate oxygen gas, which is advantageous in terms of equipment and economy. In a reaction under an air atmosphere, when the amount of crosslinked rubber is small, the reaction can proceed even in a sealed container with a sufficiently large internal volume. In this case, the internal volume of the reaction container is generally 50 parts by volume or more, more preferably 100 parts by volume or more, per 1 part by volume of crosslinked rubber. When the fourth decomposition method is carried out in a closed system, a large amount of crosslinked rubber requires a reaction vessel with a large internal volume, which is not desirable from the standpoint of equipment. Therefore, from the standpoint of equipment, it is preferable to carry out the reaction in a non-closed system that allows the flow of air, etc. In order to make the reaction system a non-closed system, methods such as opening a portion of the reaction vessel, installing a membrane that allows the flow of air, etc., or allowing air, etc., to overflow can be considered. Another advantageous embodiment is a method in which the reaction is carried out while continuously or intermittently blowing air, etc. into the solution. In this case, the blowing rate is not particularly limited, but is usually 1 to 1000 mL / min, preferably 2 to 500 mL / min, and more preferably 3 to 200 mL / min per gram of crosslinked rubber.

[0076] In the fourth decomposition method, the radical initiator may be dissolved in a solvent, or the crosslinked rubber may be immersed in a solvent to perform the decomposition. By allowing the radical initiator to act on the crosslinked rubber in a solvent, the decomposition of the crosslinked rubber can be facilitated. Any solvent that does not inhibit the decomposition reaction can be used as the solvent, and examples thereof include aromatic hydrocarbons (aromatic solvents), chlorinated hydrocarbons, aliphatic hydrocarbons, alicyclic hydrocarbons, ethers, etc. Specific examples of aromatic hydrocarbons include toluene, xylene, ethylbenzene, trimethylbenzene, and propylbenzene. Chlorinated hydrocarbons include chloroform, dichloromethane, dichloroethane, trichloroethane, tetrachloroethane, tetrachloroethene, chlorobenzene, and dichlorobenzene. Aliphatic hydrocarbons include pentane, hexane, and octane. Alicyclic hydrocarbons include cyclopentane, cyclohexane, and cyclooctane. Ethers include tetrahydrofuran, methyltetrahydrofuran, tetrahydropyran, and dioxane. Among these, aromatic hydrocarbons and chlorinated hydrocarbons are preferred from the viewpoints of reaction rate, availability, etc. Specific examples thereof include toluene, xylene, ethylbenzene, chloroform, chlorobenzene, dichlorobenzene, etc. Among aromatic hydrocarbons, ethylbenzene is preferred over toluene from the viewpoint of reaction rate. The solvent suitable for the decomposition reaction also depends on the type of crosslinked rubber. For example, when the crosslinked rubber is an NR-based, IR-based, or BR-based crosslinked rubber, aromatic hydrocarbons and chlorinated hydrocarbons are preferred from the viewpoints of reaction rate, solubility of the product, etc., specific examples thereof include toluene, ethylbenzene, chloroform, chlorobenzene, etc. On the other hand, when the crosslinked rubber is an SBR-based crosslinked rubber, chlorinated hydrocarbons are more preferred from the viewpoint of reaction rate, etc., specific examples thereof include chloroform, chlorobenzene, etc. Use of a preferred solvent facilitates the decomposition of the crosslinked rubber, allowing for more efficient production of a liquid polymer. The amount of the solvent used is preferably 2 mL or more, more preferably 10 mL or more, per 1 g of the crosslinked rubber, and is preferably 100 mL or less, more preferably 50 mL or less.If the amount of solvent used is 2 mL per 1 g of crosslinked rubber, the decomposition reaction of the crosslinked rubber is promoted, and if the amount of solvent used is 50 mL or less per 1 g of crosslinked rubber, this is preferable from the standpoint of cost.

[0077] The fourth decomposition method is preferably carried out at a temperature of 0°C or higher and 200°C or lower. By carrying out the fourth decomposition method at a temperature of 0°C or higher, the rate of decomposition reaction of the crosslinked rubber is improved, and by carrying out the fourth decomposition method at a temperature of 200°C or lower, the retention rate (selectivity) of the monomer skeleton in the crosslinked rubber is improved. In terms of improving the decomposition reaction rate of the crosslinked rubber, the fourth decomposition method is more preferably carried out at a temperature of 10°C or higher, and more preferably at a temperature of 150°C or lower, from the viewpoint of improving the selectivity of the product that retains the monomer skeleton. Furthermore, when a peroxide-based radical initiator is used, the decomposition efficiency is high, so the reaction proceeds at a low temperature of 60°C or lower. Another advantage of using a peroxide-based radical initiator is that the reaction proceeds smoothly even at around room temperature (20 to 30°C), so no special equipment for heating or cooling is required.

[0078] The fourth decomposition method can be carried out under any pressure, including reduced pressure, normal pressure, and increased pressure. Specifically, the reaction pressure is preferably 1 kPa to 10 MPa, more preferably 10 kPa to 1 MPa, and even more preferably 50 kPa to 500 kPa.

[0079] In the fourth decomposition method, it is important to efficiently stir the raw materials, namely, the crosslinked rubber, the radical initiator, and the solvent. As a stirring method, various conventionally known methods can be used, such as a method using a magnetic stirrer, a method using a mechanical stirrer, or a method using a shaker. Furthermore, to promote the reaction, ultrasonic irradiation, microwave irradiation, light irradiation, or the like may be used in combination. These methods can also be used in combination.

[0080] Other Decomposition Methods The method for decomposing crosslinked rubber to obtain recycled carbon black of this embodiment is not limited to the first, second, third, and fourth decomposition methods described above, and any decomposition method that preserves 30% or more of the basic polymer structure is sufficient. Furthermore, a decomposition method that preserves 50% or more of the polymer structure is more preferred, and a decomposition method that preserves 70% or more of the polymer structure is even more preferred.

[0081] -Separation- According to the first, second, third, and fourth decomposition methods described above, crosslinked rubber can be decomposed and reduced in molecular weight to a liquid polymer. Therefore, after the decomposition reaction, carbon black can be easily separated and recovered from the decomposition product by, for example, centrifugation, filtration, or the like. The recycled carbon black of this embodiment is preferably obtained by centrifuging the decomposition product after the decomposition of crosslinked rubber. By undergoing centrifugation, recycled carbon black with an organic content of 5% by mass or more can be easily obtained. Here, as conditions for centrifugation, for example, a centrifugal acceleration in the range of 200 to 200,000 G and a rotation time of 60 seconds to 180 minutes are preferred.

[0082] - Washing - The recycled carbon black obtained by separation and recovery as described above is preferably subjected to a washing step. By undergoing the washing step, recycled carbon black with few impurities can be easily obtained. The washing is preferably carried out, for example, with an organic solvent. The recycled carbon black of the present embodiment described above has an organic content of 5% by mass or more remaining in the recycled carbon black after washing with toluene, and therefore has excellent dispersibility in organic solvents, and washing with an organic solvent can easily reduce impurities. Here, examples of organic solvents that can be used include aromatic solvents such as toluene and xylene, aliphatic solvents such as hexane, and alicyclic solvents such as cyclohexane.

[0083] After the above-described washing step, the recycled carbon black is preferably dried at room temperature, heated, or vacuum dried to remove organic solvents and moisture. When the heated or vacuum dried, the heating temperature is preferably 200° C. or lower, more preferably 150° C. or lower, and even more preferably 100° C. or lower.

[0084] (Uses) The recycled carbon black of this embodiment can be used as a filler in rubber compositions for various rubber products. In addition to rubber compositions, the recycled carbon black of this embodiment can also be used in black inks and the like. When using the recycled carbon black in black inks, it is preferable to use fine particle size recycled carbon black.

[0085] <Mixture of Recycled Carbon Black and Liquid Polymer> The mixture of recycled carbon black and liquid polymer according to a first embodiment of the present invention is a mixture of recycled carbon black and liquid polymer obtained by decomposition of a crosslinked rubber containing a diene rubber and carbon black. In the mixture of recycled carbon black and liquid polymer according to the first embodiment, the recycled carbon black is the recycled carbon black according to the present embodiment described above (in other words, recycled carbon black in which the organic content remaining in the recycled carbon black after washing with toluene is 5% by mass or more), and the liquid polymer has a weight-average molecular weight of 300,000 or less. Here, in this specification, the liquid polymer refers to a polymer that is liquid at room temperature (23°C) and contains two or more diene monomer units.

[0086] The mixture of recycled carbon black and liquid polymer of the first embodiment can be obtained after the decomposition of the crosslinked rubber described above, without separating and recovering the recycled carbon black. By blending the mixture of recycled carbon black and liquid polymer into a rubber composition without separating and recovering the recycled carbon black, the productivity of the rubber composition can be improved. Furthermore, when the mixture of recycled carbon black and liquid polymer of the first embodiment is reused in a rubber composition, the liquid polymer acts as a softener, making it easy to knead the rubber composition.

[0087] In the mixture of recycled carbon black and liquid polymer of the first embodiment, the liquid polymer has a weight-average molecular weight of 300,000 or less, preferably 500 to 250,000. The weight-average molecular weight of the liquid polymer can be changed by the decomposition method and decomposition conditions of the crosslinked rubber. For example, the third decomposition method (solvent decomposition) makes it easy to obtain a liquid polymer with a weight-average molecular weight of 500 to 30,000. In this specification, the weight-average molecular weight (Mw) is measured by gel permeation chromatography (GPC).

[0088] The second embodiment of the present invention relates to a mixture of recycled carbon black and liquid polymer obtained by decomposing a crosslinked rubber containing a diene rubber and carbon black. The recycled carbon black and liquid polymer mixture of the second embodiment is characterized in that the recycled carbon black is the recycled carbon black of the present embodiment described above (i.e., recycled carbon black having an organic content of 5% by mass or more remaining after washing with toluene), and the liquid polymer contains 30% by mass or less of components with a molecular weight of 15,000 or less.

[0089] The mixture of recycled carbon black and liquid polymer of the second embodiment can be obtained by removing some or all of the low-molecular-weight components from the liquid polymer after decomposition of the crosslinked rubber described above, without separating and recovering the recycled carbon black. Blending the mixture of recycled carbon black and liquid polymer into a rubber composition without separating and recovering the recycled carbon black can improve the productivity of the rubber composition. Furthermore, by removing some or all of the low-molecular-weight components from the liquid polymer, the plasticizing effect of the low-molecular-weight components can be suppressed when blending the mixture of recycled carbon black and liquid polymer into a rubber composition, making it easier to obtain a rubber composition with desired physical properties.

[0090] In the mixture of recycled carbon black and liquid polymer according to the second embodiment, the liquid polymer contains 30% by mass or less of components with a molecular weight of 15,000 or less. When the proportion of components with a molecular weight of 15,000 or less is 30% by mass or less, plasticization is suppressed, making it easier to obtain a rubber composition with desired physical properties. Here, the molecular weight is measured using gel permeation chromatography (GPC).

[0091] <Rubber Composition> The rubber composition of the first embodiment of the present invention is characterized by including a rubber component and the above-described recycled carbon black. Because the rubber composition of the first embodiment includes the above-described recycled carbon black of the present embodiment, it is possible to reduce the environmental impact while maintaining physical properties. Here, the amount of recycled carbon black mixed is preferably in the range of 10 to 100 parts by mass per 100 parts by mass of the rubber component.

[0092] A second embodiment of the rubber composition of the present invention is characterized by including a rubber component and the mixture of recycled carbon black and liquid polymer of the first embodiment of the present invention. Because the rubber composition of the second embodiment includes the mixture of recycled carbon black and liquid polymer, it is possible to reduce the environmental impact while maintaining physical properties. The amount of the mixture of recycled carbon black and liquid polymer blended is preferably in the range of 10 to 100 parts by mass per 100 parts by mass of the rubber component.

[0093] A rubber composition according to a third embodiment of the present invention is characterized by including a rubber component and the mixture of recycled carbon black and liquid polymer according to the second embodiment of the present invention (i.e., a mixture in which some or all of the low-molecular-weight components in the liquid polymer have been removed). Because the rubber composition according to the third embodiment includes the mixture of recycled carbon black and liquid polymer, it can reduce the environmental impact while maintaining its physical properties. The amount of the mixture of recycled carbon black and liquid polymer blended is preferably in the range of 10 to 100 parts by mass per 100 parts by mass of the rubber component.

[0094] The rubber compositions of the first, second and third embodiments described above maintain physical properties such as tensile strength (TB) and elongation at break (EB), and are therefore all suitable as rubber compositions for tires.

[0095] The rubber composition contains a rubber component, which provides rubber elasticity to the composition. The rubber component is preferably a diene-based rubber, and examples of the diene-based rubber include isoprene-skeleton rubber, styrene-butadiene rubber (SBR), butadiene rubber (BR), and chloroprene rubber (CR). The isoprene-skeleton rubber is a rubber whose main skeleton is isoprene units, and specific examples include natural rubber (NR) and synthetic isoprene rubber (IR). These rubber components may be used alone or in a blend of two or more.

[0096] In addition to the above-mentioned rubber component, recycled carbon black, and mixture of recycled carbon black and liquid polymer, the rubber composition may contain compounding agents commonly used in the rubber industry, such as fillers (carbon black, silica, calcium carbonate, etc.), silane coupling agents, antioxidants, waxes, softeners, processing aids, resins, surfactants, organic acids (stearic acid, etc.), zinc oxide (zinc white), vulcanization accelerators, crosslinking agents (sulfur, peroxides, etc.), etc.

[0097] In the rubber composition, the recycled carbon black of this embodiment may be used in combination with virgin carbon black or other recycled carbon black (i.e., carbon black in which the organic content remaining in the recycled carbon black after toluene washing is less than 5% by mass). Here, the proportion of the recycled carbon black of this embodiment in the total amount of carbon black is preferably 10% by mass or more, and may even be 100% by mass. The carbon black used in combination with the recycled carbon black of this embodiment preferably has a dibutyl phthalate (DBP) absorption capacity of 40 to 200 mL / 100 g. In addition, the carbon black used in combination with the recycled carbon black of this embodiment preferably has a nitrogen adsorption specific surface area (N ２ SA) is 20 to 180m ２In this specification, the dibutyl phthalate (DBP) absorption amount of carbon black is determined in accordance with JIS K 6217-4:2017. In addition, in this specification, the nitrogen adsorption specific surface area (N ２ SA) is determined according to JIS K 6217-2:2017.

[0098] In the rubber composition, the recycled carbon black of this embodiment may be used in combination with silica. The silica used in combination with the recycled carbon black of this embodiment preferably has an average particle size of 0.1 to 100 μm. In this specification, the average particle size of silica is the average value of particle sizes measured by a light scattering method using a particle size distribution analyzer.

[0099] Furthermore, when the recycled carbon black of this embodiment is blended into a rubber composition, the rubber component of the rubber composition may be the same as or different from the diene rubber contained in the crosslinked rubber (i.e., the raw material of the recycled carbon black of this embodiment).

[0100] The recycled carbon black of this embodiment may be blended into the rubber composition as a wet masterbatch. When blended as a wet masterbatch, the recycled carbon black of this embodiment may be blended into the rubber composition by dispersing it in any solvent (organic solvent, water, etc.), or may be blended into the rubber composition as a mixture with the above-mentioned liquid polymer.

[0101] <Rubber Product> The rubber product of this embodiment is characterized by including a rubber member made of the rubber composition of the first, second, or third embodiment. The rubber product of this embodiment maintains its physical properties because it includes a rubber member made of the above-mentioned rubber composition.

[0102] Examples of the rubber product of the present embodiment include tires, rubber crawlers, and seismic isolation rubber, among which tires are preferred. Among rubber products, tires are produced in large quantities, and therefore, by reusing the recycled carbon black described above, the effect of reducing the environmental load is particularly significant.

[0103] - Tire - When the rubber product of this embodiment is a tire, the application portion of the rubber composition of this embodiment in the tire is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include the tread, base tread, sidewall, side reinforcing rubber, and bead filler. Conventional methods can be used to manufacture the tire. For example, components typically used in tire manufacturing, such as a carcass layer, belt layer, and tread layer, each composed of an unvulcanized rubber composition and / or cords, are laminated on a tire building drum, and the drum is removed to form a green tire. Next, the green tire is heated and vulcanized according to a conventional method to manufacture a desired tire (e.g., a pneumatic tire).

[0104] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0105] (1) Method for Analyzing the Organic Content and Maximum DTG Temperature of Recycled Carbon Black Using a Hitachi High-Tech Science Corporation product name "STA7220", thermogravimetric analysis (TGA) was performed to measure the mass (m) of the sample recycled carbon black when it was heated to 120°C and held for 1 hour. ０ ) and then heated to 550 ° C at 40 ° C / min and held for 2 hours. １ ) was measured and calculated using the following formula: Organic content (mass%) = (m ０ -m １ ) / m ０ × 100. The DTG value [μg / min] was also determined, and the temperature at which the DTG value was maximum was calculated as the maximum DTG temperature (the temperature at which the DTG value associated with the weight loss of the organic content in the thermal weight loss measurement was maximum).

[0106] (2) Method for Analyzing Weight-Average Molecular Weight (Mw) of Liquid Polymer The polystyrene-equivalent weight-average molecular weight (Mw) of the liquid polymer was determined using gel permeation chromatography (hereinafter sometimes referred to as GPC analysis; solution delivery unit: LC-20AB manufactured by Shimadzu Corporation; column: a combination of KF-803 and KF-804 manufactured by Showa Denko K.K. or a combination of G2000HXL and G4000HXL manufactured by Tosoh Corporation; detector: differential refractometer RID-10A manufactured by Shimadzu Corporation; analysis system: LabSolutions manufactured by Shimadzu Corporation; eluent: tetrahydrofuran) at a temperature of 40°C.

[0107] (Preparation of Crosslinked Rubber Sample) A rubber composition was prepared by blending 50 parts by mass of carbon black (manufactured by Tokai Carbon Co., Ltd., product name "N330"), 2.0 parts by mass of antioxidant 6PPD (N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine), 2.0 parts by mass of stearic acid, 2.25 parts by mass of zinc oxide, 0.6 parts by mass of vulcanization accelerator (N-cyclohexyl-2-benzothiazolylsulfenamide), and 1.8 parts by mass of sulfur per 100 parts by mass of natural rubber, and the rubber composition was then heat-crosslinked to prepare a crosslinked rubber. The resulting crosslinked rubber was cut into a shape of 3 mm x 3 mm x 2 mm to prepare a crosslinked rubber sample.

[0108] (Preparation of Recycled Carbon Black 1—Metathesis Decomposition) 10 mL of tetrahydrofuran (THF) was added to 0.125 g of the crosslinked rubber sample and stirred at 25°C for 24 hours to swell the rubber. Next, 24 mg of the Grubbs second-generation catalyst represented by the structural formula (1-2) above was added, and the mixture was stirred at 25°C for an additional 24 hours to carry out the metathesis decomposition reaction. After the reaction, 10 mL of methanol and 2.5 mL of ethyl vinyl ether were added to terminate the reaction. Since no rubber sample remained after the reaction, the decomposition rate of the rubber sample was calculated to be 100%. The solvent was then distilled off under reduced pressure to obtain a mixture containing a liquid polymer and recycled carbon black. The resulting mixture was centrifuged using a CP80NX centrifugal separator manufactured by Effendorf Hymatec at a centrifugal acceleration of 112,000 G for 60 minutes to recover the recycled carbon black. Toluene solvent was then added to the resulting recycled carbon black, and the mixture was centrifuged and washed under the same conditions. Thermogravimetric analysis (TGA) of the washed recycled carbon black revealed that the organic content was 9.8% by mass. The relationship between temperature and DTG value [μg / min] shown in Figure 1 and the relationship between temperature and DTG value (DTG / max DTG [%]) shown in Figure 2 indicate that the maximum DTG temperature was 370°C. The weight-average molecular weight (Mw) of the liquid polymer obtained by centrifugation was 11,000.

[0109] (Preparation of Recycled Carbon Black 2 - Solvent Decomposition) 0.4 g of a crosslinked rubber sample and 4 mL of toluene were added to a reactor and stirred under an Ar atmosphere at 240°C for 9 hours to carry out a decomposition reaction. After the reaction, the mixture was separated into a solvent (toluene)-soluble component and a solvent-insoluble component. The solvent-soluble component consisted primarily of liquid polymer, while the solvent-insoluble component consisted primarily of carbon black. The resulting solvent-insoluble component was centrifuged using an Effendorf Hymatec CP80NX centrifugal separator at a centrifugal acceleration of 112,000G for 60 minutes to recover the recycled carbon black. Further, toluene solvent was added to the resulting recycled carbon black, and the resulting recycled carbon black was centrifuged under the same conditions to wash it. The washed recycled carbon black was then vacuum-dried at 50°C for 12 hours. Thermogravimetric analysis (TGA) of the washed recycled carbon black revealed an organic content of 11.9% by mass. From the relationship between temperature and DTG value [μg / min] shown in Figure 1 and the relationship between temperature and DTG value (DTG / maximum DTG [%]) shown in Figure 2, the maximum DTG temperature at which the DTG value was maximized was 390°C. Furthermore, the weight average molecular weight (Mw) of the liquid polymer obtained by centrifugation was analyzed and found to be 28,000.

[0110] (Preparation and Evaluation of Rubber Compositions) Rubber compositions were prepared according to the formulation shown in Table 1. In addition to the components shown in Table 1, the rubber compositions were compounded with 2.0 parts by mass of antioxidant 6PPD [N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine], 2.0 parts by mass of stearic acid, 2.25 parts by mass of zinc oxide, 0.6 part by mass of vulcanization accelerator (N-cyclohexyl-2-benzothiazolylsulfenamide), and 1.8 parts by mass of sulfur per 100 parts by mass of natural rubber (rubber component). The tensile strength (TB) of the obtained rubber compositions was measured by the following method.

[0111] (3) Measurement of Tensile Strength (TB) The rubber composition was vulcanized to prepare vulcanized rubber test pieces. The test pieces were subjected to a tensile test in accordance with JIS K 6251 to measure the tensile strength (TB).

[0112]

[0113] * 1 Virgin carbon black: Tokai Carbon Co., Ltd., trade name "N330", organic content = 0.9 mass%, maximum DTG temperature = 333 ° C. * 2 Commercially available recycled carbon black: Enrestec, trade name "PB365", organic content = 2.2 mass%, maximum DTG temperature = 315 ° C. * 3 Recycled carbon black 1: Recycled carbon black obtained by metathesis decomposition, organic content = 9.8 mass%, maximum DTG temperature = 370 ° C. * 4 Recycled carbon black 2: Recycled carbon black obtained by solvent decomposition, organic content = 11.9 mass%, maximum DTG temperature = 390 ° C.

[0114] Table 1 shows that the rubber compositions of Examples 1 and 2, which contain recycled carbon black containing 5% by mass or more of organic matter remaining in the recycled carbon black after toluene washing according to the present invention, have the same tensile strength (TB) as the rubber composition of Comparative Example 1, which contains virgin carbon black. On the other hand, the rubber composition of Comparative Example 2, which contains commercially available recycled carbon black containing less than 5% by mass of organic matter remaining in the recycled carbon black after toluene washing, has a significantly lower tensile strength (TB) than the rubber composition of Comparative Example 1, which contains virgin carbon black.

[0115] The recycled carbon black of the present invention can be used in rubber products such as tires, rubber crawlers, and seismic isolation rubber.

Claims

1. Regenerated carbon black obtained by decomposing crosslinked rubber containing diene rubber and carbon black, characterized in that the organic content remaining in the regenerated carbon black after washing with toluene is 5 mass% or more.

2. The recycled carbon black according to claim 1, having a maximum DTG temperature (the temperature at which the DTA value associated with the weight loss of the organic component in a thermal gravimetric loss measurement is maximum) of 350°C or higher.

3. A mixture of recycled carbon black and liquid polymer obtained by decomposition of crosslinked rubber containing diene rubber and carbon black, wherein the recycled carbon black is the recycled carbon black described in claim 1, and the liquid polymer has a weight average molecular weight of 300,000 or less.

4. A mixture of recycled carbon black and liquid polymer obtained by decomposition of crosslinked rubber containing diene rubber and carbon black, wherein the recycled carbon black is the recycled carbon black described in claim 1, and the liquid polymer contains 30 mass% or less of components with a molecular weight of 15,000 or less.

5. A rubber composition comprising a rubber component and the recycled carbon black according to claim 1.

6. A rubber composition comprising a rubber component and a mixture of the recycled carbon black and liquid polymer according to claim 3.

7. A rubber composition comprising a rubber component and a mixture of the recycled carbon black and liquid polymer according to claim 4.

8. The rubber composition according to any one of claims 5 to 7, which is for use in tires.

9. A rubber product comprising a rubber member made of the rubber composition according to any one of claims 5 to 7.

10. The rubber product of claim 9 which is a tire.

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