Rubber composition and tires

Abstract

In rubber compositions using recycled rubber containing SBR, the tensile strength and elongation at break are improved. [Solution] The rubber composition according to the embodiment contains 0.1 to 30 parts by mass of recycled rubber containing styrene-butadiene rubber with respect to 100 parts by mass of unvulcanized rubber component. The recycled rubber has a chloroform extract content of 15 to 30% by mass obtained by Soxhlet extraction, and the chloroform extract content contains oil and thermoplastic resin, and has a solubility in toluene of 25% by mass or more.

Description

Technical Field

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[0001] The present invention relates to a rubber composition and a tire using the same.

Background Art

[0002] From the viewpoints of waste treatment and effective utilization of resources, regeneration of SBR (styrene-butadiene rubber)-based rubber vulcanizates centered on passenger car tires has been actively studied (see Patent Documents 1, 2 and Non-Patent Documents 1, 2). However, it is difficult to regenerate SBR-based rubber vulcanizates in the same manner as NR-based rubber vulcanizates.

[0003] The oil pan method known as a method for producing recycled rubber is a technique in which a regenerant and oil are used to perform treatment at a high temperature of about 200° C. to plasticize. NR (natural rubber)-based rubber vulcanizates are plasticized by the oil pan method, and the resulting recycled rubber has a product strength that can be put to practical use depending on the application, even if it is not as high as that of the original vulcanized rubber. On the other hand, when SBR-based rubber vulcanizates are regenerated by the oil pan method, gelation is caused due to the characteristics of SBR, resulting in hardening, so it is considered difficult to reuse. Therefore, recycled rubber containing SBR obtained by regenerating SBR-based rubber vulcanizates is hardly distributed. Currently, SBR-based rubber vulcanizates are often used as fine powders with a particle size of 100 μm or less without heating, but it has been found that various physical properties such as mechanical properties deteriorate.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0005]

Non-Patent Document 1

[0006] As described above, SBR-based vulcanized rubber is not recycled as recycled rubber like NR-based vulcanized rubber. Therefore, in order to promote recycling, it is necessary to improve the mechanical properties such as tensile strength and elongation at break in rubber compositions using recycled SBR-based vulcanized rubber.

[0007] In view of the above, embodiments of the present invention aim to improve the breaking strength and breaking elongation in a rubber composition using recycled rubber containing SBR. [Means for solving the problem]

[0008] The present invention includes embodiments shown below. [1] A rubber composition comprising 0.1 to 30 parts by mass of recycled rubber containing styrene-butadiene rubber per 100 parts by mass of unvulcanized rubber component, wherein the recycled rubber has a chloroform extract content of 15 to 30% by mass obtained by Soxhlet extraction, and the chloroform extract content contains oil and thermoplastic resin, and has a solubility in toluene of 25% by mass or more. [2] The rubber composition according to [1], wherein the amount of styrene in the rubber polymer contained in the recycled rubber is 10 to 60% as a peak area ratio measured by pyrolysis gas chromatography in accordance with JIS K6231-2:2007. [3] The rubber composition according to [1] or [2], further comprising 20 to 150 parts by mass of a reinforcing filler per 100 parts by mass of the unvulcanized rubber component. [4] A tire comprising vulcanized rubber obtained by vulcanizing any one of the rubber compositions described in [1] to [3]. [Effects of the Invention]

[0009] According to embodiments of the present invention, the tensile strength and elongation at break can be improved in a rubber composition using recycled rubber containing SBR. [Brief explanation of the drawing]

[0010] [Figure 1] A graph to explain the method for measuring chloroform extract. [Modes for carrying out the invention]

[0011] The rubber composition according to this embodiment is made by compounding an unvulcanized rubber component with recycled rubber containing styrene-butadiene rubber, wherein the recycled rubber used has a chloroform extract content of 15 to 30% by mass obtained by Soxhlet extraction, and the chloroform extract contains oil and thermoplastic resin, and has a solubility in toluene of 25% by mass or more. The oil and thermoplastic resin act as regenerating agents (desulfurizing agents) to facilitate the regeneration of the vulcanized rubber. By setting the chloroform extract containing such oil and thermoplastic resin within the above-mentioned specific range, and by suppressing the gelation of styrene-butadiene rubber by setting its solubility in toluene to 25% by mass or more, the compatibility between the recycled rubber and the unvulcanized rubber component is improved, and mechanical properties such as tensile strength and elongation at break can be improved.

[0012] In this embodiment, recycled rubber containing styrene-butadiene rubber (SBR) is used. Specifically, recycled rubber obtained by recycling SBR-based vulcanized rubber, which is a vulcanized rubber containing SBR, is used. Here, recycled rubber is made by recycling vulcanized rubber, and more specifically, it refers to vulcanized rubber that has been physically and / or chemically treated to restore its adhesiveness and plasticity.

[0013] SBR-based rubber vulcanized products are rubbers obtained by vulcanizing a rubber polymer containing SBR and a vulcanizing agent such as sulfur. The SBR may be solution-polymerized styrene-butadiene rubber (SSBR), emulsion-polymerized styrene-butadiene rubber (ESBR), or both may be used in combination. The SBR content is preferably 20% by mass or more, more preferably 50% by mass or more, more preferably 70% by mass or more, and may be 100% by mass (i.e., SBR alone) based on 100% by mass of the rubber polymer. Preferred rubber polymers used in combination with SBR include, for example, diene-based rubbers such as natural rubber (NR), synthetic isoprene rubber (IR), and / or butadiene rubber (BR). These rubber polymers may be unmodified rubbers or modified rubbers in which the ends or main chains are modified.

[0014] SBR-based rubber vulcanized products may contain reinforcing fillers such as carbon black or silica. In that case, recycled rubber will also contain the reinforcing fillers. The amount of reinforcing fillers is not particularly limited and may be 20 to 150 parts by mass, 40 to 120 parts by mass, or 50 to 100 parts by mass per 100 parts by mass of rubber polymer.

[0015] SBR-based rubber vulcanized products may contain oil. In that case, recycled rubber will also contain the same oil. The oil content in SBR-based rubber vulcanized products is not particularly limited and may be 0 to 50 parts by mass or 5 to 40 parts by mass per 100 parts by mass of rubber polymer.

[0016] In addition to the rubber polymer, vulcanizing agent, reinforcing filler, and oil mentioned above, the unvulcanized rubber composition used in the manufacture of SBR-based rubber vulcanized products may also contain various additives commonly used in rubber compositions, such as zinc oxide, stearic acid, antioxidants, waxes, silane coupling agents, and vulcanization accelerators. Therefore, SBR-based rubber vulcanized products may contain these additives and / or their reaction products, and recycled rubber may also contain these additives and / or their reaction products.

[0017] The regeneration treatment for SBR rubber vulcanizates is preferably carried out by the oil pan method. Specifically, the SBR rubber vulcanizate may be pulverized in advance to prepare powdered rubber, and after mixing the powdered rubber with a regenerant, the regenerated rubber may be prepared by heating and pressurizing under a steam atmosphere.

[0018] Examples of the regenerant include oil, peptizing agent, and thermoplastic resin. Any one or two or more of these may be used, and more preferably, all three are used in combination. By performing the regeneration treatment in the presence of a thermoplastic resin together with oil and peptizing agent, the effect of suppressing the gelation of SBR is enhanced, and a cohesive regenerated rubber can be obtained. It is considered that the thermoplastic resin that softens by heating imparts adhesiveness to the regenerated rubber, thereby suppressing the gelation of SBR.

[0019] Examples of the oil added as the regenerant include mineral oils such as paraffin oil, naphthene oil, and aroma oil, and plant-derived oils such as turpentine oil. Any one or a combination of two or more of these can be used.

[0020] Examples of the peptizing agent added as the regenerant include aromatic disulfides such as diphenyldisulfide and 2,2-dibenzamidodiphenyldisulfide.

[0021] Examples of the thermoplastic resin added as the regenerant include tackifying resins such as coumarone resin, petroleum resin, terpene resin, and rosin resin. Any one or a combination of two or more of these can be used. The softening point of the thermoplastic resin is preferably 50 to 130 °C, more preferably 70 to 120 °C. The softening point of the resin is measured using a ring and ball softening point measuring device in accordance with JIS K6220-1:2015.

[0022] Coumarone resins are resins that contain coumarone as a constituent monomer, and examples include coumarone resin and coumarone-indene resin. Examples of petroleum resins include aliphatic petroleum resins (C5 petroleum resins), aromatic petroleum resins (C9 petroleum resins), and aliphatic / aromatic copolymer petroleum resins (C5 / C9 petroleum resins). Terpene resins are resins obtained by polymerizing terpene compounds such as α-pinene, β-pinene, limonene, and dipentene, and have units derived from terpene compounds. Terpene resins may be polyterpene resins obtained by polymerizing only terpene monomers, or modified terpene resins (e.g., terpene phenol resins) obtained by polymerizing terpene compounds and monomers other than terpenes. Examples of rosin resins include natural resin rosin, and rosin-modified resins (e.g., hydrogenated rosin esters, rosin-modified maleic acid resins) obtained by hydrogenation, disproportionation, dimerization, esterification, etc. Among these, it is preferable to use a coumarone-based resin as the thermoplastic resin.

[0023] The amounts of oil, desorbent, and thermoplastic resin added to the SBR-based rubber vulcanized product as regenerators are not particularly limited as long as the chloroform extract content of the regenerated rubber obtained by regeneration is 15 to 30% by mass. For example, the amount of oil added as a regenerator may be 0 to 10 parts by mass or 2 to 7 parts by mass per 100 parts by mass of the SBR-based rubber vulcanized product. The amount of desorbent added as a regenerator may be 0 to 3 parts by mass or 0.5 to 2 parts by mass per 100 parts by mass of the SBR-based rubber vulcanized product. The amount of thermoplastic resin added as a regenerator may be 1 to 15 parts by mass or 5 to 12 parts by mass per 100 parts by mass of the SBR-based rubber vulcanized product. If oil, desorbent, or thermoplastic resin is originally contained in the SBR-based rubber vulcanized product, the amount added as a regenerator may be adjusted taking that amount into consideration. In other words, the amounts of oil, descaling agent, and thermoplastic resin contained in the chloroform extract include not only the amount added as a regenerator, but also the amount originally present in the SBR-based rubber vulcanized product, as long as they remain in the recycled rubber.

[0024] When heating and pressurizing a mixture of powdered rubber and a regenerating agent, for example, the process may be carried out using an autoclave under a steam atmosphere at a temperature of 150-300°C, a pressure of 0.2-2.0 MPa, and for 1-6 hours.

[0025] In this embodiment, the recycled rubber containing SBR is one in which the chloroform extract obtained by Soxhlet extraction is 15 to 30% by mass. The chloroform extract is a chloroform-soluble component and includes oil and thermoplastic resin. By having a chloroform extract containing oil and thermoplastic resin of 15 to 30% by mass, the compatibility with the unvulcanized rubber component is improved, even though it is recycled rubber containing SBR, thereby improving the breaking strength and elongation at break. The chloroform extract is more preferably 17 to 29% by mass, more preferably 18 to 28% by mass, more preferably 19 to 25% by mass, and even more preferably 20 to 23% by mass. The method for measuring the chloroform extract is as described in the Examples section.

[0026] The ratio of oil to thermoplastic resin in recycled rubber is not particularly limited; for example, the mass ratio of oil to thermoplastic resin may be 1 / 3 to 4 / 1, 1 / 2 to 3 / 1, or 2 / 3 to 2 / 1.

[0027] Furthermore, since the deconjugating agent is consumed by reaction with the rubber polymer during the regeneration process of SBR-based rubber vulcanized products, it does not need to be present in the regenerated rubber, but some unreacted portion may be included in the chloroform extract. The chloroform extract mainly consists of oil and thermoplastic resin, and may contain, for example, 80% or more, 90% or more, or 100% by mass of oil and thermoplastic resin combined, but may also contain other additives such as antioxidants.

[0028] In this embodiment, the recycled rubber containing SBR has a solubility in toluene of 25% by mass or more. The solubility in toluene is also called the sol fraction, and the higher this fraction, the more advanced the desulfurization, which improves compatibility with unvulcanized rubber components and can improve tensile strength and elongation at break. The solubility of the recycled rubber in toluene is more preferably 27% by mass or more. There is no particular upper limit to the solubility in toluene, but it may be, for example, 50% by mass or less, or 40% by mass or less. The method for measuring the solubility in toluene is as described in the Examples section.

[0029] As described above, recycled rubber contains SBR as a rubber polymer. As an indicator of the SBR content, the styrene content of the rubber polymer contained in recycled rubber is preferably 10-60% in terms of peak area ratio measured by pyrolysis gas chromatography in accordance with JIS K6231-2:2007. The styrene content is more preferably 15-50%. The butadiene content of the rubber polymer is not particularly limited, but is preferably 15-60% in terms of a similar peak area ratio, and more preferably 20-50%. The isoprene content of the rubber polymer is not particularly limited, but is preferably 0-50% in terms of a similar peak area ratio, and more preferably 20-40%. The methods for measuring these peak area ratios are as described in the Examples section.

[0030] The amount of rubber polymer in recycled rubber is not particularly limited, but is preferably 30 to 60% by mass, and more preferably 40 to 50% by mass, as measured by thermogravimetric analysis (TGA) in accordance with JIS K6226-1:2003. The amount of carbon black in recycled rubber as measured by TGA is not particularly limited, and may be, for example, 3 to 20% by mass or 5 to 10% by mass. The ash content in recycled rubber as measured by TGA is not particularly limited, and may be, for example, 10 to 35% by mass or 15 to 30% by mass. The ash content includes inorganic components such as silica and zinc compounds such as zinc oxide. The methods for measuring these mass ratios are as described in the Examples section.

[0031] In the rubber composition according to this embodiment, the unvulcanized rubber component is not particularly limited and includes, for example, diene rubbers such as natural rubber (NR), synthetic isoprene rubber (IR), styrene-butadiene rubber (SBR), and butadiene rubber (BR). These can be used individually or in combination of two or more. A diene rubber is a rubber having repeating units corresponding to a diene monomer with a conjugated double bond, and the main chain of the polymer contains a carbon-carbon double bond. Furthermore, the diene rubber may be unmodified rubber or modified rubber in which the ends or main chain are modified.

[0032] In one embodiment, the unvulcanized rubber component preferably contains SBR. The SBR may be SSBR, ESBR, or both may be used in combination. For example, 100 parts by mass of the unvulcanized rubber component preferably contains 20 parts by mass or more of SBR, more preferably 50 parts by mass or more of SBR, and even more preferably 70 parts by mass or more. Alternatively, the unvulcanized rubber component may contain NR and / or BR along with SBR. For example, 100 parts by mass of the unvulcanized rubber component may contain 50 to 90 parts by mass of SBR and 10 to 50 parts by mass of NR and / or BR, or 65 to 85 parts by mass of SBR and 15 to 35 parts by mass of NR and / or BR.

[0033] The rubber composition according to this embodiment contains 0.1 to 30 parts by mass of recycled rubber per 100 parts by mass of unvulcanized rubber component. The recycled rubber content is more preferably 1 to 30 parts by mass per 100 parts by mass of unvulcanized rubber component, more preferably 5 to 25 parts by mass, and even more preferably 10 to 20 parts by mass.

[0034] The rubber composition according to this embodiment preferably further contains a reinforcing filler, the amount of which is preferably 20 to 150 parts by mass per 100 parts by mass of the unvulcanized rubber component. The amount of reinforcing filler is more preferably 40 to 120 parts by mass, and even more preferably 50 to 100 parts by mass. The amount of reinforcing filler referred to herein does not include the amount of reinforcing filler contained in recycled rubber.

[0035] As reinforcing fillers to be incorporated into the rubber composition, silica and / or carbon black are preferred. Examples of silica include wet silica and dry silica, and preferably, wet silica such as wet sedimentation silica and wet gelation silica is used. The silica content is not particularly limited and may be 20 to 140 parts by mass, 30 to 110 parts by mass, or 40 to 90 parts by mass per 100 parts by mass of unvulcanized rubber component. The carbon black content is not particularly limited and may be 0 to 100 parts by mass, 5 to 50 parts by mass, or 10 to 30 parts by mass per 100 parts by mass of unvulcanized rubber component.

[0036] In addition to the unvulcanized rubber component, recycled rubber, and reinforcing filler described above, the rubber composition according to this embodiment may also contain various additives commonly used in rubber compositions, such as silane coupling agents, oils, zinc oxide, stearic acid, antioxidants, waxes, sulfur, and other vulcanizing agents and vulcanization accelerators.

[0037] The amounts of these additives are not particularly limited, and the amounts used in general rubber compositions can be applied. For example, the amount of silane coupling agent may be 3 to 20 parts by mass or 5 to 15 parts by mass per 100 parts by mass of silica. The amount of oil may be 5 to 50 parts by mass or 10 to 30 parts by mass per 100 parts by mass of unvulcanized rubber component. The amount of zinc oxide may be 0 to 10 parts by mass, 0.5 to 5 parts by mass or 1 to 4 parts by mass per 100 parts by mass of unvulcanized rubber component. The amount of stearic acid may be 0 to 10 parts by mass, 0.5 to 5 parts by mass or 1 to 4 parts by mass per 100 parts by mass of unvulcanized rubber component. The amount of antioxidant may be 0 to 10 parts by mass, 0.5 to 5 parts by mass or 1 to 4 parts by mass per 100 parts by mass of unvulcanized rubber component. The amount of vulcanizing agent may be 0.1 to 10 parts by mass, 0.5 to 5 parts by mass, or 1 to 3 parts by mass per 100 parts by mass of unvulcanized rubber component. The amount of vulcanization accelerator may be 0.1 to 10 parts by mass, 1 to 7 parts by mass, or 2 to 5 parts by mass per 100 parts by mass of unvulcanized rubber component.

[0038] The rubber composition according to this embodiment can be prepared by kneading in accordance with conventional methods using a commonly used mixer such as a Banbury mixer, kneader, or roll. That is, for example, in the first mixing stage, other additives excluding the vulcanizing agent and vulcanization accelerator can be added and mixed with the rubber component, and then, in the final mixing stage, the vulcanizing agent and vulcanization accelerator can be added and mixed with the resulting mixture to prepare the rubber composition.

[0039] The rubber composition according to this embodiment can be used in various rubber products such as tires, vibration damping rubber, and conveyor belts, and is preferably used in tires. Examples of tires include passenger car tires, large truck and bus tires (heavy-duty tires), and pneumatic tires of various applications and sizes. Since it preferably contains SBR, it is used in passenger car tires. Examples of application parts in tires include tread rubber and sidewall rubber.

[0040] The rubber composition is molded into a predetermined shape by conventional methods, for example, by extrusion, and then heated and vulcanized to become vulcanized rubber. When the rubber composition is used in a pneumatic tire, it is molded into a predetermined shape by extrusion or the like, combined with other parts to produce a green tire, and then the green tire is vulcanized at, for example, 130 to 190°C. This makes it possible to manufacture a pneumatic tire in which the vulcanized rubber of the above rubber composition is incorporated into the rubber part. [Examples]

[0041] The following are examples of the present invention, but the present invention is not limited to these examples.

[0042] [Preparation of recycled rubber] 1. Preparation of vulcanized products 1 and 2 Using a Banbury mixer, rubber compositions were prepared according to the formulations (parts by mass) shown in Table 1 below. Specifically, first, compounding agents excluding sulfur and vulcanization accelerator were added to the rubber polymer and kneaded. Then, sulfur and vulcanization accelerator were added to the resulting mixture and kneaded to prepare the rubber composition. Subsequently, the obtained rubber compositions were vulcanized at 160°C for 20 minutes to obtain vulcanized product 1 and vulcanized product 2.

[0043] [Table 1]

[0044] The components in Table 1 are as follows: • SBR-1: Unmodified ESBR, manufactured by ENEOS Material Co., Ltd. as "SBR1502" • SBR-2: Terminally modified SSBR, manufactured by ENEOS Material Co., Ltd., "HPR350" • SBR-3: Terminally modified SSBR, "HPR355" manufactured by ENEOS Material Co., Ltd. • SBR-4: Unmodified SSBR, manufactured by Asahi Kasei Corporation as "Toughden 1834" (37.5 phr oil-expandable rubber) • NR: RSS#3

[0045] • Carbon Black N339: "Diamond Black N339" manufactured by Mitsubishi Chemical Corporation. • Carbon Black ISAF: "Seast 6" manufactured by Tokai Carbon Co., Ltd. • Silica: "TOKUSIL USG-A" manufactured by OSC SIAMSILICA CO.,LTD. • Silane coupling agent: "Si75" manufactured by Evonik Japan Co., Ltd. • Process oil: ENEOS Corporation's "Process NC-140" • Stearic acid: "Stearic acid N-50" manufactured by NOF Corporation • Zinc oxide: "Zinc Oxide Type 2" manufactured by Mitsui Mining & Smelting Co., Ltd. • Vulcanization accelerator A: "Sokucinol DG" manufactured by Sumitomo Chemical Co., Ltd. • Vulcanization accelerator B: "Noxellar CZ-G" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. • Sulfur: "Oil-treated 150-mesh powdered sulfur" manufactured by Tsurumi Chemical Industries Co., Ltd.

[0046] 2. Preparation of powdered rubber 1 and 2 Using a Fritsch Japan Co., Ltd. Universal Cutting Mill P-19 as a coarse grinder, vulcanized material 1 and vulcanized material 2 were coarsely ground to approximately 2-3 mm squares. The coarsely ground powders were then ground to 30 mesh or less using a cryogenic grinder to obtain powdered rubber 1 and powdered rubber 2. A Varder Scientific Co., Ltd. CryoMill 100-240V 50 / 60Hz was used as the cryogenic grinder.

[0047] 3. Preparation of recycled rubber 1 To 100 parts by mass of powdered rubber 1, 5 parts by mass of process oil (Process NC-140, manufactured by ENEOS Corporation), 1 part by mass of diphenyl disulfide, and 10 parts by mass of coumaron resin (PS-65, manufactured by Nippon Paint Co., Ltd.) were added and mixed. The resulting mixture was placed in a 300cc autoclave and desulfurized under a steam atmosphere at a temperature of approximately 200°C and a pressure of 1.67 MPa for 3 hours. After the desulfurization reaction, the mixture was rolled into a sheet using a roller to obtain recycled rubber 1.

[0048] 4. Preparation of recycled rubber 2 Recycled rubber 2 was obtained by using powdered rubber 2 instead of powdered rubber 1, and otherwise following the same procedure as for preparing recycled rubber 1.

[0049] 5. Preparation of recycled rubber 3 In the method for preparing recycled rubber 1, the desulfurization time was changed from 3 hours to 6 hours, and the other procedures were the same to obtain recycled rubber 3.

[0050] 6. Preparation of recycled rubber 4 In the method for preparing recycled rubber 1, recycled rubber 4 was obtained by omitting the addition of coumarone resin and otherwise proceeding in the same manner.

[0051] [Analysis of recycled rubber] For recycled rubber samples 1-4 and powdered rubber samples 1-2, the chloroform extract, solubility in toluene (sol fraction), and rubber polymer composition were measured. The measurement method is as follows.

[0052] 1. Chloroform extract Recycled rubber samples 1-4 and powdered rubber samples 1-2 were used as samples, and analysis was performed in accordance with JIS K6226-2:2003 "Rubber - Method for determining the composition of vulcanized and unvulcanized rubber by thermogravimetric analysis (quantitative)".

[0053] In detail, soluble components were extracted using chloroform with an automated Soxhlet extractor (E-800, manufactured by Buch Japan Co., Ltd.). The extraction conditions followed JIS K6229:2015, with a sample of 2 g treated with chloroform as the solvent at 90°C for 8 hours.

[0054] Using a thermogravimetric analyzer (TGA) (METTLER TOLEDO "TGA / DSC 3+" thermal analysis system), 10 mg each of extracted samples (those extracted with chloroform) and unextracted samples were measured under the thermogravimetric analysis conditions shown in Table 2 below. [Table 2]

[0055] As shown in Figure 1, for the unextracted sample, the weight loss after treatment at 700°C under a nitrogen atmosphere was defined as organic content "A" (mass%), the residue after treatment at 700°C under an air atmosphere was defined as ash content "C" (mass%), and the weight loss during treatment at 700°C under an air atmosphere was defined as carbon content "E" (mass%). For the extracted sample, the weight loss after treatment at 700°C under a nitrogen atmosphere was defined as organic content "B" (mass%), and the residue after treatment at 700°C under an air atmosphere was defined as ash content "D" (mass%). The mass of ash content does not change whether or not extraction is performed, but the ratio of ash content differs depending on whether or not extraction is performed. Therefore, the amount of rubber polymer in the unextracted sample is calculated using the difference in the ash content ratio before and after extraction, according to the following formula (1). Equation (1): Amount of rubber polymer (mass%) = B × C / D The chloroform extract (Ext) is calculated using the following formula (2). Equation (2): Chloroform extract (Ext) (mass%) = AB × C / D The amount of carbon black (mass %) is determined as carbon "E" for unextracted samples.

[0056] 2. Amount of solubility in toluene (sol fraction) The mass (P) of each sample was measured using recycled rubber 1-4 and powdered rubber 1-2. Each sample was wrapped in a 120-150 mesh wire mesh, and its mass (Q) was measured. The wire-mesh-wrapped samples were immersed in a flask containing toluene for 24 hours. After immersion, the wire-mesh-wrapped samples were removed, dried using a vacuum dryer, and their mass (T) was measured. The solubility in toluene was calculated using the following formula. Solubility in toluene (sol fraction) = (QT) / P × 100

[0057] 3. Rubber polymer composition Recycled rubber 1-4 and powdered rubber 1-2 were used as samples, and the ratios of styrene, butadiene, and isoprene were determined in accordance with JIS K6231-2:2007 "Rubber - Pyrolysis Gas Chromatography Method". Details are as follows. Acetone extraction was performed as a pretreatment for each sample. Specifically, soluble components were extracted using acetone with an automated Soxhlet extractor (E-800, manufactured by Nippon Buch Co., Ltd.). The extraction conditions followed JIS K6229:2015, with 2g of sample being treated with acetone as the solvent at 90°C for 8 hours.

[0058] A 0.2 mg sample, prepared before processing, was wrapped in pyrofoil and introduced into a pyrolysis gas chromatograph (GC2010Plus, Shimadzu Corporation) to perform pyrolysis and obtain a pyrogram. The conditions for pyrolysis and gas chromatography are as follows. Carrier gas: He Carrier gas flow rate: 25.0 cm / s Column type: Agilent J&W "HP-1" Column size: 0.25 mm × 30 m × 0.25 μm Sample introduction method: Split, 1 / 50 Sample vaporization chamber temperature: 280℃ Column oven temperature (program): 40°C (5 mins) → (increase temperature by 10°C / min) → 200°C → (increase temperature by 20°C / min) → 280°C (5 mins) Detector type: FID Makeup gas type, flow rate: N2, 45 mL / min Hydrogen gas flow rate: 40 mL / min Airflow rate: 450 mL / min

[0059] The peak areas of styrene (ST), butadiene (BD), isoprene (IP), butadiene dimer (4VCH), and isoprene dimer (DP) in the obtained pyrogram were determined, and the ratios (%) of the peak areas of ST, BD, and IP to the total peak area were calculated as the amounts of styrene, butadiene, and isoprene, respectively, using the following formula. Styrene content (%) = (Styrofoam peak area / Total peak area) × 100 Butadiene content (%) = (Peak area of ​​BD / Total peak area) × 100 Isoprene content (%) = (Peak area of ​​IP / Total peak area) × 100

[0060] The results are shown in Table 3 below. Powdered rubbers 1 and 2 were simply vulcanized rubber that had been crushed and not recycled, resulting in low solubility in toluene and a low sol fraction. Recycled rubber 4 was recycled without the addition of coumarone resin, a thermoplastic resin, and the amount of chloroform extract was less than the specified amount. Furthermore, due to the regeneration process, the gelation of SBR in recycled rubber 4 progressed and hardened, resulting in insufficient tackiness, poor cohesiveness, and a low sol fraction. In contrast, recycled rubbers 1 and 2, which were recycled with the addition of a thermoplastic resin along with oil and a desulfurizer, had chloroform extract within the specified range, and the use of a thermoplastic resin suppressed the gelation of SBR, resulting in a high sol fraction and improved tackiness. On the other hand, recycled rubber 3 was recycled with the addition of a thermoplastic resin, but the desulfurization time was too long, causing the gelation of SBR to progress and resulting in a sol fraction lower than the specified amount.

[0061] [Table 3]

[0062] [Preparation of rubber composition] Using the recycled rubbers 1-4 and powdered rubbers 1-2 described above, rubber compositions for Examples 1-8 and Comparative Examples 1-16 were prepared according to the formulations (parts by mass) shown in Tables 4 and 5 below. Specifically, first, compounding agents excluding sulfur and vulcanization accelerators were added to the unvulcanized rubber components and kneaded. Then, sulfur and vulcanization accelerators were added to the resulting mixture and kneaded to prepare the rubber composition.

[0063] The components in Tables 4 and 5 are as follows: • SBR: Unmodified ESBR, manufactured by ENEOS Material Co., Ltd., "SBR1502" • NR: RSS#3 • Silica: "TOKUSIL USG-A" manufactured by OSC SIAM SILICA CO.,LTD. • Silane coupling agent: "Si75" manufactured by Evonik Japan Co., Ltd. • Carbon Black: Mitsubishi Chemical Corporation's "Dia Black N339" • Oil: Process NC-140 manufactured by ENEOS Corporation • Zinc oxide: "Zinc Oxide Type 2" manufactured by Mitsui Mining & Smelting Co., Ltd. • Stearic acid: "Stearic acid N-50" manufactured by NOF Corporation • Anti-aging agent: "Nocrac 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. • Sulfur: "Oil-treated 150-mesh powdered sulfur" manufactured by Tsurumi Chemical Industries Co., Ltd. • Vulcanization accelerator A: "Sokucinol DG" manufactured by Sumitomo Chemical Co., Ltd. • Vulcanization accelerator B: "Noxellar CZ-G" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0064] The breaking strength and elongation at break were measured for test specimens obtained by vulcanizing each rubber composition at 170°C for 15 minutes. Specifically, in accordance with JIS K6251:2017, dumbbell-shaped test specimens (Type 3) were prepared, and tensile tests were performed at a tensile speed of 500 mm / min to measure the tensile strength (breaking strength) and elongation at break (breaking elongation). In Table 4, the values ​​of the examples and comparative examples are shown as indices, with the value of Comparative Example 1 set to 100. In Table 5, the values ​​of the examples and comparative examples are shown as indices, with the value of Comparative Example 9 set to 100. A larger index indicates greater breaking strength and elongation at break.

[0065] [Table 4]

[0066] [Table 5]

[0067] The results are shown in Tables 4 and 5. Table 4 shows examples where the unvulcanized rubber component is SBR alone. Comparative Examples 5 to 8 contained powdered rubber 1 and 2 that had not been recycled, resulting in inferior tensile strength and elongation at break. Comparative Examples 3 and 4 contained recycled rubber 4 that had been recycled using oil and a decomposing agent. Because recycled rubber 4 was poorly formed due to the progression of gelation, it had poor compatibility with the unvulcanized rubber component, and there was almost no improvement in tensile strength and elongation at break compared to Comparative Examples 5 to 8. In contrast, in Examples 1 to 4, which contained recycled rubber 1 and 2 that had been recycled using a thermoplastic resin along with oil and a decomposing agent, the gelation of recycled rubber 1 and 2 was suppressed and tackiness was imparted, resulting in good compatibility with the unvulcanized rubber component, and a significant improvement in tensile strength and elongation at break compared to Comparative Examples 5 to 8. Comparative Examples 1 and 2, which incorporated recycled rubber 3 with a low sol fraction despite the chloroform extract being within the specified range, did not necessarily show sufficient improvement in tensile strength and elongation compared to Comparative Examples 5-8.

[0068] Table 5 shows examples in which SBR and NR were used in combination as unvulcanized rubber components. Examples 5-8, which incorporated recycled rubber 1 and 2, showed significant improvements in breaking strength and elongation compared to Comparative Examples 9-16, which incorporated recycled rubber 3 and 4 and powdered rubber 1 and 2.

[0069] Furthermore, the various numerical ranges described in this specification can be any combination of their upper and lower limits, and all such combinations are described herein as preferred numerical ranges. Also, the description of a numerical range as "X~Y" means X or greater and Y or less.

Claims

1. The mixture contains 0.1 to 30 parts by mass of recycled rubber containing styrene-butadiene rubber per 100 parts by mass of unvulcanized rubber. The recycled rubber has a chloroform extract content of 15 to 30% by mass obtained by Soxhlet extraction, and the chloroform extract contains oil and thermoplastic resin, and its solubility in toluene is 25% by mass or more. Rubber composition.

2. The rubber composition according to claim 1, wherein the amount of styrene in the rubber polymer contained in the recycled rubber is 10 to 60% as a peak area ratio measured by pyrolysis gas chromatography in accordance with JIS K6231-2:2007.

3. The rubber composition according to claim 1, further comprising 20 to 150 parts by mass of a reinforcing filler per 100 parts by mass of the unvulcanized rubber component.

4. A tire comprising vulcanized rubber obtained by vulcanizing the rubber composition according to any one of claims 1 to 3.

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