Method for producing olefinic thermoplastic elastomer

Abstract

This method for producing an olefinic thermoplastic elastomer comprises a recovery step, a first mixing step, and a solvent removal step. The recovery step is a step for carrying out a solid-liquid separation process while mixing a recycled raw material containing an olefinic resin with a solvent that dissolves olefinic resins, to obtain a resin solution containing the recycled raw material and the solvent. The first mixing step is a step for obtaining a resin-rubber mixed solution by mixing a rubber component with an adjusted resin solution provided by carrying out an adjustment that lowers the solvent concentration of the resin solution obtained by the recovery step. The solvent removal step is a step for obtaining a solid product of the olefinic thermoplastic elastomer by removing the solvent from the resin-rubber mixed solution obtained by the first mixing step.

Description

Method for producing olefin-based thermoplastic elastomer

[0001] The present disclosure relates to a method for producing an olefin-based thermoplastic elastomer.

[0002] Patent Document 1 discloses a method for producing a rubber composition by kneading an olefin-based copolymer rubber and an olefin-based resin using a twin-screw extruder. In the production method of Patent Document 1, the olefin-based copolymer rubber and the olefin-based resin are mixed in the twin-screw extruder to finely disperse the olefin-based resin that is difficult to finely disperse. Specifically, the olefin-based copolymer rubber, which is mixed with 10% by mass or less of an organic solvent and is in a molten state, is introduced into the twin-screw extruder. The olefin-based resin is introduced into the twin-screw extruder in a molten state from a supply unit provided separately from the supply unit into which the rubber mixture is introduced. Then, the olefin-based copolymer rubber and the olefin-based resin, both in a molten state, are kneaded in the twin-screw extruder, whereby the olefin-based resin is finely dispersed in the rubber mixture.

[0003] Patent Document 2 discloses a recycling method for recovering polypropylene contained in collected used products and the like. The recycling method of Patent Document 2 includes extracting polypropylene with a solvent, purifying the polypropylene solution obtained by the extraction, and separating polypropylene from the high-purity polypropylene solution obtained by the purification.

[0004] Japanese Patent Application Laid-Open No. 2006-037115, Japanese National Publication of International Patent Application No. 2018-518587

[0005] Consider a case where an olefin-based thermoplastic elastomer is produced by the production method of Patent Document 1 using a recycled material such as polypropylene obtained by the recycling method of Patent Document 2. In this case, in order to enhance the recycling effect, it is required to reduce the input energy required for producing the olefin-based thermoplastic elastomer.

[0006] A method for producing an olefin-based thermoplastic elastomer according to one aspect of the present disclosure includes: a recovery step of obtaining a resin solution containing the recycled raw material and the solvent by mixing a recycled raw material containing an olefin-based resin with a solvent for dissolving the olefin-based resin and performing a solid-liquid separation treatment; a first mixing step of obtaining a resin-rubber mixed solution by mixing an adjusted resin solution, which is obtained by adjusting the solvent concentration of the resin solution obtained in the recovery step, with a rubber component; and a desolventing step of obtaining a solid product of an olefin-based thermoplastic elastomer by removing the solvent from the resin-rubber mixed solution obtained in the first mixing step.

[0007] Figure 1 is an explanatory diagram showing an example of each step in the manufacturing method of the embodiment. Figure 2 is an explanatory diagram showing another example of each step in the manufacturing method of the embodiment.

[0008] The following describes one embodiment (hereinafter sometimes referred to as "the manufacturing method") that embodies the method for producing an olefin-based thermoplastic elastomer according to the present disclosure. The manufacturing method includes a recovery step, a first mixing step, and a desolventing step. The manufacturing method further includes a second mixing step performed before the desolventing step or during the desolventing step.

[0009] (Recovery Process) The recovery process is the process of recovering olefin resin from recycled raw materials. In the recovery process, first, an intermediate treatment liquid is obtained in which the olefin resin is dissolved in the solvent by mixing the recycled raw materials with a solvent that dissolves the olefin resin. The intermediate treatment liquid contains solid components that make up the recycled raw materials but are insoluble in the solvent. Next, a solid-liquid separation treatment is performed on the intermediate treatment liquid to obtain a resin solution from which the solid components have been separated. In the recovery process, the olefin resin is recovered in the form of a resin solution.

[0010] Olefin resins contained in recycled raw materials are resins that can be used as resin components in olefin-based thermoplastic elastomers. Examples of olefin resins include polyethylene resin and polypropylene resin. Examples of polyethylene resin include ethylene homopolymers such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, and linear low-density polyethylene. Examples of polypropylene resin include propylene homopolymer, propylene block copolymer, and propylene random copolymer. Other examples of olefin resins include crystalline ethylene-α-olefin copolymers consisting of ethylene and α-olefins having 3 to 20 carbon atoms, and crystalline homopolymers or copolymers of α-olefins having 3 to 20 carbon atoms such as propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene.

[0011] It is preferable that recycled materials be processed by crushing, crushing, or cutting to a predetermined size in order to improve their solubility in solvents. The original use of recycled materials is not particularly limited. Examples of recycled materials include transportation equipment such as automobile parts, machine parts, building materials, daily necessities, and ELV materials, PCR materials, and PIR materials obtained from them. An example of a recycled material is at least one selected from ELV materials containing polypropylene, PCR materials, and PIR materials.

[0012] The solvent is not particularly limited as long as it dissolves the olefin resin to be recovered. The solvent is appropriately selected depending on the type of olefin resin to be recovered. Examples of solvents include aromatic hydrocarbons such as benzene, toluene, and xylene, aromatic halogenated hydrocarbons such as orthodichlorobenzene, and mixtures thereof.

[0013] In the recovery process, various conditions such as the time required for mixing the recycled material and solvent can be appropriately set according to the type of recycled material and solvent, the physical properties of the resulting resin solution, etc.

[0014] The mixing method for combining recycled materials and solvents is not particularly limited. Examples of such mixing methods include stirring, ultrasonic treatment, and shaking. The mixing ratio when mixing recycled materials and solvents is, for example, 5 parts by mass or more, 10 parts by mass or more, or 15 parts by mass or more of solvent per 1 part by mass of olefin resin in the recycled materials. As the proportion of solvent increases, the olefin resin can be dissolved in a shorter time or under milder conditions. Alternatively, the mixing ratio can be, for example, 35 parts by mass or less, 30 parts by mass or less, or 25 parts by mass or less of solvent per 1 part by mass of olefin resin in the recycled materials. As the proportion of solvent decreases, the time required for subsequent processes including solvent removal can be shortened.

[0015] The first temperature, which is the temperature at which the recycled material and solvent are mixed, is, for example, 80°C or higher, 100°C or higher, or 120°C or higher. As the first temperature increases, the olefin resin can be dissolved in the solvent more efficiently. Alternatively, the first temperature can be, for example, 160°C or lower, 150°C or lower, or 140°C or lower. As the first temperature decreases, the energy input (thermal energy) required for the recovery process can be reduced. Furthermore, in the solid-liquid separation treatment performed on the intermediate treatment liquid after mixing, and in the processes after the recovery process, it is preferable to maintain a temperature of the first temperature or higher in order to suppress the precipitation of the dissolved olefin resin.

[0016] The method of solid-liquid separation is not particularly limited, and known methods for separating solid and liquid components can be applied. An example of a solid-liquid separation method is a filtration method using a column packed with a packing material. Examples of packing materials include silica, Celite, and activated carbon. One type of packing material may be used alone, or two or more types may be used in combination. The packing material is appropriately selected according to the purpose, application, etc. For example, the packing material may have the function of adsorbing and capturing some or all of the unwanted components. Unwanted components refer to components other than olefin resins among the components dissolved in the solvent from the recycled raw material. Unwanted components include additives such as colorants.

[0017] The resin solution obtained by performing a solid-liquid separation treatment on the intermediate treatment liquid contains an olefin resin and a solvent. The first concentration, which is the solvent concentration of the resin solution, is, for example, 80% by mass or more, 90% by mass or more, or 93% by mass or more. The first concentration is, for example, 98% by mass or less, 97% by mass or less, or 96.5% by mass or less.

[0018] As shown in Figure 1, an example of the recovery process is carried out using a recovery device 10 comprising a first mixing tank 11 and a filtration unit 12. Recycled raw material 14 and solvent 15 are introduced into the first mixing tank 11. The recovery device 10 is configured to introduce the recycled raw material 14 via a raw material input pipe 16. The recovery device 10 is configured to introduce the solvent 15 via a solvent input pipe 17. The first mixing tank 11 is equipped with a stirring blade 11a for mixing the recycled raw material 14 and the solvent 15.

[0019] After the recycled material 14 and solvent 15 are mixed, the intermediate processing liquid 18 obtained by dissolving soluble components such as olefin resins in the recycled material 14 into the solvent 15 is transported to the filtration section 12 via the first piping 19.

[0020] The filtration section 12 has a column containing a packing material having a predetermined particle size. As the intermediate processing liquid 18 passes through the filtration section 12, solid components contained in the intermediate processing liquid 18 are removed. Therefore, by passing it through the filtration section 12, a resin solution A is produced from which solid components have been removed from the intermediate processing liquid 18. In addition, depending on the type of packing material, unwanted components contained in the intermediate processing liquid 18 are captured by the packing material and removed as the intermediate processing liquid 18 passes through the filtration section 12.

[0021] (First Mixing Step) The first mixing step is a step of mixing the adjusted resin solution, which is obtained by adjusting the solvent concentration of the resin solution obtained in the recovery step, with the rubber component. In the first mixing step, first, an adjusted resin solution is obtained in which the solvent concentration is reduced by removing a portion of the solvent contained in the resin solution. At this time, it is preferable to reduce the solvent concentration within a range in which the dissolved olefin resin does not precipitate. As a method for removing a portion of the solvent contained in the resin solution, for example, a method of volatilizing the solvent by heating can be mentioned.

[0022] The second concentration, which is the solvent concentration of the prepared resin solution, is, for example, 78% by mass or more, 80% by mass or more, or 83% by mass or more. The second concentration is, for example, 96% by mass or less, 94% by mass or less, 90% by mass or less, or less than 80% by mass. The solvent concentration of the prepared resin solution can be measured using known measuring devices such as a refractometer, light scattering meter, or viscometer.

[0023] Next, a solid rubber component is added to the prepared resin solution, and the resin solution and the rubber component are mixed. This yields a resin-rubber mixture in which the olefin resin is dissolved in the solvent, and the rubber component is dissolved or finely dispersed.

[0024] The rubber component is a rubber that can be applied as a rubber component of an olefin-based thermoplastic elastomer. Examples of rubber components include α-olefin-non-conjugated polyene copolymer rubber and ethylene-α-olefin copolymer. A specific example of α-olefin-non-conjugated polyene copolymer rubber is the rubber disclosed in Patent Document 1.

[0025] In the first mixing step, various conditions such as the time for mixing the adjusted resin solution and the rubber component can be appropriately set according to the type of olefin resin, the type of rubber component, etc. The rubber component to be mixed is, for example, granular or lumpy. As an example, as will be described later, when the solid product to be manufactured is molded into a predetermined shape such as a pellet using a molding apparatus 46, the rubber component is adjusted so that the average particle size (equivalent diameter of projected area circle) of the rubber component observed with an electron microscope in the cross-section of the pellet is 0.1 μm or more and 2 μm or less.

[0026] The mixing method for mixing the adjusted resin solution and the rubber component is not particularly limited. Examples of the above mixing method include stirring, ultrasonic treatment, and shaking. The mixing ratio of the rubber component in the first mixing step is, for example, 5 to 30 parts by mass, 15 to 25 parts by mass, or 5 to 15 parts by mass per 100 parts by mass of the olefin resin component in the adjusted resin solution.

[0027] The second temperature, which is the temperature of the prepared resin solution when mixing the rubber component, may be the same as the first temperature or different from the first temperature. The second temperature may be, for example, 60°C or higher, 90°C or higher, or 120°C or higher. As the second temperature increases, the rubber component can be efficiently finely dispersed in the resin solution. In addition, by raising the second temperature, olefin resin precipitation caused by lowering the solvent concentration can be suppressed. The second temperature may be, for example, 160°C or lower, 150°C or lower, or 140°C or lower. By lowering the second temperature, the energy input (thermal energy) required for the first mixing step can be reduced.

[0028] It is preferable to add the rubber component little by little while stirring the prepared resin solution. For example, the rate at which the rubber component is added to the prepared resin solution is 1 g / second or more and 100 g / second or less. The resin-rubber mixed solution obtained by mixing the prepared resin solution and the rubber component contains an olefin resin, a rubber component, and a solvent. The third concentration, which is the solvent concentration of the resin-rubber mixed solution, is, for example, 75% by mass or more, 79% by mass or more, or 81% by mass or more. The third concentration is, for example, 94% by mass or less, 90% by mass or less, 85% by mass or less, or less than 78% by mass.

[0029] As shown in Figure 1, an example of the first mixing step is carried out using a mixing apparatus 20 equipped with a second mixing tank 21. Resin solution A and rubber component 22 are introduced into the second mixing tank 21. The mixing apparatus 20 is configured to introduce resin solution A via a first pipe 19. The mixing apparatus 20 is configured to introduce rubber component 22 via a rubber component introduction pipe 23.

[0030] The second mixing tank 21 is equipped with a stirring blade 21a, a measuring device 21b, and a heating device 21c. The stirring blade 21a is used to mix the resin solution A and the rubber component 22 in the tank. The measuring device 21b is used to measure the concentration of the resin solution A in the second mixing tank 21. The heating device 21c is used to adjust the concentration of the resin solution A in the second mixing tank 21.

[0031] After a predetermined amount of resin solution A is added to the second mixing tank 21, the resin solution A in the second mixing tank 21 is heated by the heating device 21c to volatilize a portion of the solvent contained in the resin solution A. This yields a modified resin solution with a reduced solvent concentration. Subsequently, rubber component 22 is added to the second mixing tank 21. The modified resin solution and rubber component 22 are mixed in the second mixing tank 21 to produce a resin-rubber mixed solution B.

[0032] (Solvent Removal Process and Second Mixing Process) The solvent removal process is a process of removing the solvent from the resin-rubber mixed solution. By removing the solvent, a solid product of the olefin-based thermoplastic elastomer is obtained. The final concentration, which is the solvent concentration of the solid product, is, for example, 0.1% by mass or less. As a method for removing the solvent from the resin-rubber mixed solution, for example, a method of volatilizing the solvent by heating can be used.

[0033] The second mixing step involves mixing an antioxidant into a resin-rubber mixture solution with an adjusted solvent concentration. The second mixing step may be performed before the solvent removal step or during the solvent removal step.

[0034] [Details of the second mixing step before the solvent removal step] When the second mixing step is performed before the solvent removal step, first, a modified resin-rubber mixed solution is obtained by removing a portion of the solvent contained in the resin-rubber mixed solution obtained in the first mixing step, thereby reducing the solvent concentration. At this time, it is preferable to reduce the solvent concentration within a range in which the dissolved olefin resin and rubber components do not precipitate. As a method for removing a portion of the solvent contained in the resin-rubber mixed solution, for example, a method of volatilizing the solvent by heating can be used.

[0035] The fourth concentration, which is the solvent concentration of the adjusted resin-rubber mixed solution, is, for example, 33% by mass or more, 38% by mass or more, or 40% by mass or more. The fourth concentration is, for example, 84% by mass or less, 82% by mass or less, 79% by mass or less, or less than 75% by mass. The solvent concentration of the adjusted resin-rubber mixed solution can be measured using known measuring devices such as a refractometer, light scattering meter, or viscometer.

[0036] Next, an antioxidant is added to the prepared resin-rubber mixture, and the prepared resin-rubber mixture and the antioxidant are mixed. Examples of antioxidants include phosphite-based antioxidants and phenol-based antioxidants. An example of a phosphite-based antioxidant is tris(2,4-di-t-butylphenyl) phosphite (Irgafos168, manufactured by SF Japan). An example of a phenol-based antioxidant is pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (RIANOX1010, manufactured by Rianlon).

[0037] Here, antioxidants are prone to deterioration in the presence of solvents. In particular, combinations of antioxidants and solvents that are prone to deterioration include, for example, the combination of xylene and Irgafos 168, and the combination of xylene and RIANOX 1010.

[0038] In the second mixing step, the solvent concentration of the resin-rubber mixture is reduced before adding the antioxidant in order to suppress deterioration of the antioxidant. More specifically, by reducing the solvent concentration of the resin-rubber mixture before adding the antioxidant, the solvent can be removed in a shorter time during the subsequent desolventing step. This shortens the time from when the antioxidant is added until the solvent is removed, i.e., the time during which the antioxidant and solvent coexist. As a result, deterioration of the antioxidant caused by the coexistence of the solvent can be suppressed. On the other hand, in order to uniformly mix the antioxidant, it is preferable to mix it in solution, that is, to maintain a solvent concentration above a certain level.

[0039] In the second mixing step, various conditions such as the time for mixing the adjusted resin-rubber mixture solution with the antioxidant can be appropriately set according to the type of olefin resin, the type of rubber component, the type of antioxidant, etc.

[0040] The mixing method for mixing the adjusted resin-rubber mixture solution with the antioxidant is not particularly limited. Examples of the above mixing method include stirring, ultrasonic treatment, and shaking. The mixing ratio of the antioxidant in the second mixing step is, for example, 0.01 parts by mass to 2 parts by mass, 0.05 parts by mass to 0.15 parts by mass, or 0.5 parts by mass to 1 part by mass per 100 parts by mass of the olefin resin in the adjusted resin-rubber mixture solution.

[0041] The third temperature, which is the temperature of the adjusted resin-rubber mixture solution when mixing in the antioxidant, may be the same as or different from either the first and second temperatures, or both. The third temperature may be, for example, 40°C or higher, 60°C or higher, or 80°C or higher. Raising the third temperature can suppress the precipitation of olefin resin and rubber components caused by lowering the solvent concentration. The third temperature may be, for example, 120°C or lower, 100°C or lower, or 80°C or lower. Lowering the third temperature can reduce the energy input (thermal energy) required for the second mixing step.

[0042] As shown in Figure 1, an example of the second mixing step and the solvent removal step is carried out using the mixing apparatus 20 used in the first mixing step. The mixing apparatus 20 is configured to introduce the antioxidant 31 via the additive introduction pipe 30.

[0043] After the first mixing step, the second mixing tank 21 accommodates the resin-rubber mixed solution B generated in the first mixing step. After the first mixing step, the resin-rubber mixed solution B in the second mixing tank 21 is heated by a heating device 21c to volatilize part of the solvent contained in the resin-rubber mixed solution B. In this way, an adjusted resin-rubber mixed solution whose concentration is adjusted to reduce the solvent concentration is obtained. Thereafter, an antioxidant 31 is charged into the second mixing tank 21. Then, in the second mixing tank 21, the antioxidant 31 is mixed with the adjusted resin-rubber mixed solution. This completes the second mixing step.

[0044] Next, the adjusted resin-rubber mixed solution mixed with the antioxidant 31 in the second mixing tank 21 is heated by the heating device 21c to volatilize the remaining solvent contained in the adjusted resin-rubber mixed solution. In this way, a solid product of an olefin-based thermoplastic elastomer is obtained.

[0045] [Details of the case where the second mixing step is performed in the middle of the solvent removal step] When the second mixing step is performed in the middle of the solvent removal step, the solvent removal step is performed to remove the solvent from the resin-rubber mixed solution while stirring or kneading the resin-rubber mixed solution. In the solvent removal step, the solvent concentration of the resin-rubber mixed solution gradually decreases from a third concentration to a final concentration. At the timing when the solvent concentration of the resin-rubber mixed solution in the middle of the solvent removal step has decreased to a fourth concentration, an antioxidant is added to the resin-rubber mixed solution, and the solvent removal step is continued.

[0046] As shown in FIG. 2, an example of the second mixing step and the solvent removal step is carried out using an extruder 40. The configuration of the recovery device 10 shown in FIG. 2 is the same as that of the recovery device 10 shown in FIG. 1. The configuration of the mixing device 20 shown in FIG. 2 is the same as that of the mixing device 20 shown in FIG. 1 except that the antioxidant 31 and the pipe 30 for adding additives are omitted.

[0047] The extruder 40 is a vented extruder having a supply port, a discharge port, and a vent. A specific configuration of the extruder is not particularly limited, and for example, it may be a single-screw type or a twin-screw type.

[0048] The extruder 40 includes a first supply port 41 located at an upstream end portion, and a discharge port 42 located at a downstream end portion. The extruder 40 further includes a second supply port 43 and a plurality of vents 44 disposed between the first supply port 41 and the discharge port 42. The vents 44 are provided at both a position upstream of the second supply port 43 and a position downstream of the second supply port 43. The first supply port 41 of the extruder 40 is connected to the second mixing tank 21 via a second pipe 45. A molding device 46 such as a pelletizer for molding the solid product discharged from the discharge port 42 is attached to the discharge port 42 of the extruder 40.

[0049] The resin-rubber mixed solution B in the second mixing tank 21 is supplied to the first supply port 41 of the extruder 40 via the second pipe 45. At this time, if necessary, the solvent concentration of the resin-rubber mixed solution B supplied to the first supply port 41 may be adjusted. The solvent concentration of the resin-rubber mixed solution B supplied to the first supply port 41 is, for example, 50% by mass or more and 80% by mass or less.

[0050] The resin-rubber mixed solution B supplied to the first supply port 41 is conveyed to the discharge port 42 while being kneaded. The solvent contained in the resin-rubber mixed solution B is discharged from the vents 44 at a plurality of locations on the way when the resin-rubber mixed solution B is conveyed to the discharge port 42. Therefore, each time the resin-rubber mixed solution B passes through the vents 44 on the way of being conveyed to the discharge port 42, the solvent concentration gradually decreases. The arrangement of the second supply port 43 and the vents 44 is adjusted such that the solvent concentration of the resin-rubber mixed solution B reaches the fourth concentration at the timing when the solution passes through the second supply port 43.

[0051] The antioxidant is supplied from the second supply port 43 to the resin-rubber mixed solution B that is being conveyed. The resin-rubber mixed solution B is conveyed to the discharge port 42 on the downstream side of the second supply port 43 while being kneaded with the antioxidant. Then, a solid product of the olefin-based thermoplastic elastomer is discharged from the discharge port 42. The solid product discharged from the discharge port 42 is molded into a predetermined shape such as a pellet by the molding device 46.

[0052] (Function and Effects) The function and effects of this embodiment will be described below. (1) The method for producing an olefin-based thermoplastic elastomer includes a recovery step, a first mixing step, and a desolventing step. The recovery step is a step of obtaining a resin solution containing recycled raw materials and a solvent by mixing recycled raw materials containing an olefin-based resin with a solvent that dissolves the olefin-based resin and performing a solid-liquid separation treatment. The first mixing step is a step of obtaining a resin-rubber mixed solution by mixing an adjusted resin solution, which is adjusted to reduce the solvent concentration of the resin solution obtained in the recovery step, with a rubber component. The desolventing step is a step of obtaining a solid product of an olefin-based thermoplastic elastomer by removing the solvent from the resin-rubber mixed solution obtained in the first mixing step.

[0053] In the manufacturing method described in Patent Document 1, a solid product of an olefin-based thermoplastic elastomer is obtained by kneading a molten olefin-based resin with a molten rubber component. In this case, a large amount of energy is invested in the kneading process to finely disperse the rubber component in the olefin-based resin, or to finely disperse the olefin-based resin in the rubber component.

[0054] In contrast, in the present manufacturing method having the above configuration, the rubber component is mixed with the olefin resin in a solution state. After mixing the rubber component, the solvent is removed to obtain a solid product of the olefin thermoplastic elastomer. By mixing in a solution state, it is possible to finely disperse the rubber component in the olefin resin, or finely disperse the olefin resin in the rubber component, with less input energy (e.g., shear energy) compared to the conventional method of mixing in a molten state. In addition, the resin solution produced when olefin resin is recovered from recycled raw materials is used as the olefin resin. In this case, there is no need to add a solvent in order to mix the olefin resin and the rubber component in a solution state. Since the step of removing the solvent is a step with a large input energy (e.g., thermal energy), not needing to add a solvent just to mix in a solution state greatly contributes to reducing the input energy required for the manufacture of the olefin thermoplastic elastomer.

[0055] (2) The first concentration, which is the solvent concentration of the resin solution, is 80% by mass or more and 98% by mass or less. The second concentration, which is the solvent concentration of the prepared resin solution, is 78% by mass or more and 96% by mass or less. With the above configuration, the effect of (1) above can be obtained more significantly.

[0056] (3) A method for producing an olefin-based thermoplastic elastomer further includes a second mixing step of mixing an adjusted resin-rubber mixed solution, which is obtained by adjusting the solvent concentration of the resin-rubber mixed solution obtained in the first mixing step, with an antioxidant. The second mixing step is performed before the desolventing step or in the middle of the desolventing step.

[0057] According to the above configuration, by reducing the solvent concentration of the resin-rubber mixture before adding the antioxidant, the solvent can be removed in a shorter time during the subsequent desolventing process. This reduces the time that the antioxidant and solvent coexist. As a result, deterioration of the antioxidant caused by the coexistence of solvent can be suppressed. Furthermore, since the antioxidant is added to a solution, it can be mixed uniformly in a shorter time compared to when the antioxidant is added to molten olefin resin and molten rubber components. Reducing the time required to uniformly mix the antioxidant also contributes to reducing the energy input.

[0058] (4) The third concentration, which is the solvent concentration of the resin-rubber mixed solution, is 75% by mass or more and 94% by mass or less. The fourth concentration, which is the solvent concentration of the adjusted resin-rubber mixed solution, is 33% by mass or more and 84% by mass or less. With the above configuration, the effect of (3) above can be obtained more significantly.

[0059] (5) The second mixing step is performed in the middle of the desolventing step. The second mixing step and the desolventing step are performed using an extruder 40 equipped with a first supply port 41 to which a resin-rubber mixed solution is supplied, a second supply port 43 to which an antioxidant is supplied, and a plurality of vents 44 arranged on the upstream and downstream sides of the second supply port 43.

[0060] By using the extruder 40 with the above configuration, the solvent removal process in the desolventing step and the mixing of the antioxidant in the second mixing step can be performed simultaneously. Therefore, the time required for the desolventing step and the second mixing step can be shortened.

[0061] (Example of modification) The above embodiment can be implemented with the following modifications. The above embodiment and the following examples of modifications can be combined with each other to the extent that they do not contradict each other technically.

[0062] - In the first mixing step, the rubber component may be added in the form of a mixture containing a solvent. - Other additives other than antioxidants may be added. Examples of other additives include vulcanizing agents, colorants, and stabilizers. The timing of adding other additives is not particularly limited. For example, they may be added in the first mixing step, in the second mixing step, or at any other time. As an example, in the second mixing step, a vulcanizing agent may be added simultaneously with or separately from the antioxidant.

[0063] - In the second mixing step, the antioxidant may be added directly to the resin-rubber mixture without performing a process to reduce the solvent concentration of the resin-rubber mixture. - The timing of adding the antioxidant may be changed. For example, the antioxidant may be added when mixing the recycled material 14 and the solvent 15 in the recovery step, or the antioxidant may be added when mixing the rubber component in the first mixing step. In these cases, the second mixing step is omitted. Furthermore, the addition of the antioxidant itself may be omitted.

Claims

1. A method for producing an olefin-based thermoplastic elastomer, comprising: a recovery step of obtaining a resin solution containing the recycled raw material and the solvent by mixing recycled raw material containing an olefin-based resin with a solvent for dissolving the olefin-based resin and performing a solid-liquid separation treatment; a first mixing step of obtaining a resin-rubber mixed solution by mixing an adjusted resin solution, which is obtained by adjusting the solvent concentration of the resin solution obtained in the recovery step, with a rubber component; and a desolventing step of obtaining a solid product of an olefin-based thermoplastic elastomer by removing the solvent from the resin-rubber mixed solution obtained in the first mixing step.

2. The method for producing an olefin-based thermoplastic elastomer according to claim 1, wherein the first concentration, which is the solvent concentration of the resin solution, is 80% by mass or more and 98% by mass or less, and the second concentration, which is the solvent concentration of the adjusted resin solution, is 78% by mass or more and 96% by mass or less.

3. A method for producing an olefin-based thermoplastic elastomer according to claim 1 or 2, further comprising a second mixing step of mixing an adjusted resin-rubber mixed solution, which is obtained by adjusting the solvent concentration of the resin-rubber mixed solution obtained by the first mixing step to reduce the solvent concentration of the resin-rubber mixed solution, with an antioxidant, wherein the second mixing step is performed before the desolventing step or in the middle of the desolventing step.

4. The method for producing an olefin-based thermoplastic elastomer according to claim 3, wherein the third concentration, which is the solvent concentration of the resin-rubber mixed solution, is 75% by mass or more and 94% by mass or less, and the fourth concentration, which is the solvent concentration of the adjusted resin-rubber mixed solution, is 33% by mass or more and 84% by mass or less.

5. The method for producing an olefin-based thermoplastic elastomer according to claim 3 or 4, wherein the second mixing step is performed in the middle of the desolventing step, and the second mixing step and the desolventing step are performed using an extruder equipped with a first supply port for supplying the resin-rubber mixed solution, a second supply port for supplying the antioxidant, and a plurality of vents arranged upstream and downstream of the second supply port.

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