Method for recycling fiber-reinforced composite material and method for producing fiber-reinforced composite material

Abstract

This method for recycling a fiber-reinforced composite material that contains a resin and reinforcing fibers comprises a step for obtaining a process solution (18) by mixing a recycling feedstock (14) which comprises the fiber-reinforced composite material and a solvent (15) in which the resin is to be dissolved, a fiber separation step for separating reinforcing fibers (18a) from the process solution (18) in a state where the resin and the solvent are attached to the reinforcing fibers (18a), and a drying step for obtaining recycled fibers to which the resin is attached, by drying the reinforcing fibers (18a) to which the resin and the solvent are attached.

Description

Method for recycling fiber-reinforced composite material and method for producing fiber-reinforced composite material

[0001] The present disclosure relates to a method for recycling a fiber-reinforced composite material and a method for producing a fiber-reinforced composite material.

[0002] Patent Document 1 discloses a method for recycling thermoplastic resin products containing a non-combustible substance such as glass fiber. Specifically, it discloses a method for recycling thermoplastic resin products in which, after separating and recovering 30% by weight or more of a thermoplastic resin component, the thermoplastic resin component adhering to the non-combustible substance is burned off to recover the non-combustible substance. Patent Document 2 discloses a curable composite material including reinforcing fibers whose surfaces are coated with a silane coupling agent, and a cured resin.

[0003] Japanese Unexamined Patent Application Publication No. 2000-37726 Japanese Patent No. 4129732

[0004] Incidentally, fibers taken out by a recycling method may be reused as a raw material for fiber-reinforced composite materials and the like. However, for fibers taken out by a recycling method such as burning off the thermoplastic resin component, the silane coupling agent applied by the coating treatment is also removed by combustion. Therefore, when the fibers obtained by the above recycling method are reapplied to a fiber-reinforced composite material, it is necessary to perform a coating treatment such as applying a silane coupling agent on the surface. That is, when the taken-out fibers are reused, their usability is inferior.

[0005] A method for recycling a fiber-reinforced composite material according to one aspect of the present disclosure is a method for recycling a fiber-reinforced composite material containing a resin and reinforcing fibers, the method comprising: a step of obtaining a treatment liquid by mixing a recycled raw material made of the fiber-reinforced composite material and a solvent that dissolves the resin; a fiber separation step of separating the reinforcing fibers from the treatment liquid in a state where the resin and the solvent adhere to the reinforcing fibers; and a drying step of drying the reinforcing fibers with the resin and the solvent adhering thereto, thereby obtaining recycled fibers that are the reinforcing fibers with the resin adhering thereto.

[0006] A method for manufacturing a fiber-reinforced composite material according to one aspect of the present disclosure comprises manufacturing a fiber-reinforced composite material using recycled fibers obtained from recycled raw materials by the above-mentioned fiber-reinforced composite material recycling method.

[0007] Figure 1 shows a schematic diagram of a recycling apparatus for implementing the fiber-reinforced composite material recycling method of the first embodiment. Figure 2 shows a schematic diagram of the first filtration section in the second state of the recycling apparatus for implementing the fiber-reinforced composite material recycling method of the first embodiment.

[0008] Hereinafter, with reference to Figures 1 and 2, an embodiment of the recycling method for fiber-reinforced composite materials according to this disclosure (hereinafter referred to as the "recycling method") will be described. As shown in Figure 1, the recycling method of this embodiment is carried out using a recycling device 10 comprising a mixing tank 11, a first filtration section 12, and a second filtration section 13.

[0009] (Mixing Tank 11) The mixing tank 11 is filled with recycled material 14 and a solvent 15 that dissolves the resin in the recycled material 14. The recycled material 14 is introduced via a recycled material input pipe 16. The solvent 15 is introduced via a solvent input pipe 17. The mixing tank 11 is equipped with a stirring blade 11a for mixing the recycled material 14 and the solvent 15. After the recycled material 14 and the solvent 15 are mixed, the first processed liquid 18 obtained by dissolving the resin in the recycled material 14 in the solvent 15 is transported to the first filtration section 12 via a pipe 19. The pipe 19 is provided with a stopcock (not shown) near the connection point with the mixing tank 11.

[0010] (First Filtration Section 12) The first filtration section 12 comprises a cylindrical frame 12a and a filter 12b attached to a slit portion cut out in the axial direction on the outer surface of the frame 12a. The frame 12a is housed inside the pipe 19 such that its axis is perpendicular to the linear filtration flow direction X of the pipe 19, and is also installed so as to be able to rotate about the axis. In the first filtration section 12, the inner surface of the pipe 19 is molded so as to be able to contact and slide with the outer surface of the frame 12a. A branch pipe 20 is attached that branches off in a direction substantially perpendicular to the filtration flow direction X of the pipe 19.

[0011] As shown in Figure 1, when the frame 12a is in the first state, the first filtration section 12 has a main passage formed by the filtration fluid flow direction X, in which the fluid flows linearly from the upstream side of the piping 19 to the second filtration section 13.

[0012] As shown in Figure 2, when the frame 12a is in the second state, the first filtration section 12 forms a branch passage in the branch fluid flow direction Y, where the fluid flows from the upstream side of the piping 19 from the main passage to the branch pipe 20.

[0013] The lower limit of the mesh opening of filter 12b is not particularly limited, but is preferably 10 μm or more, more preferably 50 μm or more. When the lower limit of the mesh opening is 10 μm or more, relatively long reinforcing fibers can be selected and captured from among the reinforcing fibers contained in the recycled material 14. The upper limit of the mesh opening of filter 12b is not particularly limited, but is 500 μm or less, preferably 300 μm or less. When the upper limit of the mesh opening is 500 μm or less, longer reinforcing fibers can be selected and recovered from among the reinforcing fibers contained in the recycled material 14. Also, when the upper limit of the mesh opening is 500 μm or less, reinforcing fibers in the range of high reusability can be efficiently recovered from among the reinforcing fibers contained in the recycled material 14. The mesh opening of the filter indicates the dimension of the gap in the mesh, and can be determined by the mesh, that is, the number of wires per inch (25.4 mm), and the wire diameter, by (25.4 mm / mesh) - wire diameter ( mm). The material of the filter 12b is not particularly limited, but metal, glass, etc. are preferably used from the viewpoint of strength, chemical resistance, etc.

[0014] When the frame 12a is in the first state, the first processing liquid 18 passes through the filter 12b located on the main passage, and then long reinforcing fibers 18a with a fiber length greater than or equal to the mesh opening of the filter 12b are captured on the surface of the filter 12b. As a result, the second processing liquid 21, which contains short reinforcing fibers that were not filtered by the filter 12b and the solvent 15, is passed through from the back surface of the filter 12b.

[0015] The frame 12a has a first liquid passage hole 12c formed on its circumferential surface opposite to the filter 12b. The second treatment liquid 21 flows out of the frame 12a through the first liquid passage hole 12c and then flows toward the second filtration section 13 located downstream of the piping 19. In the first state, since the frame 12a does not have a liquid passage hole on the branch pipe 20 side, the second treatment liquid 21 does not flow into the branch pipe 20.

[0016] The flow path formed in the first filtration section 12 is formed by a frame 12a and comprises a main passage in which a filter 12b is arranged, and a branch passage provided branching off from the main passage. The flow path formed in the first filtration section 12 further includes a switching mechanism that switches between a first state in which the second processed liquid 21 supplied by passing through the filter 12b does not flow into the branch passage, and a second state in which fluid flows into the branch passage.

[0017] (Switching Mechanism) As shown in Figures 1 and 2, the frame 12a is rotated 90 degrees clockwise around its axis in the direction of arrow A1 by the switching mechanism, thereby switching from a first state in which the processed liquid is directed toward the second filtration section 13 to a second state in which it is directed toward the branch pipe 20.

[0018] In the second state, the frame 12a has a second fluid passage hole 12d formed on its circumferential surface that contacts the upstream interior of the pipe 19. The fluid flowing into the frame 12a from the second fluid passage hole 12d on the upstream side of the pipe 19 is configured to pass through the filter 12b and then the branch pipe 20 in sequence. In the second state, the frame 12a is in a position where there are no fluid passage holes in the direction of the second filtration section 13, so no fluid passes in the direction of the second filtration section 13. In the first state, the fluid passed from the front side to the back side of the filter 12b, but in the second state, the fluid passes in the opposite direction, from the back side to the front side of the filter 12b.

[0019] (Second Filtration Section 13) A second filtration section 13 is provided in the piping 19 downstream of the first filtration section 12. In the second filtration section 13, a packing material 13a having a predetermined particle size is held in a column 13b which serves as a packing section.

[0020] As the second processing liquid 21 passes through the second filtration section 13, short fibers 21a, which are reinforcing fibers with short fiber lengths, are captured by a filtration action that separates the solid and liquid components of the filler 13a. The lower limit of the average particle diameter of the filler 13a is set as appropriate, but is preferably 0.25 μm or more, more preferably 0.50 μm or more. When the lower limit of the average particle diameter is 0.25 μm or more, short reinforcing fibers with short fiber lengths that were not filtered in the first filtration section 12 can be efficiently recovered while ensuring liquid permeability. The upper limit of the average particle diameter of the filler 13a is set as appropriate, but is preferably 100 μm or less, more preferably 80 μm or less. When the upper limit of the average particle diameter is 100 μm or less, short reinforcing fibers with short fiber lengths can be efficiently recovered. The average particle diameter of the filler 13a is the value (D50) measured by the laser diffraction / scattering method.

[0021] Specific examples of the filler 13a include silica, Celite, activated carbon, etc. These are selected as appropriate depending on the purpose and application. Furthermore, one type may be used alone, or two or more types may be used in combination. Additives such as colorants derived from recycled raw materials 14 dispersed in the second processing liquid 21 are captured by the adsorption action of the filler 13a. After the second processing liquid 21 passes through the second filtration section 13, a third processing liquid 22 containing solvent 15 and resin components derived from recycled raw materials 14 is generated. The third processing liquid 22 is recovered in a recovery device (not shown) located downstream of the piping 19.

[0022] (Recycling Method) The recycling method using the above-described recycling apparatus 10 first involves preparing a first processing liquid 18 by mixing the recycled raw material 14 with a solvent 15 for dissolving the resin. Next, a fiber separation process is performed in which the long fibers 18a with the resin and solvent 15 attached are separated by passing the first processing liquid 18 through a filter 12b. Next, a drying process is performed in which the long fibers 18a with the resin and solvent 15 attached are dried to obtain recycled fibers, which are long fibers 18a with the resin attached. Furthermore, a resin separation process is performed in which the solid components and liquid components contained in the second processing liquid 21 that has passed through the filter 12b are separated to recover a third processing liquid 22 containing resin derived from the recycled raw material 14.

[0023] (Process for preparing the processing solution) The process for preparing the first processing solution 18 is carried out in the mixing tank 11. After mixing the recycled material 14 and the solvent 15, the mixture is stirred for a predetermined time with the stirring blade 11a. As a result, the resin in the recycled material 14 is dissolved in the solvent 15, and the first processing solution 18 in which the reinforcing fibers are suspended is obtained. The mixing ratio of the recycled material 14 and the solvent 15, the mixing temperature, and the mixing time are set to conditions that allow the reinforcing fibers to be recovered with the resin attached. These are also set appropriately depending on the type of recycled material 14 and the solvent 15, the physical properties of the obtained first processing solution 18, etc. For example, the mixing ratio of the recycled material 14 and the solvent 15 is set so that the resin content in the first processing solution 18 is 1% by mass or more and 10% by mass or less.

[0024] The recycled material 14 consists of a fiber-reinforced composite material and contains reinforcing fibers and resin. The fiber length of the reinforcing fibers is not particularly limited, but it is preferable that the recycled material contains relatively long fibers of 50 μm or more. Such recycled material can improve the reusability of the recovered fibers. The upper limit of the fiber length of the reinforcing fibers contained in the recycled material 14 is not particularly limited, but it is preferable that it is 5000 μm or less. Such recycled material can improve the reusability of the recovered fibers. In particular, the recovered reinforcing fibers can be reused in many molded products, such as automobile parts.

[0025] The fiber length distribution of reinforcing fibers varies depending on the type of original product and molding method of the recycled raw material 14. In the recycling method of this embodiment, it is preferable to use a filter 12b having a predetermined mesh opening to remove reinforcing fibers with a fiber length less than the predetermined mesh opening, and to selectively separate reinforcing fibers with a fiber length equal to or greater than the mesh opening.

[0026] The reinforcing fibers included in the fiber-reinforced composite material are not particularly limited, but include inorganic fibers and solvent-insoluble organic fibers, and more specifically, glass fibers, carbon fibers, cellulose fibers, wood fibers, etc. The fiber diameter of the reinforcing fibers is not particularly limited, but for example, it is between 5 μm and 20 μm.

[0027] Specific examples of resins constituting the fiber-reinforced composite material include, for example, polyethylene resin, polyolefin resins such as polypropylene resin, polyamide resin, polyurethane resin, polycarbonate resin, polyester resin, polyimide resin, polyether ester resin, and polyacrylic resin. In order to improve the solubility of the recycled material 14 in the solvent 15, it is preferable that the recycled material 14 be subjected to processing such as crushing, shredding, or cutting to a predetermined size within a range that does not significantly affect the length of the reinforcing fibers contained therein.

[0028] The type of solvent 15 is appropriately determined depending on the type of resin constituting the recycled raw material 14. Examples of solvents 15 include cyclic ether organic solvents, aromatic alcohols, aromatic hydrocarbons, aromatic halogenated hydrocarbons, aromatic halogenated organic solvents, aromatic organic solvents, aliphatic halogenated hydrocarbons, ketone organic solvents, acid or alkali solvents, etc. More specifically, the following combinations of resin and solvent are exemplified.

[0029] When the resin is polycarbonate resin, applicable solvents include, for example, cyclic ether organic solvents such as 1,3-dioxolane and tetrahydrofuran, and mixtures thereof. When the resin is polyamide resin, applicable solvents include, for example, aromatic alcohols including benzyl alcohol and 2-phenoxyethanol, acid solutions containing hydrochloric acid and sulfuric acid in cyclic ether organic solvents such as 1,4-dioxane and tetrahydrofuran, alkaline aqueous solutions containing sodium hydroxide, and mixtures thereof.

[0030] When the resin is a polyolefin resin such as polyethylene resin or polypropylene resin, applicable solvents include, for example, aromatic hydrocarbons such as benzene, toluene, and xylene, aromatic halogenated hydrocarbons such as orthodichlorobenzene, and mixtures thereof.

[0031] When the resin is a polyester resin, applicable solvents include, for example, aromatic halogenated organic solvents such as orthochlorophenol, aromatic organic solvents such as phenol and cresol, and mixtures thereof.

[0032] When the resin is acrylic resin, applicable solvents include, for example, aliphatic halogenated hydrocarbons such as chloroform and methylene chloride, ketone-based organic solvents such as acetone and methyl ethyl ketone, and mixtures thereof.

[0033] The original uses of the recycled raw materials 14 are not particularly limited, but examples include transportation equipment such as automobile parts, machine parts, building materials, daily necessities, and ELV materials, PCR materials, PIR materials obtained from them.

[0034] Among these, at least one selected from ELV material, PCR material, and PIR material, which have polypropylene as the main component, is preferred from the viewpoint of excellent environmental properties due to recycling. Furthermore, in the case of such recycled raw materials, a solvent whose main component is xylene is preferred from the viewpoint of excellent resin solubility. The main component refers to xylene accounting for 50% by mass or more of the total solvent.

[0035] The first processing liquid 18 obtained as described above is sent to the first filtration section 12 through the piping 19 by opening a stopcock (not shown). (Fiber separation process) The fiber separation process is carried out in the first filtration section 12. When the frame 12a is in the first state, the first processing liquid 18 is passed through the filter 12b located on the main passage. By passing the first processing liquid 18 through the filter 12b, long fibers 18a of the reinforcing fibers that are longer than or equal to the mesh opening of the filter 12b are selectively separated on the surface of the filter 12b. At that time, the second processing liquid 21 containing short fibers, which are reinforcing fibers with a shorter fiber length that were not filtered by the filter 12b, and the solvent 15 flows out from the back surface of the filter 12b. Note that because the reinforcing fibers are needle-thin, some of the long fibers longer than or equal to the mesh opening may pass through the filter 12b without being captured. Therefore, the recovered reinforcing fibers consist mostly of reinforcing fibers with a fiber length relatively larger than the mesh opening of the filter 12b. For example, if the mesh opening of filter 12b is 300 μm, most reinforcing fibers with a fiber length of 600 μm or less tend to pass through filter 12b, while reinforcing fibers with a fiber length of 800 μm or more tend to be captured by filter 12b. Taking this into consideration, the mesh opening of filter 12b is set so that a large amount of reinforcing fibers with the desired fiber length are captured.

[0036] As shown in Figure 1, the second processing liquid 21 flows out of the frame 12a through the first liquid passage hole 12c and then flows toward the second filtration section 13 located downstream of the piping 19 along the filtration liquid passage direction X.

[0037] As shown in Figures 1 and 2, the long fibers 18a recovered on the surface of the filter 12b move into the branch pipe 20 that constitutes the branching path after the frame 12a is switched to the second state by the switching mechanism of the first filtration section 12. The switching by the switching mechanism is performed by rotating the frame 12a, which is in the first state, by 90 degrees in the direction of arrow A1, that is, clockwise. This switches the fluid from the first state, in which it flows along the filtration fluid flow direction X toward the second filtration section 13, to the second state, in which it flows along the branching fluid flow direction Y toward the branch pipe 20.

[0038] In the first state of the frame 12a, the fluid was flowing from the front side to the back side of the filter 12b. In the second state of the frame 12a, the fluid is flowing in the opposite direction, from the back side to the front side of the filter 12b. As a result, the long fibers 18a remaining on the surface of the filter 12b are moved into the branch pipe 20 by the switching mechanism, and then moved by the fluid to a fiber recovery mechanism (not shown) further downstream, where they are recovered. After the long fibers 18a are recovered, the frame 12a is switched from the second state to the first state by the switching mechanism.

[0039] As shown in Figure 2, the frame 12a is rotated 90 degrees in the direction of arrow A2, i.e., counterclockwise, by the switching mechanism, thereby switching from a second state in which the fluid is directed toward the branch pipe 20 to a first state in which it is directed toward the second filtration section 13. As a result, the long fibers 18a are captured again by the filter 12b in the same manner. The switching mechanism ensures that the capture of the long fibers 18a by the filter 12b and the recovery of the long fibers 18a by the branch pipe 20 are performed continuously.

[0040] (Drying Process) The long fibers 18a recovered as described above are reinforced fibers with resin and solvent 15 attached. After the solvent is removed by drying, recycled fibers are obtained, which are long fibers 18a with resin attached. The drying process is appropriately selected depending on the type of solvent, but examples include heating, reduced pressure, air drying, leaving at room temperature, and combinations thereof.

[0041] In the recycled fibers, the mass proportion of long fibers 18a in the recycled fibers is 70% by mass or more and 95% by mass or less, and the mass proportion of resin in the recycled fibers is preferably 5% by mass or more and 30% by mass or less. When the mass proportion of resin in the recycled fibers is 5% by mass or more, recycled fibers having a resin layer with a predetermined film thickness can be obtained. This makes it easier to reuse recycled fibers using the resin thereof. When the mass proportion of resin in the recycled fibers is 30% by mass or less, aggregation of fibers can be suppressed, so recycled fibers excellent in dispersibility can be obtained. This can improve the quality of recycled products using the recycled fibers.

[0042] The thickness of the resin layer on the surface of the recycled fibers is appropriately set, and for example, it is 0.1 μm or more and 2.0 μm or less. When the thickness of the resin layer is, for example, 0.1 μm or more, the recycled fibers can be reused in a state where the coating agent remains on the fiber surface. When the thickness of the resin layer is, for example, 2.0 μm or less, handling properties of the recycled fibers can be improved by suppressing aggregation of the recycled fibers.

[0043] The mass proportion of resin in the recycled fibers or the thickness of the resin layer on the surface of the recycled fibers can be adjusted by the mixing ratio of the recycled raw material 14 and the solvent 15, dissolution time, dissolution temperature, and the like.

[0044] (Resin Separation Step) The resin separation step is performed in the second filtration unit 13. The resin separation step is a step of separating solid components and liquid components contained in the second treatment liquid 21 that has passed through the filter 12b. Thereby, short fibers 21a having a short fiber length that have not been captured by the filter 12b are separated, and a third treatment liquid 22 containing resin derived from the recycled raw material 14 is produced. Since the filler 13a has a predetermined particle diameter, it exerts a filtration effect of separating solid components and liquid components of the filler 13a when the liquid passes therethrough. Thereby, the short fibers 21a, which are solid components, are captured on the upper surface of the filler 13a in the column 13b.

[0045] Further, additives such as colorants derived from the recycled raw material 14 dispersed in the second treatment liquid 21 are captured by the adsorption action of the filler 13a. After the second treatment liquid 21 passes through the second filtration unit 13, a third treatment liquid 22 containing a solvent and a resin component derived from the recycled raw material 14 is produced. The third treatment liquid 22 is recovered by a recovery device (not shown) provided downstream of the pipe 19.

[0046] The third treatment liquid 22 containing the recovered solvent and resin component is subjected to separation treatment of the solvent and the resin component by a known method. Examples of the method for separating the resin component include removal of the solvent by heating such as distillation treatment, and precipitation treatment using a poor solvent. The obtained solvent may be reused in the recycling method. The obtained resin component may be dried if necessary, and then reused for various applications.

[0047] (Method for producing fiber-reinforced composite material) The recycled fibers and resin component obtained from the recycled raw material 14 by the above recycling method can be applied to appropriate uses. Recycled fibers may be re-applied to fiber-reinforced composite materials to produce recycled fiber-reinforced composite materials. The resin used in the fiber-reinforced composite material is appropriately selected from known resins according to the purpose, application, and the like. It is preferable that a recycled fiber-reinforced composite material is produced using recycled fibers and a resin of the same system as the resin contained in the recycled raw material. For example, when the recycled raw material is a polypropylene resin, it is preferable to produce a recycled fiber-reinforced composite material using a polyolefin resin as the resin of the same system.

[0048] Furthermore, a recycled fiber-reinforced composite material may be produced by using both the recycled fibers obtained from the recycled raw material 14 and the resin component. It is preferable that the recycled raw material 14 and the recycled fiber-reinforced composite material are applied to the same use. The application is not particularly limited, and examples thereof include transportation equipment such as automobile parts, mechanical parts, construction materials, and daily necessities. Examples of automobile parts include bumpers, glove boxes, and the like.

[0049] The recycling method of this embodiment will be described in more detail based on the following examples. Note that the recycling method is not limited to the configuration described in the Examples section. (First Embodiment) The recycling method of the first embodiment is carried out using a recycling device 10. In this case, a metal filter 12b with a mesh opening of 300 μm was used. In addition, activated carbon with an average particle size of 1 μm was used as the packing agent 13a. In addition, a fiber-reinforced composite material molded from polypropylene resin containing 30% by mass of glass fiber (fiber diameter 10 μm) as reinforcing fiber was used as the recycling raw material 14. The fiber length distribution of the reinforcing fiber was 200 μm to 2000 μm as measured by optical microscope.

[0050] First, recycled raw material 14, which had been crushed to a predetermined size, and xylene as a solvent 15 were added to the mixing tank 11 in a mass ratio of 1:30. By stirring at 120°C for 30 minutes, a first treatment liquid 18 was obtained. The first treatment liquid 18 was passed through the filter 12b of the first filtration section 12 and the packing material 13a of the second filtration section 13 in sequence.

[0051] Long fibers 18a with the recovered solvent and resin attached were obtained on the surface of the filter 12b. The obtained long fibers 18a were further heat-treated (100°C, 1 hour) to remove the solvent, thereby obtaining recycled fibers which are long fibers 18a with resin attached.

[0052] Optical microscope measurements of the fiber length distribution of recycled fibers revealed a range of 800 μm to 2000 μm. Furthermore, optical microscope measurements of the fiber length distribution of recycled fibers recovered on the upper surface of the filler 13a revealed a range of 200 μm to 600 μm. Magnified optical microscope examination of the surface condition of the recycled fibers confirmed the presence of resin on the fiber surface.

[0053] Furthermore, the weight of the recovered recycled fibers was measured. In addition, the recovered recycled fibers were burned at 700°C for 2 hours to completely remove the resin adhering to the surface of the long fibers 18a, and then the weight of the long fibers 18a was measured. The weight of the resin adhering to the surface of the long fibers 18a was then determined from the weight of the recycled fibers and the weight of the long fibers 18a.

[0054] As a result, the weight percentage of long fibers 18a in the recovered recycled fibers was 80% by mass, and the weight percentage of resin was 20% by mass. Furthermore, based on the surface condition of the recycled fibers observed with an optical microscope, the fiber diameter of the long fibers 18a, the weight percentage of resin, and the specific gravities of the resin and glass fibers, it was inferred that the recycled fibers were coated with resin to a thickness of 0.6 μm on the surface of the long fibers 18a. The measurement results are shown in Table 1 below.

[0055] (Second Example) A recycled material 14 made of polypropylene resin containing 30% by mass of glass fibers (fiber diameter 20 μm) was used as reinforcing fiber. The recycled material 14 and xylene as solvent 15 were added in a mass ratio of 1:30, and the mixture was stirred at 120°C for 30 minutes to obtain the first treatment solution 18. The rest of the process was carried out in the same manner as in the first example. The surface condition of the obtained recycled fibers was magnified using an optical microscope and it was confirmed that resin was attached to the fiber surface. Furthermore, the weight of the recovered recycled fibers, the weight of the long fibers 18a, and the weight of the resin attached to the surface of the long fibers 18a were determined using the same method as in the first example.

[0056] As a result, the weight percentage of long fibers 18a in the recovered recycled fibers was 80% by mass, and the weight percentage of resin was 20% by mass. Furthermore, based on the surface condition of the recycled fibers observed with an optical microscope, the fiber diameter of the long fibers 18a, the weight percentage of resin, and the specific gravities of the resin and glass fibers, it was inferred that the recycled fibers were coated with resin to a thickness of 1.2 μm on the surface of the long fibers 18a. The measurement results are shown in Table 1 below.

[0057] (Third Example) A recycled material 14 made of polypropylene resin containing 60% by mass of glass fibers (fiber diameter 10 μm) was used as reinforcing fibers. The recycled material 14 and xylene as a solvent 15 were added in a mass ratio of 1:15, and the mixture was stirred at 120°C for 30 minutes to obtain the first treatment solution 18. The rest of the process was carried out in the same manner as in the first example. The surface condition of the obtained recycled fibers was magnified using an optical microscope and it was confirmed that resin was attached to the fiber surface. Furthermore, the weight of the recovered recycled fibers, the weight of the long fibers 18a, and the weight of the resin attached to the surface of the long fibers 18a were determined using the same method as in the first example.

[0058] As a result, the weight percentage of long fibers 18a in the recovered recycled fibers was 95% by mass, and the weight percentage of resin was 5% by mass. Furthermore, based on the surface condition of the recycled fibers as measured by the optical microscope, the fiber diameter of the long fibers 18a, the weight percentage of resin, and the specific gravities of the resin and glass fibers, it was inferred that the recycled fibers were coated with resin to a thickness of 0.1 μm on the surface of the long fibers 18a. The measurement results are shown in Table 1 below.

[0059] (Fourth Example) A recycled material 14 made of polypropylene resin containing 10% by mass of glass fibers (fiber diameter 20 μm) was used as reinforcing fiber. The recycled material 14 and xylene as solvent 15 were added in a mass ratio of 1:30, and the mixture was stirred at 120°C for 30 minutes to obtain the first treatment solution 18. The rest of the process was carried out in the same manner as in the first example. The surface condition of the obtained recycled fibers was magnified using an optical microscope and it was confirmed that resin was attached to the fiber surface. Furthermore, the weight of the recovered recycled fibers, the weight of the long fibers 18a, and the weight of the resin attached to the surface of the long fibers 18a were determined using the same method as in the first example.

[0060] As a result, the weight percentage of long fibers 18a in the recovered recycled fibers was 70% by mass, and the weight percentage of resin was 30% by mass. Furthermore, based on the surface condition of the recycled fibers as measured by the optical microscope, the fiber diameter of the long fibers 18a, the weight percentage of resin, and the specific gravities of the resin and glass fibers, it was inferred that the recycled fibers were coated with resin to a thickness of 2.0 μm on the surface of the long fibers 18a. The measurement results are shown in Table 1 below.

[0061]

[0062] (Manufacturing of recycled fiber-reinforced composites) Using the recycled fibers from the first to fourth examples, recycled fiber-reinforced composites were manufactured using the same type of resin as that contained in the recycled raw materials, without applying any surface treatment such as coating. As a result, it was confirmed that all of the fiber-reinforced composites were practically usable.

[0063] It has been confirmed that the recycling method described herein yields highly reusable recycled fibers. (Effects of this embodiment) The effects of the recycling method or the method for manufacturing fiber-reinforced composite materials of this embodiment will be described.

[0064] (1) As a recycling method, first a step is performed to obtain a first processing liquid 18 by mixing a recycled raw material 14 made of fiber-reinforced composite material with a solvent 15 for dissolving resin. Next, a fiber separation step is performed to separate the long fibers 18a with the resin and solvent 15 attached from the first processing liquid 18. Next, a drying step is performed to obtain recycled fibers, which are long fibers 18a with resin attached, by drying the long fibers 18a with the resin and solvent 15 attached.

[0065] Typically, a treatment agent is applied to the surface of reinforcing fibers to improve dispersibility, handling, and adhesion to the matrix resin. With the above configuration, recycled fibers are obtained with resin remaining on the surface of the reinforcing fibers, eliminating the need for further coating with a treatment agent when reusing the recycled fibers. This facilitates the reprocessing of recycled fibers and allows for low-cost reuse of recycled fibers.

[0066] (2) The mass percentage of long fibers 18a as reinforcing fibers in the recycled fibers is 70% by mass or more and 95% by mass or less, and the mass percentage of resin in the recycled fibers is 5% by mass or more and 30% by mass or less.

[0067] According to the above configuration, when the mass percentage of resin in the recycled fiber is 5% by mass or more, recycled fiber having a resin layer with a predetermined film thickness can be obtained. As a result, when reusing recycled fiber with resin, coating treatment of the fiber becomes unnecessary, making recycling easier. When the mass percentage of resin in the recycled fiber is 30% by mass or less, aggregation of fibers can be suppressed, resulting in recycled fiber with excellent dispersibility. As a result, the quality of recycled products using recycled fiber can be improved.

[0068] (3) The reinforcing fibers contained in the recycled material 14 consist of fibers that are 50 μm or longer. With the above composition, recycled fibers containing relatively long fibers with excellent usability characteristics can be reused.

[0069] (4) The fiber separation step is a step in which the first processing liquid 18 is passed through a filter 12b with a mesh opening of 10 μm or more and 500 μm or less, thereby selectively separating long fibers from the reinforcing fibers to which the resin and solvent 15 have adhered, which are wider than or equal to the mesh opening of the filter 12b.

[0070] According to the above configuration, long fibers 18a, whose fiber length is greater than or equal to the mesh opening of the filter 12b, can be selectively separated and recovered from the reinforcing fibers contained in the recycled raw material 14. As a result, reinforcing fibers with relatively uniform fiber lengths can be obtained, thereby improving the utilization characteristics of the recovered reinforcing fibers.

[0071] (5) In the second filtration section 13, a resin separation step is performed to recover the third treatment liquid 22, which is the liquid component containing resin, by separating the solid component consisting mainly of short fibers contained in the second treatment liquid 21 from the liquid component containing solvent and resin.

[0072] According to the above configuration, only the liquid component can be extracted from the second processing solution 21. This makes it possible to separate the short reinforcing fibers in the processing solution after it has passed through the filter 12b. The third processing solution 22, which contains resin, can be easily processed.

[0073] (6) The method for manufacturing the recycled fiber-reinforced composite material is carried out using recycled fibers obtained from the recycled raw material 14 by the recycling method of the above embodiment. With the above configuration, the reinforcing fibers used in the original product can be applied. Therefore, when the recycled fiber-reinforced composite material is applied to the same product as the recycled raw material 14, it is possible to manufacture a recycled fiber-reinforced composite material that has performance close to that of the original product.

[0074] (7) The method for manufacturing the recycled fiber-reinforced composite material is carried out using recycled fibers and a resin of the same type as the resin contained in the recycled raw material 14. With the above configuration, a combination of the reinforcing fibers used in the original product and a resin of the same type as the resin to which the reinforcing fibers were applied can be adopted. Therefore, since the compatibility between the reinforcing fibers and the matrix resin is also good, it is possible to manufacture a recycled fiber-reinforced composite material that is closer to the performance of the original product.

[0075] (8) The method for manufacturing the recycled fiber-reinforced composite material is carried out using recycled fibers and resin obtained from the recycled raw material 14 by the recycling method of the above embodiment. According to the above configuration, the reinforcing fibers and resin used in the original product are combined and applied. Therefore, since the compatibility between the reinforcing fibers and the matrix resin is good, it is possible to manufacture a recycled fiber-reinforced composite material that is closer to the performance of the original product. In addition, since the recycling rate can be improved, the environmental characteristics can be improved.

[0076] (Another example of this embodiment) The above embodiment can be implemented with the following modifications. This embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0077] In the above embodiment, the fiber separation process may be configured to separate the reinforcing fibers with the resin and solvent 15 attached by omitting either the first filtration section 12 or the second filtration section 13. Even with this configuration, recycled fibers, which are reinforcing fibers with resin attached, can be obtained.

[0078] In the above embodiment, the fiber separation step using the filter 12b selectively separates long fibers 18a that are larger than or equal to the mesh opening of the filter 12b. However, it is assumed that some short fibers smaller than the mesh opening of the filter 12b may be captured due to the accumulation of long fibers on the filter 12b.

[0079] In the above embodiment, the short fibers 21a, which are reinforcing fibers with a short fiber length, captured in the second filtration section 13 may be recovered and dried, and used as recycled fibers with resin attached to the surface.

[0080] In the above embodiment, the preparation of the first treatment liquid 18 obtained by mixing the recycled material 14 and the solvent 15 may be carried out by stirring, ultrasonic treatment, shaking treatment, or the like.

[0081] - In the above embodiment, each processing liquid may be transported by a pump or the like (not shown), or by gravity. - In the above embodiment, in the first filtration section 12 or the second filtration section 13, an outlet for taking out the filtered reinforced fibers to the outside may be formed on the outer surface of the piping 19.

[0082] In the above embodiment, a pressure sensor, a flow sensor, etc., may be provided in the upstream piping 19 in order to determine whether or not the long fibers 18a can be recovered by switching the switching mechanism.

[0083] In the above embodiment, the recovery of long fibers 18a in the branch pipe 20 in the second state of the switching mechanism is preferably carried out by flowing a new solvent in order to maintain the quality of the recovered long fibers 18a. From the viewpoint of operational efficiency, it may also be carried out by flowing the first processing liquid 18 as is in the branch liquid flow direction Y.

[0084] - In the above embodiment, the first filtration unit 12 may employ other known continuous filtration mechanisms, such as a disc-shaped rotating filter. - In the above embodiment, the filter 12b may be provided at the connection point between the mixing tank 11 and the piping 19. With this configuration, the long fibers 18a can be recovered in the mixing tank 11.

[0085] - In the above embodiment, two or more filters with different mesh sizes may be placed in the main passage to obtain fractions of two or more reinforcing fibers with different fiber lengths. - In the above embodiment, the second filtration section 13 may be performed by a filter, as long as it can separate the solid components and liquid components contained in the second processing liquid 21.

Claims

1. A method for recycling a fiber-reinforced composite material comprising a resin and reinforcing fibers, the method comprising: a step of obtaining a processing liquid by mixing a recycled raw material consisting of the fiber-reinforced composite material with a solvent for dissolving the resin; a fiber separation step of separating the reinforcing fibers from the processing liquid with the resin and solvent attached to them; and a drying step of obtaining recycled fibers, which are the reinforcing fibers with the resin attached, by drying the reinforcing fibers with the resin and solvent attached to them.

2. The method for recycling a fiber-reinforced composite material according to claim 1, wherein the mass ratio of the reinforcing fibers to the recycled fibers is 70% by mass or more and 95% by mass or less, and the mass ratio of the resin to the recycled fibers is 5% by mass or more and 30% by mass or less.

3. The method for recycling a fiber-reinforced composite material according to claim 1 or 2, wherein the reinforcing fibers include fibers of 50 μm or more.

4. The method for recycling a fiber-reinforced composite material according to claim 3, wherein the fiber separation step includes passing the processing liquid through a filter with a mesh size of 10 μm or more and 500 μm or less, thereby selectively separating long fibers from the reinforcing fibers to which the resin and solvent have adhered, the long fibers being larger than the mesh size of the filter.

5. A method for recycling a fiber-reinforced composite material according to claim 4, further comprising a resin separation step of recovering the liquid component containing the resin by separating the solid component and the liquid component contained in the processing liquid that has passed through the filter.

6. A method for manufacturing a fiber-reinforced composite material, comprising manufacturing a fiber-reinforced composite material using recycled fibers obtained from recycled raw materials by the method for recycling a fiber-reinforced composite material described in any one of claims 1 to 5.

7. The method for producing a fiber-reinforced composite material according to claim 6, wherein the production of the recycled fiber-reinforced composite material includes producing the recycled fiber-reinforced composite material using recycled fibers and a resin of the same type as the resin contained in the recycled raw material.

8. A method for producing a fiber-reinforced composite material, comprising producing a recycled fiber-reinforced composite material using the recycled fibers and resin obtained from the recycled raw materials by the method for recycling a fiber-reinforced composite material described in claim 5.

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