Method for manufacturing recycled carbon fiber and apparatus used therefor

Abstract

The present invention provides a method for rapidly recovering recycled carbon fibers with an elastic modulus suitable for reuse by removing plastic material from carbon fiber reinforced plastics, and a manufacturing apparatus for use therein. [Solution] The present invention involves applying a laser light source 1 to the surface of a carbon fiber reinforced plastic 2, with an energy density of 5 W / cm². 2 This is a method for manufacturing recycled carbon fibers, comprising a laser irradiation step of irradiating the carbon fibers 3 with the above-described laser to remove the plastic material 4 coated with carbon fibers 3 and the carbon-like residue derived from the plastic material. The wavelength of the irradiated laser is preferably 200 nm to 15 μm.

Description

[Technical Field]

[0001] This invention relates to a method for producing recyclable carbon fibers from carbon fiber reinforced plastics, and an apparatus used in this method. [Background technology]

[0002] Carbon fiber reinforced plastics are composite materials consisting of carbon fibers, which have excellent physical properties such as strength and elastic modulus, and a matrix resin (such as a curable resin or thermoplastic resin). They are widely used in the aerospace industry, automotive industry, power generation equipment, home appliances, sports, leisure, toys, and more.

[0003] As the use of carbon fiber reinforced plastics (CRPs) increases, technologies are being explored to recover carbon fibers for recycling from waste materials generated during the manufacturing process of CRP products and from used CRP products, thereby reducing waste.

[0004] Patent Document 1 discloses a method for recovering carbon fibers, characterized by treating a workpiece containing carbon fiber reinforced plastic with superheated steam at 800°C or higher to remove the plastic from the carbon fiber reinforced plastic and recover the carbon fibers.

[0005] Patent Document 2 discloses a method for recovering (recycling) carbon fibers from carbon fiber-containing resins, particularly from carbon fiber-reinforced resins (CFPs or CFP materials), preferably from carbon fiber-containing and / or carbon fiber-reinforced composite materials, characterized in that the object based on a carbon fiber-containing resin having carbon fibers in a polymer matrix is ​​subjected to multiple stages of thermal decomposition in the presence of oxygen, and the polymer of the polymer matrix is ​​inter-decomposed by thermal decomposition to yield carbon fibers.

[0006] Patent Document 3 describes a method for producing recycled carbon fibers from carbon fiber reinforced plastic containing carbon fibers and matrix resin components, comprising: (a) a crushing step of crushing carbon fiber reinforced plastic waste material to produce crushed carbon fiber reinforced plastic fragments having a predetermined fiber length; (b) a transport and storage step of sending the crushed carbon fiber reinforced plastic fragments to a hopper for storage; and (c) a powder removal step of supplying the crushed carbon fiber reinforced plastic fragments from the hopper to a powder removal device, and removing the powder contained in the crushed carbon fiber reinforced plastic fragments using the powder removal device to produce powder-removed carbon fiber reinforced plastic fragments. A method for producing recycled carbon fibers is disclosed, characterized by automating the transport between each of the following steps: (d) a pyrolysis process in which the carbon fiber reinforced plastic dust removal fragments are heated while being quantitatively supplied to a pyrolysis furnace to remove the matrix resin components contained in the carbon fiber reinforced plastic dust removal fragments in order to obtain a recycled carbon fiber pyrolysis product; (e) a cooling and transport process in which the recycled carbon fiber pyrolysis product is cooled and transported to the next process; (f) a classification process in which the recycled carbon fiber pyrolysis product is classified to obtain a recycled carbon fiber classification product; and (g) an iron removal process in which metal powder is removed from the recycled carbon fiber classification product by magnetic force.

[0007] Furthermore, Patent Document 4 discloses a method for producing recycled carbon fibers, which includes heat treatment of raw materials containing a resin material and carbon fibers, characterized in that (i) the heat treatment consists of a dry distillation treatment, or (ii) the heat treatment consists of a dry distillation treatment and an oxidation treatment, and the content of residual carbon derived from the resin material in the recycled carbon fibers is greater than 10.0% by mass and 40.0% by mass or less with respect to the carbon fibers contained in the recycled carbon fibers. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2011-122032 [Patent Document 2] Special Publication No. 2016-521295 [Patent Document 3] Japanese Patent Publication No. 2019-127040 [Patent Document 4] Japanese Patent Publication No. 2023-13706 [Overview of the project] [Problems that the invention aims to solve]

[0009] While the use of recycled carbon fiber has the effect of reducing environmental impact, its physical properties are generally lower than those of carbon fiber used in the manufacture of carbon fiber reinforced plastics (hereinafter referred to as "virgin carbon fiber"), which can limit its applications. Therefore, there is a need for methods to improve the process, such as reducing manufacturing costs and shortening manufacturing time. In this invention, the "carbon fiber reinforced plastic" to be processed includes not only waste materials generated in the process of manufacturing products made of carbon fiber reinforced plastics in various industries, and waste materials of components containing carbon fiber reinforced plastics, but also materials that have been processed by conventional known methods, etc., in which the plastic material has not been completely removed. In this case, carbon-like residues derived from the plastic material, formed by known methods, may be attached to the surface of the carbon fiber, and sufficient removal of such attached substances is required.

[0010] The object of the present invention is to provide a method and apparatus for rapidly recovering carbon fibers having an elastic modulus suitable for reuse by removing the carbon fiber-coated plastic material from carbon fiber-reinforced plastic. [Means for solving the problem]

[0011] The present invention is shown below. 1. A method for obtaining carbon fibers from carbon fiber reinforced plastic, On the surface of the carbon fiber reinforced plastic, the energy density is 5 W / cm². 2A method for manufacturing recycled carbon fiber, comprising a laser irradiation step of removing plastic material and carbon-like residue derived from the plastic material by irradiating it with the above-mentioned laser. 2. The method for manufacturing recycled carbon fiber according to item 1 above, wherein the wavelength of the laser is 200 nm to 15 μm. 3. A recycled carbon fiber manufacturing apparatus equipped with a laser light source that irradiates a carbon fiber reinforced plastic body with a laser. 4. The recycled carbon fiber manufacturing apparatus according to item 3, further comprising a feeding means for moving and stopping the carbon fiber reinforced plastic body in order to continuously irradiate a long or large-area carbon fiber reinforced plastic body or a plurality of such carbon fiber reinforced plastic bodies with a laser. [Effects of the Invention]

[0012] According to the recycled carbon fiber manufacturing method and apparatus of the present invention, it is possible to quickly remove the plastic material coated with carbon fibers from waste materials generated during the manufacturing process of carbon fiber reinforced plastic products, and waste products of used carbon fiber reinforced plastic products, and to produce recycled carbon fibers suitable for reuse, with an elastic modulus calculated using tensile load and displacement based on JIS R 7606, for example, 250 GPa or more. Conventionally, in known heat treatment methods, the heat from the heat source is also used to heat the heat treatment apparatus itself, which requires a predetermined heat capacity, and only a portion is used to heat the workpiece, making it unavoidable that the process will take a long time, and if continuous processing is required, the heat treatment apparatus will be heavy and bulky. In comparison, the laser irradiation method is a method of directly heating the workpiece by irradiating it with a laser that has enough energy to remove the plastic material, and in particular, since carbon fibers have a high absorption capacity for lasers (electromagnetic waves), it is possible to remove the plastic material coated with carbon fibers in a very short time, and the recycled carbon fiber manufacturing method and apparatus of the present invention are efficient. [Brief explanation of the drawing]

[0013] [Figure 1]It is a schematic diagram for explaining a laser irradiation process according to a method for manufacturing recycled carbon fibers of the present invention. [Figure 2] It is a schematic diagram showing an example of a recycled carbon fiber manufacturing apparatus of the present invention. [Figure 3] It is a schematic diagram showing another example of a recycled carbon fiber manufacturing apparatus of the present invention. [Figure 4] It is a schematic diagram showing a recycled carbon fiber manufacturing apparatus used in [Examples]. [Figure 5] It is a graph showing the elastic modulus of recycled carbon fibers obtained in Examples 1 to 12.

Embodiments for Carrying Out the Invention

[0014] The method for manufacturing recycled carbon fibers of the present invention is a method for removing a plastic material coating carbon fibers from carbon fiber reinforced plastics and obtaining carbon fibers having an elastic modulus suitable for reuse, and on the surface of the carbon fiber reinforced plastics, a laser having an energy density of 5 W / cm 2 or more is irradiated in a laser irradiation process. The method for manufacturing recycled carbon fibers of the present invention may include other processes as necessary after the laser irradiation process.

[0015] The carbon fiber reinforced plastics as a raw material for manufacturing are materials in which at least one of virgin carbon fibers and sizing agent - attached carbon fibers is included as a reinforcing material in a matrix containing a plastic material.

[0016] The virgin carbon fibers are not particularly limited and can be, for example, polyacrylonitrile - based carbon fibers, pitch - based carbon fibers, rayon - based carbon fibers, etc. Also, sizes such as fiber diameter and fiber length are not particularly limited.

[0017] Sizing agent-attached carbon fibers can be made by attaching a sizing agent containing, for example, an aliphatic epoxy compound and an aromatic epoxy compound, a polymer having one of the following types of bonds in its main chain: an ester bond, a urethane bond, or a carbonate bond, or a phenolic resin, to at least a portion of the surface of a virgin carbon fiber.

[0018] The plastic material used to coat the virgin carbon fibers or carbon fibers coated with a sizing agent may be either a thermoplastic resin or a curable resin derived from a curable resin (such as a thermosetting resin composition, a photocurable resin composition, or a room-temperature curable resin composition).

[0019] Thermoplastic resins include styrene-based resins such as polystyrene, styrene-acrylonitrile copolymer, styrene-maleic anhydride copolymer, (meth)acrylic acid ester-styrene copolymer, and ABS resin; rubber-reinforced thermoplastic resins; olefin-based resins such as polyethylene, polypropylene, ionomer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, cyclic olefin copolymer, and chlorinated polyethylene; vinyl chloride-based resins such as polyvinyl chloride, ethylene-vinyl chloride polymer, and polyvinylidene chloride; acrylic resins such as (co)polymers using one or more (meth)acrylic acid esters such as polymethyl methacrylate (PMMA); polyamide-based resins (PA) such as polyamide 6, polyamide 6,6, and polyamide 6,12; and polyethylene Examples include polyester resins such as phthalates (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate; polyacetal resins (POM); polycarbonate resins (PC); polyarylate resins; polyphenylene ether; polyphenylene sulfide; fluororesins such as polytetrafluoroethylene and polyvinylidene fluoride; liquid crystal polymers; imide resins such as polyimide, polyamideimide, and polyetherimide; ketone resins such as polyetherketone and polyetheretherketone; sulfone resins such as polysulfone and polyethersulfone; urethane resins; polyvinyl acetate; polyethylene oxide; polyvinyl alcohol; polyvinyl ether; polyvinyl butyral; phenoxy resins; and biodegradable plastics.

[0020] Examples of curable resins include epoxy resins, acrylic resins (including acrylic polymers having epoxy groups), phenolic resins, unsaturated polyester resins, alkyd resins, melamine resins, urethane resins, urea resins, silicone resins, polyimide resins, bismaleimide-triazine resins, furan resins, xylene resins, guanamine resins, and dicyclopentadiene resins.

[0021] In the present invention, the composition of the carbon fiber reinforced plastic is as described above, but the shape of the carbon fiber reinforced plastic to which the laser is irradiated is not particularly limited. Since the present invention is a technology for recovering carbon fibers from carbon fiber reinforced plastic, the raw materials for production can be waste materials generated in the process of manufacturing products made of carbon fiber reinforced plastic in fields such as the aerospace industry, automotive industry, power generation equipment, home appliances, sports, leisure, and toys, or waste materials of components containing carbon fiber reinforced plastic. The shape of the raw materials for production can be either fixed (plate-shaped, rod-shaped, lump-shaped, etc.) or irregular. Furthermore, the raw materials for production may be the above-mentioned waste materials from which the content ratio (amount of coating) of the plastic material coating the carbon fibers has been reduced in advance by conventionally known methods.

[0022] The laser irradiation process according to the present invention is shown in Figure 1. When a laser emitted from a laser light source 1 is irradiated onto the carbon fiber reinforced plastic 2, the plastic material coated with carbon fibers is removed, leaving behind the carbon fibers 3 contained in the carbon fiber reinforced plastic 2, which are then recovered.

[0023] The type of laser used to irradiate the carbon fiber reinforced plastic is not particularly limited, and semiconductor lasers, solid-state lasers, gas lasers, fiber lasers, etc., can be used. Only one type may be used, or two or more types may be used. Furthermore, the laser oscillation method may be either continuous oscillation or pulsed oscillation. In this invention, multiple laser light sources may be used depending on the shape, size, etc., of the carbon fiber reinforced plastic.

[0024] The wavelength of the laser is not particularly limited and can be 200 nm to 15 μm, but preferably 1 to 12 μm. When a laser with a wavelength within the above range is irradiated onto carbon fiber reinforced plastic, the plastic material coated with carbon fibers is explosively sublimated or vaporized in a short time and easily removed, leaving only the carbon fibers.

[0025] The laser energy density (laser intensity) is 5 W / cm² from the perspective of the removal efficiency of plastic materials. 2The above is preferable, with a density of 8 W / cm². 2 More preferably 10 W / cm² 2 That concludes the explanation. Note that the upper limit of energy density is typically 40 W / cm². 2 That is the case.

[0026] When irradiating carbon fiber reinforced plastic with a laser, the atmosphere is not particularly limited and can be at least one selected from air, nitrogen gas, argon gas, helium gas, superheated steam, etc. Furthermore, when the laser irradiation process is carried out in a closed system, it is preferable to irradiate the laser while discharging the decomposition gases of the plastic material, and a reduced pressure atmosphere can be created using a vacuum pump or the like. On the other hand, when irradiating a large amount or large area of ​​carbon fiber reinforced plastic with a laser under normal pressure, decomposition gases of the plastic material may accumulate between the laser light source and the carbon fiber reinforced plastic. In this case, it is preferable to configure the system so that the laser is directly irradiated onto the carbon fiber reinforced plastic by introducing a gas to create the above-mentioned atmosphere and discharging the decomposition gases.

[0027] The method of irradiating carbon fiber reinforced plastics with a laser is usually selected appropriately depending on the shape of the carbon fiber reinforced plastic. For example, the laser can be irradiated from directly above the carbon fiber reinforced plastic (see Figure 1), or from diagonally above the carbon fiber reinforced plastic. Furthermore, as described above, multiple laser light sources may be used, so multiple laser light sources may be used to irradiate the same part or different parts of the carbon fiber reinforced plastic with lasers. In the method of irradiating carbon fiber reinforced plastic with a laser from directly above, a large amount of decomposition gas generated by the laser irradiation may accumulate between the laser light source and the carbon fiber reinforced plastic, making it difficult to smoothly remove the plastic material. Therefore, when irradiating with a laser under conditions where decomposition gas is not discharged, it is preferable to irradiate the carbon fiber reinforced plastic with the laser from diagonally above. When the carbon fiber reinforced plastic is placed horizontally, the irradiation angle of the laser to the carbon fiber reinforced plastic is preferably 45 to 85 degrees, more preferably 60 to 85 degrees.

[0028] When irradiating carbon fiber reinforced plastic with a laser, one method can be applied in which the carbon fiber reinforced plastic is fixed and irradiated while scanning the laser or changing the optical path through a light diffusion lens, or in which the carbon fiber reinforced plastic is moved (including rotation) while irradiating with a laser with a fixed optical path. In carbon fiber reinforced plastics, which are used as raw materials for manufacturing, if the thickness of the plastic material covering the carbon fibers is not uniform, and the plastic material is removed prematurely, the exposed carbon fiber surface may be continuously irradiated with a laser. This can cause damage or a decrease in the physical properties of the carbon fibers that are ultimately produced. Therefore, in addition to irradiating with a constant laser energy density throughout the process, a method of irradiating while varying the energy density may also be applied.

[0029] The laser irradiation time for carbon fiber reinforced plastics is not particularly limited and is set appropriately depending on the shape, size, and amount of plastic material coated with carbon fibers.

[0030] In the recycled carbon fiber manufacturing method of the present invention, recycled carbon fiber can also be manufactured by irradiating carbon fibers with a sizing agent attached with a laser, instead of using carbon fiber reinforced plastic.

[0031] In the recycled carbon fiber manufacturing method of the present invention, as described above, other steps may be included as needed after the laser irradiation step. For example, the obtained carbon fibers can be subjected to a heat treatment step, a washing step, a drying step, a cutting step, and so on.

[0032] According to the present invention, recycled carbon fibers suitable for reuse can be efficiently produced from waste materials generated during the manufacturing process of carbon fiber reinforced plastic products in fields such as the aerospace industry, automotive industry, power generation equipment, home appliances, sports, leisure, and toys, or from waste materials of components containing carbon fiber reinforced plastic, with an elastic modulus of, for example, 200 GPa or more obtained by tensile testing. Since the elastic modulus of virgin carbon fibers or carbon fibers with sizing agents attached is usually 200 GPa or more, when recycled carbon fibers obtained according to the present invention are used to make carbon fiber reinforced plastic again, they will have excellent rigidity, similar to carbon fiber reinforced plastic materials obtained using virgin carbon fibers or carbon fibers with sizing agents attached, and can be suitably used in each of the above fields.

[0033] Next, the recycled carbon fiber manufacturing apparatus of the present invention will be described. The recycled carbon fiber manufacturing apparatus of the present invention is an apparatus having the configuration shown in Figure 1, and is equipped with one or more laser light sources for irradiating a carbon fiber reinforced plastic body, which has a long shape or large surface area due to containing carbon fibers of 500 mm or more, with a laser to remove the plastic material coated with carbon fibers and carbon-like residue derived from the plastic material from the carbon fiber reinforced plastic body, and to obtain carbon fibers suitable for reuse. The recycled carbon fiber manufacturing apparatus of the present invention usually includes a processing stage on which the carbon fiber reinforced plastic body is placed, and may further include a depressurization means for exhausting decomposition gases of the plastic material generated after laser irradiation. From the viewpoint of suppressing the diffusion of decomposition gases, the recycled carbon fiber manufacturing apparatus of the present invention preferably has the carbon fiber reinforced plastic body and the processing stage on which it is placed arranged in a sealed system.

[0034] The carbon fiber reinforced plastic body according to the present invention can be an article made of carbon fiber reinforced plastic having the above-described structure, or an article in which the proportion of plastic material covering the carbon fibers (covering amount), etc., has been reduced in advance by conventionally known methods, and in either case, it can be a fixed shape or an irregular shape. Therefore, it is preferable that the processing stage on which the carbon fiber reinforced plastic body is placed has a function to move to a position where it is easy to irradiate with a laser. If the carbon fiber reinforced plastic body is long or large in area and contains long carbon fibers as described above, it is possible to irradiate a large area of ​​the carbon fiber reinforced plastic body with a laser at once by using multiple laser light sources. However, if, for example, a small number of laser light sources are used, and each laser light source has a fixed optical path, recycled carbon fibers can be continuously obtained by irradiating the carbon fiber reinforced plastic body with a laser while repeatedly moving and stopping it on the processing stage. Such a method is also suitable when irradiating multiple carbon fiber reinforced plastic bodies with a laser continuously, even if they are not large in size. Furthermore, as shown in Figure 1, when using a laser light source positioned above the horizontal line of the placed carbon fiber reinforced plastic body, the laser is irradiated onto the upper surface of the carbon fiber reinforced plastic body to remove the plastic material. However, depending on the size of the carbon fiber reinforced plastic body, it may be necessary to irradiate the lower surface of the carbon fiber reinforced plastic body as well. In that case, a separate laser light source directed towards the lower surface of the carbon fiber reinforced plastic body may be placed below the horizontal line of the placed carbon fiber reinforced plastic body, or the processing stage may be equipped with a means to rotate the irradiated surface of the carbon fiber reinforced plastic to the upper side.

[0035] Figures 2 and 3 illustrate an example of a recycled carbon fiber manufacturing apparatus equipped with means for moving and stopping the carbon fiber reinforced plastic body 2. As described above, it is preferable that the laser irradiation of the carbon fiber reinforced plastic body 2 be performed in a closed system in order to suppress the diffusion of decomposition gases of the plastic material generated by irradiating the carbon fiber reinforced plastic body 2 with a laser. However, in Figures 2 and 3, the chamber that constitutes the closed system, the exhaust means for discharging decomposition gases (vacuum pump, etc.), etc. are omitted from the display.

[0036] The recycled carbon fiber manufacturing apparatus 10A in Figure 2 includes an endless belt 6 and a pair of belt rollers 5 that suspend the belt 6 as means for moving and stopping the carbon fiber reinforced plastic body 2. The pair of belt rollers 5 rotate to move the belt 6 around a predetermined circumference, and the rotation is stopped to position the carbon fiber reinforced plastic body 2 in a predetermined location.

[0037] In Figure 2, the recycled carbon fiber manufacturing apparatus 10A is shown, with the carbon fiber reinforced plastic body 2 placed on a belt 6, which also serves as a processing stage. The present invention is not limited to this embodiment, and the carbon fiber reinforced plastic body 2 may be moved and stationary on the belt 6 while placed on a separately prepared processing stage. Also, although Figure 2 shows a total of two laser light sources 1A and 1B, the number of laser light sources may be one or three or more. Furthermore, the position of the laser light sources, taking into account the laser irradiation position on the surface of the carbon fiber reinforced plastic body 2 and the laser irradiation angle to the carbon fiber reinforced plastic body 2, is not particularly limited.

[0038] In the recycled carbon fiber manufacturing apparatus 10A shown in Figure 2, by starting or stopping the rotation of the belt roller 5 in the direction of the arrow, the laser irradiation position on the surface of the carbon fiber reinforced plastic body 2 can be set to a desired position. By repeatedly moving the carbon fiber reinforced plastic body 2 and irradiating it with the laser, the entire surface of the carbon fiber reinforced plastic body 2 can be efficiently irradiated with the laser, removing the plastic material and obtaining recycled carbon fiber.

[0039] In the recycled carbon fiber manufacturing apparatus 10A shown in Figure 2, which is equipped with laser light sources 1A and 1B, carbon fiber can be obtained by thoroughly removing the coated plastic material with the laser from laser light source 1B, which is the second laser to emit. In this case, a method can be applied in which lasers with the same energy density are irradiated from both laser light sources 1A and 1B, or a method can be applied in which the energy densities of the lasers emitted from each laser light source are different. The laser irradiation time may also be adjusted.

[0040] The recycled carbon fiber manufacturing apparatus 10B in Figure 3 incorporates a means that reflects a conventionally known method for manufacturing recycled carbon fibers, which involves contacting a carbon fiber-reinforced plastic body 2 with superheated steam, into the recycled carbon fiber manufacturing apparatus 10A in Figure 2. In the recycled carbon fiber manufacturing apparatus 10B of Figure 3, this means can be used to efficiently remove the plastic material coating the carbon fibers and the carbon-like residue derived from the plastic material by contacting the carbon fiber-reinforced plastic body 2 with superheated steam while performing laser irradiation. Furthermore, it can be used as a means to reduce the content ratio (amount of coating) of the plastic material coating the carbon fibers and the carbon-like residue derived from the plastic material by contacting the carbon fiber-reinforced plastic body 2 with superheated steam before performing laser irradiation, or as a means to contact the carbon fibers with superheated steam after laser irradiation if a coating of plastic material remains on the surface of the carbon fibers. For example, the belt 6 can have a breathable mesh structure, and the structure can be configured to supply superheated steam generated by the superheated steam generator 8 upwards so as to blow it onto the lower surface of the carbon fiber reinforced plastic body 2.

[0041] The recycled carbon fiber manufacturing apparatus 10B in Figure 3 is configured to supply superheated steam from below. However, in other embodiments, the apparatus may be equipped with superheated steam supply means at a position not limited to below, so that the carbon fiber reinforced plastic body 2 is in contact with the superheated steam in a closed system.

[0042] According to the recycled carbon fiber manufacturing apparatus of the present invention, recycled carbon fibers can be manufactured by irradiating a sizing agent-adhered carbon fiber (bundle) with a laser instead of using a carbon fiber-reinforced plastic body 2. [Examples]

[0043] The embodiments of the present invention will be described in more detail below with reference to examples. However, the present invention is not limited in any way to these examples.

[0044] 1. Recycled carbon fiber manufacturing equipment In the following Examples 1 to 12, the recycled carbon fiber manufacturing apparatus 20 shown in Figure 4, including the configuration in Figure 1, was used. The apparatus in Figure 4 has a configuration in which a laser is irradiated onto a test material (carbon fiber reinforced plastic body) 22 inside a chamber 21 that can be depressurized by exhaust from a vacuum pump (not shown). The test material 22 is placed on the surface of a porous alumina insulation material 26 placed on a processing stage 24. The laser light source 1 is located outside the chamber 21, and the laser is irradiated onto the test material 22 through a transmission window 27. The irradiation angle of the laser onto the test material 22, which is placed horizontally on the insulation material 26, is approximately 70 degrees. In addition, a radiation thermometer 28 (observation wavelengths: 1.6 μm, 1.8 μm) was placed outside the chamber 21 to measure the surface temperature of the test material 22 during laser irradiation. In Example 13, a recycled carbon fiber manufacturing apparatus 10A (see Figure 2) was used, which irradiated the test specimen 2 with a laser by driving only the laser light source 1A. Although not shown in Figure 2, the configuration was the same as in Figure 4, with laser irradiation performed inside the chamber, and a radiation thermometer (observation wavelengths: 1.6 μm, 1.8 μm) was placed outside the chamber to measure the surface temperature of the test material 2 during laser irradiation.

[0045] 2. Test material In Examples 1 to 12, a carbon fiber-reinforced plastic body (size: 70 mm × 15 mm × 0.5 mm) was obtained by impregnating a large number of carbon fiber bundles with an epoxy resin composition and heat curing it. This was then exposed to superheated steam at 500°C for 2 hours. Approximately 80% of the epoxy-cured resin coating on the carbon fiber-reinforced plastic body was removed, but the surface of the carbon fibers (bundles) remained covered with carbon-like residue formed by the superheated steam treatment. This irregularly shaped fiber aggregate was obtained and used as the test material. In Example 13, a long, primary treated specimen with dimensions of 500 mm × 50 mm × 0.5 mm, obtained in the same manner as described above, was used as the test material.

[0046] 3. Manufacturing and evaluation of recycled carbon fiber (Part 1, Examples 1-12) The above-mentioned test material, placed in the recycled carbon fiber manufacturing apparatus 20 shown in Figure 4, was irradiated with a semiconductor laser (wavelength: 1.07 μm) to decompose and remove carbon-like residue from the carbon fiber surface, and numerous carbon fibers were recovered. Laser irradiation was performed on a 50 mm × 20 mm area on the surface of the test material, while varying the irradiation conditions and scanning a 5 mm beam diameter longitudinally (scanning speed: 2000 mm / sec). Subsequently, using an Instron "Universal Material Tester 5942," 20 single fibers were extracted from each of the recovered carbon fibers, and tensile tests were performed according to the method compliant with JIS R 7606 to measure the tensile load and displacement. The elastic modulus was then calculated from these measurements, and a graph was created for the laser irradiation conditions (energy density), which is shown in Figure 5. The plots in Figure 5 reflect the average value of 20 measurements, and the error bars above and below the plots reflect the standard deviation σ of the normal distribution of the measured values.

[0047] Example 1 In Figure 4, with the chamber 21 of the recycled carbon fiber manufacturing apparatus 20 set to an atmospheric environment, the energy density of a predetermined portion of the test material 22 is 10 W / cm². 2 The carbon fiber surface was irradiated with a laser for 60 seconds to remove carbon-like residue and obtain recycled carbon fiber. Approximately 10 seconds after the start of laser irradiation, the surface temperature of the test material 22 reached approximately 580°C, and thereafter the surface temperature remained almost stable in the range of 575°C to 585°C until 60 seconds had elapsed since the start of laser irradiation. Subsequently, tensile tests were conducted on the obtained recycled carbon fibers, and the elastic modulus (average value) was found to be 255 GPa (see Figure 5).

[0048] Example 2 Energy density is 15 W / cm² 2 Recycled carbon fibers were obtained by performing the same procedure as in Example 1, except that the laser was irradiated for 60 seconds. Approximately 10 seconds after the start of laser irradiation, the surface temperature of the test material 22 reached approximately 680°C, and thereafter the surface temperature remained almost stable in the range of 665°C to 680°C until 60 seconds had elapsed since the start of laser irradiation. Subsequently, a tensile test was conducted on the obtained recycled carbon fiber, and the elastic modulus (average value) was 268 GPa (see Fig. 5).

[0049] Example 3 A laser with an energy density of 20 W / cm 2 was irradiated for 60 seconds, and the same operations as in Example 1 were performed to obtain recycled carbon fiber. When about 13 seconds had elapsed since the start of the laser irradiation, the surface temperature of the test material 22 became about 755°C. Thereafter, the surface temperature remained substantially stable in the range of 750°C to 760°C until 60 seconds had elapsed since the start of the laser irradiation. Subsequently, a tensile test was conducted on the obtained recycled carbon fiber, and the elastic modulus (average value) was 271 GPa (see Fig. 5).

[0050] Example 4 A laser with an energy density of 25 W / cm 2 was irradiated for 60 seconds, and the same operations as in Example 1 were performed to obtain recycled carbon fiber. When about 20 seconds had elapsed since the start of the laser irradiation, the surface temperature of the test material 22 became about 840°C. Thereafter, the surface temperature remained substantially stable in the range of 835°C to 845°C until 60 seconds had elapsed since the start of the laser irradiation. Subsequently, a tensile test was conducted on the obtained recycled carbon fiber, and the elastic modulus (average value) was 268 GPa (see Fig. 5).

[0051] Example 5 A laser with an energy density of 30 W / cm 2 was irradiated for 60 seconds, and the same operations as in Example 1 were performed to obtain recycled carbon fiber. When about 15 seconds had elapsed since the start of the laser irradiation, the surface temperature of the test material 22 became about 915°C. Thereafter, the surface temperature remained substantially stable in the range of 915°C to 900°C until 60 seconds had elapsed since the start of the laser irradiation. Subsequently, a tensile test was conducted on the obtained recycled carbon fiber, and the elastic modulus (average value) was 268 GPa (see Fig. 5).

[0052] Example 6 A laser with an energy density of 20 W / cm2 Recycled carbon fibers were obtained by performing the same procedure as in Example 1, except that the laser was irradiated for 30 seconds. Subsequently, a tensile test was performed on the obtained recycled carbon fibers, and the elastic modulus (average value) was 256 GPa (see Figure 5).

[0053] Example 7 Energy density is 25 W / cm² 2 Recycled carbon fibers were obtained by performing the same procedure as in Example 1, except that the laser was irradiated for 30 seconds. Subsequently, a tensile test was performed on the obtained recycled carbon fibers, and the elastic modulus (average value) was 270 GPa (see Figure 5).

[0054] Example 8 Energy density is 30 W / cm² 2 Recycled carbon fibers were obtained by performing the same procedure as in Example 1, except that the laser was irradiated for 30 seconds. Subsequently, a tensile test was performed on the obtained recycled carbon fibers, and the elastic modulus (average value) was 253 GPa (see Figure 5).

[0055] Example 9 Energy density is 40 W / cm² 2 Recycled carbon fibers were obtained by performing the same procedure as in Example 1, except that the laser was irradiated for 30 seconds. Approximately 8 seconds after the start of laser irradiation, the surface temperature of the test material 22 reached approximately 1045°C, and thereafter the surface temperature remained almost stable in the range of 1050°C to 1040°C until 30 seconds had elapsed since the start of laser irradiation. Subsequently, tensile tests were conducted on the obtained recycled carbon fibers, and the elastic modulus (average value) was found to be 272 GPa (see Figure 5).

[0056] Example 10 Energy density is 25 W / cm² 2 Recycled carbon fibers were obtained by performing the same procedure as in Example 1, except that the laser was irradiated for 10 seconds. Subsequently, a tensile test was performed on the obtained recycled carbon fibers, and the elastic modulus (average value) was 264 GPa (see Figure 5).

[0057] Example 11 Energy density is 30 W / cm² 2 Recycled carbon fibers were obtained by performing the same procedure as in Example 1, except that the laser was irradiated for 10 seconds. Subsequently, a tensile test was performed on the obtained recycled carbon fibers, and the elastic modulus (average value) was 269 GPa (see Figure 5).

[0058] Example 12 Energy density is 40 W / cm² 2 Recycled carbon fibers were obtained by performing the same procedure as in Example 1, except that the laser was irradiated for 10 seconds. Subsequently, a tensile test was performed on the obtained recycled carbon fibers, and the elastic modulus (average value) was 272 GPa (see Figure 5).

[0059] 4. Manufacturing and evaluation of recycled carbon fiber (Part 2, Example 13) Example 13 The long test material described above was fed longitudinally onto the belt 6 of the recycled carbon fiber manufacturing apparatus 10A having the configuration shown in Figure 2. While moving along the belt 6 at a speed of 5 mm per minute, a semiconductor laser (wavelength: 1.07 μm) was irradiated so that it was irradiated at a specific position for 5 minutes, and the energy density was adjusted so that the surface temperature remained stable in the range of 770°C to 790°C. This decomposed and removed the carbonous residue on the surface of the carbon fibers, and a large number of carbon fibers were recovered. Subsequently, a tensile test was performed in the same manner as described above. As a result, the elastic modulus (average value) was 270 GPa, and the tensile strength (average value) was 94% of the relative strength of untreated carbon fibers. [Industrial applicability]

[0060] According to the present invention, recycled carbon fibers suitable for reuse, having an elastic modulus of, for example, 250 GPa or more, can be efficiently produced from waste materials generated during the manufacturing process of products made of carbon fiber reinforced plastics in fields such as the aerospace industry, automotive industry, power generation equipment, home appliances, sports, leisure, and toys, as well as from waste materials of components containing carbon fiber reinforced plastics. [Explanation of Symbols]

[0061] 1,1A,1B: Laser light source 2: Carbon fiber reinforced plastic (body) 3: Carbon fiber 4: Plastic materials 5: Belt roller 6: Belt 8: Superheated steam generator 10A, 10B: Recycled carbon fiber manufacturing equipment 20: Recycled carbon fiber manufacturing equipment 21: Chamber 22: Test material (carbon fiber reinforced plastic body) 24: Processing stage 26: Insulation 27: Transparent window 28: Radiation thermometer

Claims

1. A method for obtaining carbon fibers from carbon fiber reinforced plastic, On the surface of the carbon fiber reinforced plastic, the energy density is 5 W / cm². ２ A method for manufacturing recycled carbon fiber, comprising a laser irradiation step of removing plastic material and carbon-like residue derived from the plastic material by irradiating it with the above-mentioned laser.

2. The method for producing recycled carbon fiber according to claim 1, wherein the wavelength of the laser is 200 nm to 15 μm.

3. A recycled carbon fiber manufacturing device equipped with a laser light source that irradiates carbon fiber reinforced plastic bodies with a laser.

4. The recycled carbon fiber manufacturing apparatus according to claim 3, further comprising a feeding means for moving and stopping the carbon fiber reinforced plastic body in order to continuously irradiate a long or large-area carbon fiber reinforced plastic body or a plurality of the carbon fiber reinforced plastic bodies with a laser.

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