How to recycle reinforced fibers

Abstract

To provide a method to easily recycle reinforcing fibers from tanks, for example.SOLUTION: This embodiment is a method for recycling reinforcing fibers, comprising the steps of: preparing a tank having at least a liner, a first protective layer disposed over the outer surface of the liner and comprising a reinforcing fiber bundle and a resin-impregnated fiber bundle containing a first matrix resin to be wound onto the liner, and a second protective layer comprising the first matrix resin on the first protective layer; removing a portion of the second protective layer to expose an end portion of a resin-impregnated fiber bundle at the end of winding; peeling off the exposed end portion; and pulling out the resin-impregnated fiber bundle by pulling on the peeled end portion.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for recycling reinforcing fibers. [Background technology]

[0002] Carbon fiber reinforced plastic (CFRP) is a lightweight, highly rigid material that can withstand high-pressure gas. For this reason, it is used as a reinforcing material for hydrogen tanks in fuel cell (FC) vehicles. Hybrid fiber reinforced plastics, in which a layer of glass fiber reinforced plastic (GFRP) is placed on top of a carbon fiber reinforced plastic layer as a protective material, are also being used.

[0003] Patent Document 1, for example, discloses a high-pressure tank for storing gas, which includes at least a resin liner for accommodating gas, a fiber-reinforced resin reinforcing layer that covers the outer surface of the liner and is made of carbon fiber and has a glass fiber as the reinforcing fiber, and a protective layer that covers the outer surface of the reinforcing layer and is made of fiber-reinforced resin and has a glass fiber as the reinforcing fiber, wherein the protective layer includes a first protective layer that covers the outer surface of the reinforcing layer and is made of fiber-reinforced resin composed of glass fiber and a matrix resin, and a second protective layer that covers the outer surface of the first protective layer and contains the matrix resin, the protective layer having a lower matrix resin content than the reinforcing layer, and the second protective layer has a crack that extends around the high-pressure tank and reaches from the surface of the second protective layer to the interface between the first and second protective layers. Specifically, the high-pressure tank disclosed in Patent Document 1 has a reinforcing layer made of fiber-reinforced resin with carbon fiber as the reinforcing fiber, and a protective layer covering the outer peripheral surface of the reinforcing layer and made of fiber-reinforced resin with glass fiber as the reinforcing fiber, and the protective layer includes a first protective layer covering the outer peripheral surface of the reinforcing layer and made of fiber-reinforced resin composed of glass fiber and a matrix resin, and a second protective layer covering the outer peripheral surface of the first protective layer and containing the matrix resin.

[0004] However, the carbon fibers and glass fibers contained in carbon fiber reinforced resins or glass fiber reinforced resins are expensive, generate a large amount of CO2 during production, and are difficult to dispose of, resulting in a high environmental impact. Therefore, methods for recovering and recycling carbon fibers and glass fibers from used fiber reinforced resins have been studied.

[0005] Patent documents that disclose methods for recycling reinforcing fibers such as carbon fibers and glass fibers from tanks include, for example, Patent Documents 2 and 3 below.

[0006] Patent Document 2 discloses a reinforcing fiber recovery method including an unwinding step of unwinding reinforcing fibers while separating the resin from the reinforced part, a sizing step of passing the unwound reinforcing fibers through a sizing liquid to coat the reinforcing fibers with the sizing liquid, and a winding step of winding the reinforcing fibers coated with the sizing liquid around a mandrel. Furthermore, Patent Document 1 discloses an embodiment in which the unwinding step includes a swelling step of immersing the reinforced part in a swelling liquid to swell the resin in the reinforced part, a dissolving step of passing the reinforcing fibers through a dissolving liquid while unwinding them from the reinforced part to dissolve the resin impregnated in the reinforcing fibers, and an intermediate winding step of winding the rein-dissolved reinforcing fibers through an intermediate winder.

[0007] Patent Document 3 discloses a method for obtaining a carbon fiber base material as a recycled carbon fiber bundle from a carbon fiber reinforced resin containing a plurality of carbon fiber base materials and a matrix resin, in which the carbon fiber reinforced resin is heated to thermally decompose the matrix resin to obtain a heat-treated product, and the heat-treated product is crushed to separate the plurality of carbon fiber base materials. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2020-37978 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-104847 [Patent Document 3] International Publication No. 2018 / 212016 Summary of the Invention [Problem to be solved by the invention]

[0009] For example, as disclosed in Patent Document 1, there is a tank that has at least a liner, a first protective layer that is arranged on the outer peripheral surface of the liner and is configured so that resin-impregnated fiber bundles containing reinforcing fiber bundles and a matrix resin are wound around the liner, and a second protective layer that is formed of the matrix resin on the first protective layer, and there is a need for a method of recovering reinforcing fibers from such a tank, i.e., a recycling method.

[0010] However, if a reinforced part is immersed in a swelling liquid before the reinforcing fibers are extracted from the tank in order to recycle the reinforcing fibers, as described in Patent Document 2, the position of the end of the fiber-reinforced resin winding may become difficult to determine. For example, a display indicating the position of the end of the winding, provided on the surface of the tank, may disappear or become difficult to see. Furthermore, the process of immersing the entire tank in a swelling liquid may be complicated in terms of the type of swelling liquid used, the equipment, the immersion time, etc.

[0011] Furthermore, if the entire tank is heated to pyrolyze the matrix resin in order to recycle the reinforcing fibers from the tank described above, as described in Patent Document 3, the shape of the tank may be distorted, making it impossible to continuously pull out the reinforcing fibers, and the position of the winding end of the resin-impregnated fiber bundle may become difficult to determine. Furthermore, in Patent Document 3, the matrix resin is pyrolyzed by heating the carbon fiber reinforced resin at a high temperature, but heating at a high temperature may deteriorate the reinforcing fibers and reduce their strength. Furthermore, heating the resin-impregnated fiber bundle at a high temperature may change the properties of the resin, such as its solubility, making it difficult to remove the resin in subsequent processes.

[0012] Therefore, an object of the present disclosure is to solve at least one of the above-mentioned problems, specifically to provide a method for easily recycling reinforcing fibers from a tank having at least a first protective layer configured so that reinforcing fiber bundles and resin-impregnated fiber bundles containing a matrix resin are wound around a liner, and a second protective layer configured of the matrix resin on top of the first protective layer. [Means for solving the problem]

[0013] One aspect of this embodiment is as follows. (1) A method for recycling reinforcing fibers, comprising: a step of preparing a tank having at least a liner, a first protective layer disposed on an outer peripheral surface of the liner and configured so that a resin-impregnated fiber bundle containing a reinforcing fiber bundle and a first matrix resin is wound around the liner, and a second protective layer formed of the first matrix resin on the first protective layer; removing a portion of the second protective layer to expose the winding end of the resin-impregnated fiber bundle; peeling the exposed end of the winding; and The process of pulling the peeled end of the winding and pulling out the resin-impregnated fiber bundle. A method comprising: (2) The method according to (1), wherein the second protective layer is a layer formed by curing a portion of the first matrix resin contained in the first protective layer in an exuded state. (3) The method according to (1) or (2), wherein the first matrix resin is an epoxy resin. (4) The method according to any one of (1) to (3), wherein a portion of the second protective layer is removed by laser treatment. (5) The method according to (4), wherein the laser used in the laser treatment is a carbon dioxide laser, a YAG laser, a fiber laser, or a semiconductor laser. (6) The method according to (5), wherein the laser used in the laser treatment is a carbon dioxide laser. (7) The method according to (6), wherein the output of the carbon dioxide laser is 100 W or less. (8) The method according to any one of (1) to (3), wherein the portion of the second protective layer is removed by bringing a dissolving solution into contact with the portion of the second protective layer. (9) The method according to (8), wherein the dissolving liquid contains at least one liquid selected from an acidic solution, an organic solvent, a hydrogen peroxide solution, and an ionic liquid. (10) The method according to any one of (1) to (3), wherein the part of the second protective layer is removed by subjecting the part of the second protective layer to a heat treatment. (11) The method according to (10), wherein the temperature of the heat treatment is 550°C or higher and 700°C or lower. (12) The method according to any one of (1) to (11), wherein the reinforcing fiber bundles are glass fiber bundles or carbon fiber bundles. (13) The method according to (12), wherein the reinforcing fiber bundles are glass fiber bundles. (14) The method according to (13), further comprising a reinforcing layer between the protective layer and the liner, the reinforcing layer being configured such that carbon fiber bundles and resin-impregnated carbon fiber bundles containing a second matrix resin are wound around the liner. [Effects of the Invention]

[0014] According to the present disclosure, at least one of the above-mentioned problems can be solved, and specifically, a method can be provided that can easily recycle reinforcing fibers from a tank that has at least a first protective layer configured so that reinforcing fiber bundles and resin-impregnated fiber bundles containing a matrix resin are wound around a liner, and a second protective layer configured of the matrix resin on top of the first protective layer. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a flowchart illustrating one embodiment of a recycling method according to the present embodiment. [Figure 2] FIG. 1 is a schematic cross-sectional view showing an example of the configuration of a tank 100 that can be used in this embodiment, taken along a plane along the axial direction. [Figure 3] FIG. 3 is a schematic diagram showing a state in which the second protective layer 30b constituting the surface of the tank 100 shown in FIG. 2 has been partially removed to expose the first protective layer 30a. [Figure 4] FIG. 4 is an enlarged schematic view of the area surrounded by the dotted line in FIG. 3, showing the exposed winding end portion of the resin-impregnated fiber bundle. [Figure 5]1 is a schematic diagram showing the shape of the winding end of a resin-impregnated fiber bundle in which the winding end is cured or solidified and fixed without being bent. FIG. [Figure 6] This is an image showing the state after removing the epoxy resin as the second protective layer with a low-power (average power: 30 W) carbon dioxide laser (10.6 μm, continuous wave). [Figure 7] 1 is a graph showing the relationship between the number of laser irradiations and etching depth (mm) when an epoxy resin serving as a second protective layer is removed using a low-power (average power: 30 W) carbon dioxide laser (10.6 μm, continuous wave). [Figure 8] 8 shows images of the tank surface at the 10th, 20th, and 50th irradiations in the experiment shown in FIG. 7. [Figure 9] 1 is a schematic diagram showing one embodiment of a tank having a bent portion at the winding end of the resin-impregnated fiber bundle, where the resin-impregnated fiber bundle is fixed in a bent state. FIG. [Figure 10] FIG. 1 is a schematic diagram illustrating the problem of vertical tearing of the fiber bundle that can occur when peeling off the winding end using a tool such as a scraper. [Figure 11] FIG. 1 is a schematic diagram illustrating the problem of tearing of the fiber bundle in the left-right direction, which may occur when peeling off the winding end using a tool such as a scraper. [Figure 12] FIG. 10 is a schematic diagram showing a configuration in which the resin-impregnated fiber bundle in the rear portion of the bent portion is bent and fixed so as to be on top of the resin-impregnated fiber bundle in the front portion of the bent portion. [Figure 13] FIG. 10 is a schematic diagram showing a configuration in which the resin-impregnated fiber bundle in the rear portion of the bent portion is bent and fixed so as to be below the resin-impregnated fiber bundle in the front portion of the bent portion. [Figure 14] FIG. 10 is a schematic diagram showing a configuration in which the resin-impregnated fiber bundle in the rear portion of the bent portion is folded back and fixed so as to be on top of the resin-impregnated fiber bundle in the front portion of the bent portion. [Figure 15]FIG. 10 is a schematic diagram showing a configuration in which the resin-impregnated fiber bundle in the rear portion of the bent portion is folded back and fixed so as to be below the resin-impregnated fiber bundle in the front portion of the bent portion. [Figure 16] 10 is a schematic diagram for explaining the bending angle θ, showing the bending portion viewed in the radial direction from outside the tank. FIG. [Figure 17] 10A and 10B are schematic diagrams for explaining a drawing step under heating in the present embodiment. [Figure 18A] FIG. 1 is a graph showing an example of the thermal properties of an epoxy resin, and is a graph showing a weight change chart (TG curve) of thermogravimetric analysis obtained by heating the resin under a nitrogen atmosphere (horizontal axis: temperature, vertical axis: weight loss rate). [Figure 18B] FIG. 1 is a graph showing an example of the thermal properties of an epoxy resin, and is a graph showing a weight change chart (TG curve) of thermogravimetric analysis obtained by heating the resin in an air atmosphere (horizontal axis: temperature, vertical axis: weight loss rate). [Figure 19] 1 is a graph showing the thermal properties of carbon fiber as an example of reinforcing fiber, and is a graph showing the strength ratio (tensile strength after heating / tensile strength before heating) when carbon fiber is heated in the atmosphere at predetermined temperatures (300°C, 400°C, 500°C) for predetermined times (horizontal axis). [Figure 20] 1 is a graph showing the tensile shear strength ratio of a resin (epoxy resin) at a predetermined temperature. [Figure 21] FIG. 21 is a schematic diagram for explaining the configuration of a test piece used in a tensile shear test for measuring the tensile shear strength ratio shown in FIG. 20. DETAILED DESCRIPTION OF THE INVENTION

[0016] This embodiment relates to a method for recycling reinforcing fibers, which includes the steps of: preparing a tank having at least a liner; a first protective layer disposed on the outer peripheral surface of the liner and configured so that a resin-impregnated fiber bundle containing a reinforcing fiber bundle and a first matrix resin is wound around the liner; and a second protective layer formed of the first matrix resin on the first protective layer; removing a portion of the second protective layer to expose a winding end of the resin-impregnated fiber bundle; peeling off the exposed winding end; and pulling the peeled winding end to pull out the resin-impregnated fiber bundle.

[0017] According to this embodiment, a method can be provided for easily recycling reinforcing fibers from a tank having at least a first protective layer configured so that reinforcing fiber bundles and resin-impregnated fiber bundles containing a first matrix resin are wound around a liner, and a second protective layer configured of the first matrix resin on top of the first protective layer.

[0018] The recycling method of this embodiment will be described in detail below.

[0019] An example of a flowchart for explaining the recycling method according to this embodiment is shown in Fig. 1. As shown in Fig. 1, this embodiment includes at least a tank preparation step, a second protective layer partial removal step, a peeling step, and a pulling-out step. Each step will be described in detail below.

[0020] (Tank preparation process) The recycling method according to this embodiment includes the step of preparing a tank having at least a liner, a first protective layer disposed on the outer peripheral surface of the liner and configured so that a resin-impregnated fiber bundle containing a reinforcing fiber bundle and a first matrix resin is wound around the liner, and a second protective layer formed of the first matrix resin on the first protective layer.

[0021] Examples of the tanks that may be prepared include those that have been used for various purposes after manufacture and then collected, and those that are defective during the manufacturing process.

[0022] The reinforcing fibers used in the reinforcing fiber bundles of the resin-impregnated fiber bundles (fiber-reinforced resin layer) are not particularly limited, but examples thereof include inorganic fibers such as glass fibers, carbon fibers, metal fibers, and alumina fibers, synthetic organic fibers such as aramid fibers, and natural organic fibers such as cotton. These fibers may be used alone or in combination (as mixed fibers).

[0023] The first matrix resin used in the resin-impregnated fiber bundle is not particularly limited, but examples thereof include phenolic resin, urea resin, unsaturated polyester resin, vinyl ester resin, polyimide resin, bismaleimide resin, polyurethane resin, diallyl phthalate resin, epoxy resin, and mixtures thereof.

[0024] Examples of the first matrix resin include a thermosetting resin or a thermoplastic resin. The first matrix resin is preferably a thermosetting resin. Examples of the thermosetting resin include an epoxy resin, an epoxy-modified polyurethane resin, a polyester resin, a phenolic resin, a polyurethane resin, and a thermosetting polyimide resin. Examples of the epoxy resin include, but are not limited to, bisphenol A epoxy resin, bisphenol AD ​​epoxy resin, bisphenol F epoxy resin, phenol novolac epoxy resin, cresol novolac epoxy resin, and glycidyl ester epoxy resin. The epoxy resin may be linear or branched. One type of first matrix resin may be used alone, or two or more types may be used in combination.

[0025] The resin-impregnated fiber bundles used to form a layer (fiber-reinforced resin layer) made of resin-impregnated fiber bundles can be prepared by a method conventionally known in the art. The resin-impregnated fiber bundles are not particularly limited, but can be prepared, for example, by prepreg molding in which reinforcing fiber bundles are impregnated with a liquid resin.

[0026] The resin-impregnated fiber bundle can be wound by a conventionally known method. For example, a conventionally known filament winding device can be used to wind the resin-impregnated fiber bundle. The filament winding device can repeatedly wind the resin-impregnated fiber bundle around the periphery of a mold, thereby forming a fiber layer of the resin-impregnated fiber bundle around the periphery of the mold. When a thermosetting resin (e.g., epoxy resin) is used as the resin, a fiber layer impregnated with the epoxy resin is formed around the periphery of the mold. The resin is then cured by heating or the like. The number of windings is not limited, but the resin-impregnated fiber bundle is wound until the thickness of the fiber layer formed around the periphery of the mold is usually 10 mm to 30 mm. After winding, the resin-impregnated fiber bundle is cured by appropriate heat treatment to obtain a fiber-reinforced resin layer. For example, a heat curing oven can be used for the heat treatment.

[0027] An embodiment according to the present invention will be described in detail below.

[0028] A configuration example of the tank in this embodiment will be described below with reference to Fig. 2. Note that the following configuration example shows one embodiment, and it is not intended that this embodiment be limited by the description of the following configuration example.

[0029] FIG. 2 is a cross-sectional view showing an example of the configuration of a tank 100 that can be used in this embodiment. FIG. 2 shows a cross-sectional view taken along a plane parallel to and passing through the central axis of the tank 100. The central axis of the tank 100 (dotted line X) coincides with the axis passing through the center of the circle of the tank body, which has a substantially cylindrical shape. The tank 100 can be used, for example, to fill with a gas such as compressed hydrogen. For example, the tank 100, filled with compressed hydrogen, is mounted on a fuel cell vehicle to supply hydrogen to the fuel cell.

[0030] FIG. 2 is a schematic cross-sectional view along the axial direction of a tank 100 according to this embodiment. The tank 100 is a hollow container centered on a central axis X, and is a pressure vessel for storing high-pressure fluids such as high-pressure hydrogen gas and high-pressure natural gas. As shown in FIG. 2, the tank 100 includes at least a resin liner 10 for storing gas, a reinforcing layer 20 covering the outer circumferential surface of the liner 10, and a protective layer 30 covering the outer circumferential surface of the reinforcing layer 20. A valve-side nozzle 40 and an end-side nozzle 60 are provided at both ends of the tank 100, respectively. A valve 50 is attached to the valve-side nozzle 40.

[0031] The liner 10 has a body and two side ends, forms an internal space for storing gas, and has gas barrier properties that seal the internal space to prevent gases such as hydrogen from leaking to the outside. The body is a cylindrical portion extending a predetermined length along the central axis X of the tank 100 shown in Figure 2. The side ends are dome-shaped portions formed continuously on both sides of the body, and each side end decreases in diameter as it moves away from the body, with an opening formed in the center of the most reduced diameter portion, and each opening is provided with a valve-side nozzle 40 and an end-side nozzle 60.

[0032] The liner 10 is made of a resin having gas barrier properties. Examples of such resins include polyethylene resin, polypropylene resin, and nylon resin. One type of resin may be used alone, or two or more types may be used in combination. The liner 10 may also be made by mixing a gas-impermeable material such as a hydrogen storage alloy into the above-mentioned resin.

[0033] The reinforcing layer 20 is formed of resin-impregnated carbon fiber bundles (carbon fiber reinforced plastic (CFRP)) containing carbon fiber bundles and a second matrix resin. The reinforcing layer 20 is configured so that the resin-impregnated carbon fiber bundles containing carbon fiber bundles and a second matrix resin are wound around the liner. The reinforcing layer 20 can be formed, for example, by winding the fibers of the resin-impregnated carbon fiber bundles around the outer circumferential surface of the liner 10 using hoop winding and / or helical winding. The layer (carbon fiber reinforced resin layer) 20 made of the resin-impregnated carbon fiber bundles mainly functions to reinforce the liner 10 (reinforcing layer). Examples of the second matrix resin impregnated into the carbon fiber bundles include thermosetting resins and thermoplastic resins. Carbon fibers can be prepared by methods conventionally known in the technical field. Any material containing carbon as a main component may be used as the carbon fiber, and examples thereof include carbon fibers made from acrylic, pitch, or polyvinyl alcohol. Among these, PAN-based carbon fibers produced from polyacrylonitrile fibers are preferred.

[0034] The protective layer 30 is composed of a first protective layer 30a and a second protective layer 30b. The first protective layer 30a is formed of resin-impregnated glass fiber bundles (glass fiber reinforced plastic (GFRP)) using glass fiber bundles as reinforcing fiber bundles, and is configured so that the resin-impregnated fiber bundles containing the glass fiber bundles and a first matrix resin are wound around a liner. Specifically, the first protective layer 30a is formed by winding the glass fibers of the resin-impregnated glass fiber bundles around the outer circumferential surface of the reinforcing layer 20, for example, by helical winding and / or hoop winding. The first matrix resin impregnated into the glass fiber bundles can be, for example, a thermosetting resin or a thermoplastic resin.

[0035] The protective layer 30 includes a first protective layer 30a that covers the outer peripheral surface of the reinforcing layer 20, and a second protective layer 30b that covers the outer peripheral surface of the first protective layer 30a. The second protective layer 30b may be a layer formed by hardening a portion of the first matrix resin impregnated into the glass fiber bundles in a state where the resin seeps out onto the surface of the glass fiber reinforced resin that has been wound to form the first protective layer 30a, during a heat curing step after the winding is completed.

[0036] The first protective layer 30a is made of a resin-impregnated fiber bundle composed of glass fibers and a first matrix resin. The first matrix resin contained in the first protective layer 30a may be made of the same material as the second matrix resin of the reinforcing layer 20. Furthermore, the first matrix resin contained in the first protective layer 30a may be made of the same material as the second matrix resin contained in the reinforcing layer 20, or may be made of a different material.

[0037] The second protective layer 30b contains a first matrix resin as its main material. As described above, this first matrix resin may be a portion of the first matrix resin impregnated into the glass fiber bundles of the first protective layer 30a that has seeped out to the surface of the first protective layer 30a. The content of the first matrix resin in the second protective layer 30b is higher than the content of the first matrix resin in the first protective layer 30a. Such a second protective layer 30b may contain only the first matrix resin, or may contain a portion of the glass fibers separated from the first protective layer 30a.

[0038] In FIG. 2 , the valve-side nozzle 40 is generally cylindrical and is fitted and fixed between the liner 10 and the reinforcing layer 20. The generally cylindrical opening of the valve-side nozzle 40 functions as the opening of the tank 100. In this embodiment, the valve-side nozzle 40 can be made of, for example, stainless steel, but it may also be made of other metals such as aluminum, or may be made of resin. The valve 50 has a male thread formed on its cylindrical portion, which is threaded into a female thread formed on the inner surface of the valve-side nozzle 40, thereby closing the opening of the valve-side nozzle 40 with the valve 50. The end-side nozzle 60 can be made of, for example, aluminum, and is assembled with a portion exposed to the outside, functioning to direct heat from inside the tank to the outside.

[0039] The second matrix resin is independent of the first matrix resin, and may be made of the same material as the first matrix resin, for example. Examples of the second matrix resin include a thermosetting resin or a thermoplastic resin. As described above, the first matrix resin and the second matrix resin may be made of the same material or different materials. The second matrix resin is preferably a thermosetting resin. Examples of thermosetting resins include those described above for the first matrix resin. The second matrix resin may also be used alone or in combination of two or more.

[0040] A layer made of resin-impregnated fiber bundles (fiber-reinforced resin layer) can be formed, for example, by a filament winding method. A filament winding molded product can be produced by aligning multiple reinforcing fiber bundles as needed, impregnating them with a matrix resin, and winding them at an appropriate angle and under tension to an appropriate thickness around a rotating substrate or mold.

[0041] (Step of Partially Removing Second Protective Layer) The recycling method according to this embodiment includes a step of removing a portion of the second protective layer to expose the winding end of the resin-impregnated fiber bundle.

[0042] FIG. 3 is a schematic diagram showing a state in which the second protective layer 30b constituting the surface of the tank 100 shown in FIG. 2 has been partially removed to expose the first protective layer 30a. FIG. 4 is an enlarged schematic diagram of the area surrounded by the dotted line in FIG. 3, showing the exposed end of the resin-impregnated fiber bundle. The end of the resin-impregnated fiber bundle is fixed by curing or solidification while attached to the surface of a layer (fiber-reinforced resin layer) made of the resin-impregnated fiber bundle. FIG. 5 is a schematic diagram showing the shape of the end of the resin-impregnated fiber bundle, which is fixed by curing or solidification without being bent. In FIG. 5, only the end of the resin-impregnated fiber bundle is shown, and the underlying layer, specifically the resin-impregnated fiber bundle, is omitted. Furthermore, since tanks usually have curved surfaces, the end of the resin-impregnated fiber bundle is fixed along the curved surface. A marking portion indicating the position of the end of the resin-impregnated fiber bundle may be provided on the tank surface. By providing the indicator on the surface of the tank, the area where the second protective layer is to be partially removed can be easily identified.

[0043] The method for removing a portion of the second protective layer is not particularly limited, and any method can be used as long as it can remove a portion of the second protective layer and expose the winding end of the resin-impregnated fiber bundle. Examples of the method for removing a portion of the second protective layer include laser treatment, dissolution treatment, heat treatment, and a combination thereof.

[0044] As described above, laser processing can be used to remove a portion of the second protective layer. Examples of lasers used in laser processing include carbon dioxide lasers (CO2 lasers), YAG lasers, fiber lasers, and semiconductor lasers. Among these, a carbon dioxide laser is preferred. A carbon dioxide laser is a type of gas laser that uses gaseous carbon dioxide (carbon dioxide) as a medium to generate continuous waves or high-power pulse waves in the infrared region. Laser light in the 10.6 μm wavelength band commonly used in carbon dioxide lasers is easily absorbed by resins, particularly epoxy resins, and can efficiently remove a portion of the second protective layer. On the other hand, while carbon dioxide lasers can efficiently remove resins, they also tend to damage reinforcing fibers such as glass fiber and carbon fiber. Therefore, a low-power carbon dioxide laser is preferred. For example, the average power of a continuous-wave carbon dioxide laser is preferably 100 W or less, more preferably 50 W or less, more preferably 40 W or less, and even more preferably 30 W or less.

[0045] Figure 6 is an image showing the state after removing the epoxy resin serving as the second protective layer using a low-power (average power: 30 W) carbon dioxide laser (10.6 μm, continuous wave). It was confirmed that the use of a low-power carbon dioxide laser allowed for efficient removal of the resin layer without damaging the glass fibers in the first protective layer. When removing the second protective layer with the laser, the first matrix resin in the first protective layer may also be partially removed.

[0046] Figure 7 shows the relationship between the number of laser irradiations and the etching depth (mm) when removing the epoxy resin second protective layer using a low-power (average power: 30 W) carbon dioxide laser (10.6 μm, continuous wave). Each laser irradiation is performed by scanning a continuous-wave carbon dioxide laser with a predetermined beam cross-sectional area at a constant speed so that the entire target area is irradiated. The laser is scanned to minimize overlapping of the same area during each laser irradiation. The dotted line represents the etching depth from the surface of the second protective layer to the surface of the glass fiber bundles in the first protective layer, while the solid line represents the distance from the surface of the second protective layer to the surface of the resin in the first protective layer. As shown in Figure 7, the etching depth to the resin surface in the first protective layer increases with increasing number of irradiations, while the etching depth to the surface of the glass fiber bundles remains constant after approximately 15 irradiations. This indicates that the resin layer can be efficiently removed without damaging the glass fibers in the first protective layer by using a low-power carbon dioxide laser.

[0047] Figure 8 shows images of the tank surface after the 10th, 20th, and 50th irradiations in the experiment shown in Figure 7. These images also confirm that the resin is etched as the number of irradiations increases, and that the glass fibers are not damaged even after the 20th and 50th irradiations.

[0048] As described above, a dissolution treatment can be used as a method for removing a portion of the second protective layer. Specifically, the portion of the second protective layer can be removed by bringing a dissolving solution into contact with the portion of the second protective layer.

[0049] The first matrix resin constituting the second protective layer is dissolved using a dissolving liquid capable of dissolving the resin. The dissolving liquid is not particularly limited as long as it can dissolve the first matrix resin, and includes, for example, at least one liquid selected from an acidic solution, an organic solvent, a hydrogen peroxide solution, and an ionic liquid. These liquids are capable of dissolving or swelling the resin, allowing the resin to be removed efficiently. One type of dissolving liquid may be used alone, or two or more types may be used in combination.

[0050] Examples of acidic solutions include phosphoric acid and sulfuric acid. Examples of acidic solutions include a solution containing sulfuric acid (for example, a concentration of 90% by mass or more) as described in JP 2020-37638 A, and a solution containing phosphoric acid as described in JP 2020-50704 A. One acidic component may be used alone, or two or more may be used in combination. For example, the resin can be dissolved and removed by immersing the resin-impregnated fiber bundle in concentrated sulfuric acid. The temperature of the concentrated sulfuric acid can be, for example, 100 to 300°C. Furthermore, no substantial decrease in strength is observed in the carbon fiber after the resin has been removed with the dissolving solution.

[0051] Examples of organic solvents include aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, alcohol solvents, ketone solvents, ether solvents, amide solvents, and ester solvents. One type of organic solvent may be used alone, or two or more types may be used in combination. Examples of aliphatic hydrocarbon solvents include pentane, hexane, heptane, and octane. Examples of aromatic hydrocarbon solvents include benzene, toluene, and xylene. Examples of organic solvents containing two or more components include petroleum benzine and ligroin. The organic solvent may contain a decomposition catalyst. Examples of the decomposition catalyst include alkali metal compounds such as those described in JP 2020-45407 A.

[0052] Examples of the ionic liquid include ionic liquids containing at least one cation selected from imidazolium-based, pyridinium-based, pyrrolidinium-based, quaternary ammonium-based, and quaternary phosphonium-based cations. One type of ionic liquid may be used alone, or two or more types may be used in combination.

[0053] The method for contacting a portion of the second protective layer with the dissolving liquid is not particularly limited, but an example is a method in which a sponge member soaked in the dissolving liquid is placed in contact with the target area of ​​the second protective layer.

[0054] In this embodiment, a combination of laser processing and dissolution processing may be used as a method for removing a portion of the second protective layer. For example, first, the resin is roughly removed by laser processing, and then the remaining resin is removed by a dissolving solution.

[0055] As described above, a heat treatment can be used as a method for removing a portion of the second protective layer. Specifically, the portion of the second protective layer can be removed by selectively heating it. The temperature of the heat treatment can be, for example, 550°C or higher and 700°C or lower, from the viewpoint of thermally decomposing the resin.

[0056] The means for partially heating the second protective layer is not particularly limited, but for example, a heater can be used.

[0057] In this embodiment, as shown in FIG. 9, the end of the resin-impregnated fiber bundle may be cured or solidified in a folded state and fixed. That is, the tank used may have a bending point at the end of the resin-impregnated fiber bundle where the resin-impregnated fiber bundle is fixed in a folded state. In this embodiment, the bending point refers to the end created by bending the resin-impregnated fiber bundle. Generally, the end of the resin-impregnated fiber bundle is not bent, but is cured or solidified and fixed in a state attached to the underlying resin-impregnated fiber bundle, as shown in FIGS. 4 and 5. The end of the resin-impregnated fiber bundle can be peeled by inserting a tool such as a scraper between the end and the underlying resin-impregnated fiber bundle. However, since the end of the end of the resin-impregnated fiber bundle has a configuration in which the end of the reinforcing fiber is exposed or close to the end, it is not possible to insert the tool completely between them. As a result, as shown in FIG. 10, only the upper part of the reinforcing fiber bundle may peel off, leaving the lower part (vertical tearing). Furthermore, the reinforcing fiber bundle may not only split upward and downward, but may also split left and right as shown in Figure 11 (left-right split). If the resin-impregnated fiber bundle is pulled out in a split state, the split may remain in the reinforcing fiber bundle and peel off from the tank surface, resulting in problems such as inability to accurately collect the reinforcing fibers into the bobbin, breakage of the reinforcing fibers, and reduced workability. Therefore, as shown in Figures 9 and 12, it is preferable that the winding end of the resin-impregnated fiber bundle be cured or solidified and fixed in a folded state. If the winding end is cured or solidified and fixed in a folded state, a tool such as a scraper can be accurately inserted between the folded portion and the layer below, preventing splitting and making it easier to peel off the winding end. In other words, the bent portion formed by bending and fixing the resin-impregnated fiber bundle functions as a guide between the bent portion and the resin-impregnated fiber bundle underneath when inserting an instrument such as a scraper, thereby making it possible to easily peel off the resin-impregnated fiber bundle from the bent portion while suppressing the occurrence of tearing.Furthermore, the winding end of the resin-impregnated carbon fiber bundle that constitutes the reinforcing layer (intermediate layer) 20 may also be cured or solidified and fixed in a bent state, which allows the winding end to be easily peeled off when pulling out the resin-impregnated fiber bundle that constitutes the reinforcing layer (intermediate layer).

[0058] The folded state may be such that the resin-impregnated fiber bundle in the portion behind the folding point (the portion closest to the tip of the winding end) is above the resin-impregnated fiber bundle in the portion ahead of the folding point (the portion wound first, the portion opposite the tip of the winding end), or such that the resin-impregnated fiber bundle in the portion behind the folding point is below the resin-impregnated fiber bundle in the portion ahead of the folding point. Fig. 12 is a schematic diagram showing a form in which the resin-impregnated fiber bundle in the portion behind the folding point is folded and fixed above the resin-impregnated fiber bundle in the portion ahead of the folding point. Fig. 13 is a schematic diagram showing a form in which the resin-impregnated fiber bundle in the portion behind the folding point is folded and fixed below the resin-impregnated fiber bundle in the portion ahead of the folding point.

[0059] The manner in which the resin-impregnated fiber bundle is fixed in a folded state is not particularly limited, but examples include a manner in which the resin impregnated in the reinforcing fiber bundle is cured or solidified and fixed in a folded state. Fixing can be performed, for example, by performing a heat treatment to harden the end of the winding in a folded state. For example, hot air may be blown around the end of the winding in a folded state to harden the end of the winding.

[0060] As described above, when recycling reinforcing fibers from resin-impregnated fiber bundles, the end of the resin-impregnated fiber bundle is first peeled from the tank surface using a tool such as a scraper to secure the end to the take-up roller. Fixing the resin-impregnated fiber bundle in a bent state at the end of the resin-impregnated fiber bundle makes it easier to insert a tool such as a scraper between the bent portion at the end of the winding and the resin-impregnated fiber bundle located below. This is because the bent portion formed by bending and fixing the resin-impregnated fiber bundle functions as a guide between the end of the winding to be peeled and the resin-impregnated fiber bundle located below it when inserting a tool such as a scraper, allowing the resin-impregnated fiber bundle to be easily peeled from the bent portion without causing tearing.

[0061] The bending portion preferably extends to both longitudinal sides of the resin-impregnated fiber bundle. That is, it is preferable that the edge formed by bending the resin-impregnated fiber bundle reach two (both) longitudinal sides of the resin-impregnated fiber bundle. By bending the resin-impregnated fiber bundle so that it extends to both longitudinal sides, tearing of the fiber bundle can be more effectively suppressed when the winding end portion of the resin-impregnated fiber bundle is peeled off from the bending portion.

[0062] As shown in Figures 12 and 13, it is preferable that the resin-impregnated fiber bundle is bent so that the bending direction is different from the winding direction. The winding end of the resin-impregnated fiber bundle may be fixed in a folded-back state. In this specification, the term "folded-back state" refers to a state in which the resin-impregnated fiber bundle is bent so that both longitudinal sides of the resin-impregnated fiber bundle in the rear portion of the bend coincide with both longitudinal sides of the resin-impregnated fiber bundle in the front portion of the bend, and is a term that indicates one aspect of the "folded" form. Figure 14 is a schematic diagram showing a form in which the resin-impregnated fiber bundle in the rear portion of the bend is folded back and fixed so that it is above the resin-impregnated fiber bundle in the front portion of the bend. Figure 15 is a schematic diagram showing a form in which the resin-impregnated fiber bundle in the rear portion of the bend is folded back and fixed so that it is below the resin-impregnated fiber bundle in the front portion of the bend.

[0063] 12 and 13 are schematic diagrams showing a configuration in which a resin-impregnated fiber bundle is bent so that the bending direction is different from the winding direction. Fig. 16 is a schematic diagram for explaining the bending angle, showing the bending point as viewed in the radial direction from outside the tank. In Fig. 16, the bending angle θ is indicated between the longitudinal direction of the resin-impregnated fiber bundle in front of the bending point (dotted arrow) and the longitudinal direction of the resin-impregnated fiber bundle in the rear of the bending point (solid arrow). In this embodiment, "the bending direction is different from the winding direction" means that the bending angle θ between the longitudinal direction of the resin-impregnated fiber bundle in front of the bending point and the longitudinal direction of the resin-impregnated fiber bundle in the rear of the bending point is greater than 0° and less than 180°. In this embodiment, the bending angle θ between the longitudinal direction of the resin-impregnated fiber bundle in the portion before the bending point and the longitudinal direction of the resin-impregnated fiber bundle in the portion after the bending point is preferably 1° or more, preferably 5° or more, preferably 10° or more, preferably 15° or more, and preferably 20° or more. Furthermore, the bending angle is preferably 150° or less, preferably 120° or less, preferably 90° or less, and preferably 80° or less. The upper and / or lower limits of these numerical ranges can be arbitrarily combined to define a preferred range. For example, the bending angle is 1° or more and 150° or less, 10° or more and 120° or less, or 20° or more and 90° or less.

[0064] The bending angle θ may be defined as the angle between a plane passing through the center line (line along the dotted arrow in Fig. 16) in the short direction of the resin-impregnated fiber bundle in the front part (immediately before the bending point) and perpendicular to the axis of the tank (chain line X in Fig. 2), and a plane passing through the center line (line along the solid arrow in Fig. 16) in the short direction of the resin-impregnated fiber bundle in the rear part of the bending point and perpendicular to the axis of the tank. The above-mentioned ranges can be applied as the preferable numerical ranges.

[0065] Regarding the bending length, the length of the resin-impregnated fiber bundle behind the bending point is not particularly limited, but is, for example, 10 mm to 300 mm.

[0066] (peeling process) Next, the recycling method according to this embodiment includes a step of peeling off the exposed winding end portion.

[0067] In the peeling step, as described above, a tool such as a scraper is inserted between the end of the winding and the layer below, thereby peeling the exposed end of the winding from the tank surface. As described above, if the resin-impregnated fiber bundle is fixed in a bent state at the end of the winding, it becomes easier to insert a tool such as a scraper between the bent part at the end of the winding and the resin-impregnated fiber bundle located below.

[0068] (Pulling process) The recycling method according to this embodiment includes a step of pulling the peeled end of the winding to pull out the resin-impregnated fiber bundle.

[0069] By applying tension to the peeled end of the winding and pulling it, the resin-impregnated fiber bundle can be pulled out from the tank.

[0070] The drawing step is preferably a step of drawing the resin-impregnated fiber bundle while subjecting the bundle to a heat treatment in a tank, the heat treatment temperature being preferably equal to or higher than the glass transition temperature of the first matrix resin and lower than the thermal decomposition starting temperature and lower than the thermal degradation temperature of the reinforcing fibers.

[0071] The heating treatment softens the first matrix resin in the resin-impregnated fiber bundle while suppressing thermal decomposition of the first matrix resin and a decrease in the strength of the reinforcing fibers. Because the tank is heated at or above the glass transition temperature of the resin, the resin in the resin-impregnated fiber bundle softens. By performing the drawing process in a softened resin state, the resin-impregnated fiber bundle can be easily drawn. Specifically, the resin-impregnated fiber bundle can be drawn from the tank with less tension. Drawing with less tension can prevent breakage or damage to the reinforcing fibers. Furthermore, heating the tank at a temperature below the thermal decomposition onset temperature can prevent thermal decomposition of the resin. By suppressing thermal decomposition of the resin, excessive deformation and carbonization of the resin can be prevented, and as a result, the resin in the resin-impregnated fiber bundle can be easily dissolved, even when a dissolution process is performed in a subsequent process. Furthermore, because suppressing thermal decomposition of the resin can prevent a decrease in the strength of the resin, the drawn resin-impregnated fiber bundle can be used for other purposes as is or after desired processing (e.g., cutting) without undergoing a resin removal process. Furthermore, by carrying out the heat treatment at a temperature lower than the thermal degradation temperature of the reinforcing fibers, it is possible to suppress thermal degradation of the reinforcing fibers, and thus to suppress a decrease in the strength of the reinforcing fibers.

[0072] In this embodiment, "pulling out the resin-impregnated fiber bundle" means pulling out the resin-impregnated fiber bundle from the tank in a continuous state, and also includes the concept of peeling the resin-impregnated fiber bundle from the tank. In one embodiment, the resin-impregnated fiber bundle is pulled out while the resin in the tank is softened by heating, so that the resin-impregnated fiber bundle can be easily pulled out. When pulling out the resin-impregnated fiber bundle from the tank, a blade-shaped jig may be used to pull it out. The resin-impregnated fiber bundle can be easily peeled out by bringing the blade-shaped jig into contact with the portion (resin portion) between the resin-impregnated fiber bundle and the tank surface so as to cut the adhesive portion (resin portion) between the tank and the resin-impregnated fiber bundle.

[0073] The method for unwinding the resin-impregnated fiber bundle is not particularly limited, and for example, the resin-impregnated fiber bundle can be unwound by directly or indirectly connecting the winding end of the resin-impregnated fiber bundle to a winding roller and rotating the roller.

[0074] The heat treatment can be carried out, for example, in a heat treatment chamber. The tank is heated in the heat treatment chamber to soften the matrix resin of the tank. The heat treatment chamber may be a heating furnace or a heating device having a space configured to allow a heating medium to be introduced and / or discharged therein.

[0075] As a method for drawing out the resin-impregnated fiber bundle while subjecting it to heat treatment in a tank, for example, as shown in Figure 17, a method can be used in which the tank is placed in a heat treatment chamber and a portion of the resin-impregnated fiber bundle is drawn out of the heat treatment chamber while the heat treatment is being performed. The resin-impregnated fiber bundle can be transported to the outside, for example, from an outlet provided in part of the heat treatment chamber. The resin-impregnated fiber bundle can be transported continuously, for example, by transport rollers.

[0076] In one embodiment in which glass fibers are used as the reinforcing fibers, the heat treatment temperature is equal to or higher than the glass transition temperature of the first matrix resin and lower than the thermal decomposition onset temperature and lower than the thermal degradation temperature of the glass fibers. In another embodiment in which carbon fibers are used as the reinforcing fibers, the heat treatment temperature is equal to or higher than the glass transition temperature of the first matrix resin and lower than the thermal decomposition onset temperature and lower than the thermal degradation temperature of the carbon fibers.

[0077] The thermal decomposition starting temperature of the resin can be measured using a thermogravimetric analyzer.

[0078] In one embodiment, the thermal decomposition onset temperature is preferably a temperature showing a 5% weight loss in a weight change chart obtained by thermogravimetric analysis in which the resin is heated from 30°C to 550°C at 5°C / min under a nitrogen atmosphere. Preferably, the thermal decomposition onset temperature is a temperature showing a 3% weight loss in a weight change chart obtained by thermogravimetric analysis in which the resin is heated from 30°C to 550°C at 5°C / min under a nitrogen atmosphere. Preferably, the thermal decomposition onset temperature is a temperature showing a 1% weight loss in a weight change chart obtained by thermogravimetric analysis in which the resin is heated from 30°C to 550°C at 5°C / min under a nitrogen atmosphere. Generally, the above thermal decomposition onset temperature under a nitrogen atmosphere is considered to be the temperature at which decomposition of the main chain and / or side chains of the resin begins.

[0079] In one embodiment, the thermal decomposition onset temperature is preferably a temperature showing a 5% weight loss in a weight change chart obtained by thermogravimetric analysis in which the resin is heated from 30°C to 550°C at 5°C / min in an air atmosphere. Preferably, the thermal decomposition onset temperature is a temperature showing a 3% weight loss in a weight change chart obtained by thermogravimetric analysis in which the resin is heated from 30°C to 550°C at 5°C / min in an air atmosphere. Preferably, the thermal decomposition onset temperature is a temperature showing a 1% weight loss in a weight change chart obtained by thermogravimetric analysis in which the resin is heated from 30°C to 550°C at 5°C / min in an air atmosphere. Generally, when heated in air, oxidative decomposition proceeds due to oxygen contained in the air, and therefore, assuming the same weight loss rate, the thermal decomposition onset temperature measured in air will be lower than the thermal decomposition onset temperature measured in a nitrogen atmosphere.

[0080] In one embodiment using glass fibers as reinforcing fibers, the tank is heated below the thermal degradation temperature of the glass fibers to prevent the strength of the glass fibers from decreasing. The thermal degradation temperature of glass fibers can be defined as the lowest temperature at which a decrease in tensile strength of 1% or more occurs when the glass fibers are heat-treated in air. The decrease in strength can be calculated by measuring the tensile strength of the glass fibers used in the resin-impregnated fiber bundle before and after heat treatment.

[0081] In one embodiment using carbon fiber as the reinforcing fiber, the tank is heated below the thermal degradation temperature of the carbon fiber, thereby suppressing the decrease in strength of the carbon fiber. The thermal degradation temperature of carbon fiber can be defined as the lowest temperature at which a decrease in tensile strength of 1% or more occurs when the carbon fiber is heat-treated in the atmosphere. The decrease in strength can be calculated by measuring the tensile strength of the carbon fiber used in the resin-impregnated fiber bundle before and after the heat treatment.

[0082] In one embodiment, the heat treatment temperature is preferably 100°C or higher, preferably 120°C or higher, preferably 140°C or higher, preferably 160°C or higher, preferably 180°C or higher, and preferably 200°C or higher. The heat treatment temperature is preferably lower than 400°C, preferably lower than 390°C, preferably lower than 380°C, preferably lower than 370°C, preferably lower than 360°C, preferably lower than 350°C, preferably lower than 340°C, preferably lower than 330°C, preferably lower than 320°C, preferably lower than 310°C, preferably lower than 300°C, preferably lower than 290°C, and preferably lower than 280°C. When the heat treatment temperature is 100°C or higher, the resin in the resin-impregnated fiber bundle can be effectively softened. When the heat treatment temperature is lower than 400°C, thermal decomposition of the resin in the resin-impregnated fiber bundle can be easily suppressed, and degradation of reinforcing fibers such as glass fibers and carbon fibers can also be easily suppressed. The upper and / or lower limits of these numerical ranges can be combined in any manner to define a preferred range.

[0083] For example, the glass transition temperature of epoxy resin is approximately 100°C to 200°C, and the thermal decomposition onset temperature of epoxy resin is approximately 240°C to 360°C. Heating above the thermal decomposition onset temperature causes excessive thermal decomposition of the resin, significantly reducing its strength. Furthermore, excessive deformation and carbonization of the resin occur, making it difficult to dissolve and remove with a solvent. Figure 18A shows a weight change chart of a thermogravimetric analysis of an example epoxy resin obtained by heating the resin from 30°C to 550°C at a rate of 5°C / min in a nitrogen atmosphere. In Figure 18A, the temperature at which a 5% weight loss occurs is approximately 350°C, and this temperature can be defined as the thermal decomposition onset temperature. Figure 18B also shows a weight change chart of a thermogravimetric analysis of an example epoxy resin obtained by heating the resin from 30°C to 550°C at a rate of 5°C / min in an air atmosphere. Inflection points are also shown in Figures 18A and 18B. In Figure 18B, the temperature at which a 5% weight loss occurs is 340°C, and this temperature can also be defined as the thermal decomposition onset temperature. As mentioned above, when heated in air, oxidative decomposition occurs due to the oxygen contained in the air. Therefore, for the same weight loss rate, the thermal decomposition onset temperature measured in an air atmosphere is lower than that measured in a nitrogen atmosphere. At temperatures above the thermal decomposition onset temperature, excessive thermal decomposition of the resin occurs, resulting in excessive decomposition of the resin's main chain and / or side chains, and in some cases, carbonization of the resin. Such thermal decomposition makes it difficult to dissolve and remove the resin with a solvent. Furthermore, the strength of the resin decreases, making it impossible to reuse the resin-impregnated fiber bundle itself. On the other hand, in a range above the glass transition temperature and below the thermal decomposition onset temperature defined in one embodiment, the resin can be softened while suppressing thermal decomposition. Therefore, by drawing the resin-impregnated fiber bundle in this state, a high-quality continuous resin-impregnated fiber bundle can be easily obtained. Thermogravimetric analysis is a method for measuring the weight change when the temperature of a substance is changed according to a predetermined program. In one embodiment, thermogravimetric analysis can be performed by, for example, placing a test piece of about 10 mg in an aluminum, alumina, or platinum container and measuring the change in weight when the temperature is increased at a constant heating rate (5°C / min).

[0084] From the viewpoint of more effectively suppressing the thermal decomposition of the resin, the temperature of the heat treatment is preferably at least 1°C lower than the thermal decomposition onset temperature, preferably at least 5°C lower than the thermal decomposition onset temperature, preferably at least 10°C lower than the thermal decomposition onset temperature, preferably at least 15°C lower than the thermal decomposition onset temperature, preferably at least 20°C lower than the thermal decomposition onset temperature, preferably at least 25°C lower than the thermal decomposition onset temperature, and preferably at least 30°C lower than the thermal decomposition onset temperature.

[0085] FIG. 19 is a graph showing the thermal properties of carbon fiber, an example of a reinforcing fiber, and shows the strength ratio (tensile strength after heating / tensile strength before heating) when carbon fiber is heated in air at predetermined temperatures (300°C, 400°C, 500°C) for predetermined times (horizontal axis). As shown in FIG. 19, it can be seen that the strength of carbon fiber does not decrease even when heated at 400°C. On the other hand, it can be seen that the strength decreases when carbon fiber is heated at 500°C, the temperature used in conventional heat treatments. This is thought to be due to oxidative degradation of the carbon fiber caused by heat and oxygen. In general, the thermal decomposition onset temperature of resins is thought to be lower than the thermal degradation temperature of carbon fiber.

[0086] Figure 20 is a graph showing the tensile shear strength ratio of a resin (epoxy resin) at a given temperature. Specifically, Figure 20 shows the tensile shear strength ratio (tensile shear strength during heating / tensile shear strength before heating (strength at 23°C)) at a given temperature (23°C, 100°C, 150°C, 250°C, horizontal axis). The dotted line from 250°C to 350°C indicates a virtual curve. The tensile shear strength is the strength at which the adhesive bond breaks when two plates are bonded together with resin, as shown in Figure 21, due to shear stress, which is a load that tends to displace the adherends in opposite directions. As shown in Figure 20, the tensile shear strength decreases as the heating temperature of the resin increases. When the tensile shear strength is reduced, the resin-impregnated fiber bundle can be easily pulled out. For example, when the heating temperature is 150°C, the tensile shear strength ratio is 0.2 or less, and the tensile shear strength during heating is 20% or less of the tensile shear strength before heating, which shows that the resin-impregnated fiber bundle can be pulled out with less force. In this embodiment, the heat treatment temperature is preferably a temperature at which the tensile shear strength ratio is 20% or less, preferably a temperature at which the tensile shear strength ratio is 15% or less, preferably a temperature at which the tensile shear strength ratio is 10% or less, and preferably a temperature at which the tensile shear strength ratio is 5% or less.

[0087] In this embodiment, the tank is not usually crushed or pulverized. Only the cylindrical portion of the tank may be used as the tank. Metal parts and the like in the tank may be removed before or after the heating process.

[0088] The heating method in one embodiment is not particularly limited. For example, heating in the atmosphere can be used. Heat treatment in the atmosphere can be easily performed and is also advantageous in terms of cost. This method is particularly effective because it can suppress deterioration of carbon fibers even in the presence of oxygen, such as in the atmosphere. The heat treatment can also be performed using superheated steam. By using superheated steam, the proportion of oxygen-containing air in the treatment atmosphere can be reduced, thereby effectively suppressing decomposition and damage to the reinforcing fibers. For example, the heat treatment can be performed by introducing atmospheric superheated steam into an atmospheric pressure reaction vessel. The heat treatment can also be performed in an inert atmosphere, such as nitrogen, without any particular limitations. The heat treatment can also be performed while supplying heated superheated steam and / or an inert gas (such as nitrogen) into a heat treatment chamber.

[0089] In the recycling method according to this embodiment, the resin-impregnated fiber bundle drawn in the drawing step maintains its bundle shape due to the reinforcing fibers and matrix resin. In one embodiment, this resin-impregnated fiber bundle can be reused as is because the strength of the resin and reinforcing fibers is prevented from decreasing. Depending on the circumstances, the obtained resin-impregnated fiber bundle may be subjected to a desired processing treatment before reuse. Examples of processing treatment include cutting to a desired size. For example, the cut resin-impregnated fiber bundle can be mixed with a binder resin or the like and solidified to produce a sheet-like product.

[0090] (Removal process) The recycling method according to this embodiment may include a step of removing the resin from the resin-impregnated fiber bundle to obtain reinforcing fibers. The method for removing the resin from the resin-impregnated fiber bundle is not particularly limited, but preferably includes dissolving and removing the resin using a solvent. Dissolving and removing the resin using a solvent can suppress deterioration of the reinforcing fibers (e.g., glass fibers or carbon fibers).

[0091] Hereinafter, a dissolving and removing step using a dissolving liquid will be described as an example of a step for removing resin.

[0092] The dissolving and removing step is a step of dissolving and removing the resin in the drawn resin-impregnated fiber bundle with a solvent.

[0093] In one embodiment, the resin in the drawn resin-impregnated fiber bundle is removed by a dissolving and removing step. The resin can be dissolved and removed by bringing the resin-impregnated fiber bundle into contact with a dissolving liquid. Dissolving and removing the resin can avoid heat stress and suppress deterioration of the reinforcing fibers (e.g., glass fibers or carbon fibers). Specifically, removal by a dissolving liquid causes less deterioration of the reinforcing fibers than removal by thermal decomposition. Furthermore, in one embodiment, excessive deformation and carbonization of the resin are suppressed in the preceding drawing step under heating, so the resin in the resin-impregnated fiber bundle can be efficiently dissolved.

[0094] The resin is dissolved using a solvent capable of dissolving the resin in the resin-impregnated fiber bundle. The solvent is not particularly limited as long as it can dissolve the resin, but may include, for example, at least one liquid selected from the above-mentioned acidic solution, organic solvent, hydrogen peroxide solution, and ionic liquid. These liquids are capable of dissolving or swelling the resin, allowing the resin to be removed efficiently. One solvent may be used alone, or two or more solvents may be used in combination.

[0095] The resin is dissolved and removed by bringing the resin-impregnated fiber bundle into contact with a dissolving solution. The method for bringing the resin-impregnated fiber bundle into contact with the dissolving solution is not particularly limited, and examples thereof include dipping, die coating, bar coating, roll coating, and gravure coating. Among these, the dipping method is preferred. Specifically, the resin-impregnated fiber bundle can be brought into contact with the reinforcing fibers by conveying the resin-impregnated fiber bundle with rollers so as to be immersed in the dissolving solution placed in a bath. In one embodiment, the resin-impregnated fiber bundle can be immersed in the dissolving solution while being conveyed with conveying rollers or the like.

[0096] The degree of solubility of the resin in the dissolving and removing step can be adjusted by the type of dissolving solution, the treatment temperature, the treatment time, etc. The treatment time can be adjusted, for example, by the conveying speed of the resin-impregnated fiber bundle. The treatment time is not particularly limited and can be set appropriately depending on the type of dissolving solution, the type of resin, etc.

[0097] The temperature of the dissolving liquid (liquid temperature) can be set appropriately taking into consideration the degree of dissolution and removal, and is, for example, 20°C or higher, 40°C or higher, 60°C or higher, or 80°C or higher, or, for example, 300°C or lower, 250°C or lower, 200°C or lower, 150°C or lower, or 100°C or lower.

[0098] The resin may be dissolved and removed by spraying a solvent onto the resin-impregnated fiber bundle. That is, by applying a spray pressure to the solvent to bring it into contact with the resin-impregnated fiber bundle, the resin in the resin-impregnated fiber bundle can be removed by utilizing the spray pressure. There are no particular limitations on the spraying device used to spray the solvent, and for example, a high-pressure cleaning device or the like can be used.

[0099] The nozzle pressure when spraying the dissolving liquid is preferably 1 MPa or more, preferably 5 MPa or more, preferably 8 MPa or more, and preferably 10 MPa or more. At this pressure, the resin can be efficiently removed from the resin-impregnated fiber bundle. Furthermore, the nozzle pressure is preferably 30 MPa or less, preferably 25 MPa or less, preferably 22 MPa or less, and preferably 20 MPa or less. At this pressure, damage to the reinforcing fibers by the dissolving liquid can be effectively suppressed. When spraying the dissolving liquid, the distance between the nozzle and the resin-impregnated fiber bundle as the spray target is preferably 10 to 200 cm, and preferably 30 to 100 cm.

[0100] The resin may be dissolved and removed by a combination of immersion in a dissolving solution and spraying of the dissolving solution.

[0101] (Sizing agent application process) The recycling method according to this embodiment may include a step of attaching a sizing agent to the reinforcing fibers (for example, glass fibers or carbon fibers) obtained by removing the resin.

[0102] After the removal process, the reinforcing fibers have had virtually all of the resin removed, and the reinforcing fiber bundles have been loosened into single fibers. By adding a sizing agent to these reinforcing fibers, the reinforcing fiber bundles can be easily wound onto a bobbin, and the occurrence of fuzzing of the reinforcing fibers and entanglement of the single fibers can be suppressed.

[0103] The sizing agent is not particularly limited, but examples thereof include epoxy resins, urethane resins, vinyl ester resins, polyamide resins, nylon resins, polyolefin resins (polyethylene and polypropylene), polyester resins, phenolic resins, and mixtures thereof. Among these, epoxy resins, urethane resins, vinyl ester resins, and polyolefin resins are preferred, and epoxy resins are more preferred. By using an epoxy resin as a sizing agent, the adhesion between the reinforcing fibers and the epoxy resin can be improved. One type of sizing agent may be used alone, or two or more types may be used in combination.

[0104] The application of the sizing agent to the reinforcing fibers is carried out by bringing the sizing agent into contact with the reinforcing fibers. The method for applying the sizing agent is not particularly limited, and examples thereof include dipping, die coating, bar coating, roll coating, and gravure coating. Among these, the dipping method is preferred. Specifically, the sizing agent can be applied to the reinforcing fibers by transporting the reinforcing fibers with a roller so that the fibers are immersed in the sizing agent placed in a sizing bath. The sizing agent is preferably dispersed or dissolved in water or an organic solvent such as acetone and used as a dispersion or solution. To enhance the dispersibility of the sizing agent and improve the liquid stability, a surfactant may be added to the dispersion or solution as appropriate.

[0105] (winding process) The recycling method according to the present embodiment may include a step of winding the reinforcing fibers from which the resin obtained in the removing step has been removed. The step of winding the reinforcing fibers is carried out after the removing step, and if a sizing agent application step is included, the step of winding the reinforcing fibers is preferably carried out after the sizing agent application step.

[0106] Winding can be performed using, for example, a winding roller. The winding roller is equipped with a drive device that provides a driving force for winding the reinforcing fiber. In addition, some of the guide rollers may also be equipped with a drive device that rotates the guide roller. The winding tension, i.e., the tension applied to the reinforcing fiber, is preferably as small as possible. By setting the winding tension within an appropriate range, thread breakage and winding slippage of the reinforcing fiber can be prevented, and as a result, longer continuous fiber can be obtained.

[0107] One embodiment includes a step of drawing a resin-impregnated fiber bundle while performing a heat treatment, a step of removing the resin from the drawn and transported resin-impregnated fiber bundle, and a step of winding the transported reinforcing fiber from which the resin has been removed, in which the resin-impregnated fiber bundle is drawn upstream while the reinforcing fiber is wound downstream. That is, in one embodiment, a step of drawing a resin-impregnated fiber bundle under heating is performed upstream while a step of winding the reinforcing fiber is performed downstream, and a removal step and, optionally, a sizing agent application step are performed between the upstream drawing step and the downstream winding step. Also, in one embodiment, a step of drawing a resin-impregnated fiber bundle under heating is performed upstream while a step of winding the reinforcing fiber is performed downstream, and a dissolving and removal step and, optionally, a sizing agent application step are performed between the upstream drawing step and the downstream winding step. In such an embodiment, the dissolving and removal step can be performed immediately after the drawing step under heating, and the resin-impregnated fiber bundle can be contacted with the dissolving solution at a high temperature, allowing the resin to be efficiently removed with the dissolving solution. Specifically, a portion (preferably an end portion) of the resin-impregnated fiber bundle is removed from the tank, and this removed portion of the resin-impregnated fiber bundle is connected directly or indirectly to a winding machine. The winding machine applies tension to the resin-impregnated fiber bundle, and the resin-impregnated fiber bundle is drawn out in the form of continuous fibers. The resin is removed from the drawn resin-impregnated fiber bundle using a dissolving liquid. The reinforcing fiber obtained after the resin removal is then wound up on the winding machine.

[0108] In the reinforcing fiber recycling method according to this embodiment, which includes the above steps, reinforcing fibers suitable for reuse can be efficiently obtained.

[0109] According to the method for recycling reinforcing fibers of the present embodiment described above, it is possible to efficiently obtain high-quality reinforcing fibers suitable for reuse. The obtained reinforcing fibers can be used in a wide range of applications.

[0110] The upper and / or lower limit values ​​of the numerical ranges described herein can be arbitrarily combined to define a preferred range. For example, the upper and lower limit values ​​of the numerical ranges can be arbitrarily combined to define a preferred range, the upper limit values ​​of the numerical ranges can be arbitrarily combined to define a preferred range, and the lower limit values ​​of the numerical ranges can be arbitrarily combined to define a preferred range.

[0111] Any reference throughout this specification to "one embodiment," "one(a) embodiment," or "an embodiment" means that the particular feature, structure, or characteristic described with respect to that embodiment is included in at least one embodiment. Thus, references to the cited phrases or variations thereof stated throughout this specification are not necessarily all referring to the same embodiment.

[0112] Although the present embodiment has been described in detail above, the specific configuration is not limited to this embodiment, and even if there are design changes within the scope that do not deviate from the gist of this disclosure, they are included in this disclosure. [Explanation of symbols]

[0113] 10 Liner 20 Reinforcement layer (middle layer) 30 protective layer 30a First protective layer 30b Second protective layer 40 Valve side nozzle 50 valves 60 End side cap 100 Tanks

Claims

1. 1. A method for recycling reinforcing fibers, comprising: a step of preparing a tank having at least a liner, a first protective layer disposed on an outer peripheral surface of the liner and configured so that a resin-impregnated fiber bundle containing a reinforcing fiber bundle and a first matrix resin is wound around the liner, and a second protective layer formed of the first matrix resin on the first protective layer; removing a portion of the second protective layer to expose the winding end of the resin-impregnated fiber bundle; peeling the exposed end of the winding; and The process of pulling the peeled end of the winding and pulling out the resin-impregnated fiber bundle. Including, a winding end portion of the resin-impregnated fiber bundle is fixed in a folded state in the first protective layer of the tank; a portion of the second protective layer is removed by contacting a dissolving solution with the portion of the second protective layer; The method, wherein the step of drawing out the resin-impregnated fiber bundle is a step of drawing out the resin-impregnated fiber bundle while subjecting the tank to a heat treatment, and the temperature of the heat treatment is equal to or higher than the glass transition temperature of the first matrix resin and lower than the thermal decomposition initiation temperature, and lower than the thermal degradation temperature of the reinforcing fibers.

2. The method according to claim 1, wherein the second protective layer is a layer formed by curing a part of the first matrix resin contained in the first protective layer in a state where the first matrix resin has oozed out.

3. The method of claim 1 , wherein the first matrix resin is an epoxy resin.

4. The method according to claim 1 , wherein the dissolution liquid comprises at least one liquid selected from an acidic solution, an organic solvent, a hydrogen peroxide solution, and an ionic liquid.

5. The method according to any one of claims 1 to 4, wherein the reinforcing fiber bundles are glass fiber bundles or carbon fiber bundles.

6. The method of claim 5, wherein the reinforcing fiber bundles are glass fiber bundles.

7. The method according to claim 6, further comprising a reinforcing layer between the protective layer and the liner, the reinforcing layer being configured such that resin-impregnated carbon fiber bundles containing carbon fiber bundles and a second matrix resin are wound around the liner.

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