Method for determining recycling condition of carbon fiber bundle

Abstract

The present invention provides a method for determining conditions for recycling a carbon fiber bundle from a structure which has a hollow base material and a carbon fiber-reinforced resin layer that contains a matrix resin and a carbon fiber bundle which is wound around the hollow base material. When recycling the carbon fiber bundle, the structure is heated in a first environment that contains oxygen so as to decompose the matrix resin, and subsequently, an intermediate carbon fiber bundle, to which the decomposition residue of the matrix resin is adhered, is unwound from the carbon fiber-reinforced resin layer in which the matrix resin has been decomposed, wherein when the structure is heated, the structure is maintained at a temperature X1 (°C) for a specific time period and is subsequently heated to a temperature X2 (°C). In this method for determining recycling conditions of a carbon fiber bundle, if EP (°C) is the thermal decomposition initiation temperature of the matrix resin, EP' (°C) is the thermal decomposition end temperature of the matrix resin, CP (°C) is the thermal decomposition initiation temperature of the carbon fiber, A1 (°C∙h) is the area of a region where the temperature in the temperature profile when the structure is heated is not less that EP' (°C), and Z1 (-) is the volume ratio of oxygen in the first environment, X1, X2, A1 and Z1 are determined so as to satisfy formula (1) EP ≤ X1 ≤ EP' < X2 < CP and formula (2) 5 ≤ A1∙Z1 ≤ 2,000.

Description

Method for determining conditions for recycling carbon fiber bundles

[0001] The present invention relates to a method for determining regeneration conditions for carbon fiber bundles.

[0002] In recent years, efforts to significantly reduce waste generation through waste prevention, reduction, recycling, and reuse have become increasingly active. To achieve this, research and development is being conducted on methods for recovering carbon fiber from carbon fiber reinforced resins.

[0003] Patent Document 1 describes a carbon fiber recycling method including a step of pyrolyzing the resin in a carbon fiber reinforced resin molding by a first heat treatment and a step of drawing out and winding the carbon fiber from the carbon fiber reinforced resin molding after the first heat treatment. The winding step includes a step of pyrolyzing the resin residue adhering to the carbon fiber by a second heat treatment and a step of applying a sizing agent to the carbon fiber after the second heat treatment. The carbon fiber reinforced resin molding is a tank including a liner and a carbon fiber reinforced resin layer.

[0004] Japanese Patent Application Laid-Open No. 2022-15366

[0005] However, if the amount of resin residue adhering to the carbon fibers is small, the carbon fibers may be damaged when they are pulled out from the carbon fiber reinforced resin molding.

[0006] An object of the present invention is to provide a method for determining regeneration conditions for a carbon fiber bundle that can suppress damage to an intermediate carbon fiber bundle when the intermediate carbon fiber bundle is unwound.

[0007] [1] A method for determining conditions for recycling carbon fiber bundles from a structure having a hollow substrate and a carbon fiber reinforced resin layer containing carbon fiber bundles and matrix resin wound around the hollow substrate, wherein when recycling the carbon fiber bundles, the structure is heated in a first environment containing oxygen to decompose the matrix resin, and then an intermediate carbon fiber bundle having decomposition residues of the matrix resin attached thereto is unwound from the carbon fiber reinforced resin layer in which the matrix resin has been decomposed, and when heating the structure, the temperature is maintained at X1 [°C] for a predetermined time and then increased to X2 [°C], and the thermal decomposition onset temperature of the matrix resin is EP [°C], the thermal decomposition end temperature of the matrix resin is EP' [°C], the thermal decomposition onset temperature of the carbon fibers is CP [°C], the area of ​​a region in a temperature profile in heating the structure where the temperature is equal to or higher than EP' [°C] is A1 [°C h], and the volume ratio of oxygen in the first environment is Z1 [-], the following equation is satisfied: EP≦X1≦EP'<X2<CP (1) A method for determining regeneration conditions for a carbon fiber bundle, the method comprising determining X1, X2, A1, and Z1 so as to satisfy the following condition: 5≦A1·Z1≦2000 (2).

[0008] [2] The method for determining the regeneration conditions for carbon fiber bundles according to [1], wherein the intermediate carbon fiber bundle has a content of decomposition residues of the matrix resin of 5% by weight or more and 10% by weight or less.

[0009] [3] The method for determining regeneration conditions for a carbon fiber bundle according to [1] or [2], wherein, when regenerating the carbon fiber bundle, the unwound intermediate carbon fiber bundle is heated in a second environment containing oxygen to decompose decomposition residues of the matrix resin to obtain a recycled carbon fiber bundle, and then the recycled carbon fiber bundle is wound up and heated, the intermediate carbon fiber bundle is maintained at a temperature X3 [°C] for a predetermined time, and X3, Y3 and Z3 are determined so as to satisfy the following equations: X2≦X3<CP (3) 15≦A1·Z1+(X3−EP′)·Y3·Z3 (4)

[0010] [4] The method for determining the regeneration conditions for carbon fiber bundles according to [3], wherein the recycled carbon fiber bundles have a content of decomposition residues of the matrix resin of 4% by weight or less.

[0011] [5] The method for determining recycling conditions for a carbon fiber bundle according to any one of [1] to [4], wherein the matrix resin is a cured product of an epoxy resin.

[0012] According to the present invention, it is possible to provide a method for determining regeneration conditions for a carbon fiber bundle that can suppress damage to an intermediate carbon fiber bundle when the intermediate carbon fiber bundle is unwound.

[0013] FIG. 4 is a cross-sectional view showing an example of a high-pressure hydrogen tank. FIG. 5 is a graph showing temperature profiles in a first heating step and a second heating step. FIG. 6 is a diagram showing an example of a first heating unit used in a first heating step. FIG. 7 is a cross-sectional view showing a rotation unit that rotates the high-pressure hydrogen tank in the heat treatment chamber of FIG. 3. FIG. 8 is a side view showing a rotation unit that rotates the high-pressure hydrogen tank in the heat treatment chamber of FIG. 3. FIG. 9 is a front view showing an example of an unwinding unit used in an unwinding step. FIG. 10 is a schematic view showing examples of a second heating unit, a sizing unit, and a winding unit used in a second heating step, a sizing step, and a winding step.

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0015] A method for determining conditions for recycling carbon fiber bundles according to one embodiment of the present invention is a method for determining conditions for recycling carbon fiber bundles from a structure having a hollow substrate and a carbon fiber reinforced resin layer containing carbon fiber bundles and a matrix resin wound around the hollow substrate. The structure is not particularly limited, but examples thereof include known high-pressure hydrogen tanks (Types 2 to 4).

[0016] The carbon fibers constituting the carbon fiber bundle are not particularly limited, but examples thereof include polyacrylonitrile (PAN)-based carbon fibers and pitch-based carbon fibers. Here, the carbon fibers constituting the carbon fiber bundle are long fibers. The fiber length of the carbon fibers is not particularly limited, but is, for example, 1 m or more. The matrix resin is not particularly limited, but examples thereof include a cured product of a thermosetting resin such as an epoxy resin, and a thermoplastic resin.

[0017] FIG. 1 shows an example of a high-pressure hydrogen tank.

[0018] The high-pressure hydrogen tank T has a liner L as a hollow substrate, a carbon fiber reinforced resin layer F containing carbon fiber bundles and a matrix resin wound around the liner L, and mouthpieces C1, C2 installed at both ends in the longitudinal direction. The material constituting the liner L is not particularly limited, but examples include metals such as aluminum and chromium molybdenum steel, and resins such as polyamide and polyethylene.

[0019] The method for manufacturing the high-pressure hydrogen tank T is not particularly limited, but may be, for example, a filament winding method.

[0020] An example of a method for regenerating a carbon fiber bundle will be described below. The method for regenerating a carbon fiber bundle includes a first heating step of heating a high-pressure hydrogen tank T in a first environment containing oxygen to decompose the matrix resin, and an unwinding step of unwinding an intermediate carbon fiber bundle I to which decomposition residues of the matrix resin adhere from a carbon fiber reinforced resin layer F where the matrix resin has been decomposed. The method for regenerating a carbon fiber bundle further includes a second heating step of heating the unwound intermediate carbon fiber bundle I in a second environment containing oxygen to decompose the decomposition residues of the matrix resin to obtain a recycled carbon fiber bundle R, and a winding step of winding up the recycled carbon fiber bundle R.

[0021] As shown in FIG. 2 , in the first heating step, the matrix resin is decomposed by first maintaining a temperature X1 [°C] above the thermal decomposition onset temperature EP [°C] of the matrix resin and below the thermal decomposition end temperature EP' [°C] of the matrix resin for a predetermined time (first step). Next, the temperature is raised to a temperature X2 [°C] above the thermal decomposition end temperature EP' [°C] of the matrix resin and below the thermal decomposition onset temperature CP [°C] of the carbon fiber to decompose the decomposition residue of the matrix resin (second step). This suppresses the rapid generation of thermal decomposition gas of the matrix resin, thereby suppressing combustion of the thermal decomposition gas of the matrix resin and, as a result, suppressing deterioration of the carbon fiber bundle. In this case, X2 is, for example, above the thermal decomposition onset temperature of the decomposition residue of the matrix resin. Here, the thermal decomposition onset temperature and the thermal decomposition end temperature can be determined by measuring a DTA curve of the carbon fiber reinforced resin layer F in a nitrogen environment. The time for maintaining the temperature X1 [°C] is not particularly limited as long as it is possible to sufficiently decompose the matrix resin, but is, for example, 1.5 hours or more. The rate of temperature increase from X1 [°C] to X2 [°C] is not particularly limited, but is, for example, 0.1°C / min or more and 10°C / min or less. Examples of the first heating part used in the first heating step include a hot air circulation oven and a gas oven.

[0022] Here, if the area of ​​the region where the temperature in the temperature profile when heating the high-pressure hydrogen tank T in the first heating step is equal to or higher than EP' [°C] is A1 [°C·h], and the volume ratio of oxygen in the first environment is Z1 [-], X1, X2, A1, and Z1 are determined so as to satisfy the following equations: EP≦X1≦EP'<X2<CP (1) 5≦A1·Z1≦2000 (2). This adjusts the content of the matrix resin decomposition residue in the intermediate carbon fiber bundle I to a predetermined range, thereby suppressing damage to the intermediate carbon fiber bundle I when unwinding the intermediate carbon fiber bundle I to which the matrix resin decomposition residue adheres from the carbon fiber reinforced resin layer where the matrix resin has been decomposed. Furthermore, X1, X2, A1, and Z1 can be flexibly set taking into account the availability of the equipment. Furthermore, energy waste is suppressed, and the occurrence of defective recycled carbon fiber bundles R is suppressed. The content of the decomposition residue of the matrix resin in the intermediate carbon fiber bundle I is not particularly limited as long as it is possible to suppress damage to the carbon fibers, but is, for example, 5% by weight or more and 10% by weight or less.

[0023] When the matrix resin is a cured product of bisphenol A, for example, X1 is 330° C. or more and 370° C. or less, and X2 is 410° C. or more and 450° C. or less. In this case, examples of pyrolysis gases include bisphenol A, phenol, and isopropenyl phenol.

[0024] In the second heating step, the temperature is maintained at X3 [°C], which is equal to or higher than X2 [°C] and lower than CP [°C], for a predetermined time to decompose the decomposition residue of the matrix resin, thereby suppressing deterioration of the intermediate carbon fiber bundle I.

[0025] Here, assuming that the time for heating the intermediate carbon fiber bundle I is Y3 [h] and the volume ratio of oxygen in the second environment is Z3 [-], X3, Y3, and Z3 are determined so as to satisfy the following equations: X2≦X3<CP (3) 15≦A1·Z1+(X3−EP′)·Y3·Z3 (4). This reduces the content of decomposition residues of the matrix resin in the recycled carbon fiber bundle R. Note that Y2 is not particularly limited as long as it is possible to sufficiently decompose the decomposition residues of the matrix resin, but for example, it is 4 hours or more. Furthermore, the content of decomposition residues of the matrix resin in the recycled carbon fiber bundle R is not particularly limited, but for example, it is 4 wt % or less.

[0026] FIG. 3 shows a heat treatment furnace as an example of the first heating section used in the first heating step.

[0027] The heat treatment furnace 10 has a heat treatment chamber 11 and a combustion chamber 12 .

[0028] The heat treatment chamber 11 is an enclosed space surrounded by an outer wall 11a and an inner wall 11b. Burners 11c are provided above the outer wall 11a on the left side and below the outer wall 11a on the right side in the drawing so that combustion gas flows into the inner wall 11b. When gas fuel and air are mixed and burned by the burners 11c, the combustion gas convects within the inner wall 11b, stabilizing the temperature within the inner wall 11b.

[0029] The heat treatment chamber 11 has a sealed door installed on a portion of the outer wall 11a and inner wall 11b for accommodating a high-pressure hydrogen tank T. The high-pressure hydrogen tank T is placed on a thermal insulator 11d installed so as to penetrate the bottom surface of the inner wall 11b. A load cell 11e serving as a mass detector is installed between the bottom surface of the outer wall 11a and the thermal insulator 11d and detects the mass of the high-pressure hydrogen tank T in real time based on the amount of strain. This optimizes the heating conditions in the heat treatment chamber 11, suppressing variations in the amount of decomposition of the matrix resin due to individual differences in the material, shape, etc., constituting the high-pressure hydrogen tank T and improving management accuracy. Furthermore, since the heating time in the heat treatment chamber 11 does not need to be longer than necessary, this contributes to shortening the heating time and reducing energy consumption.

[0030] The mass detector may detect in real time the amount of mass loss of the high-pressure hydrogen tank T. If necessary, the mass detector may be omitted.

[0031] The decomposition gas of the matrix resin generated within the inner wall 11b is discharged from an exhaust port 11f formed at the top of the inner wall 11b in the figure, and then introduced into the combustion chamber 12 via a pipe 11g installed to penetrate the outer wall 11a.

[0032] The combustion chamber 12 is an enclosed space surrounded by an outer wall 12a and an inner wall 12b. A burner 12c is provided in the center of the outer wall 12a (left side of the figure) so that combustion gas flows into the inner wall 12b. Meanwhile, the pipe 11g penetrates the outer wall 12a, then penetrates the inside and outside of the inner wall 12b within the outer wall 12a, and finally connects to the upper left of the inner wall 12b. While passing through the pipe 11g inside the inner wall 12b, the decomposition gas of the matrix resin is heated by the combustion gas flowing within the inner wall 12b, and then introduced from the upper left of the inner wall 12b and comes into contact with the combustion gas. After combustion, the decomposition gas of the matrix resin is exhausted to the outside through the exhaust port 12d.

[0033] The heat treatment furnace 10 may further include a pipe for supplying the exhaust heat from the combustion chamber 12 to a tubular furnace 40, which will be described later.

[0034] 4A and 4B show an example of a rotating unit that rotates the high-pressure hydrogen tank T in the heat treatment chamber 11. FIG.

[0035] The rotating part 20 has a rotation axis 21 extending in a substantially horizontal direction that penetrates the wall W of the heat treatment chamber 11, so that the temperature distribution of the carbon fiber reinforced resin layer F in the vertical direction in the drawing is made uniform.

[0036] The rotation shaft 21 may be oriented in a direction other than the substantially horizontal direction, for example, the rotation shaft 21 may be oriented in the substantially vertical direction. When the rotation shaft 21 is oriented in the substantially vertical direction, the temperature distribution of the carbon fiber reinforced resin layer F in the heat treatment chamber 11 is made uniform to the same extent as when the rotation shaft 21 is oriented in the substantially horizontal direction.

[0037] The high-pressure hydrogen tank T is connected to the rotating shaft 21 via a flanged jig 22 and a rotating shaft flange 23 that utilize the shapes of the mouthpieces C1 and C2. At this time, the flanged jig 22 and the rotating shaft flange 23 are fixed with, for example, bolts and nuts. The high-pressure hydrogen tank T is placed on a pedestal 24, and a bearing 25 is installed on the pedestal 24. Furthermore, a heat insulating material 26 is installed inside the wall W of the heat treatment furnace 10. Furthermore, a motor that rotates the rotating shaft 21 is installed outside the wall W of the heat treatment furnace 10, and a cooling jacket 27 is installed around the rotating shaft 21.

[0038] 5A and 5B show an example of an unwinding unit used in the unwinding process.

[0039] The unwinding section 30 has a rotating jig 31 that rotatably supports the high-pressure hydrogen tank T1 in which the matrix resin has been decomposed, and a motor 32 that rotates the high-pressure hydrogen tank T1. The rotational power of the motor 32 is transmitted to the rotating jig 31 via a belt 33. As a result, the intermediate carbon fiber bundle I is unwound via rollers 34, 35, and 36. At this time, the roller 34 is positioned so that the intermediate carbon fiber bundle I is unwound outside the tangent line at the position where the intermediate carbon fiber bundle I is unwound from the high-pressure hydrogen tank T1. Furthermore, the rollers 34, 35, and 36 have long axes that correspond to the unwinding of the intermediate carbon fiber bundle I in the longitudinal direction of the high-pressure hydrogen tank T1. Furthermore, a dancer roller 37 that controls the unwinding tension is provided to absorb the difference in the unwinding amount per rotation between hoop winding and helical winding of the intermediate carbon fiber bundle I.

[0040] Instead of the roller 34, a blade may be provided.

[0041] Furthermore, after a sizing step of sizing the recycled carbon fiber bundle R is carried out, the sized recycled carbon fiber bundle R may be unwound.

[0042] FIG. 6 shows an example of the second heating section, sizing section, and winding section used in the second heating step, sizing step, and winding step.

[0043] The tubular furnace 40, serving as the second heating section, has a quartz tube 41 and, at both ends thereof, insulating covers 42 formed with through-holes through which the intermediate carbon fiber bundle I, to which the decomposition residue of the matrix resin adheres, can pass. The tubular furnace 40 also has an electric wire heater 43, an insulating material 44, and a protective cover 45 sequentially disposed in the center of the quartz tube 41. Therefore, the electric wire heater 43 heats the intermediate carbon fiber bundle I, decomposing the decomposition residue of the matrix resin, and thus a recycled carbon fiber bundle R is obtained. At this time, the temperature distribution within the tubular furnace 40 is made uniform, and heating of parts other than the intermediate carbon fiber bundle I is suppressed.

[0044] The sizing unit 50 passes the recycled carbon fiber bundles R through a sizing solution 51. At this time, the sizing solution 51 is heated by a heater 52. In addition, a roller 53 prevents the sizing solution 51 from being applied excessively to the recycled carbon fiber bundles R.

[0045] If necessary, a drying oven may be installed to dry the recycled carbon fiber bundles R.

[0046] The feeding mechanism 60 has feeder rollers 61, 62, and 63, and by utilizing the friction between the feeder rollers 61, 62, and 63 and the recycled carbon fiber bundle R, the linear speed of the recycled carbon fiber bundle R is controlled to a linear speed that is easy to manage in the process.

[0047] The winding unit 70 includes a winding motor 71 for winding the recycled carbon fiber bundle R around the paper core P, and a slide roller 72 for traverse-winding the recycled carbon fiber bundle R. At this time, the winding tension of the recycled carbon fiber bundle R is controlled by controlling the torque of the winding motor 71.

[0048] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and the above-described embodiments may be modified as appropriate within the scope of the spirit of the present invention.

[0049] Next, examples of the present invention will be described, but the present invention is not limited to these examples. [Preparation of Test Specimens] Test specimens were cut out from a carbon fiber reinforced resin layer F containing a carbon fiber bundle and a cured product of bisphenol A that was wound around a liner L of a high-pressure hydrogen tank T. Here, a DTA curve of the carbon fiber reinforced resin layer F was measured in a nitrogen environment using a differential scanning calorimeter (DSC). The thermal decomposition onset temperature and thermal decomposition end temperature of the cured product of bisphenol A, the thermal decomposition onset temperature of the decomposition residue of the cured product of bisphenol A, and the thermal decomposition onset temperature of the carbon fiber were 270°C, 390°C, 390°C, and 460°C, respectively.

[0050] [Reference Example 1] When a test piece was heated for 1.2 hours at 440°C (X2) in an atmospheric environment with an oxygen volume fraction of 0.21 using a ceramics electric furnace, the content of epoxy resin decomposition residue in the test piece was 5% by weight. In addition, the product A·Z of the area (A) of the region in the temperature profile during heating where the temperature was equal to or higher than EP' [°C] and the volume fraction (Z) of oxygen in the atmospheric environment was 12.6 [°C·h].

[0051] [Reference Example 2] When a test piece was heated in an electric pottery furnace at 440°C for 0.85 hours in an atmospheric environment, the content of decomposition residue of the epoxy resin in the test piece was 10% by weight, and A·Z was 8.9 [°C·h].

[0052] [Reference Example 3] When a test piece was heated in an electric pottery furnace at 420°C for 1.8 hours in an atmospheric environment, the content of decomposition residue of the epoxy resin in the test piece was 5% by weight, and A·Z was 11.3 [°C·h].

[0053] [Reference Example 4] When a test piece was heated in an electric pottery furnace at 420°C for 1.35 hours in an atmospheric environment, the content of decomposition residue of the epoxy resin in the test piece was 10% by weight, and A·Z was 8.5 [°C·h].

[0054] It can be seen from Reference Examples 1 to 4 that when A·Z is 8.5°C·h or more and 12.6°C·h or less, the content of epoxy resin decomposition residue in the test piece is 5% by weight or more and 10% by weight or less. Here, in Reference Examples 1 to 4, heating was performed in the temperature range X2 in the temperature profile of Figure 2, but it is presumed that a similar tendency would occur even if the temperature range X1 was also added.

[0055] 10 Heat treatment furnace 40 Tubular furnace F Carbon fiber reinforced resin layer I Intermediate carbon fiber bundle L Liner R Recycled carbon fiber bundle T, T1 High-pressure hydrogen tank

Claims

1. A method for determining conditions for recycling carbon fiber bundles from a structure having a hollow substrate and a carbon fiber reinforced resin layer containing carbon fiber bundles and a matrix resin wound around the hollow substrate, wherein when recycling the carbon fiber bundles, the structure is heated in a first environment containing oxygen to decompose the matrix resin, and then an intermediate carbon fiber bundle having decomposition residues of the matrix resin attached thereto is unwound from the carbon fiber reinforced resin layer where the matrix resin has been decomposed, and when heating the structure, the temperature is maintained at X1 [°C] for a predetermined time and then increased to X2 [°C], and the thermal decomposition onset temperature of the matrix resin is EP [°C], EP' [°C], CP [°C], the area of ​​a region in the temperature profile when heating the structure where the temperature is equal to or higher than EP' [°C] is A1 [°C·h], and the volume ratio of oxygen in the first environment is Z1 [-], the following equation is satisfied: EP≦X1≦EP'<X2<CP... (1) A method for determining regeneration conditions for a carbon fiber bundle, the method comprising determining X1, X2, A1, and Z1 so as to satisfy the following condition: 5≦A1·Z1≦2000 (2).

2. A method for determining the regeneration conditions for carbon fiber bundles according to claim 1, wherein the intermediate carbon fiber bundles have a content of decomposition residues of the matrix resin of 5% by weight or more and 10% by weight or less.

3. The method for determining the regeneration conditions for carbon fiber bundles according to claim 1 or 2, wherein, when regenerating the carbon fiber bundle, the unwound intermediate carbon fiber bundle is heated in a second environment containing oxygen to decompose the decomposition residue of the matrix resin to obtain a recycled carbon fiber bundle, and then the recycled carbon fiber bundle is wound up; when heating the intermediate carbon fiber bundle, the temperature is maintained at X3 [°C] for a predetermined time; and X3, Y3 and Z3 are determined so as to satisfy the following equations, where Y3 [h] is the time for heating the intermediate carbon fiber bundle and Z3 [-] is the volume ratio of oxygen in the second environment: X2≦X3<CP ... (3) 15≦A1·Z1+(X3-EP')·Y3·Z3 ... (4).

4. A method for determining the conditions for recycling carbon fiber bundles as described in claim 3, wherein the recycled carbon fiber bundles have a content of decomposition residues of the matrix resin of 4% by weight or less.

5. A method for determining the recycling conditions for carbon fiber bundles according to any one of claims 1 to 4, wherein the matrix resin is a cured product of an epoxy resin.

Images