Carbon fiber-containing fragment manufacturing method and four-shaft shear crusher

Abstract

In one example, this carbon fiber-containing fragment manufacturing method comprises crushing a carbon fiber-reinforced composite material by using a four-shaft shear crusher provided with a main rotation shaft (A1), a main rotation shaft (A2), and a screen (3) installed below said main rotation shafts. A main cutter blade (11) having a maximum radius of r1 and a main cutter blade (11) having a maximum radius of r2 are respectively attached to the main rotation shaft A1 and the main rotation shaft A2. A plurality of holes (31) are formed in the screen (3). The screen (3) does not have a hole (31) within a range extending by a distance of 0.25×r1 horizontally from the line L indicated in fig. 1 toward the main rotation shaft A1 or a range extending by a distance of 0.25×r2 horizontally from the line L toward the main rotation shaft A2.

Description

Method for producing carbon fiber-containing crushed fragments and quadruple-shaft shear shredder

[0001] The present invention relates primarily to a method for producing carbon fiber-containing crushed pieces and a quadrature shear crusher. This application claims priority based on Japanese Patent Application No. 2024-225387, filed with the Japan Patent Office on December 20, 2024, the contents of which are incorporated herein by reference.

[0002] Carbon fiber reinforced composite materials, obtained by impregnating carbon fibers with matrix resin, are widely used in aerospace, sports and leisure, and other applications due to their excellent mechanical properties. However, since the production of carbon fibers consumes a large amount of energy, methods for recovering the carbon fibers contained in carbon fiber reinforced composite materials have recently attracted attention from the perspective of reducing environmental impact.

[0003] For example, Patent Document 1 describes a method for obtaining carbon fibers by first crushing a carbon fiber composite material, then further crushing it to produce crushed fragments, removing the powder, and then removing the matrix resin by thermal decomposition. Non-Patent Document 1 describes a method for predicting the filament length distribution of fibers that can be recovered from crushed fragments obtained by crushing a fiber-reinforced composite material using a thermoplastic resin with a crusher.

[0004] Regarding carbon fibers recovered from carbon fiber reinforced composite materials, there is research into utilizing them in a form with high feedability. For example, Patent Document 2 proposes using spindle-shaped carbon fiber aggregates obtained by rolling a mixture containing carbon fibers and a binder-containing liquid in a container to improve feedability. Patent Document 3 proposes a method for producing prepregs using carbon fiber aggregates obtained by mixing carbon fiber cotton and a bundling liquid.

[0005] Japanese Patent Publication No. 2019-127040, International Publication No. 2022 / 210591, International Publication No. 2022 / 265099

[0006] Composites Part B 176 (2019) 107197

[0007] The present invention primarily aims to provide a method and machine for crushing carbon fiber-reinforced composite materials for recovering carbon fibers suitable for obtaining a highly feedable form. The present invention also aims to provide a sheet molding compound with high basis weight stability and good mechanical properties. Problems that can be solved by the present invention may be explicitly or implicitly disclosed herein.

[0008] The present invention encompasses, but is not limited to, the following embodiments: [1] A method for manufacturing carbon fiber-containing crushed pieces, comprising crushing a carbon fiber-reinforced composite material using a four-axis shear crusher equipped with a pair of main rotating shafts A1 and A2, and a screen installed below the main rotating shafts A1 and A2, wherein a main cutter blade having a maximum radius r1 is attached to the main rotating shaft A1, a main cutter blade having a maximum radius r2 is attached to the main rotating shaft A2, and a plurality of holes are formed in the screen. A method for manufacturing carbon fiber-containing crushed fragments, characterized in that, on a straight line connecting the main rotation axis A1 and the main rotation axis A2, a point D is identified where the distance from the outer edges C1 and C2 defined from each main rotation axis based on r1 and r2 is equal, and when the line drawn in the direction of the main rotation axis on the screen directly below point D is defined as line L, the screen does not have the holes in a range of 0.25 × r1 horizontally from line L toward the main rotation axis A1 and a range of 0.25 × r2 horizontally from line L toward the main rotation axis A2. [2]: A method for manufacturing carbon fiber-containing crushed fragments according to [1], wherein the screen does not have the holes in a range of 0.5 × r1 horizontally from line L toward the main rotation axis A1 and a range of 0.5 × r2 horizontally from line L toward the main rotation axis A2. [3]: The method for manufacturing carbon fiber-containing crushed pieces according to [1], wherein the screen does not have the holes in a range of 1.0 × r1 horizontally from the line L toward the main rotation axis A1 and a range of 1.0 × r2 horizontally from the line L toward the main rotation axis A2. [4]: ​​When the thickness of the main cutter blade in the direction of the rotation axis is W and the average value of the area of ​​each hole in the screen is A / W ２ A method for producing carbon fiber-containing crushed pieces according to any one of [1] to [3], wherein the ratio is 0.28 or higher. [5]: A / W ２A method for manufacturing carbon fiber-containing crushed pieces according to [4], wherein the value is 3.5 or less. [6] A method for manufacturing carbon fiber-containing crushed pieces according to any one of [1] to [5], wherein the average value of the clearance between the outer edge defined from the main rotating shaft A1 and the main rotating shaft A2 based on the maximum radius and the screen is 3 to 50 mm. [7] A method for manufacturing carbon fiber-containing crushed pieces according to any one of [1] to [6], wherein the four-axis shear crusher further comprises a sub-rotating shaft to which a sub-cutter blade is attached at a position higher vertically than the main rotating shaft A1 and the main rotating shaft A2. [8] A method for manufacturing carbon fiber-containing crushed pieces according to any one of [1] to [7], wherein the carbon fiber-reinforced composite material is recycled. [9] A method for manufacturing carbon fiber-containing crushed pieces according to any one of [1] to [8], wherein the carbon fiber-reinforced composite material contains carbon fibers with a filament length of 100 mm or more.

[10] A method for manufacturing carbon fiber-containing crushed pieces according to any one of [1] to [9], wherein the carbon fiber-reinforced composite material contains a thermosetting resin.

[11] The carbon fiber reinforced composite material is a composite material in which carbon fibers are oriented in multiple directions, A / W ２ A method for producing carbon fiber-containing crushed pieces according to [4], wherein is 1.1 or greater.

[12] The carbon fiber-reinforced composite material is a composite material in which carbon fibers are substantially oriented in one direction, and A / W ２A method for producing carbon fiber-containing crushed fragments according to [4], wherein the ratio is 1.5 or less.

[13] A method for producing carbon fiber-containing crushed fragments according to any one of [1] to

[12] , further comprising removing metal powder from the carbon fiber-containing crushed fragments by magnetic force.

[14] A method for producing a group of carbon fibers, comprising recovering carbon fibers by decomposing and removing the matrix resin from the carbon fiber-containing crushed fragments produced by the method according to any one of [1] to

[13] .

[15] A method for producing a group of carbon fibers according to

[14] , wherein the group of carbon fibers contains 5% by weight or more of carbon fibers with a filament length of 3W mm or more, when the average value of the thickness in the rotation axis direction of the main cutter blade is W.

[16] A method for producing a carbon fiber aggregate, comprising drying a mixture of the group of carbon fibers produced by the method according to

[14] or

[15] and a binder-containing liquid.

[17] : A method for producing a carbon fiber aggregate, comprising cutting a group of carbon fibers produced by the manufacturing method described in

[14] or

[15] , and drying a mixture of the cut carbon fiber group and a binder-containing liquid.

[18] : A method for producing a carbon fiber mat, comprising scattering a carbon fiber aggregate produced by the method described in

[16] or

[17] .

[19] : A method for producing a sheet molding compound, comprising impregnating a carbon fiber mat produced by the method described in

[18] with a resin.

[20] A four-shaft shear shredder used for crushing carbon fiber reinforced composite materials, comprising a pair of main rotating shafts A1 and A2, and a screen installed below the main rotating shafts A1 and A2, wherein the main rotating shaft A1 is fitted with a main cutter blade having a maximum radius r1, the main rotating shaft A2 is fitted with a main cutter blade having a maximum radius r2, and the screen has a plurality of holes formed therein. A four-axis shear shredder in which, on a straight line connecting the main rotating shaft A1 and the main rotating shaft A2, a point D is identified where the distance from the outer edges C1 and C2, respectively defined from each main rotating shaft based on r1 and r2, is equal, and when the line drawn in the direction of the main rotating shaft on the screen directly below point D is defined as line L, the screen does not have the holes in a range of 0.25 × r1 horizontally from line L toward the main rotating shaft A1 and a range of 0.25 × r2 horizontally from line L toward the main rotating shaft A2.

[21] : The four-axis shear shredder according to

[20] , in which the screen does not have the holes in a range of 0.5 × r1 horizontally from line L toward the main rotating shaft A1 and a range of 0.5 × r2 horizontally from line L toward the main rotating shaft A2.

[22] : The quadrature shear shredder according to

[20] , wherein the screen does not have the holes in a range of 1.0 × r1 horizontally from the line L toward the main rotation axis A1 and a range of 1.0 × r2 horizontally from the line L toward the main rotation axis A2.

[23] : A group of shredded pieces made of a composite material, comprising carbon fibers and a matrix resin, and satisfying at least one of the following conditions (i) and (ii): Condition (i) containing 50% by weight or more of shredded pieces that pass through a circular hole with a diameter of 30 mm and do not pass through a circular hole with a diameter of 6 mm; Condition (ii) containing 62% by weight or more of shredded pieces that pass through a circular hole with a diameter of 15 mm and do not pass through a circular hole with a diameter of 6 mm.

[24] : A group of carbon fibers wherein the variation rate of filament length obtained by the fibrograph method specified in JIS L1019:2006 section 7.2.2 is 15 to 69%.

[0009] According to a preferred embodiment of the present invention, carbon fibers suitable for obtaining a highly feedable form can be recovered. Furthermore, by using the recovered carbon fibers as a raw material, a sheet molding compound with high basis weight stability and good mechanical properties can be manufactured.

[0010] Figure 1 is a side cross-sectional view showing an example of a quadruple-shaft shear shredder. Figure 2 is a plan view showing an example of the main rotating shaft of a quadruple-shaft shear shredder. Figure 3 is a plan view showing an example of the screen of a quadruple-shaft shear shredder. Figure 4 is a photograph of the appearance of the carbon fiber-containing shredded material obtained in Example 1. Figure 5 is a photograph of the appearance of the carbon fiber-containing shredded material obtained in Comparative Example 1. Figure 6 is a photograph of the appearance of the carbon fiber group obtained in Example 2. Figure 7 is a photograph of the appearance of the carbon fiber aggregate obtained in Example 2.

[0011] When manufacturing carbon fiber aggregates as described in Patent Documents 2 and 3, if the filament lengths of the carbon fibers contained in the raw material are uneven, the resulting carbon fiber aggregate will have an irregular shape. Furthermore, carbon fibers with filament lengths exceeding 50 mm can cause the formation of tangled, clump-like carbon fiber aggregates. Therefore, it is preferable that most of the carbon fibers contained in the raw material have filament lengths of 10 to 50 mm.

[0012] However, when carbon fibers are recovered by thermally decomposing the matrix resin of a carbon fiber composite material, the resulting carbon fibers are cotton-like and have random fiber orientations, making them difficult to handle and difficult to adjust to the desired length. In addition, cutting them in this cotton-like state generates a significant amount of dust. Therefore, it is considered effective to first crush the carbon fiber reinforced composite material to produce carbon fiber-containing fragments with the desired filament length, and then recover the carbon fibers by thermally decomposing the matrix resin from these carbon fiber-containing fragments.

[0013] Therefore, the inventors investigated a method for crushing carbon fiber-reinforced composite materials such that most of the carbon fibers contained in the crushed carbon fiber fragments have a filament length of 10 to 50 mm. The present invention was made during the course of such investigations.

[0014] In this specification, a numerical range expressed using "~" means a range that includes the numbers written before and after "~" as the lower and upper limits, and "A~B" means that it is greater than or equal to A and less than or equal to B.

[0015] 1. Method for Manufacturing Carbon Fiber-Containing Fragments One embodiment of the present invention relates to a method for manufacturing carbon fiber-containing fragments. In the method for manufacturing carbon fiber-containing fragments according to the embodiment, a carbon fiber-reinforced composite material is crushed using a four-axis shear crusher equipped with a pair of main rotating shafts A1 and A2, and a screen installed below the main rotating shafts A1 and A2. A main cutter blade with a maximum radius of r1 is attached to the main rotating shaft A1, and a main cutter blade with a maximum radius of r2 is attached to the main rotating shaft A2. A plurality of holes are formed in the screen. The method for manufacturing carbon fiber-containing fragments according to the embodiment is characterized in that the holes are absent in the screen in a range of 0.25 × r1 horizontally from line L toward the main rotating shaft A1 and in a range of 0.25 × r2 horizontally from line L toward the main rotating shaft A2, which are determined by the following method. Line L is determined as follows. First, on the straight line connecting the main rotation axis A1 and the main rotation axis A2, a point D is identified where the distance from the outer edges C1 and C2, which are defined based on the respective maximum radii r1 and r2 from each main rotation axis, are equal. Next, a line L is determined to be drawn on the screen directly below point D in the direction of the main rotation axis, that is, parallel to the main rotation axis. Here, the straight line connecting the main rotation axis A1 and the main rotation axis A2 means the line segment that connects the centers of the main rotation axis A1 and the main rotation axis A2 by the shortest distance when viewed from the side.

[0016] 1.1. Carbon Fiber Reinforced Composite Materials Recycled materials may be used as the carbon fiber reinforced composite materials to be crushed. Recycled materials may include, for example, scraps, off-spec or defective products, unused or used waste materials generated in the manufacturing process of carbon fiber reinforced composite materials. The carbon fiber reinforced composite material may be a composite material in which the carbon fibers are oriented in multiple directions, or it may be a composite material in which the carbon fibers are substantially oriented in one direction. Substantially unidirectional orientation of the reinforcing fibers means that 90% or more of the reinforcing fibers are within ±10° of the average orientation angle of the fiber direction of all reinforcing fibers.

[0017] The present invention is particularly preferably applicable when the carbon fiber reinforced composite material to be crushed contains carbon fibers with a filament length of 100 mm or more. Examples of carbon fiber reinforced composite materials containing carbon fibers with a filament length of 100 mm or more include carbon fiber reinforced composite materials obtained by curing a carbon fiber prepreg containing carbon fibers with a filament length of 100 mm or more, and carbon fiber reinforced composite materials manufactured by RTM (resin transfer molding), VaRTM (vacuum-assisted RTM), filament winding molding, or pultrusion molding. The present invention is particularly preferably applicable when the carbon fiber reinforced composite material to be crushed contains a thermosetting resin.

[0018] 1.2. Four-Shaft Shear Crusher The production of carbon fiber-containing crushed pieces can be carried out, for example, using a four-shaft shear crusher as shown in Figure 1. The four-shaft shear crusher shown in Figure 1 comprises a main rotating shaft A1 to which a main cutter blade 11 with a maximum radius r1 is attached, a main rotating shaft A2 to which a main cutter blade 11 with a maximum radius r2 is attached, and a screen 3 installed at the lower part of the main rotating shafts A1 and A2. The screen 3 has a plurality of holes 31 formed in it.

[0019] r1 and r2 may be the same value or may be different from each other. If multiple main cutter blades are mounted on a single main rotation axis, r1 and r2 shall be the average value per blade. A four-axis shear shredder may further include a sub-rotary shaft 2 to which sub-cutter blades 21 are mounted, positioned higher than the main rotation axes A1 and A2. In the example shown in Figure 1, a line L will be drawn on the screen 3 directly below point D in the direction of the main rotation axis, that is, perpendicular to the back of the paper. Point D is identified as a point on the straight line connecting the main rotation axes A1 and A2 such that its distance from the outer edges C1 and C2, which are defined based on the maximum radii r1 and r2 from each main rotation axis, is equal. The outer edge C1 is the trajectory formed by the outer edge of the main cutter blade 11 attached to the main rotation axis A1 during rotation. In a side view, this trajectory passes through a point located horizontally from the main rotation axis A1 toward the main rotation axis A2 at a distance r1, which is equal to the maximum radius. Similarly, the outer edge C2 is the trajectory formed by the outer edge of the main cutter blade 11 attached to the main rotation axis A2 during rotation. In a side view, this trajectory passes through a point located horizontally from the main rotation axis A2 toward the main rotation axis A1 at a distance r2, which is equal to the maximum radius.

[0020] As shown in Figure 2, disc-shaped main cutter blades 11 and spacers 12 are alternately mounted on the main rotating shaft A1 and the main rotating shaft A2 in a plan view. Further illustrations are omitted, but similarly, disc-shaped secondary cutter blades and spacers may be alternately mounted on the secondary rotating shaft in a plan view.

[0021] When crushing carbon fiber reinforced composite materials using the four-axis shear crusher described above, the material is crushed to the width of the thickness of the cutter blades 11 while being gripped by the shear force between the main cutter blades 11. After that, the carbon fiber-containing crushed pieces that are small enough to pass through the holes 31 of the screen 3 pass through the screen 3. The carbon fiber-containing crushed pieces that are too small to pass through the holes 31 are moved on the screen 3 by the main cutter blades 11 and the sub-cutter blades 21, and are transported back onto the main cutter blades 11 from the sub-rotating shaft 2 and the wall of the crushing device, where they are crushed in a circulating manner until they are small enough to pass through the holes 31. At this time, the sub-cutter blades 21 scrape out the carbon fiber-containing crushed pieces that have become stuck in the spacer 12 on the main rotating shaft 1, so that the carbon fiber-containing crushed pieces are continuously crushed.

[0022] The rotational speed of the main cutter blade is preferably 5 to 100 rpm. The lower limit of the rotational speed of the main cutter blade is more preferably 7 rpm from the viewpoint of processing capacity. The upper limit of the rotational speed of the main cutter blade is more preferably 60 rpm from the viewpoint of generated torque. In some embodiments, the rotational speeds of the main cutter blade and the sub-cutter blade may be different and are not particularly limited.

[0023] A plan view of screen 3 is shown in Figure 3. The four-axis shearing machine is characterized in that there are no holes 31 in the screen 3 in a range of 0.25 × r1 horizontally from line L toward the main rotation axis A1 and in a range of 0.25 × r2 horizontally from line L toward the main rotation axis A2. This feature improves the yield of carbon fiber-containing fragments of a size corresponding to the size of the holes 31. This is thought to be because carbon fiber-containing fragments larger than the holes 31 are prevented from passing through the holes 31 vertically, and are circulated and crushed to a size corresponding to the holes 31. As a result, the size of the obtained carbon fiber-containing fragments becomes uniform, and consequently, the filament length of the contained carbon fibers becomes uniform. It is preferable that there are no holes 31 in a horizontal range of 0.5 × r1 from line L toward the main rotation axis A1 and in a horizontal range of 0.5 × r2 from line L toward the main rotation axis A2, and it is more preferable that there are no holes 31 in a horizontal range of 1.0 × r1 from line L toward the main rotation axis A1 and in a horizontal range of 1.0 × r2 toward the main rotation axis A2.

[0024] When the thickness of the main cutter blade 11 in the rotational axis direction is W and the average value of the area of each hole 31 of the screen 3 is A, A / W ２ is preferably 0.28 or more. Thereby, it is possible to more effectively suppress carbon fiber-containing crushed pieces larger than the holes 31 from passing vertically through the holes 31. A / W ２ is more preferably 0.4 or more, and even more preferably 0.5 or more. Also, A / W ２ is preferably 3.5 or less. Thereby, clogging of the screen 3 can be suppressed, and the amount of crushing per unit time can be increased. A / W ２ is more preferably 3.4 or less, and even more preferably 3.3 or less. When a plurality of main cutter blades 11 are attached, W is the average value per sheet.

[0025] The average value of the clearance (hereinafter, also simply referred to as "clearance") between the outer edges C1 and C2 defined based on the respective maximum radii from the main rotation axis A1 and the main rotation axis A2 and the screen is preferably 3 to 50 mm. When the average value of the clearance is not less than the lower limit within the above numerical range, it is possible to prevent the material from being compacted between the cutter blade and the screen during crushing. When the average value of the clearance is not more than the upper limit within the above numerical range, the material moves on the screen by the rotation of the main rotation axis and the sub-rotation axis and is circulated and crushed. The lower limit of the average value of the clearance is more preferably 6 mm or more. The lower limit is more preferably 30 mm or less.

[0026] When the carbon fiber reinforced composite material to be crushed is a composite material in which carbon fibers are oriented in multiple directions, many angular carbon fiber-containing crushed pieces with a small aspect ratio are obtained, and due to the low permeability of the screen 3, A / W ２ is preferably 1.1 or more. Also, when the carbon fiber reinforced composite material to be crushed is a composite material in which carbon fibers are substantially oriented in one direction, many needle-like carbon fiber-containing crushed pieces that are easily cracked in the fiber direction and have a large aspect ratio are obtained, and due to the high permeability of the screen 3, A / W ２ is preferably 1.5 or less.

[0027] The shape of the holes 31 in the screen 3 can be circular or angular. From the viewpoint of less clogging during crushing and excellent workability in manufacturing the screen and durability of the screen, a circular shape is preferable. The size of the holes 31 can be appropriately adjusted according to the size of the desired carbon fiber-containing crushed pieces. For example, when crushing a carbon fiber reinforced composite material in which carbon fibers are oriented in multiple directions and a large number of carbon fiber-containing crushed pieces with a size of about 6 to 30 mm are desired, the holes 31 are preferably circular with a diameter of 12 to 60 mm. When it is desired to obtain carbon fiber-containing crushed pieces with a size of about 6 to 15 mm, the holes 31 are preferably circular with a diameter of 12 to 30 mm. For example, when crushing a carbon fiber composite material in which carbon fibers are substantially oriented in one direction and a large number of carbon fiber-containing crushed pieces with a size of about 6 to 30 mm are desired, the holes 31 are preferably circular with a diameter of 6 to 15 mm. If it is desired to obtain carbon fiber-containing crushed pieces with a size of about 6 to 15 mm, the holes 31 are preferably circular with a diameter of 6 to 10 mm.

[0028] The shape and size of the holes 31 may be partially different. For example, in the central part of the screen 3 or in the part where the holes 31 are opened in the horizontal direction, the shape of the holes 31 can be a long hole, a rhombus, etc., and it is preferable to make the size 6 to 60 mm smaller than other parts. From the viewpoint of durability, the thickness of the holes 31 is preferably 5 mm or more, and more preferably 7 mm or more.

[0029] 1.3. Removal of metal powder The carbon fiber-containing crushed pieces obtained using a four-axis shear crusher may be subjected to removal of metal powder by magnetic force. As the magnet, for example, a rare earth magnet, a ferrite magnet, an alloy magnet, and an electromagnet can be used. From the viewpoints of the strength of the magnetic force and the running cost, a rare earth magnet is preferable, and a neodymium magnet is more preferable. For the removal of metal powder, for example, unit type magnet bars and plates, and cylindrical, housing type, rotary type, and conveyor type magnetic separators can be used. In particular, it is preferable to use a conveyor type magnetic separator on the belt conveyor for transporting from the crusher to the next process because clogging does not occur and metal powder can be continuously removed.

[0030] 2. Fragmentation group One embodiment of the present invention relates to a group of fragments made of a composite material. The fragmentation group according to the embodiment comprises carbon fibers and a matrix resin, and satisfies at least one of the following conditions (i) and (ii).

[0031] (i) Contains 50% by weight or more of fragments that pass through a 30 mm diameter hole but do not pass through a 6 mm diameter hole. (ii) Contains 62% by weight or more of fragments that pass through a 15 mm diameter hole but do not pass through a 6 mm diameter hole.

[0032] According to a group of crushed fragments that satisfy at least one of conditions (i) and (ii), most of the carbon fibers in the group of crushed fragments will have a filament length of 10 to 50 mm. Therefore, carbon fibers suitable for obtaining a highly feedable form in the carbon fiber manufacturing method described later can be recovered.

[0033] In condition (i), it is more preferable to contain 60% by weight or more of fragments that pass through a circular hole with a diameter of 30 mm but do not pass through a circular hole with a diameter of 6 mm, and even more preferable to contain 65% by weight or more.

[0034] In condition (ii), it is more preferable to contain 63% by weight or more of fragments that pass through a circular hole with a diameter of 15 mm but do not pass through a circular hole with a diameter of 6 mm, and even more preferable to contain 64% by weight or more of such fragments. A group of fragments that satisfies at least one of conditions (i) and (ii) can be obtained, for example, by the method for producing carbon fiber-containing fragments according to the embodiment described above.

[0035] 3. Method for Manufacturing Carbon Fiber Groups One embodiment of the present invention relates to a method for manufacturing carbon fiber groups. The method for manufacturing carbon fiber groups according to the embodiment includes recovering carbon fiber groups by decomposing and removing the matrix resin from carbon fiber-containing crushed pieces obtained by the method for manufacturing carbon fiber-containing crushed pieces according to the embodiment, or from a group of crushed pieces according to the embodiment. Preferably, the recovered carbon fiber groups are cotton-like in a dry state, and the matrix resin residue is in the range of 0 to 5% by mass.

[0036] Methods for decomposing and removing the matrix resin include, for example, the use of thermal decomposition and chemical decomposition, as described below. The matrix resin may also be decomposed and removed by combining these methods with multiple physical removal methods.

[0037] Japanese Patent Publication No. 6-99160 describes a method for treating a carbon fiber reinforced composite material without combustion in a gas atmosphere with an oxygen concentration in the range of 3 to 18 volume percent and a temperature in the range of 300 to 600°C. Japanese Patent Publication No. 7-33904 describes a method for treating a carbon fiber reinforced composite material after dry distillation, with an oxygen concentration in the range of 0.1 to 25 volume percent and a temperature in the range of 300 to 1000°C without combustion. Japanese Patent Publication No. 7-118440 describes a method for dry distilling a carbon fiber reinforced composite material at a temperature in the range of 300 to 1000°C.

[0038] For example, the matrix resin of a carbon fiber reinforced composite material may be decomposed and removed by a semiconductor thermal activation method using oxide semiconductors such as chromium oxide, titanium oxide, zinc oxide, vanadium oxide, tungsten oxide, molybdenum oxide, cobalt oxide, iron oxide, and copper oxide. For specific procedures of the semiconductor thermal activation method, see, for example, International Publication No. 2022 / 050281.

[0039] In one example, the matrix resin of the carbon fiber reinforced composite material may be decomposed and removed using an acidic solution such as nitric acid or sulfuric acid, or an alkaline solution containing an alkali metal compound, or an organic solvent such as an alkali metal compound and triethylene glycol. In another example, the matrix resin of the carbon fiber reinforced composite material may be decomposed and removed using a subcritical or supercritical fluid. Resin residue that cannot be completely removed by this method can be removed by heat treatment in an oxidizing atmosphere. In yet another example, the matrix resin of the carbon fiber reinforced composite material may be decomposed and removed by microwave heating.

[0040] 4. One embodiment of a carbon fiber group relates to a carbon fiber group. The carbon fiber group according to this embodiment has a filament length variation rate of 15 to 69% obtained by the fibrograph method specified in JIS L1019:2006 section 7.2.2. By satisfying the above, the carbon fiber group can be made to have a form with high feedability in the carbon fiber assembly manufacturing method described later.

[0041] A group of carbon fibers having a filament length variation rate of 15 to 69% can be obtained, for example, by the method for manufacturing a group of carbon fibers according to the embodiment described above. In this case, it is preferable that the group of carbon fibers contains 5% by weight or more of carbon fibers having a filament length of 3W mm or more, relative to the average value W of the thickness in the rotation axis direction of the main cutter blade.

[0042] 5. Method for Manufacturing Carbon Fiber Aggregates One embodiment of the present invention relates to a method for manufacturing carbon fiber aggregates. The method for manufacturing carbon fiber aggregates according to the embodiment includes drying a mixture of carbon fiber aggregates and binder-containing liquid obtained by the manufacturing method according to the above embodiment.

[0043] The group of carbon fibers used in the production of the carbon fiber aggregate may include only the group of carbon fibers obtained by the production method according to the above embodiment, or it may include a group of carbon fibers obtained by a different production method having a similar filament length. Uniform filament lengths of the carbon fibers used improve the shape stability of the resulting carbon fiber aggregate and ensure good feedability. While it is preferable that the carbon fibers are not bonded to each other, very loose bonding is acceptable.

[0044] The binder-containing liquid preferably contains water as a liquid component. The capillary effect caused by the strong surface tension of water causes the carbon fiber filaments to aggregate, which preferably forms a carbon fiber aggregate.

[0045] The binder included in the binder-containing liquid can be a sizing agent commonly used in the manufacture of carbon fibers, such as polyurethane resin, polyester resin, polyether resin, and copolymers or mixtures thereof. The amount of the binder-containing liquid can be, for example, 30 to 100 parts by mass per 100 parts by mass of carbon fiber, but is not limited to that amount. The amount of the binder-containing liquid can be adjusted as appropriate while observing the state of the mixture.

[0046] The method for mixing the carbon fiber group and the binder-containing liquid is not particularly limited, but from the viewpoint of efficient mixing in a short time, stirring is preferred. A stirring granulator or a rolling granulator can preferably be used for stirring.

[0047] The resulting carbon fiber aggregate tends to be needle-shaped, spindle-shaped, or wire-shaped, suitable for reinforcing sheet prepregs, when the carbon fiber group used contains a large proportion of carbon fibers with a filament length of 5 to 50 mm. When the carbon fiber group used contains a large proportion of carbon fibers with a filament length of 1 to 15 mm, and especially when it contains a large proportion of carbon fibers with a filament length of 12 mm or less, it tends to be spindle-shaped, which can be fed into a kneader using a feeder. For example, International Publication No. 2022 / 210591 discloses a method for producing spindle-shaped carbon fiber aggregates.

[0048] Needle-shaped, spindle-shaped, or wire-shaped carbon fiber aggregates preferably have a number-average length in the longitudinal direction of 10 to 50 mm. The weighted-average length is preferably 15 to 60 mm. The bulk density is 0.01 to 0.13 g / cm³. ３ Preferably, the lower limit is 0.03 g / cm³. ３ The upper limit is 0.10 g / cm³. ３ It is preferable that it be so.

[0049] One embodiment relates to a method for producing a carbon fiber aggregate. The method for producing a carbon fiber aggregate includes cutting a group of carbon fibers obtained by the production method according to the present invention, and drying a mixture of the cut carbon fiber group and a binder-containing liquid.

[0050] The carbon fiber group used may include only the carbon fiber group obtained by the manufacturing method according to the present invention, or it may include the carbon fiber group obtained by a manufacturing method different from that of this embodiment. In the carbon fiber group, it is preferable that the filaments are not bonded to each other, but very loose bonding is acceptable.

[0051] For cutting carbon fiber bundles, a cutting machine or shredder such as a guillotine cutter can be used. Multiple cutting machines or shredders may be used. For example, by using two cutting machines and cutting with the second machine perpendicular to the direction in which the first machine cut, a large amount of carbon fiber with a filament length corresponding to the cutting interval set on the cutting machines can be obtained. It is preferable to connect the two cutting machines with a belt conveyor, arrange them vertically, and cut continuously while maintaining the orientation of the fibers.

[0052] The binder-containing liquid, the method for mixing the carbon fiber group with the binder-containing liquid, and the shape of the resulting carbon fiber aggregate are the same as described above.

[0053] 6. One embodiment of a method for manufacturing a carbon fiber mat relates to a method for manufacturing a carbon fiber mat. The method for manufacturing a carbon fiber mat according to the embodiment includes scattering a carbon fiber aggregate obtained by the manufacturing method according to the above embodiment. By using a carbon fiber aggregate with high shape stability and good feedability obtained by the manufacturing method according to the above embodiment, the basis weight stability of the resulting carbon fiber mat is improved.

[0054] For example, carbon fiber assemblies can be transported to the discharge end of a conveyor belt for transporting carbon fiber assemblies, which has an uneven surface and a gradient section. As the carrier film runs along the conveyor belt, the carbon fiber assemblies can be dropped onto the carrier film to form a carbon fiber mat. Here, the width direction of the carrier film and the width direction of the conveyor belt are parallel to each other. As the conveyor belt for transporting carbon fiber assemblies, for example, a spiked lattice can be used. Furthermore, the bundle length of the carbon fiber assemblies is preferably in the range of 5 to 100 mm.

[0055] Furthermore, as an example of a means of scraping off a portion of the carbon fiber assemblies being transported by the belt conveyor for transporting carbon fiber assemblies, a scraping roller can be optionally provided in the middle or at the top of the upward sloping section of the belt conveyor. This allows for uniform distribution of the carbon fiber assemblies. The scraping roller has a rotating shaft parallel to the width direction of the belt conveyor for transporting carbon fiber assemblies, and a cylindrical portion with the rotating shaft as its central axis. Preferably, blades are arranged on the outer circumferential surface of the cylindrical portion, either parallel or perpendicular to the rotating shaft.

[0056] Additionally, a raw material supply conveyor may be provided as an option. The raw material supply conveyor is positioned upstream of the carbon fiber aggregate conveying belt conveyor, and its T-direction is the same as that of the carbon fiber aggregate conveying belt conveyor. Here, the T-direction of the belt conveyor means a direction that is perpendicular to the conveying direction of the raw material supply conveyor and is also horizontal. The T-direction is usually parallel to the width direction of the conveyor belt of the raw material supply conveyor.

[0057] Carbon fiber assemblies supplied from the raw material conveyor are transported toward the carbon fiber assembly transport belt conveyor. The belt speed of the raw material conveyor is usually lower than that of the carbon fiber assembly transport belt conveyor.

[0058] 7. Method for Manufacturing Sheet Molding Compound One embodiment relates to a method for manufacturing sheet molding compound. The method for manufacturing sheet molding compound according to this embodiment includes impregnating a carbon fiber mat obtained by the manufacturing method according to this embodiment with a resin. By using a carbon fiber mat with high basis weight stability obtained by the manufacturing method according to this embodiment, the basis weight stability of the resulting sheet molding compound is improved. Furthermore, defects caused by uneven basis weight are reduced, resulting in good mechanical properties.

[0059] In a preferred example, a sheet molding compound can be manufactured by following the first, second, third, and fourth steps. First step: Applying a liquid thermosetting resin composition to the respective surfaces of a first protective film and a second protective film. Second step: Laminating a carbon fiber mat onto the surface of the first protective film coated with the liquid thermosetting resin composition. Third step: Forming a laminate by bonding the second protective film to the first protective film with the carbon fiber mat in between, so that the surfaces coated with the liquid thermosetting resin composition face each other. Fourth step: Impregnating the carbon fiber mat containing the carbon fiber aggregate with the liquid thermosetting resin composition by pressurizing the laminate to obtain a sheet molding compound. Each step will be described in detail below.

[0060] 7.1. First Step In the first step, a liquid thermosetting resin composition is applied to the surfaces of the first protective film and the second protective film, respectively. The amount of liquid thermosetting resin composition to be applied is adjusted considering the basis weight and fiber content of the sheet molding compound to be manufactured.

[0061] 7.1.1. Protective Films The first protective film and the second protective film are synthetic resin films. Their materials can be appropriately selected from polyolefins such as polyethylene and polypropylene, polyvinylidene chloride, vinyl chloride resin, polyamide, etc. The first protective film and the second protective film may be multilayer films. The specifications of the first protective film and the second protective film may be the same or different. The first protective film and the second protective film may be carrier films unwound from a roll.

[0062] 7.1.2. Liquid Thermosetting Resin Compositions Examples of base resins for liquid thermosetting resin compositions include, but are not limited to, vinyl ester resins, unsaturated polyester resins, epoxy resins, polyimide resins, maleimide resins, and phenolic resins. One type of thermosetting resin may be blended into the liquid thermosetting resin composition, or two or more types may be blended. Liquid thermosetting resin compositions usually contain a curing agent in addition to the base resin. In addition, the liquid thermosetting resin composition may optionally contain polymerization inhibitors, thickeners, reactive diluents, low shrinkage agents, antioxidants, internal release agents, colorants, modifiers (e.g., rubber, elastomers, or thermoplastic resins), flame retardants, antibacterial agents, etc.

[0063] Liquid thermosetting resin compositions are preferably solvent-free, in other words, not varnishes. If they are varnishes, it is necessary to impregnate a carbon fiber mat containing carbon fiber aggregates with the solvent and then evaporate and remove it. Reactive diluents are not included in the term "solvent" as used here. One preferred example of a non-varnish liquid thermosetting resin composition is a vinyl ester resin-based composition, which contains a vinyl ester resin, an unsaturated polyester resin, an ethylenically unsaturated monomer, a thickener, a polymerization initiator, and a polymerization inhibitor.

[0064] Another preferred example of a liquid thermosetting resin composition that is not a varnish is an epoxy resin-based composition, which is a combination of epoxy resin and epoxy curing agent, and optionally further a thickener.

[0065] 7.1.2.1. Vinyl Ester Resins Preferred examples of vinyl ester resins are bisphenol A type epoxy vinyl ester resins and novolac vinyl ester resins. Either one or both may be blended. The mass ratio of the blended vinyl ester resin to the unsaturated polyester resin may be 1:9 to 9:1, 1:7 to 7:1, 1:4 to 4:1, 1:2 to 2:1, etc.

[0066] 7.1.2.2. Ethylene-unsaturated monomers Ethylene-unsaturated monomers are to be added as reactive diluents. At least one monofunctional ethylenically unsaturated monomer, at least one polyfunctional ethylenically unsaturated monomer, or both may be added.

[0067] A preferred example of a monofunctional ethylenically unsaturated monomer is styrene. Other examples include, but are not limited to, monofunctional (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, benzyl (meth)acrylate, methylbenzyl (meth)acrylate, phenoxyethyl (meth)acrylate, methylphenoxyethyl (meth)acrylate, morpholine (meth)acrylate, phenylphenoxyethyl acrylate, phenylbenzyl (meth)acrylate, phenyl methacrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, and dicyclopentanyl methacrylate.

[0068] Examples of polyfunctional ethylenically unsaturated monomers include, but are not limited to, difunctional (meth)acrylates such as ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, bisphenol di(meth)acrylate, and 1,4-cyclohexanedimethanol di(meth)acrylate.

[0069] 7.1.2.3. Thickeners Polyisocyanates may be used as thickeners. Polyisocyanates are organic compounds having two or more isocyanate groups (-NCO) per molecule. Preferred examples of polyisocyanates are diisocyanates such as 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate.

[0070] 7.1.2.4. Polymerization Initiators The polymerization initiator can be an organic peroxide that is commonly used as a curing agent for vinyl ester resins or unsaturated polyester resins. Examples of organic peroxides include ketone peroxides, hydroperoxides, diacyl peroxides, dialkyl peroxides, peroxyketals, alkyl peresters, parkervonates, etc.

[0071] 7.1.2.5. Polymerization Inhibitors Polymerization inhibitors can be appropriately selected from various compounds generally known as polymerization inhibitors. Preferred examples include catechol, hydroquinone, and benzoquinone.

[0072] 7.1.2.6. Epoxy Resins There are no limitations on the type of epoxy resin that can be used. Various types of epoxy resins can be used, including bisphenol-type epoxy resins, naphthalene-type epoxy resins, biphenyl-type epoxy resins, novolac-type epoxy resins, glycidylamine-type epoxy resins, epoxy resins having an oxazolidone ring structure, alicyclic epoxy resins, and aliphatic epoxy resins.

[0073] In preferred examples, bisphenol-type epoxy resins such as bisphenol A-type epoxy resin or bisphenol F-type epoxy resin are incorporated. Some commercially available bisphenol-type liquid epoxy resins have a low viscosity of 5 Pa·s or less at 25°C. Bisphenol-type epoxy resin may constitute 50% or more, 60% or more, 65% or more, 70% or more, or 75% or more by mass of the total epoxy resin incorporated.

[0074] 7.1.2.7. Epoxy Curing Agents It is preferable to use latent curing agents as epoxy curing agents. Latent curing agents are solids with low solubility in epoxy resins at room temperature, but when heated they melt or dissolve in the epoxy resin and exhibit their function as curing agents. Various imidazoles, dicyandiamides, and boron trifluoride-amine complexes are typical examples of latent curing agents.

[0075] Imidazoles are compounds that have an imidazole ring. This includes not only substituted imidazoles, in which the hydrogen atoms of imidazole are replaced by substituents, but also imidazolium salts and imidazole complexes.

[0076] Preferred examples of substituted imidazoles that act as latent curing agents include substituted imidazoles having aromatic rings, which may be heteroaromatic rings, in the molecule, such as 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2-phenyl-4-methylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-phenyl-4-benzyl-5-hydroxymethylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-paratoluyl-4-methyl-5-hydroxymethylimidazole, 2-paratoluyl-4,5-dihydroxymethylimidazole, 2-metatoluyl-4-methyl-5-hydroxymethylimidazole, 2-metatoluyl-4,5-dihydroxymethylimidazole, and 1-cyanoethyl-2-phenylimidazole.

[0077] Imidazolium salts such as 1-cyanoethyl-2-ethyl-4-methylimidazolium trimellitate, 1-cyanoethyl-2-undecylimidazolium trimellitate, and 1-cyanoethyl-2-phenylimidazolium trimellitate are also suitable examples of imidazole-based latent curing agents.

[0078] Isocyanuric acid adducts of various substituted imidazoles such as 2-phenylimidazole, 2-methylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, and 2-phenyl-4-methyl-5-hydroxymethylimidazole, in particular isocyanuric acid adducts of substituted imidazoles having a triazine ring, such as 2,4-diamino-6-(2'-methylimidazolyl-(1'))-ethyl-s-triazine, 1-(4,6-diamino-s-triazine-2-yl)ethyl-2-undecylimidazole, and 2,4-diamino-6-[2-(2-ethyl-4-methyl-1-imidazolyl)ethyl]-s-triazine, are particularly preferred imidazole-based latent curing agents.

[0079] Amine adducts are also a suitable example of latent curing agents. Amine adducts are produced by reacting imidazole and / or tertiary amines with epoxy resin and / or isocyanates to increase their molecular weight, and they have relatively low solubility in epoxy resins.

[0080] The latent curing agent may be used individually or in combination of two or more. When dicyandiamide is used as the latent curing agent, urea derivatives such as 4,4'-methylenebis(phenyldimethylurea) and 2,4-bis(3,3-dimethylureido)toluene can be preferably used as curing accelerators.

[0081] In addition to latent curing agents, or in place of latent curing agents, epoxy curing agents other than latent curing agents, such as carboxylic acid anhydrides, aromatic amines, and phenolic resins, can also be used. Among carboxylic acid anhydrides, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, and methyl-5-norbornene-2,3-dicarboxylic acid anhydride (methyl-3,6-endomethylene-1,2,3,6-tetrahydrophthalic anhydride) all have a viscosity of less than 0.5 Pa·s at 25°C, and may be used to reduce the viscosity of the composition.

[0082] It is known that carboxylic acid anhydrides react with epoxy compounds at low temperatures and form bonds through the catalytic action of a tertiary amine, which may be glycidylamine. Therefore, when 20 parts by mass or less of carboxylic acid anhydride are blended with a tertiary amine per 100 parts by mass of epoxy compound, it acts as a thickening agent.

[0083] Amine compounds also act as thickeners when added in an amount such that the amount of active hydrogen per epoxy group is 0.1 to 0.5 equivalents. Examples of amine compounds that can be preferably used as thickeners include, but are not limited to, isophoronediamine, bis(4-aminocyclohexyl)methane, and 1,3-bis(aminomethyl)cyclohexane.

[0084] Polyisocyanates, which may also be diisocyanates, particularly those having aromatic rings in their molecular structure, such as bis(4-isocyanatophenyl)methane and toluene diisocyanate, are suitable examples of thickeners. Polyisocyanates exhibit a higher thickening effect when preferably combined with polyols. Examples of polyols include, but are not limited to, ethylene glycol, polyethylene glycol, isosorbide, neopentyl glycol, cyclohexanediol, cyclohexanedimethanol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, and 1,6-hexanediol.

[0085] 7.1.2.8. Flame retardants The flame retardants that can be incorporated into liquid thermosetting resin compositions are as follows. Preferred flame retardants include phosphorus-containing flame retardants. Examples of phosphorus-containing flame retardants include non-halogenated phosphate esters such as trimethyl phosphate, triethyl phosphate, tributyl phosphate, trioctyl phosphate, tributoxyethyl phosphate, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, and aromatic polyphosphates.

[0086] Other examples of phosphorus-containing flame retardants include halogenated phosphate esters such as tris(chloroethyl) phosphate, tris(dichloropropyl) phosphate, tris(chloropropyl) phosphate, bis(2,3-dibromopropyl)2,3-dichloropropyl phosphate, tris(2,3-dibromopropyl) phosphate, bis(chloropropyl)octyl phosphate, alkyl halogenated polyphosphates, and alkyl halogenated polyphosphates.

[0087] Further examples of phosphorus-containing flame retardants include metal phosphinates. These metal phosphinates include not only metal salts of phosphinic acid without organic groups, but also metal salts of organic phosphinic acids such as diphenylphosphinic acid, monophenylphosphinic acid, dialkylphosphinic acid, monoalkylphosphinic acid, and alkylphenylphosphinic acid, as well as metal salts of diphosphinic acids such as methane(dimethylphosphinic acid) and benzene-1,4-di(methylphosphinic acid). Examples of dialkylphosphinic acids include dimethylphosphinic acid, ethylmethylphosphinic acid, diethylphosphinic acid, and methyl-n-propylphosphinic acid. Examples of monoalkylphosphinic acids include methylphosphinic acid, ethylphosphinic acid, and n-propylphosphinic acid. An example of alkylphenylphosphinic acid is methylphenylphosphinic acid. Metal phosphinates may include, but are not limited to, aluminum phosphinate, zinc phosphinate, calcium phosphinate, and magnesium phosphinate. Further examples of phosphorus-containing flame retardants include red phosphorus, ammonium polyphosphate, melamine phosphate, guanidine phosphate, and guanylurea phosphate.

[0088] Liquid thermosetting resin compositions can contain phosphorus-free flame retardants in addition to phosphorus-containing flame retardants. Examples of phosphorus-free flame retardants include melamine compounds such as melamine cyanurate, nitrogen-based flame retardants such as triazine compounds, guanidine compounds, ammonium phosphate, and ammonium carbonate, hydrated metals such as aluminum hydroxide and magnesium hydroxide, and organometallic salt flame retardants such as ferrocene and acetylacetone metal complexes. In preferred examples, all materials incorporated into the liquid thermosetting resin composition, including the flame retardants, are selected to be halogen-free. This results in a halogen-free flame-retardant sheet molding compound.

[0089] 7.2. Second Step In the second step, a carbon fiber mat is laminated onto the surface of the first protective film coated with the liquid thermosetting resin composition. For example, carbon fiber aggregates may be directly scattered and laminated, or they may be laminated while maintaining their mat shape. The basis weight of the carbon fiber mat formed on the first protective film is adjusted considering the basis weight and fiber content of the sheet molding compound to be manufactured.

[0090] 7.3. Third Step In the third step, the second protective film is bonded to the first protective film with a carbon fiber mat containing a carbon fiber aggregate in between, so that the surfaces coated with the liquid thermosetting resin composition face each other, thereby forming a laminate.

[0091] 7.4. Fourth Step In the fourth step, the laminate is pressurized to impregnate the carbon fiber mat containing the carbon fiber aggregate with a liquid thermosetting resin composition to obtain a sheet molding compound. If a thickener is added to the liquid thermosetting resin composition, it is preferable to allow the sheet molding compound to mature after the fourth step until the viscosity of the liquid thermosetting resin composition becomes sufficiently high.

[0092] The basis weight of the sheet molding compound can be designed as appropriate depending on the application. For example, the basis weight could be 300 g / m². ２ More than 500g / m ２ Less than 500g / m² ２ More than 1000g / m ２ Less than 1000 g / m² ２ More than 2000g / m ２ Less than 2000 g / m² ２ More than 4000g / m ２ Less than 4000 g / m² ２ More than 6000g / m ２ Less than 6000 g / m² ２ More than 8000g / m ２ Less than 8000 g / m² ２ More than 10000g / m ２ It may be less than.

[0093] The fiber content of the sheet molding compound may be 20% by mass or more but less than 30% by mass, 30% by mass or more but less than 40% by mass, 40% by mass or more but less than 50% by mass, 50% by mass or more but less than 60% by mass, 60% by mass or more but less than 70% by mass, 70% by mass or more but less than 80% by mass, or 80% by mass or more but less than 90% by mass. The higher the fiber content, the better the mechanical properties of the carbon fiber reinforced composite material obtained by curing the sheet molding compound. The lower the fiber content, the easier it is to flow during pressure molding, thus increasing the degree of freedom in designing the shape of the carbon fiber reinforced composite material molded from the sheet molding compound.

[0094] The thickness of the sheet molding compound may be designed to be, for example, 0.5 mm or more but less than 1.5 mm, 1.5 mm or more but less than 3 mm, or 3 mm or more but 5 mm or less, but is not limited to these.

[0095] 8. Method for Manufacturing Carbon Fiber Reinforced Composite Materials When manufacturing carbon fiber reinforced composite materials from sheet molding compounds, press molding is preferably used as the molding method, but it is not limited to this method. Other molding methods, such as autoclave molding, can also be used.

[0096] The embodiments will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0097] [Measurement Method] (Filament Length and Variation Rate in Carbon Fiber Groups) The filament length and variation rate in the fabricated carbon fiber group were measured as follows, in accordance with JIS L1019:2006 Section 7.2.2, the method using a fiberograph. After attaching a comb with the teeth facing upwards to the fiberograph sampler, approximately 300g of sample was placed in the sample setting position and sandwiched from above with a perforated sample plate. The sampler's comb was moved horizontally over the sample plate to pick up the sample with the comb. Carbon fibers not caught on the comb were removed with a brush. The comb was removed from the sampler, attached to the fiberograph, and any floating fibers were removed with a brush and the comb was straightened. Then, the sample was irradiated while scanning with a photocell to determine the filament length and its variation rate (CV value). The measurement was performed three times, and the average measurement value was adopted.

[0098] (Bulk density of carbon fiber aggregates) The bulk density of the prepared carbon fiber aggregates was measured as follows: The carbon fiber aggregates were dropped into a 2L disposable polypropylene cup with measuring marks (AS ONE V2000C, opening diameter 15.5 cm, depth 18.5 cm). At this time, any aggregates in which the carbon fibers were entangled rather than forming isolated bundles were removed. When the volume read from the measuring marks on the disposable cup reached 2L, the weight was measured. The measured weight of the carbon fiber aggregate (unit: g) was measured in units of 2000 (unit: cm³). ３ The value obtained by dividing by ) is the bulk density (unit: g / cm³). ３ The measurement was performed five times, and the average value was used.

[0099] (Variation in the thickness of carbon fiber mats) The CV value was measured as an index of the variation in the thickness of the fabricated carbon fiber mats as follows: The uncompressed carbon fiber mat immediately after application was passed under a height profile sensor, and the height of the mat was obtained for areas every 200 mm in the longitudinal direction. The average value and standard deviation of the mat height for each 200 mm area over a length of 1 m or more in the longitudinal direction were calculated to determine the CV value.

[0100] (Evaluation of Bending Properties of Carbon Fiber Reinforced Composite Materials) The bending strength and bending modulus of the fabricated carbon fiber reinforced composite material were measured as follows. Five test pieces, each 25 mm wide and 110 mm long, were cut from a plate-shaped carbon fiber reinforced composite material. A three-point bending test was performed on each test piece using a universal testing machine (Instron 4465, manufactured by Instron Corporation) under the conditions of a crosshead speed of 5 mm / min, a span distance of 40 mm, a nose radius of 5, and a support radius of 3.2, and the bending strength and bending modulus were measured. The average value was calculated from the measurements obtained for the five test pieces.

[0101] [Example 1] For the preparation of the crushed carbon fiber reinforced composite material, Mitsubishi Chemical Corporation's Pyrofil (registered trademark) TR350I250S (carbon fiber weight 250 g / m²), which is a thermosetting carbon fiber UD prepreg, was used. ２ Resin content 36% by mass, prepreg weight 390 g / m ２ ) was used.

[0102] First, 20 sheets of UD prepreg, cut to 75 cm x 35 cm with the short side facing the fiber direction and 75 cm x 35 cm with the long side facing the fiber direction, were stacked to form a laminate, with the fiber directions alternating and perpendicular to each other, symmetrically arranged at the center of the thickness. Next, the resulting laminate was bagged and then cured in an autoclave molding machine at 0.6 MPa and a heating rate of 2°C / min, maintaining 130°C for 90 minutes to produce a carbon fiber reinforced composite material with orthogonal lamination.

[0103] Ten kg of the fabricated carbon fiber reinforced composite material was fed one piece at a time into a quadruple-shaft shear shredder (EnMa F350-1000, manufactured by ENMA JAPAN Co., Ltd.) and shredded. Main cutter blades with a maximum radius of r were attached to the main rotating shafts A1 and A2 of this quadruple-shaft shear shredder. Table 1 shows the thickness W in the direction of rotation of the main cutter blade, the maximum radius r, the rotation speed of the main cutter blade, and the clearance. The screen used had no holes in the 1.0 × r range horizontally from line L, and had circular holes with a diameter of 50 mm in the remaining range.

[0104] A photograph of the appearance of the obtained carbon fiber-containing fragments is shown in Figure 4. The carbon fiber-containing fragments were sieved through a perforated metal with 30 mm diameter holes. Subsequently, the carbon fiber-containing fragments that passed through the 30 mm diameter holes were sieved through a perforated metal with 6 mm diameter holes, and the weight of each was weighed. The weight ratio of carbon fiber-containing fragments that passed through the 30 mm diameter holes but not the 6 mm diameter holes was calculated as the yield. The weight ratio of carbon fiber-containing fragments that did not pass through the 30 mm diameter holes was calculated as the longitudinal penetration rate. The results are shown in Table 1.

[0105] [Comparative Example 1] Carbon fiber-containing fragments were obtained in the same manner as in Example 1, except that a screen was used which had no holes in the horizontal range of 0.1 × r from line L, and had circular holes with a diameter of 50 mm in the other range. A photograph of the appearance of the obtained carbon fiber-containing fragments is shown in Figure 5. Subsequently, the carbon fiber-containing fragments were sieved in the same manner as in Example 1, and the yield and longitudinal penetration rate were calculated. The results are shown in Table 1.

[0106] [Example 2] For the preparation of the crushed carbon fiber reinforced composite material, Mitsubishi Chemical Corporation's Pyrofil (registered trademark) TR350I250S (carbon fiber weight 250 g / m²), which is a thermosetting carbon fiber UD prepreg, was used. ２ Resin content 36% by mass, prepreg weight 390 g / m ２ First, UD prepreg was rolled into a 300 mm diameter cylinder 10 m long in the fiber direction, and then compressed in the diametrical direction to create a laminate in which the fibers were oriented in one direction. Next, the resulting laminate was heated at 90°C for 3 hours to produce a carbon fiber reinforced composite material.

[0107] Ten kg of the prepared carbon fiber reinforced composite material was fed one piece at a time into a quadrature shear shredder similar to that used in Example 1 and shredded. The thickness W in the direction of rotation of the main cutter blade, the radius r, the rotation speed of the main cutter blade, and the clearance are shown in Table 1. The screen used had no holes in the horizontal range of 0.5 × r from line L, and circular holes with a diameter of 25 mm in the remaining range.

[0108] The obtained carbon fiber-containing fragments were carbonized at 700°C for 0.5 hours. Then, the matrix resin was decomposed and removed by holding the material at 600°C for 1.5 hours in an atmosphere containing 21% by volume of oxygen, yielding a cotton-like group of carbon fibers. Table 1 shows the average filament length and CV value of this carbon fiber group. The obtained carbon fiber-containing fragments were then sieved through a perforated metal with 15 mm diameter holes. Subsequently, the carbon fiber-containing fragments that passed through the 15 mm diameter holes were sieved through a perforated metal with 6 mm diameter holes, and their respective weights were measured. The weight ratio of carbon fiber-containing fragments that passed through the 15 mm diameter holes but not the 6 mm diameter holes was calculated as the yield. The weight ratio of carbon fiber-containing fragments that did not pass through the 15 mm diameter holes was calculated as the longitudinal penetration rate. The results are shown in Table 1.

[0109] Next, the carbon fiber-containing fragments that passed through the 15 mm diameter filter but not the 6 mm diameter filter were subjected to dry distillation at 700°C for 0.5 hours. Subsequently, the matrix resin was decomposed and removed by holding the mixture at 600°C for 1.5 hours in an atmosphere containing 21% oxygen, yielding the cotton-like carbon fiber group shown in Figure 6. The average filament length of this carbon fiber group was 18.5 mm (CV value 29.8%).

[0110] Next, 600 g of the obtained carbon fiber group and 270 g of the binder-containing liquid were mixed using a 25 L SP granulator (manufactured by Dalton Co., Ltd.) as a stirring granulator. The binder-containing liquid was prepared by adding 0.2 wt% of FineSurf NDB-800 (manufactured by Aoki Oil Co., Ltd.) as an additive to an aqueous dispersion of Hydran N320 (manufactured by DIC Corporation) adjusted so that the solid content was 6 parts by weight per 100 parts by weight of carbon fiber. The obtained binder-containing liquid was introduced into the stirring granulator using a pressure spray bottle at a spray pressure of 0.1 to 0.4 MPa and mixed for 1 minute at an agitator rotation speed of 118 rpm and a chopper rotation speed of 1500 rpm. Subsequently, it was mixed for a further 5 minutes at an agitator rotation speed of 470 rpm and a chopper rotation speed of 3000 rpm. The same procedure was repeated 10 times to obtain 8700 g of the mixture. The resulting mixture was dried at 120°C for 2 hours to obtain 6360 g of carbon fiber aggregate. As shown in Figure 7, the shape of the carbon fiber aggregate was needle-like or wire-like, and its bulk density was 0.071 g / cm³. ３ The results showed that when measuring the length of more than 300 carbon fiber assemblies using image analysis software, the number-average length in the longitudinal direction was 24.0 mm and the weighted-average length was 28.3 mm.

[0111] 5000g of the carbon fiber aggregate was entirely loaded onto a raw material supply conveyor and transported at 3.3m / min to a carbon fiber aggregate transport belt conveyor. The carbon fiber aggregate transport belt conveyor used had a spiked lattice and an upward slope of 67°. The carbon fiber aggregate was transported at 12.0m / min to the discharge end of the carbon fiber aggregate transport belt conveyor, and the carbon fiber aggregate was dropped onto the carrier film while the carrier film was moved at 5m / min, resulting in a yield of 1643g / m³. ２ A carbon fiber mat was fabricated. The carbon fiber aggregates showed good feedability during a series of transport processes. In the obtained carbon fiber mat, the carbon fiber aggregates were randomly oriented, and the CV value of the thickness in the longitudinal direction was 4.7%.

[0112] The obtained carbon fiber mat was impregnated with a liquid thermosetting resin composition containing vinyl ester resin, unsaturated polyester resin, styrene, polyisocyanate, and a radical polymerization initiator, and left to thicken at 25°C for 7 days to produce a sheet molding compound. The basis weight of the sheet molding compound was 3100 g / m². ２ The fiber content was 53% by mass. Two 26 cm x 26 cm pieces of sheet molding compound were cut from the sheet molding compound and stacked together. They were then press-molded at a temperature of 140°C, a pressure of 8 MPa, and a pressurizing time of 3 minutes to produce a plate-shaped carbon fiber reinforced composite material with dimensions of 30 cm in length and width and a thickness of 2 mm. The results of the bending property evaluation of this carbon fiber reinforced composite material are shown in Table 2.

[0113] [Comparative Example 2] Carbon fiber-containing crushed fragments were obtained in the same manner as in Example 2, except that a screen was used in which there were no holes in the horizontal direction of 0.1 × r from line L, and circular holes with a diameter of 25 mm in the other areas. Subsequently, the matrix resin was decomposed and removed in the same manner as in Example 2 to obtain a cotton-like carbon fiber group. The average value of the filament length and the CV value of the carbon fiber group are shown in Table 1. Also, sieving was performed in the same manner as in Example 2, and the yield and longitudinal penetration rate were calculated. The results are shown in Table 1. Subsequently, using carbon fiber-containing crushed fragments that passed through a diameter of 15 mm but not through a diameter of 6 mm, the matrix resin was decomposed and removed in the same manner as in Example 2 to obtain a cotton-like carbon fiber group. The average value of the filament length of the carbon fiber group was 22.8 mm (CV value 29.2%). 5000 g of the obtained carbon fiber group and 2250 g of binder-containing liquid were mixed using a 75 L incentive mixer (manufactured by Nippon Eirich Co., Ltd.) as a rolling granulator. The binder-containing liquid was prepared in the same manner as in the example. The binder-containing liquid was introduced into a rolling granulator using a pressure spray bottle at a spray pressure of 0.4 to 0.5 MPa, and mixed for 3 minutes at a rotor speed of 160 rpm and a pan speed of 24 rpm. Subsequently, the mixture was further mixed for 10 minutes at a rotor speed of 600 rpm and a pan speed of 24 rpm to obtain a mixture. The obtained mixture was dried at 120°C for 2 hours to obtain a carbon fiber aggregate. The shape of the carbon fiber aggregate was needle-like or wire-like, and the bulk density was 0.071 g / cm³. ３ The results showed that measuring the length of more than 300 carbon fiber aggregates using image analysis software revealed that the number-average length in the longitudinal direction was 35.2 mm and the weighted-average length was 40.4 mm. Using the carbon fiber aggregates, a carbon fiber mat was prepared in the same manner as in Example 2. In the obtained carbon fiber mat, the carbon fiber aggregates were randomly oriented, and the CV value of the thickness in the longitudinal direction was 14.0%. Using the obtained carbon fiber mat, a sheet molding compound was prepared in the same manner as in Example 2. The basis weight of the sheet molding compound was 3100 g / m². ２The fiber content was 53% by mass. Using the sheet molding compound, a plate-shaped carbon fiber reinforced composite material was prepared in the same manner as in Example 2. The results of the bending property evaluation of the carbon fiber reinforced composite material are shown in Table 2.

[0114]

[0115]

[0116] As shown in Table 1, in Example 1, where carbon fiber-containing fragments were produced from a carbon fiber composite material with fibers oriented orthogonally, the longitudinal penetration rate was lower than in Comparative Example 1, and carbon fiber-containing fragments of the desired size of 6 to 30 mm were obtained in high yield. Similarly, in Example 2, where carbon fiber-containing fragments were produced from a carbon fiber composite material with fibers oriented in one direction, the longitudinal penetration rate was lower than in Comparative Example 2, and carbon fiber-containing fragments of the desired size of 6 to 30 mm were obtained in high yield. Furthermore, in Example 2, the carbon fiber aggregate produced using the carbon fiber group recovered from the obtained carbon fiber-containing fragments showed good feedability. Also, as shown in Table 2, in Example 2, a carbon fiber mat with less variation in thickness was obtained than in Comparative Example 2. Moreover, the carbon fiber-reinforced composite material produced using this carbon fiber mat showed high bending strength with a small CV value and uniform bending characteristics.

[0117] Recycled carbon fibers recovered from CFRP waste can be suitably used as a reinforcing material for carbon fiber reinforced resins.

[0118] A1 Main rotation axis A2 Main rotation axis 2 Sub-rotation axis 3 Screen 11 Main cutter blade 21 Sub-cutter blade 31 Hole L Line L C1, C2 Outer edge D Point on the straight line connecting main rotation axes A1 and A2, where the distance from outer edges C1 and C2 is equal.

Claims

1. A method for manufacturing carbon fiber-containing crushed pieces, comprising crushing a carbon fiber-reinforced composite material using a four-axis shear crusher equipped with a pair of main rotating shafts A1 and A2, and screens installed at the lower parts of the main rotating shafts A1 and A2, wherein the main rotating shaft A1 is fitted with a main cutter blade having a maximum radius r1, the main rotating shaft A2 is fitted with a main cutter blade having a maximum radius r2, and the screen has a plurality of holes formed therein. A method for manufacturing carbon fiber-containing crushed pieces, characterized in that, on a straight line connecting the main rotation axis A1 and the main rotation axis A2, a point D is identified where the distance from the outer edges C1 and C2, respectively defined from each main rotation axis based on r1 and r2, is equal, and when line L is drawn in the direction of the main rotation axis on the screen directly below point D, the screen does not have the holes in a range of 0.25 × r1 horizontally toward the main rotation axis A1 from line L and a range of 0.25 × r2 horizontally toward the main rotation axis A2 from line L.

2. The method for producing carbon fiber-containing crushed pieces according to claim 1, wherein the screen does not have holes in a range of 0.5 × r1 horizontally from the line L toward the main rotation axis A1 and in a range of 0.5 × r2 horizontally from the line L toward the main rotation axis A2.

3. The method for producing carbon fiber-containing crushed pieces according to claim 1, wherein the screen does not have holes in a range of 1.0 × r1 horizontally from the line L toward the main rotation axis A1 and in a range of 1.0 × r2 horizontally from the line L toward the main rotation axis A2.

4. When W is the thickness of the main cutter blade in the direction of rotation axis and A is the average value of the area of ​​each hole in the screen, A / W ２ A method for producing carbon fiber-containing crushed pieces according to claim 1, wherein the ratio is 0.28 or higher.

5. A / W ２ A method for producing carbon fiber-containing crushed pieces according to claim 4, wherein the ratio is 3.5 or less.

6. The method for producing carbon fiber-containing crushed pieces according to claim 1, wherein the average value of the clearance between the outer edge, which is defined from the main rotating shaft A1 and the main rotating shaft A2 based on the maximum radius, and the screen is 3 to 50 mm.

7. The method for manufacturing carbon fiber-containing shredded pieces according to claim 1, wherein the four-shaft shear shredder further comprises a sub-rotating shaft on which a sub-cutter blade is attached, positioned at a vertically higher position than the main rotating shaft A1 and the main rotating shaft A2.

8. The method for producing carbon fiber-containing crushed fragments according to claim 1, wherein the carbon fiber-reinforced composite material is a recycled product.

9. The method for producing carbon fiber-containing crushed fragments according to claim 1, wherein the carbon fiber-reinforced composite material contains carbon fibers with a filament length of 100 mm or more.

10. The method for producing carbon fiber-containing crushed fragments according to claim 1, wherein the carbon fiber-reinforced composite material contains a thermosetting resin.

11. The carbon fiber reinforced composite material is a composite material in which carbon fibers are oriented in multiple directions, A / W ２ A method for producing carbon fiber-containing crushed pieces according to claim 4, wherein the ratio is 1.1 or higher.

12. The carbon fiber reinforced composite material is a composite material in which carbon fibers are substantially oriented in one direction, and A / W ２ A method for producing carbon fiber-containing crushed pieces according to claim 4, wherein the ratio is 1.5 or less.

13. The method for producing carbon fiber-containing crushed fragments according to claim 1, further comprising removing metal powder from the carbon fiber-containing crushed fragments by magnetic force.

14. A method for producing a group of carbon fibers, comprising recovering carbon fibers by decomposing and removing a matrix resin from carbon fiber-containing crushed pieces produced by the manufacturing method described in any one of claims 1 to 13.

15. The method for manufacturing a carbon fiber group according to claim 14, wherein when the average value of the thickness in the rotation axis direction of the main cutter blade is W, the carbon fiber group contains 5% by weight or more of carbon fibers having a filament length of 3W mm or more.

16. A method for producing a carbon fiber aggregate, comprising drying a mixture of carbon fiber aggregates produced by the manufacturing method described in claim 14 and a binder-containing liquid.

17. A method for producing a carbon fiber aggregate, comprising: cutting a group of carbon fibers produced by the manufacturing method described in claim 14; and drying a mixture of the cut carbon fiber group and a binder-containing liquid.

18. A method for producing a carbon fiber mat, comprising scattering a carbon fiber aggregate produced by the method of claim 16.

19. A method for producing a sheet molding compound, comprising impregnating a carbon fiber mat produced by the method of claim 18 with a resin.

20. A four-shaft shear shredder used for crushing carbon fiber reinforced composite materials, comprising a pair of main rotating shafts A1 and A2, and a screen installed below the main rotating shafts A1 and A2, wherein the main rotating shaft A1 is fitted with a main cutter blade having a maximum radius r1, the main rotating shaft A2 is fitted with a main cutter blade having a maximum radius r2, and the screen has a plurality of holes formed therein. A four-axis shear shredder in which, on a straight line connecting the main rotating shaft A1 and the main rotating shaft A2, a point D is identified where the distance from the outer edges C1 and C2, respectively defined from each main rotating shaft based on r1 and r2, is equal, and when line L is drawn in the direction of the main rotating shaft on the screen directly below point D, the screen does not have the holes in a range of 0.25 × r1 horizontally from line L toward the main rotating shaft A1 and a range of 0.25 × r2 horizontally from line L toward the main rotating shaft A2.

21. The four-axis shear shredder according to claim 20, wherein the screen does not have the holes in a range of 0.5 × r1 horizontally from the line L toward the main rotation axis A1 and in a range of 0.5 × r2 horizontally from the line L toward the main rotation axis A2.

22. The four-axis shear shredder according to claim 20, wherein the screen does not have the holes in a range of 1.0 × r1 horizontally from the line L toward the main rotation axis A1 and in a range of 1.0 × r2 horizontally from the line L toward the main rotation axis A2.

23. A group of fragments made of a composite material, comprising carbon fibers and a matrix resin, and satisfying at least one of the following conditions (i) and (ii): Condition (i) Contains 50% by weight or more of fragments that pass through a circular hole with a diameter of 30 mm and do not pass through a circular hole with a diameter of 6 mm. Condition (ii) Contains 62% by weight or more of fragments that pass through a circular hole with a diameter of 15 mm and do not pass through a circular hole with a diameter of 6 mm.

24. A group of carbon fibers having a filament length variation of 15-69% obtained by the fibrograph method specified in JIS L1019:2006 Section 7.2.2.

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