JP7326752B2 - Manufacturing method of recycled carbon fiber - Google Patents

Description

The present invention relates to a manufacturing method of thermally decomposing a matrix resin component of carbon fiber reinforced plastic (hereinafter referred to as CFRP ) to recycle carbon fiber from CFRP.

CFRP has excellent mechanical properties such as specific strength and specific modulus, so it is widely used in aerospace applications, sports and leisure applications such as fishing rods, golf shafts, tennis rackets, and other applications. , waste generated in the manufacturing process and disposal of unnecessary items have been a big problem. Carbon fiber is incombustible and never rots, so currently there is no alternative but to landfill it. However, from the viewpoint of underground pollution due to landfill processing, if disposal can be avoided even a little, it will greatly contribute to reducing the environmental load. In addition, as is well known, carbon fibers are obtained by firing precursor fibers such as polyacrylonitrile fibers at a high temperature of 1000 to 3000° C., and the energy consumed for their production is considerable. Therefore, it is important to recycle them effectively instead of throwing them in landfills. By the way, carbon fibers are non-flammable, but the thermosetting resin forming the matrix resin is combustible, so if CFRP is placed in a heating furnace and the thermosetting resin is burned, the carbon fibers can be recovered.

Patent Document 1 (Japanese Patent Application Laid-Open No. 2016-521295) describes a method of thermally decomposing a thermosetting resin in CFRP and then taking out and cutting carbon fibers for reuse.

Patent Document 2 (Patent No. 3180463) describes a method of crushing CFRP to an arbitrary size and then thermally decomposing the thermosetting resin in the CFRP.

Further, Patent Document 3 (Japanese Patent Application Laid-Open No. 2013-147545) describes a method of automatically charging raw materials into a pyrolysis furnace and automatically taking out products.

Japanese Patent Publication No. 2016-521295 Patent No. 3180463 Japanese Patent Application Laid-Open No. 2013-147545

However, in the method of Patent Document 1, a step of cutting the pyrolyzed fibers into arbitrary fiber lengths is required, but the carbon fibers are difficult to cut because the pyrolyzed fibers are soft. In addition, since CFRP generally includes layers having multiple lamination angles, it is necessary to align the fibers after pyrolysis in one direction before cutting, resulting in poor work efficiency.

Further, in the method of Patent Document 2, since the crushed material is put into the electric furnace in batches, the production efficiency is poor and the production cost cannot be reduced.

Furthermore, in the method of Patent Document 3, there is no description of the steps before and after the pyrolysis furnace, which are necessary for realizing continuous production.

In addition, none of the documents describes a technique for improving the yield, a technique for controlling the length of the recycled carbon fiber classified material, a technique for powder removal, or a technique for preparing the work environment. Ta.

Therefore, in view of the problems of the prior art, the present invention enables CFRP to be reused by removing the matrix resin component from waste CFRP products and chips generated during the manufacture of CFRP products. Specifically, in the process of recovering and recycling carbon fibers in CFRP at a high yield, the object is to automate transportation between manufacturing processes.

In order to solve the above problems, the present invention employs the following means. i.e.
[1] A method for producing recycled carbon fibers for obtaining recycled carbon fibers from carbon fiber reinforced plastics containing carbon fibers and matrix resin components, wherein transportation between the following steps (a) to (g) is automated. A method for producing recycled carbon fiber, characterized by:
(a) A crushing treatment step of crushing carbon fiber reinforced plastic waste to produce crushed carbon fiber reinforced plastic pieces having a predetermined fiber length (b) Pneumatic, belt conveyor, or bucket conveyor for the crushed carbon fiber reinforced plastic pieces (c) feeding the crushed pieces of carbon fiber reinforced plastic from the hopper to a powder removing device by a screw feeder method or a rotary valve method; A powder removal treatment step of removing powder contained in the crushed pieces of carbon fiber reinforced plastic with a powder removal device to generate powder removed pieces of carbon fiber reinforced plastic.
Here, in the powder removal treatment step, the hopper is equipped with a stirring blade and a fixed quantity dispensing device, and when clogging is detected in a powder suction pipe constituting the powder removing device, the stirring blade and the fixed quantity dispensing device are operated. stop and stop the supply of the carbon fiber reinforced plastic crushed pieces to the powder removing device
(d) Heating the carbon fiber reinforced plastic powder removing pieces while feeding them into a pyrolysis furnace to remove the matrix resin component contained in the carbon fiber reinforced plastic powder removing pieces to obtain recycled carbon fiber pyrolysates. Pyrolysis treatment step (e) cooling and transporting the recycled carbon fiber pyrolyzate to the next step by either belt conveyor or bucket conveyor while cooling (f) classifying the recycled carbon fiber pyrolyzate (g) an iron removal treatment step of removing metal powder from the recycled carbon fiber classified body by magnetic force [2] in the powder removal treatment step, in which the carbon fiber reinforced plastic crushed pieces are The method for producing recycled carbon fiber according to [1], wherein 5 to 30% of the powder contained is removed.
[3] The method for producing recycled carbon fibers according to [2], wherein in the powder removal treatment step, the powder is removed with a screen mesh having an opening of less than 500 μm.
[ 4 ] In the pyrolysis treatment step, a dry distillation treatment is performed with an oxygen concentration of 2 to 8%, a heat treatment temperature of 500 to 580 ° C., and a heat treatment time of 10 to 40 minutes. The method for producing recycled carbon fibers according to any one of [1] to [ 3 ], wherein the residual amount of resin is 7 to 17% by weight.
Residual amount of resin (%) = ((1-weight after resin is burned off/weight before resin is burned off) x 100)
[ 5 ] In the classification treatment step, the recycled carbon fiber pyrolyzate is sifted and classified into at least three or more classification thickness ranges according to the thickness of the recycled carbon fiber pyrolysate, and the recycled material is classified into the maximum range and the minimum range of the classification thickness range. The method for producing recycled carbon fibers according to any one of [1] to [ 4 ], wherein the carbon fiber classifier is mixed and then pulverized.
[ 6 ] The method for producing recycled carbon fibers according to [ 5 ], wherein the thickness range of the recycled carbon fiber classified body has a minimum range of 4 μm≦thickness<300 μm and a maximum range of 1 mm<thickness.
[ 7 ] The method for producing recycled carbon fibers according to [ 6 ], wherein the length of the recycled carbon fiber classified body is 1 to 20 mm.
[ 8 ] The method for producing recycled carbon fibers according to any one of [1] to [ 7 ], wherein the residence time in the classifier is 1 minute or more and 2 minutes or less in the classifying step of the recycled carbon fiber classified body.
[ 9 ] The recycled carbon according to any one of [1] to [ 8 ], wherein the powder removal capacity of the powder removal device in the powder removal process is greater than the powder removal capacity of the classifier in the classification process. Manufacturing method to fiber.
[1 0 ] The method for producing recycled carbon fibers according to any one of [1] to [ 9 ], further comprising suction means for sucking fine powder in each step.

According to the present invention, useful carbon fibers can be recovered from CFRP at a high yield and used as recycled carbon fibers. Furthermore, by automating the transportation between the manufacturing processes, it is possible to provide a highly productive recycled carbon fiber manufacturing method.

1 is a flow diagram showing the flow of steps in a method for producing recycled carbon fibers according to the present invention. FIG. 1 is a schematic diagram of a crushing treatment step in a method for manufacturing recycled carbon fibers according to the present invention; FIG. FIG. 2 is a schematic diagram of a transportation and storage step and a powder removal treatment step in the method for producing recycled carbon fiber according to the present invention. 1 is a schematic diagram of a pyrolysis treatment step in a method for producing recycled carbon fiber according to the present invention; FIG. 1 is a schematic diagram of a classification process in a method for producing recycled carbon fibers according to the present invention. FIG. FIG. 2 is a schematic view of a hopper equipped with stirring blades and a constant-quantity dispensing device in a transporting and storing step in the method for producing recycled carbon fiber according to the present invention. FIG. 2 is a schematic diagram of a screw feeder system used as a fixed-quantity dispensing device in the transportation and storage step in the method for producing recycled carbon fiber according to the present invention. FIG. 2 is a schematic diagram of a rotary valve system used as a constant-quantity dispensing device in the transportation and storage step in the method for producing recycled carbon fiber according to the present invention. 1 is a schematic diagram of recycled carbon fibers obtained by a method for producing recycled carbon fibers according to the present invention. FIG.

Embodiments of the present invention will be sequentially described below. This embodiment is an example of implementing the present invention, and the present invention is not limited to this embodiment. In the following description, CFRP does not matter what kind of matrix resin and what kind of carbon fiber (for example, graphite fiber).

The process of this recycled carbon fiber manufacturing method is a manufacturing method for extracting recycled carbon fibers from crushed CFRP waste material using a pyrolysis method, and the manufacturing method flow is shown in FIG. Details of each step are described below.

(a) Crushing treatment process Fig. 2 shows a schematic diagram of the crushing treatment process. A CFRP waste material 1 as a raw material is first put into a primary crusher 2 and roughly crushed by a biaxial blade 3 , and then conveyed to a secondary crusher 5 by a belt conveyor 4 . The CFRP waste material 1 conveyed by the belt conveyor 4 is put into the secondary crusher 5 and crushed by the fixed blade 7 and the rotary blade 8 until the size becomes smaller than the mesh size of the screen 6 . At this time, not only CFRP fragments 9 but also powder 10 are generated. After that, the crushed CFRP pieces 9 and the powder 10 are conveyed to the next step (direction of arrow 11).

(b) transportation and storage step;
FIG. 3 shows a schematic diagram of the transportation and storage process. The crushed CFRP pieces 9 and powder 10 are transported from the previous process (in the direction of arrow 11 ) and stored in a hopper 12 . Conveying methods include an air blowing method, a belt conveyor method, a bucket conveyor method, and the like. It is preferable to use the air blowing type, which has a low equipment cost.

(c) Powder Removal Treatment Process FIG. 3 shows a schematic diagram of the powder removal treatment process. The crushed CFRP pieces 9 and the powder 10 stored in the hopper 12 are quantitatively conveyed to the powder removing device 14 (in the direction of arrow 13). Here, the powder removing device 14 is preferably a vibrating sieve. After that, the CFRP crushed pieces 9 and the powder 10 are separated by the powder removing device 14, the CFRP powder removed pieces 15 are sent to the next process (arrow 16 direction), and the powder 10 is sent to another process (arrow 17 direction) and collected. Discard, etc.

(d) Thermal decomposition process FIG. 4 shows a schematic diagram of the thermal decomposition process. After the CFRP powder removal pieces 15 are stored in the pyrolysis furnace hopper 18, they are quantitatively conveyed to the pyrolysis furnace 20 (arrow 19 direction). After the CFRP powder removing pieces 15 are thermally decomposed in the thermal decomposition furnace 20, they are discharged as recycled carbon fiber thermally decomposed bodies 22 (in the direction of arrow 21). Also, the gas generated by thermal decomposition is properly treated in the gas treatment device 23 and then released to the atmosphere. Heating methods of the pyrolysis furnace 20 include electric heaters, hot air, and the like. In the present invention, the hot air method is preferred because it handles conductive carbon fibers.

Here, as a method for conveying materials in the pyrolysis furnace, there are a belt conveyor type, a bucket conveyor type, a rotary kiln type in which the pyrolysis furnace itself rotates, and the like. Since the temperature inside the pyrolysis furnace is high, a rotary kiln type that does not use a conveyor is preferable from the viewpoint of equipment life.

(e) Cooling and Conveying Process Although not shown, the cooling and conveying process has the role of cooling the recycled carbon fiber pyrolysates 22 discharged from the pyrolysis furnace and sending them to the next process. The transportation method is not particularly limited, and it is sufficient that it has heat resistance enough to transport the recycled carbon fiber thermally decomposed body 22 in a high temperature state immediately after thermal decomposition. Cooling methods include air cooling, natural cooling, and the like. Natural cooling, which does not require cooling equipment, is preferred. It is also preferable to use a belt conveyer system, a bucket conveyer system, or the like for the conveying method, and allow natural cooling during conveying.

(f) Classification Process FIG. 5 shows a schematic diagram of the classification process. The recycled carbon fiber thermally decomposed material 22 is passed through a classifier 25 (in the direction of arrow 24) from the cooling and conveying step to be classified into recycled carbon fiber classified bodies having a predetermined thickness. Here, the classifier is preferably a vibrating sieve. By changing the number of stages and the screen mesh of the vibrating sieve machine, it is possible to obtain a recycled carbon fiber classified body of a predetermined thickness. FIG. 5 illustrates how two screen meshes are used to classify recycled carbon fiber classified bodies (26, 27, 28) having three different thicknesses.

(g) Iron removal treatment process Although not shown, by installing a device for removing metal powder by magnetic force in the piping through which the recycled carbon fiber classifier passes, the iron powder generated during the treatment is recovered and recycled carbon is removed. Make sure that the fibers are free of metal powder.

In the present invention, it is preferable to remove 5 to 30% of the powder 10 contained in the CFRP crushed pieces 9, more preferably 7 to 28%, and still more preferably 10 to 25% in the powder removal treatment step. If the removal of the powder is less than 5%, the removal of the powder is inadequate, which causes a powder explosion or a defect in which the control sensor of the pyrolysis furnace is clogged with the powder. Also, if the removal of powder is more than 30%, the loss increases and the manufacturing cost increases.

In the present invention, the ratio of powder removal is defined as the powder removal rate, which is calculated as follows: powder removal rate (%)=(1-15 weight of CFRP powder-removed pieces / 9 weights of CFRP crushed pieces x 100).

According to the invention, the hopper is preferably equipped with stirring blades and a metering device. FIG. 6 shows a schematic diagram of the powder removal treatment process equipped with a stirring blade and a fixed quantity dispensing device. The hopper 12 is provided with an agitating blade 30 and a metered dispensing device 31 . Since the CFRP crushed pieces 9 are hard and have sharp ends, the CFRP crushed pieces 9 form an arched structure to form a so-called bridge, which blocks the CFRP crushed pieces 9 , so that the fixed quantity dispensing device 31 cannot dispense the CFRP crushed pieces 9 . Mechanisms for destroying the bridges include a knocker system that hits the hopper from the outside, a system that blows air onto the crushed CFRP pieces 9, and a system that destroys the bridges with a stirring blade 30 installed in the hopper. The knocker method and the air blowing method cannot break the bridges derived from the CFRP fragments 9 that are hard and sharp. As a result of intensive investigation, it was found that a method of destroying the bridges with the stirring blades 30 installed in the hopper is suitable. The installation position, shape, and number of the stirring blades 30 are not limited as long as they cover the generation range of bridges.

Further, it is preferable that the stirring blade 30 is controlled so that the rotating direction can be switched. In some cases, the powder 10 is compressed and accumulated in the gap between the stirring blade 30 and the hopper 13 and eventually the stirring blade 30 cannot rotate. As a result of intensive investigation, it was found that the accumulation of the powder 10 is easily removed by reversing the direction of rotation. Production can be continued stably by control. As a rotation direction switching mechanism, a method of switching the direction at regular intervals, a method of detecting the force applied to the stirring blade 30 and reversing the rotation of the stirring blade 30 when it exceeds a certain force, a method of monitoring the state inside the hopper by video, and abnormalities There is a method of reversing the rotation of the stirring blade 30 when is detected. In particular, the method of detecting the force applied to the stirring blades 30 and reversing the rotation of the stirring blades 30 when the force exceeds a certain value is preferable because the abnormality of the stirring blades 30 can be immediately detected.

Moreover, as the powder removing device 14, a vibrating sieve having a screen mesh having a predetermined mesh size can be exemplified. Here, the mesh size of the screen mesh is preferably less than 500 μm. It is more preferably 400 μm or less, still more preferably 300 μm or less. Moreover, the mesh size is preferably 20 μm or more. It is more preferably 100 µm or more, and still more preferably 200 µm or more.

If the mesh size of the screen mesh is 500 μm or more, loss increases and manufacturing costs increase. If the particle size is less than 20 μm, the removal of powder is insufficient, which may cause powder explosion or failure in which the control sensor of the pyrolysis furnace is clogged with powder.

According to the invention, it is preferable to feed the CFRP fragments 9 and the powder 10 quantitatively to the powder removal device 14 . If the crushed CFRP pieces 9 and the powder 10 cannot be discharged quantitatively, the supply of the crushed CFRP pieces 9 and the powder 10 will be excessive, and the powder removal processing in the powder removal device 14 will not keep up, resulting in a large amount of the powder 10. may remain. Moreover, if the discharge of the CFRP crushed pieces 9 is too small, the amount of powder removal processing is reduced, and the production speed is lowered.

Methods for discharging the CFRP crushed pieces 9 include a screw feeder method (FIG. 7), a rotary valve method (FIG. 8), and the like. Although the system is not limited, in any case, it is preferable to leave a gap of 3 to 30 mm between the screw feeder casing 33 and the screw 34 and the rotary valve casing 35 and rotor 36 . If the gap is 3 mm or less, the CFRP fragments 9 and the powder 10 may clog the gap and the screw or rotor may not move. If the gap is larger than 30 mm, the ability to feed the crushed CFRP pieces 9 and the powder 10 in a constant quantity decreases.

According to the present invention, it is preferable to stop the operation of the stirring blade 30 and the fixed quantity dispensing device 31 when clogging of the powder suction pipe 32 of the powder removing device 14 is detected. If the powder suction pipe 32 is clogged, the powder 10 cannot be sucked, so the powder removal capability is lowered and the removal of the powder 10 becomes insufficient. If the CFRP crushed pieces 9 and the powder 10 are continued to be discharged in such a state, the powder removal cannot catch up and the powder removal device becomes clogged, making production impossible.

Methods for detecting clogging of the powder suction pipe 32 include suction pressure monitoring of the powder suction pipe 32, image monitoring of the powder accumulation volume, weight monitoring of the pipe, and the like. Aspiration pressure monitoring is preferred due to the simplicity of the monitoring system.

In the present invention, the oxygen concentration in the pyrolysis treatment step is preferably 2-8%, more preferably 3-7%, and even more preferably 4-6%. In order to reduce the oxygen concentration to less than 2%, it is necessary to fill the pyrolysis furnace with an inert gas, which increases the production cost. If the oxygen concentration is higher than 8%, the CFRP powder removing piece 15 may ignite in the pyrolysis furnace.

In the present invention, dry distillation is carried out by heat treatment at 500 to 580° C. for 10 to 40 minutes in a low oxygen atmosphere. The plastic component is thermally decomposed to discharge decomposition products such as CO ₂ , CO, CH ₄ and oily benzene, toluene, styrene, etc., and carbonized decomposition residue remains. If the heating temperature is less than 500° C., thermal decomposition occurs, but the speed is slow and the treatment takes a long time. On the other hand, if the temperature exceeds 580° C., a large amount of energy is consumed to maintain the temperature of the pyrolysis furnace, which is not preferable. The heat treatment is preferably 505-575° C.×12-35 minutes, more preferably 510-570° C.×15-30 minutes.

Further, it is preferable to carry out thermal decomposition until the amount of residual resin contained in the recycled carbon fiber thermally decomposed material 22 contained after thermal decomposition is 7 to 17% by weight relative to the recycled carbon fiber. It is more preferably in the range of 8 to 16% by weight, still more preferably in the range of 9 to 15% by weight.

Residual resin after thermal decomposition serves as a so-called adhesive that binds recycled carbon fibers together. That is, the strength of binding between the recycled carbon fibers is weaker than that between the carbon fibers and the thermosetting resin in the CFRP powder removing piece 15 before pyrolysis. The shape retention of recycled carbon fiber is low, and it becomes fluffy during transportation. On the other hand, if it exceeds 17% by weight, it becomes difficult to separate the recycled carbon fibers at the time of use, even though the binding strength is reduced, and the dispersibility of the recycled carbon fibers in other materials is reduced.

In the present invention, the residual resin amount is measured by the following method. 5 g of recycled carbon fiber was burned off in an electric furnace at 600° C. for 3.5 hours in a nitrogen atmosphere. After that, the resin residual amount (%) is calculated from the weight before and after the resin is burned off = ((1-weight after resin is burned off/weight before resin is burned off) x 100).

According to the present invention, the recycled carbon fiber thermally decomposed body 22 in which the resin component is decomposed by thermal decomposition is put into the classifier 25, and a recycled carbon fiber classified body having a predetermined thickness can be obtained. Here, the classifier is preferably a vibrating sieve. By changing the number of stages and the screen mesh of the vibrating sieve machine, it is possible to obtain a recycled carbon fiber classified material of a predetermined thickness.

In the present invention, it is preferable to sieve and classify the recycled carbon fiber classified bodies having a thickness of at least 3 or more, more preferably 3 to 4, and still more preferably 3. When classified into recycled carbon fiber classified bodies having thicknesses of two or less, it is not possible to obtain recycled carbon fiber classified bodies that fall within an arbitrary thickness range. If there are more than 5, it will classify into the thickness range more than necessary, and production efficiency will worsen.

Moreover, in the classification treatment step, the retention time in the classifier is preferably 1 minute or more and 2 minutes or less. By staying for one minute or more, sufficient vibration energy is imparted to the recycled carbon fiber pyrolyzate, so even if there is an aggregated recycled carbon fiber pyrolyzate, the recycled carbon fiber can be classified to have a predetermined thickness and length. body can be obtained and the yield can be improved. On the other hand, by setting the time to 2 minutes or less, it is possible to prevent excessive overlapping of the classified bodies and to prevent deterioration of the processing capacity.

According to the present invention, it is preferable to mix and pulverize the recycled carbon fiber classified bodies classified into the maximum range and the minimum range of the classification thickness range. If the classification thickness is small, the recycled carbon fiber classified body is too light to pass through the feeder in the pulverization process. Therefore, it is preferable to mix with a heavy recycled carbon fiber classified material having a large classification thickness and pulverize it. By mixing, it becomes possible to pulverize the recycled carbon fibers that are classified within the range of the minimum classification thickness, and as a result, conductive powder can be obtained. In addition, it is also possible to effectively utilize recycled carbon fibers outside the arbitrary thickness.

The pulverizer is a milled pulverizer of a hammer mill type, and is processed into recycled carbon fibers of a certain size or less. A hammer mill, a cutter mill, a shear crusher, or the like can be used as the mill pulverizer, and a hammer mill type is preferable because the quality is stable. As for the material of the device contact surface, it is preferable to use stainless steel, which is less susceptible to contamination due to wear.

As for the thickness range of the recycled carbon fiber classified material, it is preferable that the minimum thickness range is 4 μm≦thickness<300 μm and the maximum range is 1 mm<thickness. Recycled carbon fiber classified bodies having a classification thickness range of 300 μm≦thickness≦1 mm are kneaded with a thermoplastic resin such as nylon and used as pellets. In such applications, if the classification thickness is less than 300 μm, the recycled carbon fiber classified material is light and poor in passage through the feeder of pellet equipment. Further, if the classification thickness is more than 1 mm, the feeder of the pellet equipment is clogged and the feeder is damaged. Further, the use of the recycled carbon fiber classified material having a classification thickness range of 300 μm≦thickness≦1 mm is not limited to pellets, but can also be used for non-woven fabrics and mats.

Moreover, it is preferable that the length of the recycled carbon fiber classified body is 1 to 20 mm. If the length of the recycled carbon fiber classified body is less than 1 mm, the fiber bundle is too light to pass through the feeder of pellet equipment. On the other hand, when the length of the recycled carbon fiber classified body exceeds 20 mm, the feeder passability of the pellet equipment is deteriorated. The use of the recycled carbon fiber classified material with a length of 1 to 20 mm is not limited to pellets, but can also be used for non-woven fabrics and mats.

FIG. 9 shows a schematic diagram of a recycled carbon fiber classified body in the present invention. The length in the fiber direction in the schematic top view 37 of the recycled carbon fiber classified body is defined as L, and the fiber orthogonal direction in the figure is defined as W. The maximum thickness of the schematic projection 38 rotated around the direction perpendicular to the fiber is defined as t, which is defined as the thickness of the classifier. The thickness is the average value obtained by measuring the thickness (t) of 15 recycled carbon fibers arbitrarily taken out with a vernier caliper.

Further, in the present invention, it is preferable that the powder removal processing capacity of the powder removal device in the powder removal treatment step is greater than the powder removal processing capacity of the classification device in the classification treatment step. In order to efficiently remove the fine powder contained in the crushed pieces generated between the crushing process and the powder removal process, the powder removal device in the powder removal process uses a large screen mesh and a driving motor that gives vibration. It is also preferable to use a high-output one. If fine powder can be efficiently removed in the powder removal treatment process, the influence of fine powder can be minimized in each downstream process. In particular, if the powder removal processing capacity is greater than the powder removal processing capacity of the classifier in the classification process, the classification device in the classification process can save the trouble of removing fine powder, and the recovery rate of recycled carbon fibers classified into each mesh size. can increase

Further, in the present invention, it is preferable to further provide suction means for sucking fine powder in each step. Since fine powder generated during transportation of processes other than the above-mentioned powder removal device and classifier can be sucked and removed each time, equipment failure due to fine powder is less likely to occur, and fine powder floating in the air is extremely small. , can provide a worker-friendly environment. Many of the fine powders are invisible with a size of 1 mm or less, and if they come into direct contact with the skin of workers, they may cause itching, and if they are inhaled, they may pose a health hazard.

EXAMPLES Next, the present invention will be described with reference to Examples, but the present invention is not limited to these Examples.

(Example 1)
After laminating a predetermined number of carbon fiber prepreg “Torayca (registered trademark) prepreg” #3900-2B manufactured by Toray Industries, Inc., and curing at 180° C. for 10 hours, a CFRP waste material of 100 mm×100 mm×5 mm was produced. After the CFRP waste material was crushed by a uniaxial crusher, it was passed through an 8 mm screen to obtain CFRP crushed pieces having a predetermined fiber length. After that, after storing the CFRP crushed pieces and powder in a hopper, a 400 μm screen mesh was installed with a rotary valve while rotating a bridge breaker manufactured by Ekele Co., Ltd. in the hopper. was metered to the At this time, a 100A powder suction pipe was used. The weight before and after powder removal was measured, and the powder removal rate was calculated. As a result, the powder removal rate was 18%. The powder-free CFRP pieces were put into a rotary kiln type pyrolysis furnace and thermally decomposed under the conditions of oxygen concentration of 5%, heat treatment temperature of 520 ° C., and heat treatment time of 20 minutes. Thermal decomposition continued for 6 hours. Confirmed that it can be done. The amount of residual resin in the obtained recycled carbon fiber pyrolyzate was 12%. The recycled carbon fiber pyrolyzate was classified with a vibrating sieve machine (1003 type) manufactured by Dalton Co., Ltd. equipped with two screen meshes (0.5 mm and 3 mm). After that, cylindrical magnets with a diameter of 20 mm and a magnetic force of 10,000 G with a center-to-center distance of 30 mm are arranged in four rows. Four pieces of iron with a thickness of 2 mm were recovered. The thickness of the obtained recycled carbon fiber was measured with a caliper (manufactured by Shinwa Measurement Co., Ltd., product number 19975) and found to be 120 μm, 0.6 mm and 1.4 mm. Finally, after mixing recycled carbon fiber classifiers having thicknesses of 120 μm and 1.4 mm, the mixture was pulverized through a Micro Pulverizer (AP-2DH) manufactured by Hosokawa Micron Corporation.

A recycled carbon fiber classifier with a thickness of 0.6 mm is obtained by making a flat plate from compounded recycled carbon fiber pellets, performing a three-point bending test, and obtaining the same physical properties as a molded product using ordinary carbon fiber cut fiber. It was confirmed.

The carbon fibers recovered by the method of the present invention are pulverized and mixed into rubber or thermoplastic resins to improve their abrasion resistance, or mixed into cement, mortar, concrete, etc. to improve their mechanical properties. can be used to

1 CFRP waste material 2 Primary crusher 3 Biaxial blade 4 Belt conveyor 5 Secondary crusher 6 Screen 7 Fixed blade 8 Rotary blade 9 CFRP crushed pieces 10 Powder 11 CFRP crushed pieces and powder from the crushing process to the transportation and storage process The direction in which the body moves 12 Hopper 13 The direction in which crushed CFRP pieces and powder move from the transportation and storage process to the powder removal treatment process 14 Powder removal device 14 a Screen mesh 15 CFRP powder removal pieces 16 From the powder removal treatment process to the thermal decomposition process CFRP Direction 17 in which powder removing pieces move Direction 18 in which powder is collected Pyrolysis furnace hopper 19 Direction 20 in which CFRP powder removing pieces move from the pyrolysis furnace hopper to the pyrolysis furnace Pyrolysis furnace 21 CFRP is removed in the pyrolysis furnace Direction in which powder pieces move 22 Recycled carbon fiber pyrolyzate 23 Gas treatment device 24 Direction in which CFRP pyrolyzate moves from the cooling transportation process to the classification process 25 Classifier 26 Recycled carbon fiber pyrolyzate including maximum thickness 27 Maximum And recycled carbon fiber pyrolyzate 28 not including minimum thickness Recycled carbon fiber pyrolyzer 30 including minimum thickness Stirring blade 31 Fixed quantity dispensing device 32 Powder suction pipe 33 Screw feeder casing 34 Screw feeder screw 35 Rotary valve Casing 36 Rotary valve rotor 37 Schematic top view of recycled carbon fiber 38 Schematic projection view of recycled carbon fiber rotated around the fiber direction

Claims (10)

A method for producing recycled carbon fibers for obtaining recycled carbon fibers from carbon fiber reinforced plastic containing carbon fibers and matrix resin components, comprising automating transportation between the following steps (a) to (g). A method for producing recycled carbon fiber.
(a) A crushing treatment step of crushing carbon fiber reinforced plastic waste to produce crushed carbon fiber reinforced plastic pieces having a predetermined fiber length (b) Pneumatic, belt conveyor, or bucket conveyor for the crushed carbon fiber reinforced plastic pieces (c) feeding the crushed pieces of carbon fiber reinforced plastic from the hopper to a powder removing device by a screw feeder method or a rotary valve method; A powder removal treatment step of removing powder contained in the crushed pieces of carbon fiber reinforced plastic with a powder removal device to generate powder removed pieces of carbon fiber reinforced plastic.
Here, in the powder removal treatment step, the hopper is equipped with a stirring blade and a fixed quantity dispensing device, and when clogging is detected in a powder suction pipe constituting the powder removing device, the stirring blade and the fixed quantity dispensing device are operated. stop and stop the supply of the carbon fiber reinforced plastic crushed pieces to the powder removing device
(d) Heating the carbon fiber reinforced plastic powder removing pieces while feeding them into a pyrolysis furnace to remove the matrix resin component contained in the carbon fiber reinforced plastic powder removing pieces to obtain recycled carbon fiber pyrolysates. Pyrolysis treatment step (e) cooling and transporting the recycled carbon fiber pyrolyzate to the next step by either belt conveyor or bucket conveyor while cooling (f) classifying the recycled carbon fiber pyrolyzate (g) an iron removal treatment step of removing metal powder from the recycled carbon fiber classified body by magnetic force; 2. The method for producing recycled carbon fibers according to claim 1, wherein 5 to 30% of the powder contained in the crushed pieces of carbon fiber reinforced plastic is removed in the powder removal treatment step. 3. The method for producing recycled carbon fibers according to claim 2, wherein in the powder removal treatment step, the powder is removed with a screen mesh having a mesh size of less than 500 [mu]m. In the pyrolysis treatment step, a dry distillation treatment is performed with an oxygen concentration of 2 to 8%, a heat treatment temperature of 500 to 580 ° C., and a heat treatment time of 10 to 40 minutes. station
The method for producing recycled carbon fibers according to any one of claims 1 to 3, wherein the amount is 7 to 17% by weight.
Residual amount of resin (%) = ((1-weight after resin is burned off/weight before resin is burned off) x 100) In the classification treatment step, the recycled carbon fibers are classified into at least three or more classification thickness ranges according to the thickness of the recycled carbon fiber pyrolyzate, and classified into the maximum range and the minimum range of the classification thickness range. The method for producing recycled carbon fibers according to any one of claims 1 to 4 , wherein the bodies are mixed and then pulverized. 6. The method for producing recycled carbon fibers according to claim 5 , wherein the thickness range of the recycled carbon fiber classified body has a minimum range of 4 μm≦thickness<300 μm and a maximum range of 1 mm<thickness. 7. The method for producing recycled carbon fibers according to claim 6 , wherein the recycled carbon fiber classifier has a length of 1 to 20 mm. The method for producing recycled carbon fibers according to any one of claims 1 to 7, wherein the residence time in the classifier is 1 minute or more and 2 minutes or less in the classifying step of the recycled carbon fiber classified body. The method for producing recycled carbon fibers according to any one of claims 1 to 8 , wherein the processing capacity of the powder removal device in the powder removal treatment step is greater than the powder removal treatment capacity of the classifier in the classification treatment step. The method for producing recycled carbon fibers according to any one of claims 1 to 9 , further comprising suction means for sucking fine powder in each step.