Method for recovering defibrated carbon nanotubes

Abstract

This disclosure aims to provide a method for recovering defibrated carbon nanotubes that can efficiently and easily recover carbon nanotubes from raw material carbon nanotubes. [Solution] This disclosure provides a method for recovering defibrated carbon nanotubes, comprising a step of defibrating raw material carbon nanotubes, wherein a shredder is used for the defibration step.

Description

[Technical Field]

[0001] This disclosure relates to a method for recovering defibrated carbon nanotubes. [Background technology]

[0002] Carbon nanotubes (hereinafter also referred to as "CNTs"), even if they appear as a single fibrous strand externally, are actually bundles of dozens of CNTs twisted together, making them difficult to defibrillate. CNTs in this state have strong cohesive forces and are difficult to disperse even when mixed with a solvent. Dispersed CNTs exhibit excellent conductivity. Therefore, there is a need for technology to obtain easily dispersible CNTs.

[0003] Patent Document 1 (International Publication No. 2010 / 076885) discloses a method for peeling a single-walled carbon nanotube (WW) oriented aggregate from a substrate, including a method of directly picking up the WW oriented aggregate with tweezers and peeling it off the substrate. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2010 / 076885 [Overview of the project] [Problems that the invention aims to solve]

[0005] When considering the large-scale trading of CNTs for practical application, the method described in Patent Document 1 for obtaining easily dispersible CNTs has room for improvement in terms of efficiency. Furthermore, easily dispersible CNTs have a bulk density (approximately 0.01 g / cm³). 3 The low carbon dioxide (CNT) content increases its dispersibility. Therefore, easily dispersed CNTs present the problem of being difficult to recover. For this reason, there is a need to develop technologies that can efficiently and easily acquire CNTs while maintaining their characteristics.

[0006] This disclosure is made in view of the above circumstances and aims to provide a method for recovering defibrated carbon nanotubes that can efficiently and easily recover carbon nanotubes from raw material carbon nanotubes. [Means for solving the problem]

[0007] This disclosure includes the following method for recovering defibrated carbon nanotubes. (1) A method for recovering defibrated carbon nanotubes, Equipped with a process for defibrillating raw material carbon nanotubes, The defibration process is a method for recovering defibrated carbon nanotubes using a shredding machine. (2) The process further includes removing magnetic material using a magnetic separator capable of separating magnetic and non-magnetic material after the defibration process. [Effects of the Invention]

[0008] According to this disclosure, a method for recovering defibrated carbon nanotubes can be provided that allows for efficient and easy recovery of carbon nanotubes from raw material carbon nanotubes. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram showing one embodiment of a shredder used in the method for recovering defibrated carbon nanotubes according to Embodiment 1. [Figure 2] This is a schematic diagram showing one aspect of the defibration chamber provided in a shredder used in the method for recovering defibrated carbon nanotubes according to Embodiment 1. [Figure 3] This is a schematic diagram showing one embodiment of a roller cutter provided in a shredder used in the method for recovering defibrated carbon nanotubes according to Embodiment 1. [Figure 4] These are photographs of defibrated CNTs from Examples 1-2 and CNTs from Comparative Examples 1-3. [Modes for carrying out the invention]

[0010] Hereinafter, embodiments of the present invention will be described while referring to the drawings. However, the present embodiment is not limited thereto. In all the following drawings, the scale is appropriately adjusted for easy understanding of each component, and the scale of each component shown in the drawings does not necessarily match the scale of the actual component.

[0011] 〔Method for recovering defibrated carbon nanotubes (CNTs)〕 The method for recovering defibrated CNTs according to an embodiment of the present invention (hereinafter also referred to as "Embodiment 1") includes a step of defibrating raw material CNTs (hereinafter also referred to as the "defibrating step"). In the above defibrating step, a shredder is used. Thereby, defibrated CNTs are recovered from the raw material CNTs.

[0012] In the method according to Embodiment 1, by using a shredder, defibrated CNTs can be efficiently and easily obtained from the raw material CNTs. In this specification, defibrating means unraveling a fiber into fibers of a unit smaller than the fiber. In this specification, shredding means cutting a fiber to shorten the fiber length. Hereinafter, the method for recovering defibrated CNTs will be described.

[0013] <Preparation step> The method for recovering defibrated CNTs according to Embodiment 1 may include a step of preparing raw material CNTs and a shredder (hereinafter also referred to as the "preparation step"), and it is preferable to include the preparation step. In the preparation step, raw material CNTs and a shredder are prepared. Hereinafter, the raw material CNTs and the shredder will be described.

[0014] (Raw material CNTs) The raw material CNTs are in a state that is difficult to defibrate, called a bundle. A bundle is composed of a plurality of single CNTs bundled together. The major diameter of the raw material CNTs may be 10 mm or more. The "major diameter" means the longest side when the object is viewed planar. The minor diameter of the raw material CNTs may be 4 mm or more. The "minor diameter" means the shortest side when the object is viewed planar.

[0015] A single CNT can be a single-walled carbon nanotube (WNT), a double-walled carbon nanotube (WNT), or a multi-walled carbon nanotube (WNT). According to the present invention, even when using raw material CNTs that are difficult to handle, defibrated CNTs can be recovered efficiently and easily. Therefore, it is preferable that the raw material CNTs consist of bundles of single-walled carbon nanotubes.

[0016] The amount of elemental CNTs contained in the raw material CNT may be 50% by mass or more, 70% by mass or more, 90% by mass or more, or 95% by mass or more, based on 100% by mass of the raw material CNT. Raw material CNT with an elemental CNT content of 95% by mass or more is used as a high-purity product. The raw material CNT is obtained by performing acid washing, neutralization, dehydration, drying, etc., on raw material CNT containing a metal catalyst as described below.

[0017] The raw material CNT may contain metal catalysts and other materials that may be present in the manufacturing process, in addition to pure CNT. Examples of such metal catalysts include iron, cobalt, nickel, and silica. The content of the metal catalyst in the raw material CNT may be 0% by mass or more and 10% by mass or less, based on 100% by mass of the raw material CNT.

[0018] The fiber diameter of individual carbon nanotubes (CNTs) contained in the raw material CNTs may be between 3 nm and 20 nm, or between 3 nm and 10 nm.

[0019] The fiber length of individual carbon nanotubes (CNTs) contained in the raw material CNTs may be 0.1 μm or more and 2000 μm or less, or 0.2 μm or more and 1500 μm or less.

[0020] The bulk density of the raw material CNT is 0.001 g / cm³. 3 More than 0.006g / cm 3 It may also be less than 0.003 g / cm³. 3 More than 0.005g / cm 3 The following may also be used. The bulk density is measured in accordance with the method for measuring the bulk density of carbon black specified in JIS K 6219.

[0021] The specific surface area of the raw material CNT may be 200 m 2 / g or more and 1000 m 2 / g or less, and may also be 500 m 2 / g or more and 900 m 2 / g or less. The specific surface area of the raw material CNT is measured according to JIS K 6217-2.

[0022] As the raw material CNT, CNTs produced by known methods can be used. Examples of methods for producing CNTs include, for example, the arc method, the laser ablation method, the chemical vapor deposition method, and the like.

[0023] (Pulverizer) In the fibrillation process, a known pulverizer is used. Examples of known pulverizers include, for example, the pulverizer 100 shown in FIG. 1.

[0024] FIG. 1 is a schematic diagram showing one aspect of the pulverizer 100 used in the method for recovering fibrillated CNTs according to Embodiment 1. As shown in FIG. 1, the pulverizer 100 includes a supply port 10, a fibrillation chamber 30, and a discharge port 50. The supply port 10 is provided for supplying the raw material CNT to the pulverizer. The discharge port 50 is provided for discharging the fibrillated raw material CNT, that is, for recovering the fibrillated CNT. The fibrillation chamber 30 is provided for fibrillating the raw material CNT. The fibrillation chamber 30 includes a roller cutter 31a and a roller cutter 31b. The pulverizer 100 is preferably provided with a driving device for rotating the roller cutter 31a and the roller cutter 31b. The driving device is not shown in FIG. 1. Since the driving device prevents the intrusion of dust and the like from the outside, it preferably has a dust-proof structure.

[0025] Figure 2 is a schematic diagram showing one aspect of the defibration chamber 30 provided in the shredder 100 used in the defibration carbon nanotube recovery method according to Embodiment 1. As shown in Figure 2, the roller cutter 31a and the roller cutter 31b are constructed by stacking rotating blades 33a and 33b, respectively, on a rotating shaft 32 with a circular cross-section. The rotating blades 33a and 33b are provided with a protruding edge portion 331 and a recessed portion 332 in the direction away from the rotating shaft 32. The edge portion 331 has an edge tip 331a and an edge rear end 331b.

[0026] The roller cutters 31a and 31b are configured to interlock with each other. Specifically, for example, the tip 331a of the edge portion of the roller cutter 31a is in a positional relationship such that it temporarily slides against the rear end 331b of the edge portion of the roller cutter 31b.

[0027] Figure 3 is a schematic diagram showing one embodiment of a roller cutter provided in a shredder used in the method for recovering defibrated CNTs according to Embodiment 1. In the shredder 100, the shape of the edge tip 331a of the roller cutters 31a and 31b is not particularly limited, and examples include a wavy shape, a roughly triangular shape, a roughly rectangular shape, etc. The thickness of the roller cutters 31a and 31b may be 1 mm or more and 35 mm or less, preferably 1.5 mm or more and 6 mm or less, more preferably 2 mm or more and 5 mm or less, and even more preferably 3 mm or more and 4.5 mm or less. The number of edge portions 331 provided in a single roller cutter is not particularly limited, and may be 2 or more and 16 or less, or 4 or more and 12 or less. The number of edge portions 331 in the roller cutters 31a and 31b may be different or the same. The number of roller cutters 31a and 31b is not particularly limited. One roller cutter may be provided in the defibration chamber, or two or more may be provided.

[0028] As shown in Figures 1 and 2, the defibration chamber 30 in the shredding machine 100 preferably has a scraper 35. The scraper 35 can remove the raw material CNTs and defibrated CNTs remaining between the roller cutters. The material of the scraper is not particularly limited. From the viewpoint of preventing metal fragments from being mixed into the recovered defibrated CNTs, the material of the scraper is preferably resin.

[0029] <Defibration process> The method for recovering defibrated CNTs according to Embodiment 1 includes a step of defibrating the raw material CNTs. A shredder is used in this defibration step. This step allows the raw material CNTs to be defibrated efficiently and easily. The raw material CNTs used in this step may be those prepared in the preparation step described above. The shredder used in this defibration step may also be those prepared in the preparation step described above. The defibration step will now be described with reference to Figures 1 and 2.

[0030] This process will be explained using the raw material CNTs and the shredder 100 prepared in the above preparation process, but is not limited to this.

[0031] In this process, the raw material CNTs are defibrated as follows. The prepared raw material CNTs are supplied to the supply port 10. The supplied raw material CNTs are transported to the defibration chamber 30. In the defibration chamber 30, the raw material CNTs are detached. The detached raw material CNTs are discharged from the discharge port 50 as defibrated CNTs.

[0032] In the defibration chamber 30, roller cutters 31a and 31b rotate in opposite directions. Preferably, the roller cutters rotate in the direction of the tip of the edge portion 331a. The raw material CNTs transported to the defibration chamber 30 are bitten into by the interlocking roller cutters 31a and 31b. The raw material CNTs bitten into the roller cutters get caught on the tip of the edge portion 331a, and as the tip of the edge portion 331a and the rear end of the edge portion 331b slide against each other, they are torn apart.

[0033] It is preferable that the peripheral speeds of the roller cutter 31a and the roller cutter 31b are the same. The peripheral speeds of the roller cutter 31a and the roller cutter 31b are not particularly limited and may be, for example, 1 m / min or more and 500 m / min or less, 2 m / min or more and 100 m / min or less, 3 m / min or more and 50 m / min or less, or 5 m / min or more and 10 m / min or less.

[0034] In the defibration chamber 30, the roller cutters 31a and 31b continue to rotate as long as the drive unit is operating. Therefore, the raw material CNTs are continuously torn apart in the defibration chamber 30.

[0035] The torn raw material CNTs are normally discharged by their own weight from the discharge port 50 located below the defibration chamber 30. If the torn raw material CNTs adhere to the roller cutters 31a and 31b, the scraper forcibly removes the attached raw material CNTs and defibrated CNTs.

[0036] This process may be performed multiple times. If this process is performed multiple times, the defibrated CNTs after the defibration process may be used as raw material CNTs. If this process is performed multiple times, multiple shredders may be used. Depending on the purpose and application, shredders with different configurations may be used, or shredders with the same configuration may be used.

[0037] (Defibrated CNT) Defibrated CNTs refer to aggregates of individual CNTs obtained by defibrating raw material CNTs. In defibrated CNTs, individual CNTs do not aggregate. Defibrated CNTs have improved dispersibility and fluidity compared to raw material CNTs. The dispersibility and fluidity of CNTs are measured by the measurement method shown in the following examples. The major axis of defibrated CNTs may be less than 10 mm. The minor axis of defibrated CNTs may be less than 4 mm.

[0038] In defibrated carbon nanotubes (CNTs), individual CNTs can be single-walled CNTs, double-walled CNTs, or multi-walled CNTs. The type of individual CNT in defibrated CNTs is determined by the type of individual CNTs contained in the raw material CNTs. For example, if the raw material CNTs consist only of bundles of single-walled CNTs, the defibrated CNTs will consist only of single-walled CNTs.

[0039] In this process, the amount of defibrated CNTs recovered is preferably 90 mg or more, more preferably 95 mg or more, and even more preferably 100 mg per 100 mg of raw material CNT.

[0040] In defibrated CNTs, the fiber diameter of individual CNTs is preferably the same as that of individual CNTs contained in the raw material CNTs, in order to maintain the characteristics of individual CNTs. That is, the fiber diameter of individual CNTs in defibrated CNTs is preferably 3 nm to 20 nm, and more preferably 3 nm to 10 nm.

[0041] In defibrated CNTs, the fiber length of individual CNTs is preferably the same as that of individual CNTs contained in the raw material CNTs, since defibrated CNTs are obtained by defibrating the raw material CNTs. That is, the fiber length of individual CNTs in defibrated CNTs is preferably 0.1 μm or more and 2000 μm or less, and more preferably 0.2 μm or more and 1500 μm or less.

[0042] The bulk density of defibrated CNTs is 0.007 g / cm³, since defibrated CNTs are obtained by defibrating the raw CNTs. 3 More than 0.02g / cm 3 Preferably, it is 0.008 g / cm³. 3 More than 0.019g / cm 3 The following is more preferable: The bulk density is measured in accordance with the method for measuring the bulk density of carbon black specified in JIS K 6219.

[0043] The specific surface area of ​​the defibrated CNT is preferably the same as that of the raw material CNT. That is, the specific surface area of ​​the defibrated CNT is 200 m². 2 / g or more 1000m 2 It is preferable that it be less than / g, and 500m 2 / g or more 900m 2 It is more preferable that the value be less than or equal to / g. The specific surface area of ​​defibrated CNTs is measured according to JIS K 6217-2.

[0044] The defibrated carbon nanotubes (CNTs) may contain impurities that may be present in the raw CNTs, as well as components present in the shredder, etc. <Other processes> The method for recovering defibrated CNTs according to Embodiment 1 preferably further comprises a step (hereinafter also referred to as the "magnetic separation step") after the defibration step, in which magnetic materials are removed using a magnetic separator capable of separating magnetic and non-magnetic materials. The magnetic separation step will be described below.

[0045] The defibrated raw material CNTs may contain trace amounts of metal, particularly iron, generated, for example, when roller cutters rub against each other. The magnetic separation process can remove any magnetic materials that may be present in the defibrated raw material CNTs.

[0046] The magnetic separation process uses a known magnetic separator. The magnetic materials that can be removed in this process are iron, cobalt, and nickel. [Examples]

[0047] The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0048] Experimental Example 1: Comparison of Appearances In Experimental Example 1, raw material carbon nanotubes (CNTs) for eDIPS EC2.0-P manufactured by Meijo Nanocarbon Co., Ltd. were used.

[0049] (Example 1) The defibrated CNTs in Example 1 were obtained by feeding 0.5 g of raw CNTs into a shredder (SGX-C3144P manufactured by Sigmar Giken Co., Ltd.) with a roller cutter width of 4 mm and a peripheral speed of 8.9 m / min.

[0050] (Example 2) The defibrated CNTs of Example 2 were obtained in the same manner as the defibrated CNTs of Example 1, except that a shredder with a roller cutter width of 2 mm was used.

[0051] (Comparative Example 1) The carbon nanotubes (CNTs) of Comparative Example 1 were obtained using a pair of bent-tip tweezers with a total length of 115 mm and a width of 7 mm, from the raw CNT material.

[0052] (Comparative Example 2) The carbon nanotubes (CNTs) of Comparative Example 2 were obtained in the same manner as those of Comparative Example 1, except that a pair of bent-tip tweezers with a total length of 125 mm and a width of 8 mm was used.

[0053] (Comparative Example 3) The carbon nanotubes (CNTs) of Comparative Example 3 were obtained in the same manner as those of Comparative Example 1, except that a pair of bent-tip tweezers with a total length of 125 mm and a width of 9 mm was used.

[0054] Photographs of the defibrated CNTs from Examples 1-2 and the CNTs from Comparative Examples 1-3 are shown in Figure 4. The defibrated CNTs in Example 1 had a major axis of 5 mm or more and less than 10 mm, and a minor axis of 2 mm or more and less than 4 mm. The defibrated CNTs in Example 2 had a major axis of 5 mm or more and less than 10 mm, and a minor axis of 1 mm or more and 3 mm or less. The carbon nanotubes (CNTs) in Comparative Example 1 had a major axis of 10 mm to 20 mm and a minor axis of 4 mm to 7 mm. The CNTs in Comparative Example 2 had a major axis of 20 mm to 40 mm and a minor axis of 5 mm to 10 mm. The carbon nanotubes (CNTs) in Comparative Example 3 had a major axis of 20 mm to 50 mm and a minor axis of 10 mm to 20 mm.

[0055] Experimental Example 2: Measurement of Bulk Density In Experimental Example 2, the bulk density (g / cm³) of the defibrated CNTs in Examples 1-2 and the CNTs in Comparative Examples 1-3 was determined. 3 The measurements were taken in accordance with JIS K 6219.

[0056] The bulk densities of the defibrated CNTs in Examples 1-2 and the CNTs in Comparative Examples 1-3 are shown below. The defibrated CNTs in Example 1 had a bulk density of 0.0072 g / cm³. 3 That was the case. The defibrated CNTs in Example 2 had a bulk density of 0.016 g / cm³. 3 That was the case. The CNTs in Comparative Example 1 had a bulk density of 0.0029 g / cm³. 3 That was the case. The bulk density of the CNTs in Comparative Examples 2 and 3 could not be measured because they did not fit into the receiver.

[0057] Experimental Example 3: Evaluation of Fluidity In Experimental Example 3, the fluidity of the defibrated CNTs from Example 1 was evaluated. First, a glass beaker was placed on a horizontal surface, and a polypropylene powder funnel with an opening diameter of 20 mm was placed directly above the beaker. Next, a polypropylene semi-cylindrical container containing 0.5 g of the defibrated CNTs of Example 1 was placed at angles of 20°, 30°, and 45° relative to the horizontal surface, in a position where the defibrated CNTs of Example 1 could be poured into the powder funnel. The angle at which the defibrated CNTs of Example 1 flowed down was confirmed. In Experimental Example 3, the fluidity of the defibrated CNTs of Example 2 and the CNTs of Comparative Example 1 were evaluated in the same manner.

[0058] In both Examples 1 and 2, the defibrated CNTs gradually began to flow down from an angle of 20°, and all of them flowed into the beaker at an angle of 45°. In Comparative Example 1, even at a 45° angle, the CNTs did not all flow down but remained stopped in the powder funnel.

[0059] Experimental Example 4: Evaluation of Dispersion In Experimental Example 4, the dispersibility of the defibrated CNTs from Example 1 was evaluated. First, 100 ml of a 20% by mass ethanol aqueous solution was placed in a glass test tube with an inner diameter of 3.1 ml. Next, 0.05 g of defibrated CNTs from Example 1 were placed in the test tube, and the state of the defibrated CNTs from Example 1 was photographed every minute for 8 minutes. In Experimental Example 4, the dispersibility of the defibrated CNTs from Example 2 and the CNTs from Comparative Example 1 was evaluated in the same manner.

[0060] In Example 1, the defibrated CNTs began to settle between 7 and 8 minutes after the start of the test, reaching the bottom of the test tube after 8 minutes. In Example 2, the defibrated CNTs began to settle immediately after being added, and continued to settle until almost all of them reached the bottom of the test tube after 8 minutes. In Comparative Example 1, no sedimentation was observed in the CNTs within 8 minutes of the start of the test.

[0061] The embodiments of the present invention should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended. [Explanation of symbols]

[0062] 100 Shredder, 10 Feeding port, 30 Fiber removal chamber, 31a Roller cutter, 31b Roller cutter, 32 Rotating shaft, 33a Rotating blade, 33b Rotating blade, 50 Discharge port, 331 Edge section, 331a Front of edge section, 331b Rear of edge section, 332 Recess, 35 Scraper.

Claims

1. A method for recovering defibrated carbon nanotubes, Equipped with a process for defibrillating raw material carbon nanotubes, The aforementioned defibring process is carried out using a shredding machine. The aforementioned shredder is equipped with a set of roller cutters, The roller cutter is equipped with a rotating blade, The rotating blade comprises an edge portion having a leading edge portion and a trailing edge portion, In the aforementioned pair of roller cutters, the tip of the edge portion of one of the rotating blades and the rear end of the edge portion of the other rotating blade in the aforementioned pair of roller cutters are arranged to slide against each other. A method for recovering defibrated carbon nanotubes, wherein the bulk density of the defibrated carbon nanotubes is 0.007 g / cm³ or more and 0.019 g / cm³ or less.

2. The method for recovering defibrated carbon nanotubes according to claim 1, further comprising the step of removing magnetic material using a magnetic separator capable of separating magnetic material from non-magnetic material after the defibration step.

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