Method for manufacturing carbon nanotubes

Abstract

To provide a method for producing carbon nanotubes that can obtain carbon nanotubes with a predetermined quality even when a reused substrate is used.SOLUTION: There is provided a method for producing carbon nanotubes including the steps of: growing carbon nanotubes on a substrate by chemical vapor deposition; peeling the grown carbon nanotubes from the substrate; and making a reused substrate using the used substrate from which the carbon nanotubes have been peeled, wherein the step of making a reused substrate includes: heat-treating the used substrate at a temperature of 600 degrees Celsius or more and 1100 degrees Celsius or less in an oxygen-containing atmosphere; and cleaning the used substrate while the used substrate is immersed into an organic solvent.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing carbon nanotubes.

Background Art

[0002] Carbon nanotubes (hereinafter also referred to as "CNTs") are expected to be used in various applications in a wide range of fields because they are excellent in thermal conductivity, electrical conductivity, mechanical strength, etc.

[0003] Examples of the CNT synthesis process include an arc discharge method, a laser evaporation method, and a chemical vapor deposition method (hereinafter also referred to as "CVD method"). Among these, the CVD method is mainly used industrially from the viewpoint of mass productivity.

[0004] When the CVD method is used, a carbon nanotube manufacturing apparatus includes a reaction furnace, a raw material gas supply unit, and a gas exhaust unit. The reaction furnace includes a heating unit capable of heating the inside of the reaction chamber, a substrate fixedly arranged inside the reaction chamber, and a catalyst provided inside the reaction chamber and capable of gas-phase reaction with the raw material gas. The raw material gas supply unit is arranged on the supply port side of the reaction furnace and is capable of supplying a raw material gas containing carbon atoms into the reaction chamber. The gas exhaust unit is arranged on the exhaust end side of the reaction furnace and is capable of exhausting the gas inside the reaction chamber to the outside before supplying the raw material gas.

[0005] Under the above configuration, in a carbon nanotube manufacturing apparatus, a raw material gas containing carbon atoms and a catalyst are gas-phase reacted inside the reaction chamber, whereby CNTs can be grown on a substrate fixedly arranged inside the reaction chamber. Also, when the reaction chamber further has a cylindrical tube inside, CNTs can also be grown on the inner wall of the cylindrical tube. After the growth of CNTs is completed, the CNTs can be peeled off from the substrate and the cylindrical tube and used for a predetermined application.

[0006] Furthermore, attempts have been made to reuse used substrates after removing the carbon nanotubes (see Patent Documents 1-3). As an example of realizing substrate reuse, there is a method of physically cleaning the used substrate from which the carbon nanotubes have been removed by blasting (see Patent Document 1). As another example, there is a method of acid cleaning the used substrate from which the carbon nanotubes have been removed in order to remove any remaining catalyst (see Patent Document 2). As yet another example, there is a method of calcining the used supported catalyst, which consists of the substrate and the catalyst supported on the substrate (see Patent Document 3). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2016-172204 [Patent Document 2] Japanese Patent Publication No. 2007-91485 [Patent Document 3] Japanese Patent Publication No. 2006-27948 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, conventional methods for reusing substrates still have areas that need improvement. Specifically, physical cleaning methods using blasting on used substrates cannot completely remove carbon components; acid cleaning methods for used substrates may cause oxide films to dissolve when using substrates with oxide films; and calcination methods for used supported catalysts are based on the premise that both the substrate and the catalyst itself will be reused, raising concerns about a decline in catalyst quality. As a result, there is a risk that the quality of the resulting carbon nanotubes will be reduced.

[0009] Therefore, the present invention aims to provide a method for producing carbon nanotubes that ensures a predetermined quality even when using recycled substrates. [Means for solving the problem]

[0010] To achieve the above objective, in one embodiment of the present invention, A process for growing carbon nanotubes on a substrate by chemical vapor deposition, A step of peeling the grown carbon nanotubes from the substrate, A process for manufacturing a recycled substrate using the used substrate from which the carbon nanotubes have been removed. Includes, A method for producing carbon nanotubes is provided, wherein the process for producing the recycled substrate includes heating the used substrate in an oxygen-containing atmosphere at a temperature of 600 degrees Celsius or more and 1100 degrees Celsius or less, and washing the used substrate while immersed in an organic solvent. [Effects of the Invention]

[0011] According to one embodiment of the present invention, it is possible to obtain carbon nanotubes of a predetermined quality even when using recycled substrates. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic cross-sectional view showing a carbon nanotube manufacturing apparatus for carrying out a carbon nanotube manufacturing method according to one embodiment of the present invention. [Figure 2] This is a schematic cross-sectional view showing a method for manufacturing carbon nanotubes according to one embodiment of the present invention (when using an unused substrate). [Figure 3] This is a schematic cross-sectional view showing a method for manufacturing carbon nanotubes according to one embodiment of the present invention (a process for manufacturing recycled substrates using used substrates). [Figure 4] This is a schematic cross-sectional view showing a method for producing carbon nanotubes according to one embodiment of the present invention (when using a recycled substrate). [Figure 5] This is an SEM image of the end portion of a carbon nanotube obtained by a carbon nanotube manufacturing method according to one embodiment of the present invention.

Embodiment for Carrying Out the Invention

[0013] Hereinafter, a method for manufacturing carbon nanotubes according to an embodiment of the present invention will be described with reference to the drawings. Various elements in the drawings are merely schematically and exemplarily shown for the purpose of explaining the present invention, and the appearance, dimensional ratios, etc. may be different from the actual ones.

[0014] Furthermore, in the following description, terms indicating specific directions and positions are used as necessary. However, the use of these terms is for facilitating the understanding of the invention with reference to the drawings, and the technical scope of the present invention is not limited by the meanings of these terms. Also, parts with the same reference numerals in multiple drawings refer to the same or equivalent parts.

[0015] [Overall Configuration of Carbon Nanotube Manufacturing Apparatus] First, before explaining the characteristic part of the method for manufacturing carbon nanotubes according to an embodiment of the present invention, the overall configuration of the carbon nanotube manufacturing apparatus and the method for manufacturing carbon nanotubes (other than the characteristic part) using the apparatus will be described. Then, the characteristic part of the present invention will be explained.

[0016] The carbon nanotube manufacturing apparatus 100 is an apparatus used in the chemical vapor deposition method. As shown in FIG. 1, such a carbon nanotube manufacturing apparatus 100 includes a reaction furnace 10, a raw material gas supply unit 20 positioned on the gas supply side of the reaction furnace 10, and a gas exhaust unit 30 positioned on the gas exhaust side of the reaction furnace 10.

[0017] (Reaction Furnace) The reactor 10 includes a reaction chamber 11 and a heating unit 12 disposed above the reaction chamber 11 so as to be able to heat the inside of the reaction chamber 11. The reaction chamber 11 includes at least one substrate 50 fixedly disposed inside the reaction chamber, and a catalyst provided inside the reaction chamber and capable of gas-phase reaction with the raw material gas G. By the gas-phase reaction of the raw material gas and the catalyst, CNTs vertically oriented on the surface of the substrate 50 in the reaction chamber 11 can be grown. Although not particularly limited, the heating unit 12 can be constituted by, for example, a resistance heating heater.

[0018] For the reaction chamber 11, for example, glass, ceramic, SiC, etc. can be used. The shape of the reaction chamber 11 itself is not particularly limited as long as it can accommodate the substrate 50, and it can be cylindrical, box-shaped, etc. The reaction chamber 11 is preferably hermetically sealed so that the gas introduced into the chamber does not diffuse to the outside.

[0019] Note that the reaction chamber 11 can further include a cylindrical tube inside. In this case, the substrate 50 can be fixedly disposed in the cylindrical tube. The heating unit 12 is connected to the control unit, and thereby, the heating unit 12 can be controlled by the control unit so that the temperature inside the reaction chamber 11 can be set to a temperature at which carbon nanotubes can grow.

[0020] The temperature inside the reaction chamber 11 due to the heating of the heating unit 12 is preferably a temperature at which the sublimable catalyst inside the reaction chamber 11 and the gas supplied into the reaction chamber 11 can undergo a gas-phase reaction, that is, a temperature at which the growth reaction of carbon nanotubes can proceed. As an example, from the viewpoint of efficiently growing carbon nanotubes, the temperature inside the reaction chamber 11 can be 500 degrees or more and 1200 degrees or less, preferably 700 degrees or more and 1000 degrees or less, more preferably 800 degrees or more and 900 degrees or less. If the temperature inside the reaction chamber 11 exceeds a predetermined upper limit value, the reaction rate may increase, and the density of the obtained carbon nanotubes may decrease. On the other hand, if the temperature inside the reaction chamber 11 is below a predetermined lower limit value, the growth rate of carbon nanotubes may slow down, and productivity may decrease.

[0021] (Substrate) The substrate 50 is supported by the substrate support 40 within the reaction chamber 11. The substrate 50 is a substrate on which vertically oriented carbon nanotubes can be grown, and has a melting point above the growth temperature. As will be described later, the substrate 50 can be configured to support a catalyst on its surface.

[0022] The substrate 50 has a plate-like shape overall, and its plane may be circular (perfect circle or ellipse), rectangular, or polygonal. While not particularly limited, the substrate 50 can be a semiconductor substrate such as a silicon substrate, or an insulating substrate such as alumina, sapphire, MgO, or glass. Preferably, from the viewpoint of suitably forming carbides that serve as growth nuclei for carbon nanotubes, it can be made of, for example, quartz glass or silicon with an oxide film. The oxide film is not particularly limited, but one with a film thickness of 10 nm to 1000 nm, for example, about 100 nm to 500 nm, can be used.

[0023] The thickness of the substrate 50 is 100 μm or more and 3000 μm or less, preferably 200 μm or more and 2500 μm or less, more preferably 300 μm or more and 2000 μm or less, even more preferably 400 μm or more and 1500 μm or less, and even more preferably 500 μm or more and 1000 μm or less, for example, 550 μm.

[0024] (catalyst) The type of catalyst used in the CNT growth reaction is not limited, but it is preferable that it contains transition metal elements from Group 3 to Group 12, such as V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, W, Ag, Au, and Pt. The catalyst may also be a halide (e.g., fluoride, chloride, bromide, and iodide) or oxide of these elements.

[0025] From the viewpoint of growth rate, the catalyst may be a halide, and iron halides are particularly preferred. More specifically, examples of halides include iron fluoride, cobalt fluoride, nickel fluoride, iron chloride, cobalt chloride, nickel chloride, iron bromide, cobalt bromide, nickel bromide, iron iodide, cobalt iodide, and nickel iodide. Here, the halide may be divalent, trivalent, or polyvalent, such as iron(II) chloride and iron(III) chloride.

[0026] As an example, a sublimable catalyst (e.g., iron chloride), which can be a gas-phase catalyst, can be present in the reaction chamber as a catalyst supplied to the reaction chamber. The method of introducing the gas-phase catalyst into the reaction chamber is not particularly limited, but it may be supplied by providing a gas-phase catalyst supply unit in the reaction chamber 11, or a material in a physical state other than the gas phase (typically a solid state) (catalyst source) that provides the gas-phase catalyst may be placed inside the reaction chamber, and the gas-phase catalyst may be generated from the catalyst source by heating and / or creating negative pressure inside the reaction chamber, thereby making the gas-phase catalyst present inside the reaction chamber 11. Furthermore, a catalyst generation reaction may be carried out inside the reaction chamber 11.

[0027] For example, in the case of iron chloride, a gas-phase catalyst may be produced by heating an iron-group element-containing material such as a lump, plate, steel wool, or powdered iron in a reaction chamber to a predetermined temperature and supplying a halogen-containing substance to react with the iron-group element-containing material in the reaction chamber.

[0028] To give a specific example of generating a gas-phase catalyst using a catalyst source, anhydrous iron(II) chloride is placed inside the reaction chamber as a catalyst source, and the inside of the reaction chamber is heated and negatively pressurized to sublimate the anhydrous iron(II) chloride, thereby creating a gas-phase catalyst consisting of iron(II) chloride vapor inside the reaction chamber.

[0029] Furthermore, the catalyst used inside the reaction chamber may be one supported on the surface of the substrate 50. In this case, the surface of the substrate 50 may have a laminated structure consisting of a support layer and a catalyst layer, or the catalyst may be dispersed in the support layer. The catalyst layer can be formed, for example, by attaching catalyst particles by sputtering.

[0030] In this case, from the viewpoint of CNT growth, it is preferable to alternately form areas where catalyst particles are attached and areas where they are not. Such island-shaped catalyst layers can be fabricated, for example, by placing a mesh on a substrate and attaching catalyst particles in a certain pattern from above using a sputtering method, or by controlling the size of the catalyst particles in advance using a differential electrostatic classifier.

[0031] Furthermore, the catalyst support materials include Mo, Ti, Hf, Zr, Nb, V, TaN, and TiSi. x (For example, x=1~2), Al, Al2O3, TiO x (For example, x=1~2), the support may contain Ta, W, Cu, Au, Pt, Pd, TiN, or at least one of these. The support may have a thickness of 0.1 nm or more, 0.5 nm or more, or 1 nm or more, and may be 10 nm or less, 7.5 nm or less, or 5 nm or less.

[0032] (Raw Gas Supply Department) The raw material gas supply unit 20 is located on the gas supply port 10a side of the reactor 10 and is configured to communicate with the inside of the reaction chamber 11 via a gas supply pipe 60. With this configuration, the raw material gas supply unit 20 is configured to supply raw material gas G containing carbon atoms into the inside of the reaction chamber 11. Hydrocarbon gas can be used as the raw material gas containing carbon atoms. The direction of gas supply from the raw material gas supply unit 20 is not particularly limited and can be any direction. For example, it may be a substantially horizontal direction (a direction substantially perpendicular to the direction of gravity), a direction substantially in the direction of gravity, or a direction located between these substantially horizontal and substantially gravitational directions.

[0033] As an example, the raw material gas G may include aliphatic saturated hydrocarbons, aliphatic unsaturated hydrocarbons, aromatic hydrocarbons, alcohols, or mixtures thereof. Examples of aliphatic saturated hydrocarbons include methane, ethane, propane, butane, and / or hexane. Examples of aliphatic unsaturated hydrocarbons include ethylene, propylene, butene, isobutene, and / or acetylene. Examples of aromatic hydrocarbons include benzene, toluene, xylene, and / or naphthalene. Examples of alcohols include methanol and / or ethanol. Furthermore, considering the property that the thermal decomposition reaction can continue spontaneously, it is preferable to use an organic compound gas such as acetylene.

[0034] (Gas exhaust section) The gas exhaust unit 30 is located on the exhaust port 10b side of the reactor 10 and is configured to communicate with the inside of the reaction chamber 11 via the gas exhaust pipe 70. With this configuration, the gas exhaust unit 30 is configured to exhaust the gas inside the reaction chamber 11 to the outside before the raw material gas is supplied. A vacuum pump such as a rotary pump can be used as the gas exhaust unit 30.

[0035] [Manufacturing method for carbon nanotubes] The following describes a method for producing carbon nanotubes using the carbon nanotube manufacturing apparatus 100 described above (see Figure 2).

[0036] The above method for producing carbon nanotubes broadly includes at least two steps: 1. growing carbon nanotubes on a substrate, and 2. peeling the grown carbon nanotubes from the substrate.

[0037] (1. Carbon nanotube growth process) Circuit board installation First, the substrate 50 (corresponding to the unused substrate 50A) is fixedly placed inside the reaction chamber 11 of the reactor 10 (see Figure 2(a)).

[0038] Gas exhaust from the reaction chamber After the substrate 50 is installed and before the raw material gas is supplied, the gas in the reaction chamber 11 is discharged by the exhaust unit 30 to create a vacuum.

[0039] Heating of the reaction chamber After the exhaust process, the heating unit 12 heats the reaction chamber 11 to a temperature at which the sublimable catalyst in the reaction chamber 11 and the gas supplied to the reaction chamber 11 can undergo a gas-phase reaction, that is, a temperature at which the carbon nanotube growth reaction can proceed. For example, as described above, from the viewpoint of efficiently growing carbon nanotubes, the temperature inside the reaction chamber 11 can be 500 degrees Celsius or more and 1200 degrees Celsius or less, preferably 700 degrees Celsius or more and 1000 degrees Celsius or less, and more preferably 800 degrees Celsius or more and 900 degrees Celsius or less.

[0040] Raw material gas supply After the heating process in the reaction chamber 11, a predetermined flow rate of raw material gas is supplied to the reaction chamber 11 from the raw material gas supply unit 20 via the gas supply pipe 60. At this time, a pressure adjustment unit (not shown) adjusts the raw material gas pressure in the reaction chamber 11 to a pressure at which carbon nanotubes can grow.

[0041] The raw material gas pressure may be 1 Torr or higher, 3 Torr or higher, 5 Torr or higher, 10 Torr or higher, 25 Torr or higher, or 50 Torr or higher, preferably 1 Torr or higher. Alternatively, the raw material gas pressure may be 300 Torr or lower, 200 Torr or lower, 150 Torr or lower, 100 Torr or lower, 50 Torr or lower, 25 Torr or lower, or 12.5 Torr or lower, preferably 100 Torr or lower.

[0042] Furthermore, the flow rate of the raw material gas supplied to the reaction chamber 11 depends on the size of the reaction chamber 11, the number of substrates 50 to be installed, etc., but from the viewpoint of appropriately retaining the raw material gas in the reaction chamber 11, it may be set to 20 sccm (Standard cc per minute, volumetric flow rate at standard conditions (25 degrees Celsius, 1 atmosphere), the same applies below) or more and 3000 sccm or less, 40 sccm or more and 2000 sccm or less, 80 sccm or more and 1000 sccm or less, for example, 500 sccm.

[0043] Furthermore, a second gas may be supplied into the reaction chamber 11 simultaneously with the raw material gas. The second gas is a gas different from the raw material gas and is at least one gas selected from the group consisting of hydrocarbons having oxygen atoms and hydrogen. The second gas may have an etching effect on the catalyst. The second gas may also be a reducing substance. Specific examples include carbon monoxide, acetone, ethanol, methanol, and / or hydrogen, and preferably carbon monoxide and / or acetone.

[0044] By supplying a second gas simultaneously with the raw material gas, the growth potential of CNTs can be enhanced, and the spinnability of the manufactured CNTs can be improved. Furthermore, it is possible to achieve a reduction in the activation energy of the reaction related to the growth of the CNT array, an increase in the growth rate of the CNT array, an improvement in the growth stability of the CNT array, an extension of the lifespan of the gas-phase catalyst due to the removal of amorphous carbon which is the cause of deactivation, and an improvement in the uniformity of the growth length.

[0045] In order to supply the second gas, in addition to or instead of supplying the second gas itself, raw materials capable of forming the second gas can also be supplied. For example, in order to supply carbon monoxide as the second gas, in addition to or instead of supplying carbon monoxide itself as described above, raw materials capable of forming carbon monoxide can also be supplied. Examples of raw materials capable of forming carbon monoxide include carbon dioxide and carbonyl complexes. These raw materials can form (generate) carbon monoxide in the reaction chamber and produce the same effect as when carbon monoxide is supplied.

[0046] The ratio of the second gas pressure to the raw material gas pressure (second gas pressure / raw material gas pressure) may be 0.1% or more, 1% or more, 2% or more, 3% or more, 5% or more, 10% or more, or 20% or more, and is preferably 1% or more. Furthermore, the raw material gas pressure to the second gas pressure may be 500% or less, 300% or less, 100% or less, 50% or less, 30% or less, 20% or less, 10% or less, or 5% or less, and is preferably 30% or less.

[0047] First emission of raw material gas After a raw material gas supply process for a predetermined time, the supply of raw material gas may be stopped and the raw material gas may be partially discharged to reduce the raw material gas pressure to a reduced pressure of 5% to 95% of the growth pressure. This reduced pressure may be 5% or more, 10% or more, 20% or more, 30% or more, 40% or more, 50% or more, or 60% or more of the raw material gas pressure in the growth process, and preferably 30% or more or 50% or more. The reduced pressure may be 95% or less, 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, or 40% or less of the raw material gas pressure in the growth process, and preferably 80% or less.

[0048] The time for the raw material gas exhaust process may be 300 seconds or less, 200 seconds or less, 100 seconds or less, 60 seconds or less, or 30 seconds or less, for example, 25 seconds or less, within 20 seconds, within 15 seconds, within 10 seconds, or within 5 seconds.

[0049] Maintaining raw material gas pressure After the first discharge step of the raw material gas, the raw material gas pressure is maintained within the above-mentioned reduced pressure range for a predetermined time. During this holding step, the supply of raw material gas to the reaction chamber 11 and the discharge of gas from the reaction chamber 11 may be shut off from the viewpoint of maintaining a constant raw material gas pressure.

[0050] The predetermined time for the holding step may be, for example, 5 seconds or more, 10 seconds or more, 20 seconds or more, 30 seconds or more, 40 seconds or more, 50 seconds or more, or 60 seconds or more, and may be 300 seconds or less, 250 seconds or less, 200 seconds or less, 150 seconds or less, 100 seconds or less, or 50 seconds or less. During such a holding step, the ambient temperature of the reaction chamber 11 may be kept within a certain range, preferably the reaction chamber ambient temperature is kept at the growth temperature. The reaction chamber ambient temperature may be kept constant throughout the holding step.

[0051] Decreasing the ambient temperature of the reaction chamber After the raw material gas pressure holding step, the ambient temperature of the reaction chamber 11 may be lowered. The rate of decrease in the ambient temperature of the reaction chamber 11 may be 3 degrees / min or more, 5 degrees / min or more, 7 degrees / min or more, 9 degrees / min or more, or 12 degrees / min or more, and may be 50 degrees / min or less, 40 degrees / min or less, 30 degrees / min or less, or 20 degrees / min or less.

[0052] The reaction chamber atmosphere temperature reduction process may be carried out until the reaction chamber atmosphere temperature reaches a temperature at which oxidation of CNTs by oxygen in the air does not occur. For example, the reaction chamber atmosphere temperature may be less than 500 degrees, 400 degrees or less, or 300 degrees or less. Once the reaction chamber atmosphere temperature reaches a temperature at which CNTs are not oxidized by oxygen in the air, the substrate 50 may be released to atmospheric pressure.

[0053] Secondary emission of raw material gas Furthermore, after the raw material gas pressure maintenance step, the raw material gas is further discharged to reduce the raw material gas pressure from the reduced pressure mentioned above. This further discharge of raw material gas (corresponding to the second raw material gas step) may be performed simultaneously with the reaction chamber atmosphere temperature reduction step. In this case, if the desired reaction chamber atmosphere temperature has not been reached during the reaction chamber atmosphere temperature reduction step, the temperature reduction step may be continued even after the completion of the second raw material gas discharge step.

[0054] The raw material gas pressure after the second discharge process of the raw material gas may be 0.1 Torr or less, 0.08 Torr or less, 0.05 Torr or less, 0.03 Torr or less, or 0.01 Torr or less, and is preferably 0.05 Torr or less.

[0055] The raw material gas pressure after the second raw material gas discharge process may be 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, 5% or less, or 1% or less of the above-mentioned reduced pressure, and is preferably 10% or less. The duration of the second raw material gas discharge process may be 300 seconds or less, 200 seconds or less, 100 seconds or less, 60 seconds or less, or 30 seconds or less, for example, 25 seconds or less, within 20 seconds, within 15 seconds, within 10 seconds, or within 5 seconds.

[0056] With the above steps, the formation of CNTs grown approximately perpendicular to the substrate 50 is completed (see Figure 2(b)).

[0057] (2. CNT removal process from the substrate) After the above process, the CNTs formed on the substrate 50 may be peeled off the substrate 50 (see Figure 2(c)). Note that the CNTs on the substrate 50 are in a vertical orientation. Methods for peeling the CNTs from the substrate 50 can be physical, chemical, or mechanical. For example, methods include peeling using an electric field, magnetic field, centrifugal force, surface tension, etc., mechanically peeling from the substrate 50, and peeling from the substrate 50 using pressure or heat. It is also possible to use a vacuum pump to suck up the CNTs and peel them off the substrate. Mechanical methods for peeling from the substrate include directly picking up the CNTs with tweezers and peeling them off the substrate, or using a thin blade such as a plastic spatula or cutter blade with a sharp edge to peel the CNTs off.

[0058] By following the above process, a predetermined amount of CNTs can be obtained. As shown in Figure 5, almost no CNTs remain on the used substrate 50B after CNT removal. In other words, the residue of CNTs on the substrate 50 can be suppressed, thereby suppressing damage to the CNTs themselves.

[0059] [Features of the present invention] Based on the overall configuration of the carbon nanotube manufacturing apparatus 100 described above and the method for manufacturing carbon nanotubes using the apparatus (excluding the feature part), the feature part of the present invention will be described below. The feature part of the present invention is that, after the CNT peeling step from the substrate described above, step 3, the manufacturing of a recycled substrate using a used substrate, is further carried out, and this manufacturing of a recycled substrate is not an extension of the conventional process but is carried out from a new perspective (see Figure 3).

[0060] The inventors of this application have previously attempted to reuse substrates, which are components of carbon nanotube manufacturing equipment. However, they have found that there is a risk of the quality of carbon nanotubes obtained using recycled substrates deteriorating. As a result, they have devised a method for manufacturing recycled substrates that includes a new process, rather than simply extending previous methods, as described above.

[0061] Specifically, the distinguishing feature of the present invention is that, without employing the conventional methods of "physical cleaning of used substrates by blasting," "acid cleaning of used substrates," and "reuse of used catalysts," it performs at least a combination of "heat treatment" and "cleaning in an organic solvent" on used substrates.

[0062] A manufacturing method according to one embodiment of the present invention is characterized in that, in the process of manufacturing the recycled substrate described above, the used substrate from which the grown carbon nanotubes have been peeled off is heat-treated at a temperature of 600 degrees Celsius or more and 1100 degrees Celsius or less in an oxygen-containing atmosphere, and the used substrate is washed while immersed in an organic solvent.

[0063] In this specification, "reused substrate" refers to a substrate that has been used once and is reused as a support for carbon nanotube growth. In this specification, "used substrate" refers to a substrate that has been used once as a support for carbon nanotube growth.

[0064] According to these characteristics, by heat treatment of the used substrate, carbon-based impurities on the surface of the used substrate can be released into the atmosphere as carbon dioxide, and by cleaning the used substrate, used catalysts and other materials on the surface of the used substrate can be separated from the surface in an organic solvent. As a result, a recycled substrate can be obtained that is in a condition almost identical to that of an unused substrate. Consequently, it is possible to obtain carbon nanotubes of a predetermined quality even when using a recycled substrate.

[0065] (Process for manufacturing recycled circuit boards using used circuit boards) The "process for manufacturing recycled substrates," which is a key feature of the present invention, will be explained in detail below (see Figures 3(a) to 3(c)).

[0066] In the recycled substrate manufacturing process, after the CNT stripping process (see Figure 2(c)), the used substrate 50B is removed from the reaction chamber 11 of the reactor 10 to the outside. The removed used substrate 50B is then heat-treated in the atmosphere (oxygen-containing atmosphere) using a heating device 200 (see Figure 3(a)).

[0067] Specifically, the used substrate 50B is placed in the heating device 200, the temperature inside the device is raised to between 600°C and 1100°C at a predetermined heating rate, and then the used substrate 50B is heat-treated at this temperature under atmospheric pressure for a predetermined time. This heat treatment can remove carbon-based impurities from the surface of the used substrate 50B.

[0068] The heating rate may be 20 degrees / min or more, 30 degrees / min or more, 40 degrees / min or more, or 50 degrees / min or more, and may be 100 degrees / min or less, 90 degrees / min or less, 80 degrees / min or less, or 70 degrees / min or less.

[0069] The heating temperature for the used substrate 50B should be between 600°C and 1100°C as described above, preferably between 700°C and 1000°C, and more preferably between 800°C and 900°C, for example, 850°C.

[0070] The heating time for the used substrate 50B should be between 5 and 20 minutes, preferably between 6 and 18 minutes, more preferably between 7 and 16 minutes, even more preferably between 8 and 14 minutes, and even more preferably between 9 and 13 minutes, and for example, it can be 10 minutes.

[0071] Subsequently, the used substrate 50B is allowed to cool to room temperature, and the cooled used substrate 50B is then cleaned in an organic solvent 310 using a cleaning device 300 equipped with a space for containing organic solvents (see Figure 3(b)).

[0072] Specifically, the used substrate 50B, which has been allowed to cool to room temperature, is immersed in an organic solvent provided in the cleaning device 300 and then subjected to a cleaning treatment for a predetermined time. Preferably, the surface of the used substrate 50B is subjected to ultrasonic vibration via the organic solvent using the cleaning device 300, which is capable of providing ultrasonic vibration. In other words, ultrasonic cleaning of the used substrate 50B is performed. This cleaning treatment further removes carbon-based impurities from the surface of the used substrate 50B and separates the used catalyst from the surface in the organic solvent 310. That is, it becomes possible to further remove carbon-based impurities from the surface of the used substrate 50B and remove the catalyst present on the surface.

[0073] The cleaning time for the used substrate 50B may be 3 minutes or more and 30 minutes or less, preferably 5 minutes or more and 25 minutes or less, more preferably 7 minutes or more and 20 minutes or less, and even more preferably 9 minutes or more and 15 minutes or less, and can be 10 minutes, for example.

[0074] The organic solvent used can be, for example, at least one selected from the group consisting of alcohols, glycols, ethers, esters, ketones, and aromatic hydrocarbons. Preferably, from the viewpoint of volatility, alcohols can be used as the organic solvent. Examples of alcohols include methanol, ethanol, or isopropyl alcohol.

[0075] When the surface of the used substrate 50B is ultrasonically vibrated via an organic solvent using the cleaning device 300, the frequency for ultrasonic vibration can be, for example, 10 kHz or higher, 20 kHz or higher, 30 kHz or higher, or 40 kHz or higher, and can be 200 kHz or lower, 190 kHz or lower, 180 kHz or lower, or 170 kHz or lower.

[0076] Furthermore, the used substrate 50B that has been washed may be dried using the drying apparatus 400 at a temperature of 20°C to 50°C for 0.5 minutes to 3 minutes (see Figure 3(c)). Since the used substrate 50B may also be air-dried in the atmosphere, the drying process for the washed substrate 50 is not mandatory but optional.

[0077] Furthermore, regarding the order of heat treatment of the used substrate 50B and washing of the used substrate 50B in an organic solvent, from the viewpoint of achieving both further removal of carbon-based impurities from the surface of the used substrate 50B and removal of catalysts present on the surface, it is preferable to perform heat treatment of the used substrate 50B followed by washing of the heat-treated used substrate 50B in an organic solvent.

[0078] Based on the above, recycled circuit boards can be manufactured.

[0079] After fabricating the recycled substrate, carbon nanotubes are manufactured using this recycled substrate (see Figure 4).

[0080] In terms of the carbon nanotube manufacturing method, except for the fact that a recycled substrate 50C, which is made in place of the unused substrate 50A, is fixedly placed in the reaction chamber 11, the carbon nanotubes are repeatedly manufactured using the same method as the carbon nanotube growth process and carbon nanotube exfoliation process described above using the unused substrate 50A.

[0081] In other words, the recycled substrate 50C, which has been fabricated once, is fixed in place, and carbon nanotubes are repeatedly manufactured using the same method as the carbon nanotube growth process and the carbon nanotube peeling process from the substrate described above.

[0082] Furthermore, in terms of the configuration of the carbon nanotube manufacturing apparatus, the components are the same except that a recycled substrate 50C, which has been fabricated, is used instead of an unused substrate 50A as the substrate 50 component.

[0083] The following describes in detail the carbon nanotube growth process and the carbon nanotube removal process from the substrate when using recycled substrate 50C. Note that any parts of this description that overlap with the previously described carbon nanotube growth process and carbon nanotube removal process using unused substrate 50A will be omitted or overlooked.

[0084] (1. Carbon nanotube growth process) Circuit board installation Specifically, first, the recycled substrate 50C is fixedly placed inside the reaction chamber 11 of the reactor 10 (see Figure 4(a)).

[0085] Gas exhaust from the reaction chamber After the installation process of the recycled substrate 50C and before supplying the raw material gas, the gas in the reaction chamber 11 is discharged by the exhaust unit 30 to create a vacuum.

[0086] Heating of the reaction chamber After the exhaust process, the heating unit 12 heats the reaction chamber 11 to a temperature at which the carbon nanotube growth reaction can proceed.

[0087] Raw material gas supply After the heating process in the reaction chamber 11, a predetermined flow rate of raw material gas is supplied to the reaction chamber 11 from the raw material gas supply unit 20 via the gas supply pipe 60. A second gas may be supplied to the reaction chamber 11 simultaneously with the raw material gas.

[0088] First emission of raw material gas After a raw material gas supply process that lasts for a predetermined time, the supply of raw material gas may be stopped, and the raw material gas may be partially discharged to reduce the raw material gas pressure to a reduced pressure that is between 5% and 95% of the growth pressure.

[0089] Maintaining raw material gas pressure After the first discharge process of the raw material gas, the raw material gas pressure is maintained within the above-mentioned reduced pressure range for a predetermined time.

[0090] Decreasing the ambient temperature of the reaction chamber After the raw material gas pressure maintenance step, the ambient temperature of the reaction chamber 11 may be lowered. This reaction chamber ambient temperature reduction step may be carried out until the reaction chamber ambient temperature reaches a temperature at which oxidation of CNTs by oxygen in the air does not occur. Once the reaction chamber ambient temperature reaches a temperature at which CNTs are not oxidized by oxygen in the air, the substrate 50 may be released to atmospheric pressure.

[0091] Secondary emission of raw material gas Furthermore, after the raw material gas pressure maintenance step, the raw material gas is further discharged to reduce the raw material gas pressure from the reduced pressure mentioned above. This further discharge of raw material gas (corresponding to the second raw material gas step) may be performed simultaneously with the reaction chamber atmosphere temperature reduction step. In this case, if the desired reaction chamber atmosphere temperature has not been reached during the reaction chamber atmosphere temperature reduction step, the temperature reduction step may be continued even after the completion of the second raw material gas discharge step.

[0092] With the above steps, the formation of CNTs grown almost perpendicularly to the recycled substrate 50C is completed (see Figure 4(b)).

[0093] (CNT stripping process from recycled substrates) After the above process, the CNTs formed on the recycled substrate 50C may be peeled off from the recycled substrate 50C (see Figure 4(c)).

[0094] By going through these processes, the desired CNTs can be obtained.

[0095] Furthermore, according to the manufacturing method of the present invention, the obtained recycled substrate 50C can be used repeatedly for 1 to 50 times, for example, 40 times. This is because even when the recycled substrate 50C is used repeatedly, it is possible to ensure carbon nanotube crystallinity (G / D ratio) to be approximately the same as when an unused substrate 50A is used. Specifically, carbon nanotubes can be obtained with crystallinity (G / D ratio) of 1.0 or higher, 1.5 or higher, 2.0 or higher, or 2.5 or higher, and 6.0 or lower, 5.5 or lower, 5.0 or lower, 4.5 or lower, 4.0 or lower, or 3.5 or lower. Therefore, as described above, according to the manufacturing method of the present invention, it is possible to obtain carbon nanotubes with a predetermined quality even when the recycled substrate 50C is used repeatedly. [Examples]

[0096] The following describes embodiments of the present invention.

[0097] [Examples] Carbon nanotubes were manufactured through the following process.

[0098] (Carbon nanotube growth process) First, a substrate 50 (corresponding to an unused substrate) with a catalyst attached to its surface was fixedly placed in the reaction chamber 11 (volume 38 L) of the reactor 10 of the carbon nanotube manufacturing apparatus 100. A 4-inch diameter silicon substrate with a thermal oxide film was used as the substrate 50. The catalyst-coated substrate was obtained by heating iron(II) chloride to a temperature above its sublimation temperature and depositing its fine particles onto the substrate 50. After the substrate 50 was installed and before the raw material gas was supplied, the gas in the reaction chamber 11 was discharged using the exhaust unit 30 to create a vacuum.

[0099] After the exhaust process, the heating unit 12 heated the temperature inside the reaction chamber 11 to approximately 800 degrees Celsius so that the catalyst inside the reaction chamber 11 and the gas supplied to the reaction chamber 11 could undergo a gas-phase reaction.

[0100] After heating the reaction chamber 11, raw material gas (acetylene gas) was supplied to the reaction chamber 11 from the raw material gas supply unit 20 via the gas supply pipe 60 at a flow rate of approximately 10 L / min. Simultaneously with the raw material gas, a second gas (carbon monoxide) was supplied to the reaction chamber 11 at a flow rate of 1 L / min or less. At this time, the raw material gas pressure in the reaction chamber 11 was adjusted by a pressure adjustment unit (not shown) to a pressure (approximately 5 Torr) at which carbon nanotubes could be grown. Then, CNTs were grown on the substrate 50 for 10 to 30 minutes.

[0101] Subsequently, the supply of raw material gas was stopped, and the raw material gas was partially discharged to reduce the raw material gas pressure by approximately 2 Torr from the growth pressure. Then, the supply of raw material gas to and from reaction chamber 11 was shut off, and the growth temperature was maintained for 40 seconds. After maintaining the raw material gas pressure, the gas was discharged to approximately 0 Torr in about 20 seconds, and the reaction chamber atmosphere temperature was cooled to below 300 degrees Celsius at a rate of 15-20 degrees Celsius per minute before being opened to the atmosphere.

[0102] As a result, we were able to form CNTs (G / D ratio: 2.82, purity 99% or higher) that grew almost perpendicular to the substrate 50. The length and diameter of the obtained CNTs were determined from SEM images, the G / D ratio was determined by Raman analysis, and the purity was determined by thermogravimetric analysis. The specific specifications of the Raman analyzer used are as follows: • Manufacturer: HORIBA Corporation Model: XploRA-SDL The specific specifications of the thermogravimetric analysis used are as follows: • Manufacturer: Shimadzu Corporation ·Model: DTG-60H The specific specifications of the scanning electron microscope (SEM) used are as follows: • Manufacturer: Hitachi Model: SU8030

[0103] (Exfoliation process of carbon nanotubes from the substrate) After the above process, the CNTs formed on the substrate 50 were peeled off the substrate 50. The peeling method involved using a cutter blade to remove the CNTs that had finished growing from the substrate 50 from the surface of the substrate 50. This allowed us to obtain the CNTs.

[0104] Furthermore, as shown in Figure 5, almost no residual CNTs were observed on the substrate 50 after CNT removal. In other words, it was found that the residue of CNTs on the substrate 50 could be suppressed, thereby suppressing damage to the CNTs themselves.

[0105] (Process for manufacturing recycled circuit boards using used circuit boards) After the CNTs were removed from the substrate 50, the used substrate 50B was removed from the reaction chamber 11 of the reactor 10 to the outside. The removed used substrate 50B was heat-treated in the heating device 200 under atmospheric conditions (oxygen-containing atmosphere). Specifically, the used substrate 50B was placed inside the heating device 200, the temperature inside the device was raised to 850 degrees Celsius at a rate of 40 degrees Celsius per minute, and then the used substrate 50B was heat-treated at 850 degrees Celsius under atmospheric conditions for 10 minutes.

[0106] The specific specifications of the heating device 200 used are as follows: • Manufacturer: Koyo Thermo Systems Co., Ltd. • Model: Custom-made • Heating method: Electrical resistance heating • Heating time: 10 minutes

[0107] The above heat treatment was found to remove carbon-based impurities from the surface of the used substrate 50B. This measurement was performed using the following method.

[0108] Subsequently, the used substrate 50B, which had been allowed to cool to room temperature, was cleaned by immersing it in an organic solvent 310 using a cleaning device 300 equipped with a space for containing an organic solvent. Specifically, the used substrate 50B, which had been allowed to cool to room temperature, was immersed in an organic solvent (isopropyl alcohol) provided in the cleaning device 300 and cleaned for 10 minutes. More specifically, the surface of the used substrate 50B was ultrasonically cleaned via the organic solvent using a cleaning device 300 capable of providing ultrasonic vibrations.

[0109] The specific specifications of the cleaning device 300 used are as follows: • Manufacturer: SND Co., Ltd. ·Model: US-108 Output: 300 W • Frequency: 38 kHz

[0110] Afterward, the used substrate 50B was cleaned and then dried in the drying apparatus 400. Specifically, it was dried in the drying apparatus 400 at a temperature of 20 degrees Celsius for approximately 1 minute. Note that the drying process for the cleaned used substrate 50 is optional, as the used substrate can also be air-dried in the atmosphere.

[0111] The specific specifications of the drying apparatus 400 used are as follows: • Manufacturer: Sanei Co., Ltd. Model: KGA20001 • Rotation speed: 800 rpm • Processing time: 1 min

[0112] The above cleaning process revealed that carbon-based impurities were further removed from the surface of the used substrate 50B, and that the catalyst present on the surface was also removed. This measurement was performed using the following method.

[0113] Based on the above, recycled substrate 50C was fabricated.

[0114] Thereafter, carbon nanotubes were repeatedly manufactured using the same method as described above for the (carbon nanotube growth process) and (carbon nanotube exfoliation process from the substrate), except that a recycled substrate 50C, which had been prepared in place of an unused substrate, was fixedly placed in the reaction chamber 11. Specifically, carbon nanotubes were remanufactured using the same method as described above for the (carbon nanotube growth process) and (carbon nanotube exfoliation process from the substrate), with the recycled substrate 50C that had been prepared once fixed in place.

[0115] Subsequently, the crystallinity of the carbon nanotubes obtained from the first use of recycled substrate 50C was determined by Raman analysis to determine the G / D ratio. As a result, the G / D ratio for the first use of recycled substrate 50C was 2.78.

[0116] Similarly, with the reused substrate 50C that had been fabricated once remaining fixed in place, carbon nanotubes were repeatedly manufactured using the same methods as described above for (carbon nanotube growth process) and (carbon nanotube exfoliation process from the substrate).

[0117] Subsequently, the crystallinity of the carbon nanotubes obtained after the 20th use of recycled substrate 50C was determined by Raman analysis to determine the G / D ratio. As a result, the G / D ratio after the 20th use of recycled substrate 50C was 3.02.

[0118] Similarly, with the reused substrate 50C that had been fabricated once remaining fixed in place, carbon nanotubes were repeatedly manufactured using the same methods as described above for (carbon nanotube growth process) and (carbon nanotube exfoliation process from the substrate).

[0119] Subsequently, the crystallinity of the carbon nanotubes obtained after 40 uses of recycled substrate 50C was determined by Raman analysis to determine the G / D ratio. As a result, the G / D ratio after 40 uses of recycled substrate 50C was 2.86.

[0120] From the above, it was found that even when a recycled substrate is used repeatedly 40 times, it is possible to ensure carbon nanotube crystallinity (G / D ratio) that is approximately the same as when an unused substrate is used. In other words, it was found that a recycled substrate with a condition approximately the same as an unused substrate can be obtained. As a result, it was found that carbon nanotubes of the specified quality can be obtained even when using a recycled substrate.

[0121] Although a carbon nanotube manufacturing apparatus according to one embodiment of the present invention has been described above, the present invention is not limited thereto, and various modifications based on the knowledge of those skilled in the art are possible without departing from the spirit of the claims. [Industrial applicability]

[0122] A method for producing carbon nanotubes according to one embodiment of the present invention can be suitably used to obtain carbon nanotubes that can be used in electronic device materials, optical element materials, conductive materials, and bio-related materials, etc. [Explanation of Symbols]

[0123] 400 Drying equipment 300 Cleaning equipment 310 Organic Solvents 200 Heating device 100 Carbon nanotube manufacturing equipment 10 Reactor 10a Gas supply port 10b Exhaust port 11 Reaction Chamber 12 Heating section 20 Raw Gas Supply Department 30 Gas exhaust section 40 Substrate support section 50 circuit boards 50A unused board 50B Used circuit board 50C reused board 60 Gas supply pipe 70 Gas exhaust pipe C carbon nanotubes

Claims

1. A step of growing carbon nanotubes on a substrate in the presence of a catalyst in a reactor by chemical vapor deposition, A step of peeling the grown carbon nanotubes from the substrate, A process for manufacturing a recycled substrate using the used substrate from which the carbon nanotubes have been removed. Includes, A method for producing carbon nanotubes, wherein the process for producing the recycled substrate includes heating the used substrate at a temperature of 600 degrees Celsius or more and 1100 degrees Celsius or less in an oxygen-containing atmosphere, and washing the used substrate while immersed in an organic solvent, and the catalyst contains iron chloride.

2. A method for producing carbon nanotubes according to claim 1, wherein the used substrate is ultrasonically cleaned in the organic solvent.

3. A method for producing carbon nanotubes according to claim 1 or 2, further comprising the step of growing carbon nanotubes on the recycled substrate after the recycled substrate has been produced by chemical vapor deposition.

4. A method for producing carbon nanotubes according to any one of claims 1 to 3, wherein the used substrate is washed in an organic solvent after heat treatment of the used substrate.

5. A method for producing carbon nanotubes according to any one of claims 1 to 4, further comprising washing the used substrate in an organic solvent and then drying the washed used substrate.

6. A method for producing carbon nanotubes according to any one of claims 1 to 5, wherein the used substrate is heat-treated at a temperature of 700 degrees Celsius or higher and 1000 degrees Celsius or lower.

7. The method for producing carbon nanotubes according to any one of claims 1 to 6, wherein the organic solvent is at least one selected from the group consisting of alcohols, glycols, ethers, esters, ketones, and aromatic hydrocarbons.

8. The method for producing carbon nanotubes according to claim 7, wherein the organic solvent is an alcohol.

9. The method for producing carbon nanotubes according to claim 8, wherein the alcohol is methanol, ethanol, or isopropyl alcohol.

10. The process of growing carbon nanotubes on the substrate or the recycled substrate is carried out by supplying the raw material gas to a reactor that is capable of supplying raw material gas and exhausting internal gas, and in which a catalyst that reacts with the raw material gas in the gas phase can be positioned inside, under growth temperature and growth pressure. The method for producing carbon nanotubes according to any one of claims 1 to 9, wherein the catalyst is a gas-phase catalyst provided in the reactor, or supported on the substrate or the recycled substrate.

11. A method for producing carbon nanotubes according to claim 10, further comprising: a discharge step of discharging the raw material gas to reduce the raw material gas pressure to a reduced pressure of 5% to 95% of the growth pressure, after growing the carbon nanotubes on the substrate or the recycled substrate, before peeling the grown carbon nanotubes from the substrate or the recycled substrate; and a holding step of maintaining the raw material gas pressure within the range of the reduced pressure for a predetermined time.

12. A method for producing carbon nanotubes according to any one of claims 1 to 11, for obtaining carbon nanotubes having a G / D ratio of 1.0 or more and 6.0 or less.

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