JP2014231446A - Production method of carbon nanotubes - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of carbon nanotubes which has an amorphous layer with sufficient thickness and which is prevented from flocculation.SOLUTION: A production method of carbon nanotubes using a thermal CVD method has: a first step to grow the carbon nanotubes to a predetermined length on a substrate K kept at a constant first temperature (640°C or higher) by supplying a raw material gas (CH); and a second step to grow an amorphous layer on the carbon nanotubes grown to the predetermined length by supplying the raw material gas (CH) at 3-10 kPa on the substrate K kept at a constant second temperature (780-840°C), higher than the first temperature by 50-200°C.

Description

  The present invention relates to a method for producing carbon nanotubes.

In recent years, for the low-carbon society, the spread of batteries replacing fossil fuels is desired, and the development of high-performance batteries is being promoted.
As a currently known high-performance battery, in an electrode of a fuel cell or the like, a catalyst is supported on a vertically aligned carbon nanotube on an electrolyte membrane and an electrolyte resin is coated. Some have improved power generation efficiency.

  In addition, by growing an amorphous layer on the outer surface of the carbon nanotube, fuel not only ensures more catalyst but also suppresses aggregation of the catalyst on the surface of the carbon nanotube, thereby improving the power generation efficiency. A battery is known (see, for example, Patent Document 1).

JP 2007-257886 A

  By the way, the thickness of the amorphous layer described in Patent Document 1 is controlled by increasing or decreasing the concentration of the carbon nanotube raw material supplied in the manufacturing process. However, even when a sufficiently high concentration of the carbon nanotube raw material is supplied, the thickness of the obtained amorphous layer is insufficient to suppress the aggregation of the carbon nanotubes.

  In general, when the carbon nanotubes of the electrode are vertically aligned, the power generation efficiency is improved. However, the vertically aligned carbon nanotubes are a process of drying the applied catalyst solution and evaporating the solvent, that is, supporting the catalyst on the carbon nanotubes. There was a problem of aggregation in part of the process. Also, there is a problem that vertically aligned carbon nanotubes aggregate in the step of impregnating carbon nanotubes with Nafion, that is, the step of coating carbon nanotubes with an electrolyte resin.

  Then, an object of this invention is to provide the manufacturing method of the carbon nanotube which has an amorphous layer of sufficient thickness and can suppress aggregation.

In order to solve the above-described problem, a carbon nanotube production method according to claim 1 of the present invention is a carbon nanotube production method by a thermal CVD method,
A first step of growing carbon nanotubes to a predetermined length on the substrate by supplying a source gas to the substrate at a first temperature;
A second step of growing an amorphous layer on the carbon nanotubes grown to a predetermined length by supplying a source gas to the substrate at a second temperature that is higher than the first temperature.

  The carbon nanotube production method according to claim 2 of the present invention is the carbon nanotube production method according to claim 1, wherein the first temperature is 640 ° C. or higher and the second temperature is 50 ° C. higher than the first temperature. ˜200 ° C. higher.

  Furthermore, the carbon nanotube manufacturing method according to claim 3 of the present invention is the carbon nanotube manufacturing method according to claim 1 or 2, wherein the first temperature and the second temperature are constant.

  The carbon nanotube production method according to claim 4 of the present invention is the carbon nanotube production method according to any one of claims 1 to 3, wherein the pressure of the raw material gas supplied in the second step is: 3 to 10 kPa.

  A carbon nanotube production method according to claim 5 of the present invention is the carbon nanotube production method according to any one of claims 1 to 4, wherein the carbon nanotube has a predetermined length and has an amorphous layer grown thereon. In addition, there is a third step of peeling off the carbon nanotubes from the substrate after supplying oxygen.

The carbon nanotube according to claim 6 of the present invention is a carbon nanotube produced by a thermal CVD method and having an amorphous layer grown thereon,
The carbon nanotubes are grown to a predetermined length by supplying a source gas to a substrate at 640 ° C. or higher,
The amorphous layer is grown by supplying a source gas to the substrate at a temperature higher by 50 to 200 ° C. than the temperature at which the carbon nanotubes are grown to a predetermined length.
It is peeled from the substrate.

  According to the carbon nanotube manufacturing method, the first step of growing the length of the carbon nanotube and the second step of growing the amorphous layer of the carbon nanotube have an amorphous layer having a sufficient thickness, Carbon nanotubes capable of suppressing aggregation can be produced.

It is side part sectional drawing which shows schematic structure of the manufacturing apparatus used for the manufacturing method which concerns on the Example of this invention. It is a top view of the manufacturing apparatus. It is AA sectional drawing of the manufacturing apparatus. It is a perspective view which shows the structure in the heating chamber of the manufacturing apparatus. It is a corresponding | compatible figure which shows the relationship between each process and substrate temperature of the manufacturing apparatus. It is a graph which shows the result of the experiment conducted in order to determine the heating temperature of the board | substrate in the manufacturing method, and the pressure in a heating chamber, and shows the relationship between heating temperature and carbon nanotube length. It is a graph which shows the same result, and shows the relationship between the heating time at the time of changing a pressure and carbon nanotube length. It is a graph which shows the result, and shows the relationship between heating temperature and carbon nanotube bulk density when heating time is changed. It is a graph which shows the same result, and shows the relationship between the heating temperature at the time of changing the supply amount of source gas, and a carbon nanotube bulk density.

Hereinafter, the manufacturing method of the carbon nanotube which concerns on the Example of this invention is demonstrated based on drawing.
First, a carbon nanotube manufacturing apparatus (thermal CVD apparatus) will be described as one used in the carbon nanotube manufacturing method according to the present embodiment.

  In this example, as a substrate on which carbon nanotubes are continuously formed, a predetermined thin steel plate (an example of a thin plate material, for example, a foil material having a thickness of about 20 to 300 μm is used. In some cases, a thickness of about 300 μm to several mm is used.). The predetermined thin steel plate is a metal whose melting point is higher than the heating temperature (which will be described later, it is 840 ° C.), for example, a stainless steel plate. In addition, as the stainless steel plate, a long one having a predetermined width, that is, a strip shape is used. Therefore, this stainless steel plate is wound around a roll, and when forming carbon nanotubes, the carbon nanotubes are continuously formed by being pulled out from this roll, and the stainless steel plate on which the carbon nanotubes are formed It is intended to be wound on a roll. That is, a stainless steel plate is pulled out from one unwinding roll, carbon nanotubes are formed on the surface of the pulled stainless steel plate, and then the stainless steel plate on which the carbon nanotubes are formed is wound on the other winding roll. ing.

  Hereinafter, a manufacturing apparatus (thermal CVD apparatus) for continuously forming carbon nanotubes on the surface of the above-described strip-shaped stainless steel plate (hereinafter referred to as substrate K) by a thermal CVD method will be described.

  As shown in FIG. 1, the manufacturing apparatus includes a heating furnace 1 in which an elongated processing space for forming carbon nanotubes is provided inside a furnace body 2. The processing space provided inside is partitioned (partitioned) by a partition wall 3 into a plurality of, for example, five rooms.

  That is, the inside of the furnace body 2 is drawn out from the unwinding roll 16 and the substrate supply chamber 11 in which an unwinding roll (an example of the substrate supply unit) 16 around which the substrate K is wound is disposed. A pretreatment chamber 12 for guiding the substrate K and pretreating the surface thereof, and a heating chamber (reaction chamber) for guiding the substrate K pretreated in the pretreatment chamber 12 and forming carbon nanotubes on the surface thereof 13), a post-treatment chamber 14 for guiding the substrate K on which the carbon nanotubes are formed in the heating chamber 13 and performing post-treatment, and a substrate K that has been post-treated in the post-treatment chamber 14 is wound up. And a substrate recovery chamber (also referred to as a product recovery chamber) 15 in which a take-up roll (an example of a substrate recovery unit) 17 is disposed. Both the rolls 16 and 17 are made of metal or a predetermined resin, and their rotational axes are in the horizontal direction. Therefore, the substrate K drawn (guided) into the heating chamber 13 moves in a horizontal plane and forms carbon nanotubes on the upper surface of the substrate K. The predetermined resin is a resin that releases less gas even at a predetermined degree of vacuum (several KPa, which will be described later) inside the furnace body 2. In the following, the direction in which the substrate K is sent out is referred to as the front-rear direction, the winding roll 17 side is the front side, and the unwinding roll 16 side is the rear side. Moreover, the direction orthogonal to the front-rear direction on the horizontal plane is referred to as the left-right direction.

  In the pretreatment chamber 12, the surface of the substrate K, in particular, the surface (upper surface) for forming carbon nanotubes, application of a passive film, catalyst fine particles for forming carbon nanotubes, specifically, iron fine particles ( Metal fine particles) are applied. For cleaning, alkali cleaning or UV ozone cleaning is used. In addition, as a method for applying the passive film, a roll coater or LPD is used. As a method for applying the catalyst fine particles, sputtering, vacuum deposition, roll coater or the like is used.

In the post-processing chamber 14, the cooling of the substrate K and the inspection of the carbon nanotubes formed on the surface of the substrate K, that is, the upper surface are performed.
In the substrate recovery chamber 15, a protective film is attached to the lower surface (rear surface) of the substrate K, and the substrate K, which is a stainless steel plate to which the protective film is attached, is taken up by the take-up roll 17. The reason why the protective film is attached to the lower surface of the substrate K is to protect the carbon nanotubes formed on the wound substrate K when the substrate K is wound.

  As described above, five chambers are formed in the furnace body 2 by the partition walls 3, and of course, slits 7 through which the substrate K can pass are formed at the same height in each partition wall 3. Has been.

  As shown in FIG. 2, the rolls 16 and 17 are each driven by an AC servomotor 5 disposed outside the furnace body 2. In other words, each AC servomotor 5 arranged outside the furnace body 2 has its drive shaft passing through the left or right side wall of the furnace body 2 and connected to the rotation shafts of the rolls 16 and 17. . As a matter of course, a seal portion (for example, a magnetic seal) 6 is provided in a through portion of the drive shaft on the side wall of the furnace body 2 in order to maintain the degree of vacuum inside the furnace body 2.

Here, the heating chamber 13 will be described in detail.
As shown in FIG. 1, a heat insulating material 4 having a predetermined thickness is attached to the inner wall surface forming the heating chamber 13. The partition wall 3 and the heat insulating material 4 attached to the partition wall 3 include a slit 7 (7A) for drawing the substrate K from the pretreatment chamber 12 into the heating chamber 13, and the substrate K in the heating chamber 13. The slits 7 (7B) for sending out to the post-processing chamber 14 are formed at the same height. A plate-like quartz glass table 8 on which the substrate K is placed is fixed across the front and rear slits 7 (7A, 7B). Therefore, the quartz glass base 8 prevents the occurrence of slack without giving a great tension to the substrate K by placing and sliding the substrate K fed from the unwinding roll 16 to the winding roll 17 on its upper surface. To do.

  As shown in FIGS. 1 and 2, a plurality of, for example, 17 gas supply units 30 are horizontally arranged in the heating chamber 13 in the front-rear direction. As shown in FIGS. 3 and 4, each gas supply unit 30 is made of a raw material gas (for example, a lower hydrocarbon gas such as acetylene, methane, or butane) or a mixed gas (for example, a mixture of nitrogen gas and hydrogen gas). ) From the gas supply source 33 outside the furnace body 2 into the heating chamber 13, and a rectangular shape for guiding the source gas or mixed gas supplied through the gas supply pipe 34 to the upper surface of the substrate K A duct 31, a spacer 39 that adjusts the gap between the duct 31 and the quartz glass base 8, a gas discharge pipe 36 that discharges the source gas or mixed gas guided to the upper surface of the substrate K to the outside of the furnace body 2, The vacuum pump 37 is arranged outside the furnace body 2 and connected to the gas discharge pipe 36. The mixed gas may be a single inert gas such as nitrogen gas or helium gas, or may be a mixture of an inert gas and a reducing gas.

  Here, the gas supply pipe 34 supplies raw material gas or mixed gas to the duct 31 from the gas supply port at the lower end thereof. A gas dispersion member 41 made of porous silica having a cylindrical body and a hemispherical lower end is disposed at the gas supply port, and a raw material gas or mixed gas supplied to the duct 31 from the gas supply port The gas is dispersed radially to reach the upper surface (surface) of the substrate K at a uniform density.

  The duct 31 has a hollow rectangular parallelepiped shape with an open lower end surface, and includes gas supply holes 32 formed in the top plate for penetrating the gas supply pipe 34 and left and right side plates for penetrating the gas discharge pipe 36. Gas discharge holes 35 are formed in the lower part. Further, the duct 31 is configured such that the height from the substrate K to the lower surface of the top plate (the top wall surface of the duct 31) is equal to or greater than the hydraulic diameter D expressed by the following equation (1).

D = 4a × b / (2a + 2b) (1)
However, a shows the length of the left-right direction (or front-back direction) in the horizontal cross section of the duct 31, and b shows the length of the front-back direction (or left-right direction) in the horizontal cross section.

  Hereinafter, among these ducts 31, the first duct 31 </ b> A, the second duct 31 </ b> B,... Are referred to from the rearmost side (unwinding roll 16 side), and the frontmost side (winding roll 17 side) is referred to as the seventeenth duct 31 </ b> Q. . The spacer 39 is in contact with the left and right edges of the lower end portion of the duct 31 at the upper end surface, and is in contact with the upper surface of the quartz glass table 8 at the lower end surface to support the duct 31, thereby the duct 31 and the quartz glass. The clearance with the base 8 is adjusted. The gap is set to a value that exceeds the thickness of the substrate K in order to prevent contact between the duct 31 and the substrate K, but is set to a value at which the lower end surface of the duct 31 is sufficiently close to the substrate K. This is because when the lower end surface of the duct 31 is sufficiently close to the substrate K, the source gas or mixed gas from the duct 31 is uniformly guided to the substrate K and is prevented from flowing out of the duct 31. More specifically, the gap is set to a level obtained by adding 1.5 to 10 times (preferably 2 to 5 times) the height of the carbon nanotubes to the thickness of the substrate K on which the carbon nanotubes are formed. . In order to precisely adjust the gap, a variety of spacers 39 having different heights in units of 0.05 to 0.10 mm are prepared, and the gap is adjusted in units of 0.05 to 0.10 mm. To get. Note that the duct 31 and the spacer 39 are both made of quartz glass in order to require heat resistance and suppress the influence of thermal expansion and gas leakage. By the way, the vacuum pump 37 sucks the raw material gas or mixed gas guided to the upper surface of the substrate K to the outside of the furnace body 2 through the gas discharge pipe 36 and depressurizes the inside of the heating chamber 13 to a predetermined degree of vacuum. Is. This reduced pressure value is maintained in the range of 3 kPa to 10 kPa, preferably 3 kPa to 4 kPa. The upper limit of 10 kPa is a limit value in terms of suppression of soot and tar. The purpose of depressurizing the inside of the heating chamber 13 to a predetermined degree of vacuum is to (1) lengthen the mean free path of the source gas or mixed gas in the heating chamber 13 to improve the diffusivity, thereby providing the gas to the substrate K. (2) To reduce the convective heat transfer in the heating chamber 13 to make the temperature distribution of the substrate K uniform. (3) The details will be described in [Experiment] described later. However, by controlling the heating temperature of the substrate K, the growth process of the carbon nanotubes includes a process of growing the carbon nanotubes to a predetermined length, and an amorphous layer is grown on the carbon nanotubes grown to the predetermined length. This is because it is divided into processes.

As shown in FIG. 1, below the quartz glass table 8 in the heating chamber 13, a plurality of cylindrical (or rod-shaped) heating elements 22 for heating the substrate K in the heating chamber 13 are formed. A heating unit 21 is provided. These heating elements 22 are arranged at predetermined intervals in the front-rear direction, and extend from the rear slit 7 (7A) to the seventeenth duct 31Q which is the frontmost duct. The plane including these heating elements 22 is arranged parallel to the substrate K and the quartz glass table 8, that is, horizontally. Further, as shown in FIG. 3, each of the heating elements 22 receives power from the heater power source 23 and heats the surroundings with far infrared rays, and a nonmetallic resistance heating element is used. Specifically, silicon carbide, molybdenum silicide, lanthanum chromite, zirconia, graphite, or the like is used. In particular, silicon carbide and molybdenum silicide are used in a nitrogen gas or hydrogen gas atmosphere, lanthanum chromite is used only in the air, and graphite is used in an inert gas atmosphere (reducing atmosphere). Each heating element 22 can freely adjust the heating temperature by adjusting the power from the heater power source 23. By the way, since the quartz glass table 8 reaches the left and right side walls in the heating chamber 13, the raw material gas or the mixed gas is prevented from leaking from the duct 31 and reaching the heating unit 21, and is transparent. The substrate K is efficiently heated by transmitting far infrared rays from the unit 21. Further, in order to eliminate the influence of the raw material gas, the constituent members of the heating chamber 13 are made of an inorganic material such as silicon dioxide (SiO ₂ ), alumina (Al ₂ O ₃ ) other than those described for the materials. ing. Note that the inner wall surface of the heat insulating material 4 may be covered with quartz glass in order to prevent intrusion of foreign matter in the heating chamber 13.

  The heating chamber 13 is divided into a plurality of steps (five in this embodiment) in the front-rear direction. Specifically, as shown in FIG. 5, from the rear slit 7 (7A) to the third duct 31C is the first substrate temperature equalization (temperature raising) step, and from the fourth duct 31D to the seventh duct. Up to 31G is the first carbon nanotube growth step. The eighth duct 31H to the tenth duct 31J is the second substrate temperature equalization (temperature increase) step, and the eleventh duct 31K to the sixteenth duct 31P is the second carbon nanotube growth step. Furthermore, the 17th duct 31Q is a slow cooling process. That is, the gas supplied from the gas supply source 33 to the duct 31 is a mixed gas in the case of the first duct 31A to the third duct 31C, a raw material gas in the case of the fourth duct 31D to the seventh duct 31G, and the eighth duct 31H to the eighth duct. 10 duct 31J is a mixed gas, 11th duct 31K to 16th duct 31P is a raw material gas, and 17th duct 31Q is a mixed gas. Of the carbon nanotube growth steps, the first one grows the length of the carbon nanotubes (first step), and the second one grows the amorphous layer of the carbon nanotubes (in the second step). is there). On the other hand, each heating element 22 is set to a temperature that appropriately heats the substrate K in the corresponding process, and the temperature change for each process is not intermittently performed.

Hereinafter, the manufacturing method of the carbon nanotube by the said manufacturing apparatus is demonstrated.
First, the substrate K is pulled out from the unwinding roll 16, the slits 7 of the partition walls 3 in the preprocessing chamber 12, the heating chamber 13, and the postprocessing chamber 14 are inserted, and the leading ends thereof are wound on the winding roll 17. Here, since the substrate K is placed on the quartz glass table 8, it is not necessary to apply a great amount of tension, and the force required for feeding the substrate K is only the frictional force between the substrate K and the quartz glass table 8. Is enough. For this reason, the unwinding roll 16 and the winding roll 17 are sufficiently driven only by the AC servo motor 5.

  In the pretreatment chamber 12, after the substrate K drawn from the unwinding roll 16 is cleaned, a passive film such as silica or alumina is applied to at least the entire upper surface, and a metal film is further applied to the upper surface of the passive film. The catalyst fine particles are applied. The metal of the catalyst fine particles is, for example, iron (Fe), cobalt (Co), or nickel (Ni).

  In the heating chamber 13 into which the substrate K coated with the catalyst fine particles is drawn, the vacuum pump 37 is maintained at a predetermined degree of vacuum, for example, in the range of 3 kPa to 10 kPa, preferably 3 kPa to 4 kPa as described above. Yes. The substrate K is heated by the heating unit 21 when moving in the heating chamber 13. The temperature of the substrate K will be described. As shown in FIG. 5, the temperature of the substrate K passes through the rear slit 7 (7A) and reaches below the first duct 31A, and the first duct 31A to the seventh It moves below the duct 31G with a constant temperature of 640 ° C. to 720 ° C. (which is the first temperature). The substrate K is further heated below the eighth duct 31H to the tenth duct 31J, and remains at a constant temperature of 780 ° C. to 840 ° C. (second temperature) below the eleventh duct 31K to the sixteenth duct 31P. Moving. Further, the substrate K is gradually cooled from below the seventeenth duct 31Q until it reaches the front slit 7 (7B).

  Below the first duct 31A to the third duct 31C, the mixed gas is uniformly guided to the upper surface of the substrate K. Further, below the fourth duct 31D to the seventh duct 31G, the source gas is uniformly guided to the upper surface of the substrate K, and the length of the carbon nanotube is grown on the catalyst fine particles on the upper surface of the substrate K. And the carbon nanotube of desired height (length) is formed in the board | substrate K which passed the 7th duct 31G. In addition, the mixed gas is uniformly guided to the upper surface of the substrate K below the eighth duct 31H to the tenth duct 31J. Below the eleventh duct 31K to the sixteenth duct 31P, the source gas is uniformly guided to the upper surface of the substrate K to grow an amorphous layer of carbon nanotubes. As a result, carbon nanotubes having a desired height (length) and a sufficient amorphous layer are formed on the substrate K that has passed through the seventeenth duct 31Q. By the way, the gaps between all the ducts 31 and the quartz glass table 8 are such that the spacer 39 adds 1.5 to 10 times (preferably 2 to 5 times) the height of the carbon nanotubes to the thickness of the substrate K. Since it is set, the source gas or the mixed gas is uniformly guided to the substrate K. Further, since the inside of the heating chamber 13 is set to a predetermined degree of vacuum and the height from the substrate K to the lower surface of the top plate of the duct 31 is equal to or greater than the hydraulic diameter D, the source gas or the mixed gas is more evenly mixed. Led to. Further, the source gas or mixed gas supplied from the gas supply pipe 34 of each duct 31 is sucked by the vacuum pump 37 through the gas discharge pipe 36, so that the gas does not leak out of the duct 31 and other ducts. 31 does not adversely affect the reaction of the raw material gas.

In the post-processing chamber 14, the substrate K is cooled and inspected.
Thereafter, the substrate K is moved into the substrate recovery chamber 15, and a protective film is attached to the lower surface of the substrate K, and the substrate K is wound around the winding roll 17. That is, the substrate K on which the carbon nanotubes are formed is collected as a product. When all the substrates K on which the carbon nanotubes are formed are taken up by the take-up roll 17, they are taken out to the outside.

  Thus, according to the method for producing carbon nanotubes, carbon nanotubes having an amorphous layer with a sufficient thickness are formed, so that carbon nanotubes capable of suppressing aggregation can be produced continuously.

  Further, since the carbon nanotubes are continuously formed without applying a great amount of tension to the substrate K, the warp caused by this tension does not occur, and the substrate K is placed on the flat quartz glass table 8. By preventing the occurrence of slack, carbon nanotubes that do not cause transfer defects can be formed.

  Further, the gap between the duct 31 and the substrate K can be precisely adjusted by the spacer 39, the inside of the heating chamber 13 is set to a predetermined vacuum level, and the height from the substrate K to the lower surface of the top plate of the duct 31 is the hydraulic power. Since the diameter is equal to or larger than the diameter D, the source gas is more uniformly guided to the substrate K, whereby variation in the quality of the carbon nanotubes formed on the substrate K can be suppressed and the yield can be improved.

Moreover, by making the inside of the heating chamber 13 have a predetermined degree of vacuum, the temperature distribution of the substrate K becomes uniform, and higher quality carbon nanotubes can be obtained.
Further, since only the AC servo motor 5 is sufficient for feeding the substrate K, an expensive driving device combining a torque motor and a reduction gear is not required, and the apparatus can be made inexpensive. Furthermore, the feeding of the substrate K can be appropriately controlled by the AC servo motor 5.

In addition, since the raw material gas or the mixed gas does not reach the heating unit 21 by being blocked by the quartz glass table 8, the life of the heating unit 21 can be extended.
Further, the AC servo motor 5 can be driven with low power consumption, and each heating element 22 is set at a constant temperature, and the temperature change for each process is not intermittently performed, so that the power consumption can be greatly reduced. it can.

Moreover, high quality carbon nanotubes can be continuously formed more efficiently by including many (five) steps continuously.
Moreover, although the said Example demonstrated that the inside of the furnace main body 2 was made into the predetermined | prescribed vacuum degree, you may make the inside of the heating chamber 13 into the predetermined | prescribed vacuum degree instead of the whole inside of the furnace main body 2. FIG. In this case, the seal portion 6 is provided in the front and rear slits 7 instead of the drive shaft penetrating portion on the side wall of the furnace body 2.

  By the way, in the said Example, although the post-processing chamber 14 demonstrated cooling the board | substrate K and inspecting a carbon nanotube, what forms the electrode of a battery from the carbon nanotube which was further cooled and inspected It may be.

  Moreover, in the said Example, although the duct 31 demonstrated the hollow rectangular parallelepiped shape which the lower end surface opened, ie, the side view from the left-right direction and the front view from the front-back direction are both rectangular shapes, / Or a trapezoidal shape (square pyramid shape) whose front view spreads downward. In this case, the height from the substrate K to the lower surface of the top plate of the duct 31 is a value obtained by multiplying the value of the formula (1) shown in the above-described embodiment by the ratio (value) shown by the following formula (2). It is said.

(Hydraulic diameter of the lower end surface of the duct 31) / (hydraulic diameter of the lower surface of the top plate of the duct 31) (2)
Thus, the value of the formula (2) is multiplied in order to compensate for the fact that in the case of the quadrangular pyramid shape, the dispersion effect is slightly lower than that of the rectangular parallelepiped shape.

  Further, in the above embodiment, the carbon nanotubes are described as being wound on the winding roll 17 together with the substrate K. However, the step of peeling the carbon nanotubes from the substrate K (an example of the third step, hereinafter referred to as a peeling step) is performed. The carbon nanotubes peeled off from the substrate by this peeling step may be recovered.

Hereinafter, this peeling process will be described in detail.
[Peeling process]
Oxygen is supplied to the substrate K that has undergone the slow cooling process, that is, the substrate K on which carbon nanotubes having a sufficiently thick amorphous layer are formed. The amount of oxygen supplied is 0.1 to 0.5 μL / min per unit area (cm ² ) of the substrate K from which the carbon nanotubes are to be peeled off. The carbon nanotubes are peeled from the substrate K by continuing the supply of such a trace amount of oxygen for 5 to 20 minutes. The supply of the trace amount of oxygen is realized by supplying a mixed gas of oxygen and an inert gas (for example, nitrogen).

  Thus, the base part of the carbon nanotubes peeled off from the substrate K by the trace amount of oxygen is covered with the first amorphous layer. In this first amorphous layer, there are short carbon nanotubes generated during the growth process. The upper part of the carbon nanotube is covered with a second amorphous layer. For this reason, each carbon nanotube in the carbon nanotube is bonded by van der Waals force by the first amorphous layer and / or the short carbon nanotube and the second amorphous layer. That is, the carbon nanotube maintains the sheet shape by this van der Waals force. Therefore, the carbon nanotubes peeled off from the substrate K by a small amount of oxygen can be taken up by the take-up roll 17 and collected as a product.

  The carbon nanotubes collected in this way are used as they are for electrode members and heat radiating members. Moreover, you may support and use the back surface (base part end) of the said carbon nanotube with an electroconductive member as needed. Examples of the support by the conductive member include formation of a conductive thin film (copper, aluminum, silver, etc.) by vacuum deposition or sputtering, arrangement of carbon paper, and the like.

  By the way, in the carbon nanotube manufacturing method according to the above-described embodiment of the present invention, specific conditions such as the heating temperature of the substrate K and the pressure in the heating chamber 13 are numerically shown. The experiment and the result will be described below.

[Experiment 1]
In order to know the dependence of the length of carbon nanotubes on the heating temperature and pressure, the heating temperature is changed and the carbon nanotubes are grown at four pressures of 0.2 kPa, 1 kPa, 3 kPa, and 3.4 kPa. The lengths of these carbon nanotubes were measured. The heating time was constant at 10 minutes.

As shown in FIG. 6, the length of the carbon nanotube (CNT) did not grow above a predetermined temperature when the pressure was 3 kPa or higher, and grew even when the pressure was lower than 3 kPa.
As a result, it was found that a pressure of 3 kPa or more is suitable for controlling the growth of the length of the carbon nanotube by the heating temperature.

[Experiment 2]
In order to know the dependence of the length of the carbon nanotube on the heating time and pressure, the carbon nanotube was changed by changing the heating time from 0 to 30 minutes and changing the pressure to three types of 0.2 kPa, 1 kPa, and 3 kPa. The length of these carbon nanotubes was measured.

As shown in FIG. 7, when the length of the carbon nanotube was up to 15 minutes, it grew in proportion to the heating time, and when it was 15 minutes or longer, it did not grow any longer.
Thereby, in order to grow the length of the carbon nanotube, it was obtained that the heating time was suitable up to about 15 minutes.

[Experiment 3]
In order to know the dependence on the heating temperature and pressure for increasing the bulk density of carbon nanotubes (amorphous layer growth), the heating temperature was changed from 700 ° C. to 820 ° C., and the heating time was changed to 0 minutes, 10 minutes, Carbon nanotubes were grown in six ways of 15 minutes, 20 minutes, 25 minutes, and 30 minutes, and the bulk density of these carbon nanotubes was measured.

As shown in FIG. 8, the bulk density of the carbon nanotubes grew in proportion to the heating time.
Thereby, in order to grow the amorphous layer of a carbon nanotube, the result that it was suitable for making heating time long was obtained.

[Experiment 4]
In order to know the dependence on the heating temperature and the supply amount of the source gas for increasing the bulk density of the carbon nanotube (growth of the amorphous layer), the heating temperature is changed from 700 ° C. to 820 ° C., and the supply amount of the source gas the ^{200sccm (3.38 × 10 -2 Pa ·} m 3 /sec),400sccm(6.76×10 -2 Pa · m 3 /sec),600sccm(10.14×10 -2 Pa · m 3 / sec ) Were grown as carbon nanotubes, and the bulk density of these carbon nanotubes was measured.

As shown in FIG. 9, the bulk density of the carbon nanotubes hardly depended on the supply amount of the raw material gas.
Thereby, in order to grow an amorphous layer on a carbon nanotube, the result was obtained that the supply amount of the source gas can be arbitrarily selected from 200 sscm to 600 sscm.

DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Furnace main body 5 AC servo motor 6 Seal part 7 Slit 8 Quartz glass stand 13 Heating chamber 21 Heating part 31 Duct 31A First duct 31B Second duct 32 Gas supply hole 34 Gas supply pipe 35 Gas discharge hole 36 Gas discharge Tube 39 Spacer 41 Gas dispersion member

Claims (6)

A method for producing carbon nanotubes by a thermal CVD method,
A first step of growing carbon nanotubes to a predetermined length on the substrate by supplying a source gas to the substrate at a first temperature;
A second step of growing an amorphous layer on the carbon nanotubes grown to a predetermined length by supplying a source gas to the substrate at a second temperature that is higher than the first temperature. A method for producing carbon nanotubes.   The method for producing carbon nanotubes according to claim 1, wherein the first temperature is 640 ° C or higher, and the second temperature is 50 to 200 ° C higher than the first temperature.   The method for producing carbon nanotubes according to claim 1 or 2, wherein the first temperature and the second temperature are constant.   The method for producing carbon nanotubes according to any one of claims 1 to 3, wherein the pressure of the raw material gas supplied in the second step is 3 to 10 kPa.   5. The method according to claim 1, further comprising a third step in which oxygen is supplied to a carbon nanotube having a predetermined length on which an amorphous layer has been grown, and then the carbon nanotube is separated from the substrate. The manufacturing method of the carbon nanotube as described in any one of. A carbon nanotube with an amorphous layer grown, produced by a thermal CVD method,
The carbon nanotubes are grown to a predetermined length by supplying a source gas to a substrate at 640 ° C. or higher,
The amorphous layer is grown by supplying a source gas to the substrate at a temperature higher by 50 to 200 ° C. than the temperature at which the carbon nanotubes are grown to a predetermined length.
A carbon nanotube which is peeled from the substrate.

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