JP5182237B2 - Manufacturing method of electron source electrode - Google Patents

Description

  The present invention relates to a method for producing a field emission type electron emission electrode using carbon nanotubes.

  Carbon nanotubes are produced by a chemical vapor deposition method (CVD method) or an arc discharge method, and a sheet in which carbon atoms are regularly arranged in a hexagonal shape (hereinafter referred to as graphene sheet) is rounded into a cylindrical shape. It has attracted attention as a new material because of its unique properties.

  A single graphene sheet tube is referred to as a single-walled carbon nanotube, and has a diameter of 1 to several nm and a length of about 1 to several μm. On the other hand, a graphene sheet tube in which a plurality of layers are concentrically overlapped is referred to as a multi-walled carbon nanotube, and its diameter is several nm to several tens of nm. A graphene sheet rounded into a substantially conical shape is referred to as a carbon nanohorn, and there is a single-layer or multi-layer carbon nanohorn. In the present invention, these are collectively referred to as carbon nanotubes (hereinafter referred to as CNT). Further, this single CNT is referred to as a CNT fiber, and a collection of the CNT fibers is referred to as a CNT aggregate.

  The tip of this CNT has very high field electron emission characteristics, and its practical application as a field emission cold cathode material for fluorescent display tubes, X-ray tubes, field emission displays (FEDs), etc. has been studied. Yes.

Since CNTs are almost always produced alone by arc discharge method, CVD method, etc., CNT electrode element using this is formed by mixing CNT fiber with conductive paste material and forming film on cathode substrate by screen printing etc. Is generally used. As the paste, for example, a mixture of 1 to 33% by weight of CNT and glass powder is added and kneaded by adding a terbinol solution of ethyl cellulose as a dispersant and a binder solution, and this is used as shown in FIG. It is manufactured by screen printing, firing in the air, and raising with a tape (Patent Document 1).

JP 2007-115675 A

  The method using the above paste has a lot of CNT loss because a large amount of paste remains on the screen, and oxidation of the metal substrate occurs when removing 3 to 20 times the amount of resin by calcination, Causes CNT combustion and damage deterioration. For this reason, emission characteristics were poor, unstable and easy to discharge, and durability was not sufficient.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that a CNT high density deposition film can be obtained by preparing a CNT dispersion and filtering it with a membrane filter. Then, this was transferred to a substrate, irradiated with an electron beam in a vacuum environment to fix the CNTs on the substrate, and brushed to produce an electron source electrode. That is, in the present invention, a dispersion liquid in which carbon nanotubes are dispersed in a dispersion medium is filtered with a membrane filter, the carbon nanotubes deposited on the membrane filter are transferred to a substrate, and irradiated with an electron beam in a vacuum environment. Is provided on the substrate, and then the carbon nanotubes are raised, and a method for producing an electron source electrode is provided.

  According to the present invention, almost 100% of the raw material CNT is deposited and transferred, so there is no loss of CNT. It is not necessary to heat and burn impurities contained in a resin or the like in an oxygen environment, there is no CNT damage, and an electron source electrode with excellent emission characteristics and good durability can be obtained.

It is a figure which shows the state which is filtering the CNT dispersion liquid with a membrane filter. It is process drawing which shows the state which is transferring the CNT deposited on the membrane filter to a board | substrate. It is a figure which shows the state which irradiates the electron beam and fixed to CNT transferred by the board | substrate. It is a graph which shows the SEM photograph and emission electric field current density characteristic of the CNT electrode which raised by irradiating YAG laser to CNT adhering on a board | substrate. It is a figure which shows the emission distribution of the said CNT electrode. It is a graph which shows the SEM photograph and emission electric field current density characteristic of the CNT electrode which raised CNT fixed on the board | substrate with the tape. It is a figure which shows the emission distribution of the said CNT electrode. It is a figure which shows typically the method of adhering CNT with the conventional paste.

  The carbon nanotube (CNT) used in the present invention is excellent in electron emission characteristics such as a low emission voltage and a high allowable current density, regardless of the type such as single-walled, double-walled, or multilayered, and the manufacturing method such as the CVD method or the arc method. Is suitable. In general, the smaller the diameter (single layer) of CNT, the lower the emission voltage, and the higher the number of layers and the higher the crystallinity, the higher the allowable current density and the better the durability. The purity of the CNT obtained by the conventional arc discharge method is generally 70% by weight, but in the present invention, the purity is preferably 80% by weight or more, preferably 90% by weight or more. This purity is measured by observing using a scanning electron microscope (SEM), and means the proportion of CNT in a CNT aggregate containing impurities such as amorphous carbon. Such a CNT can be obtained, for example, by a method for producing a tape-like CNT disclosed in Japanese Patent Application Laid-Open No. 2004-292184.

  The dispersion medium for dispersing CNTs may be an organic solvent, and can be widely selected from, for example, lower alcohols such as methanol and isopropanol, ketones such as acetone and methyl ethyl ketone, chlorinated hydrocarbons such as dimethylformamide, ether and chloroform. . The dispersion concentration depends on the dispersibility of CNTs, but may be about 0.1 to 3 mg of CNTs with respect to 40 ml of the dispersion medium.

Dispersion can be performed by irradiating ultrasonic waves for several minutes to several tens of minutes using, for example, an ultrasonic oscillator or a vibration device.
This dispersion is filtered through a membrane filter. The material of the membrane filter should be excellent in the resistance to the solvent used and have good CNT releasability. Polycarbonate (PC), polytetrafluoroethylene (PTFE, generic name Teflon), polypropylene (PP), etc. are suitable. It is. The pore size (pore size) of the filter is about 0.1 to 5 μm, although it depends on the CNT type and dispersion state. The advantage of this method is that, unlike ordinary filtration deposition, it is possible to deposit CNTs with very high dispersion evenly on a CNT dispersion liquid that is easily re-aggregated because of high-speed deposition.

  At this time, impurities such as amorphous carbon and nanoparticles smaller than CNT can be simultaneously filtered and purified. Moreover, a large-diameter impurity can also be filtered and refined by sequentially filtering a filter having a pore diameter of 5 to 10 μm through which CNTs pass in order from the larger one. As the filter, a general vacuum filter can be used.

  Briefly explaining the vacuum filter shown in FIG. 1, the CNT dispersion liquid is introduced into the container on the filter in the flask under the membrane filter together with the vacuum pump or simultaneously with or before the vacuum. Since the lower part of the filter is in a reduced pressure state, the solvent is sucked to the lower part at once, and CNT is quickly deposited on the filter within several seconds to several tens of seconds.

The CNT is deposited in a thickness of 0.05 to 3 μm and a weight density of 0.1 to 3 μg / mm ² . A flow for transferring the deposited CNT film to the substrate is shown in FIG.
When the filter on which the CNTs are deposited is placed on a metal substrate for an electron source and a volatile solvent such as methanol is infiltrated into the CNTs, the solvent evaporates when pressurized at a pressure of about 0.5 to ²⁰ kg / cm ^2. Accordingly, the CNT film is transferred to the substrate side. This is considered to be caused by a difference in adhesion to the CNT between the membrane filter and the substrate surface. By matching the CNT deposition shape to the substrate shape, the used CNTs can be deposited on a 100% substrate.

The substrate is conductive. This includes Ni alloys such as stainless steel and Fe-Ni alloys, metals such as Al, Cu, W, Ti, Co, Cr, Mo, Nb, Mn, Si, and alloys thereof, as well as glass and ceramics. There are those in which a metal or a conductive semiconductor is deposited on the surface by vapor deposition or the like. Examples of semiconductors include n-type oxide semiconductors such as ITO (tin-doped indium oxide), ZnO, SnO ₂ , and TiO ₂ with good conductivity. The shape and size of the substrate are determined according to the use of the substrate, etc., but the basic shape is usually a plate shape such as a circle, a quadrangle, or a rectangle.

The surface to which the CNT film is attached can be subjected to a pre-treatment such as mirror finishing or degreasing treatment, oxide film removal such as heat treatment ion bombardment.
In the state in which the CNT is transferred, the bonding property between the CNT and the substrate is weak and needs to be fixed. In general CNT electron source manufacturing methods by screen printing (JP 2007-115675, JP 2008-176968, JP 2008-243789, etc.), low-melting-point glass particles are mixed in advance in the CNT paste to perform printing. After film formation, a method is known in which glass is melted and fixed during firing at 350 to 500 ° C. in air or nitrogen atmosphere. This method requires baking in the atmosphere or in an oxidizing atmosphere to remove a large amount of binder resin (CNT weight ratio 20 to 70 times) in the paste, and cannot be applied to a metal substrate to be oxidized. It is a method. Although low melting point glass fine particles can also be used in this method, fixing with a non-conductive material is not preferable because it impairs the electron emission properties of the CNT and causes damage such as discharge due to charge-up.

Therefore, in the present invention, a method is adopted in which the CNT transferred onto the substrate is irradiated with an electron beam in a vacuum environment to fix the CNT to the substrate.
As a method of fixing a 100% CNT (including carbon impurities such as nanocarbon and amorphous carbon) film and a metal substrate, a method of irradiating an electron beam using CNT as an electron source on a CNT film formation surface in a vacuum is used. is there. In this method, as shown in FIG. 3, when a substrate on which CNTs are formed in a vacuum is irradiated with an electron beam having an energy of 5 to 20 keV, the electron beams pass through the CNT film and reach the substrate surface. The CNT film having a thickness of about several μm transmits an electron beam of about 10 keV, and can be fixed by reacting the metal and the CNT film. Although this fixing mechanism is not clear, since CNT and metal are not altered and damaged, contents such as oxygen, hydrogen, carbon dioxide gas, and water in the metal and low energy secondary electrons are emitted by electron beam irradiation, It is considered that the carbon-based impurities adhering to the CNT are adhered to the substrate by reacting, changing, and forming a film. Also, not only the substrate but also the CNTs are fixed, and by changing the energy of the electron beam, the transmission distance of the electron beam is changed to control how much the CNT film is fixed from the substrate. can do.

The CNT film on which the substrate surface and CNTs in the vicinity thereof are fixed by electron beam irradiation is subjected to raising treatment for emitting electrons by a method such as laser irradiation, plasma surface treatment, and adhesive tape raising. In the raising treatment with a YAG laser, a pulse YAG laser having a pulse width of about 10 ns and a wavelength of 532 nm is focused on a spot or line, and the entire surface of the CNT film is irradiated in an energy density range of 50 to 500 mJ / cm ² .

  The number of irradiation is about 1 to several times, and the whole is raised. Since this laser irradiation treatment acts on the extreme surface layer portion, the order of the fixing treatment step and this step can be reversed. The details of the raising process by laser irradiation are disclosed in JP-A-2005-166432.

  In the raising method using an adhesive tape, a tape that has a dense and appropriate adhesiveness on the CNT surface and the adhesive is difficult to peel off from the tape is stuck on the CNT surface without any gap, and the tape is peeled off at a constant angle and speed. At the time of peeling, the CNT portion not fixed to the substrate side is peeled off together with the tape, the boundary portion between the CNT region fixed to the substrate and the non-fixed region is peeled off, and the CNT film on the substrate side is raised.

  Tape-like CNT described in Example 1 of JP-A No. 2004-292184 was used. This tape-shaped CNT is a high-crystal, high-purity multi-layer CNT having a diameter of about 10 nm manufactured by an arc discharge method in the atmosphere, and has a low emission voltage of single-walled CNT and a high allowable current density of multi-walled and highly crystalline CNT. And durability.

0.5 mg of this CNT was added to 40 ml of methanol, and ultrasonic waves were applied for 60 minutes to sufficiently disperse.
The CNT dispersion was filtered with a vacuum filter shown in FIG. As the membrane filter, PTFE having a pore diameter of 3 μm was used. Filtration was completed within 5 seconds, and a deposited CNT film having a thickness of 0.6 μm and a weight density of 0.6 μg / mm ² was formed on the membrane filter.

This deposited CNT film was placed on a stainless steel substrate having a diameter of 4 mm, a solvent was added , the pressure was applied at 8 kg / cm ² , and transfer was performed as shown in FIG.
Subsequently, the electron beam of 10 keV was irradiated in vacuum to fix the CNTs on the substrate, and the CNT film fixed on the substrate was brushed using a laser irradiation method.

Laser irradiation was performed once on the entire surface of the CNT film at an energy density of 220 mJ / cm ² using a pulse YAG laser having a pulse width of about 10 ns and a wavelength of 532 nm.
FIGS. 4 and 5 show the SEM photograph of the surface of the CNT electrode manufactured by the above method, the emission field current density characteristics, and the measurement result of the emission distribution. The SEM photograph shows that the CNT is raised and fixed to the substrate, and the electric field current density characteristic shows that the emission threshold electric field is as low as 1.1 V / μm and the uniformity is high.

The CNT film fixed on the substrate in Example 1 was subjected to raising treatment using an adhesive tape raising method.
In the case of raising the adhesive tape, a tape having a peel strength of 3 N / cm was attached to the CNT film and peeled off at 200 mm / min while maintaining an angle of 165 °.

  The surface SEM photograph of the CNT electrode manufactured by the above method and the results of measuring the emission characteristics and emission distribution are shown in FIGS. It can be seen that the CNTs are fixed very thinly on the substrate, and the emission threshold electric field is slightly higher than that of the laser treatment method of Example 1, but an electrode with better uniformity can be obtained.

  According to the present invention, an electron source electrode having excellent emission characteristics can be efficiently manufactured, and thus can be widely used in various electric devices and electronic devices.

Claims (1)

A dispersion liquid in which carbon nanotubes are dispersed in a decomposition medium is filtered through a membrane filter made of polycarbonate, polytetrafluoroethylene, or polypropylene and having a pore diameter of 0.1 to 5 μm, and deposited on the membrane filter. the carbon nanotubes were transferred to a metal substrate for an electron source, by irradiating an electron beam under a vacuum environment fixed carbon nanotubes on the metal substrate, then the manufacturing method of the Ru electron source electrodes brushed carbon nanotubes a is, the a dispersion medium volatile solvent, wherein the carbon nanotubes deposited on a membrane filter placed on the metal substrate, in a state where a new volatile solvent impregnated in the carbon nanotube, 0.5 by pressurizing at a pressure of 20 kg / cm ^2, the child transferred to the metal substrate Method of manufacturing an electron source electrode and said.

Images