JP2004276232A - Carbon nanotube dispersion liquid and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dispersion liquid capable of providing flat carbon nanotube film by uniformly dispersing easily flocculating carbon nanotubes and a method of manufacturing the dispersion, and an electronic emission source and a light emitting display element obtained by using the dispersion liquid. <P>SOLUTION: The carbon nanotube dispersion liquid comprises a polymeric compound having a plurality of amino groups, an organic solvent, and carbon nanotubes. The electronic emission source and the light emitting display element are obtained by using the dispersion liquid. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a uniform carbon nanotube dispersion and a method for producing the same. Furthermore, the present invention relates to an electron emission source and a display light emitting device obtained by using the dispersion.

  Carbon nanotubes are considered to be widely applied to electron sources, conductive films, batteries, and the like, and for that purpose, it is necessary to uniformly disperse nanoparticle powder of carbon nanotubes. However, since carbon nanotubes are easily aggregated and difficult to disperse, there is a problem that sufficient dispersion is not possible even when ultrasonic waves or the like are used.

  As a method of dispersing carbon nanotubes, a method of dispersing carbon nanotubes or carbon nanofibers in an organic solvent containing a dipolar aprotic solvent by ultrasonic irradiation or stirring, and performing fine particle separation by centrifugation or filtration. (For example, see Patent Document 1). However, in this method, since the carbon nanotubes are not sufficiently dispersed, if they are sorted and then slurried in the subsequent steps, they may re-aggregate when applied to a substrate or the like. For this reason, a uniform and flat carbon nanotube film could not be obtained. Therefore, when manufacturing an electron-emitting device using a carbon nanotube film as an electron-emitting source, if the insulating film is not thickened, a short circuit occurs, the electron-emitting device does not function, and even if the insulating film is thickened, There is a problem that the performance as a device is deteriorated, for example, the electron emission start voltage is increased.

JP-A-2002-255528

  An object of the present invention is to provide a dispersion liquid capable of uniformly dispersing carbon nanotubes that are easily aggregated and obtaining a flat carbon nanotube film. Another object is to provide an electron emission source obtained by using the dispersion and a display light emitting element having the electron emission source.

  The present invention relates to a carbon nanotube dispersion liquid comprising a polymer compound having a plurality of amino groups, an organic solvent, and carbon nanotubes.

  The present invention also relates to a method for producing a carbon nanotube dispersion in which carbon nanotubes are dispersed in an organic solvent containing a polymer compound having a plurality of amino groups.

  Further, the present invention relates to an electron emission source and a display light emitting device obtained by using a carbon nanotube dispersion liquid.

  ADVANTAGE OF THE INVENTION According to this invention, the carbon nanotube dispersion liquid in which the carbon nanotube fine particles which are easy to aggregate are uniformly dispersed can be obtained. An electron emission source and a light emitting display device using a flat carbon nanotube film obtained by using the carbon nanotube dispersion obtained in the present invention have excellent performance.

Embodiment 1
The carbon nanotube dispersion of the present invention comprises a polymer compound having a plurality of amino groups, carbon nanotubes, and an organic solvent.

  Carbon nanotubes are produced by arc discharge or chemical vapor deposition (CVD). By subjecting the produced carbon nanotubes to a heat treatment at 400 to 600 ° C. or an acid treatment with sulfuric acid, hydrochloric acid, nitric acid, hydrogen peroxide, or the like, impurities such as amorphous carbon are removed, and high-purity carbon nanotubes are obtained. Can be.

  As the carbon nanotube, a single-walled carbon nanotube having a single-layer structure to a multi-walled carbon nanotube having a multi-layer structure are preferably used. As the diameter of the carbon nanotube is smaller, the electric field concentration is more likely to occur and the electron emission is easier. Therefore, a single-wall carbon nanotube or a double-wall carbon nanotube is particularly preferable for the electron source. It is preferable that the diameter of the carbon nanotube is 1 to 10 nm and the length is 0.1 to 10 μm. Single-walled carbon nanotubes having a diameter of less than 1 nm tend to be greatly deteriorated by electron emission and have a shorter life.

  As the organic solvent, those having 4 or more carbon atoms having a hydroxyl group are preferable in that the carbon nanotubes are easily dispersed. Specific examples include, but are not limited to, butyl carbitol (BC), benzyl alcohol, diethylene glycol, cyclohexanol, terpineol, and abietinol. In particular, α-terpineol is desirable from the viewpoint of dispersibility of carbon nanotubes. In some cases, butyl carbitol acetate (BCA) is mixed and used.

  The amount of the organic solvent is adjusted by changing the mixing ratio depending on the film forming method. For example, in the case of a printing paste, the weight ratio of the organic solvent to the carbon nanotubes 1 is preferably 85 to 98, and the weight ratio of the organic solvent is preferably 98 or more for spin coating or spraying.

  Since the polymer compound having a plurality of amino groups used in the present invention has an amino group having an affinity for carbon nanotubes and has a portion having an affinity for a solvent, it acts as a dispersant. I do. Amino groups are excellent in that they can interact with non-structural defects of carbon nanotubes.

  Here, the high molecular compound refers to a polymer such as a polymer or an oligomer. However, when a monomer is easily polymerized in the reaction system, it is included as a high molecular compound. Among these, it is preferable to use them in an oligomer state, since carbon nanotubes can be suitably dispersed.

  Examples of the polymer compound having a plurality of amino groups include a base comb-shaped block copolymer and a silane coupling agent. By adding these, it is possible to uniformly disperse the easily aggregated carbon nanotube fine particles. .

  As shown in FIG. 1, the base comb block copolymer has an amino group having an affinity for carbon nanotubes in the main chain 1a, and a functional group (for example, a hydroxyl group, a carboxyl group, etc.) which functions as a solvate in the side chain 1b. , A carbonyl group, an ester group, etc.).

  The dispersing action of the base comb block copolymer will be described with reference to FIG. 2 represents a carbon nanotube and 3 represents an organic solvent.

  The base comb-shaped block copolymer 1, which is a dispersing agent, is one in which a plurality of side chains 1b constituting a solvation portion are bonded to the main chain 1a like a comb tooth. In the base comb block copolymer 1, an amino group is present in the main chain 1a corresponding to the back of the comb structure, and this base is adsorbed to the carbon nanotubes 2 as an anchor portion. The solvation portion is a portion having an affinity for a solvent, and refers to a hydrophilic or hydrophobic structure. The solvation portion has, for example, a hydroxyl group, a carboxyl group, a carbonyl group, an ester group and the like.

  As the base comb-shaped block copolymer, a commercially available product can be used. For example, Solsperse 13240, Solsperse 13650, Solsperse 13940, Solsperse 24000SC, Solsperse 24000GR, Solsperse 28000, and the like manufactured by Abisia Corporation can be used.

  In the carbon nanotube dispersion liquid of the present invention, the base comb-shaped block copolymer is adsorbed to the carbon nanotubes, so that the carbon nanotubes do not stick to the adjacent carbon nanotubes and are uniformly dispersed without aggregation.

  In the present invention, as shown in FIG. 2, the silane coupling agent means that the main chain 4a has a siloxane bond, and one of the side chains 4b has an amino group that is an affinity group for carbon nanotubes. 4c refers to a polymer having a functional group (for example, a hydroxyl group, a carboxyl group, a carbonyl group, an ester group, etc.) functioning as a solvate, and a monomer constituting the polymer.

  The silane coupling agent will be described with reference to FIG. 2 represents a carbon nanotube and 3 represents an organic solvent.

  The silane coupling agent 4 is preferable because it can be easily hydrolyzed to form a siloxane bond and be oligomerized. The silicon atoms in the main chain 4a have a large number of amino groups, which are groups having affinity for carbon nanotubes, and these groups adsorb to the carbon nanotubes 2 as anchor portions. The solvation portion is a portion having an affinity for a solvent, and refers to a hydrophilic or hydrophobic structure. The solvation portion has, for example, a hydroxyl group, a carboxyl group, an alkoxy group, and the like.

  Further, the silane coupling agent 4 has an amino group which is a carbon nanotube-affinitive group, but may also have a carbon nanotube-affinitive group such as a vinyl group and an epoxy group.

  Commercial products can be used as the silane coupling agent. For example, KBM-602, KBM-603, KMB-903, KBE-903 manufactured by Shin-Etsu Chemical Co., Ltd. can be used.

  The silane coupling agent is hydrolyzed, for example, by mixing a monomer shown in FIG. 3 (a) with water or an alcohol and water, to form a silanol shown in FIG. 3 (b), and further partially condensing Thus, an oligomer shown in FIG. 3C is obtained. In the present invention, it is preferable to use the silane coupling agent 4 in an oligomer state shown in FIG. However, for example, even when the monomer is used without adding water or the like, or when used in the state of a mixture thereof, the monomer is sufficiently used as a dispersant, so that it can be suitably used.

  By mixing the silane coupling agent 4 and the carbon nanotube, the silane coupling agent is adsorbed on the carbon nanotube, does not stick to the adjacent carbon nanotube, and is uniformly dispersed without aggregation.

  Further, instead of silicon in the silane coupling agent, an aluminum-based coupling agent substituted with aluminum or a titanium-based coupling agent substituted with titanium may be used.

  The addition amount of the polymer compound having a plurality of amino groups is preferably 1 part by weight or more, more preferably 1 to 100 parts by weight, based on 100 parts by weight of the carbon nanotube. If the amount is less than 1 part by weight, the amount relative to the carbon nanotube is small, so that sufficient adsorption is impossible and the dispersion state tends to be deteriorated. If the amount is more than 100 parts by weight, a supersaturated state tends to remain in the solution. There is. However, since the dispersant is decomposed and scattered in the subsequent baking step, there is no particular problem in the supersaturated state.

  The method for producing a carbon nanotube dispersion liquid of the present invention is not particularly limited. For example, a liquid obtained by dissolving a polymer compound having a plurality of amino groups in an organic solvent and then mixing the purified carbon nanotubes described above. Is stirred and dispersed using an ultrasonic wave, a ball mill, a bead mill, a stirrer, or the like, thereby producing a carbon nanotube dispersion liquid. In particular, by using a ball made of zirconia having a diameter of 0.5 to 3 mm and pulverizing with a bead mill, the particles can be efficiently pulverized and dispersed. At this time, the average particle size of the carbon nanotubes is 0.1 to 1.5 μm.

  In the present invention, when dispersing carbon nanotubes in an organic solvent, the type of the organic solvent and the viscosity of the dispersion may be adjusted in accordance with the method of applying the carbon nanotube dispersion to be produced. For example, when a film is formed by a printing method, carbon nanotubes are dispersed in an organic solvent such as terpineol or butyl carbitol, and an appropriate amount of the organic solvent is removed by centrifugation, and then ethyl cellulose, an acrylic resin, butyral A resin such as a resin can be added and mixed in a mortar or the like to form a paste. Note that a resin such as ethyl cellulose may be added at the final stage of the stirring and dispersion treatment. These resins are mixed to increase the viscosity when forming a paste to form a film and to form a pattern, and to bond the carbon nanotube particles to a substrate. When adding a resin such as ethyl cellulose, it is preferable to add 0 to 300 parts by weight based on 100 parts by weight of the carbon nanotube. If the amount exceeds 300 parts by weight, the viscosity increases, and it becomes difficult to form a film by a general film forming method such as a spin coating method or an ink jet method.

Embodiment 2
The configuration and manufacturing method of an electron emission source and a display light emitting device using the carbon nanotube dispersion liquid of the present invention will be described.

  FIG. 4 shows a configuration of a display light emitting device using a carbon nanotube dispersion liquid. In FIG. 4, 5 is an upper substrate, 6 is a lower substrate, 7 is a cathode electrode, 10 is a gate electrode, 11 is a phosphor layer, 12 is an aluminum film layer, and 13 is an opening.

  As the upper substrate 5, soda glass, white glass, or the like, which is easy to form a panel, is used, and the same substrate as the upper substrate 5 is used for the lower substrate 6. On the lower substrate 6, a conductive film layer serving as the cathode electrode 7 is formed. The cathode electrode 7 can be formed using a material such as ITO, silver, or aluminum by a printing method, a vacuum evaporation method, a sputtering method, or the like. Using the carbon nanotube dispersion liquid of the present invention, a carbon nanotube film 8 is formed on the obtained cathode electrode 7 by a printing method, a spin coating method, an inkjet method, or the like. The thickness of the carbon nanotube film 8 is preferably 1 to 8 μm, particularly preferably 2 to 5 μm. If the thickness of the carbon nanotube film 8 is less than 1 μm, the carbon nanotube film is damaged in the etching step for forming the opening, and tends to be unable to maintain a sufficient film thickness. Therefore, there is a tendency that a uniform film cannot be formed. The formed carbon nanotube film 8 serves as an electron emission source. An insulating layer 9 is formed on the carbon nanotube film 8 by printing, spin coating, or the like using a glass paste or the like. Next, a gate electrode 10 serving as a lead electrode is formed on the insulating layer 9 using silver, aluminum, or the like by a vacuum evaporation method or a printing method.

  Subsequently, a resist film (for example, AZP4330 manufactured by Clariant) is applied by a spin coating method by a photolithography technique, and a pattern is formed by mask exposure. After that, a minute opening 13 of 5 to 10 μm is formed in the gate electrode 10 and the insulating layer 9 by a dry etching method or a wet etching method, so that the carbon nanotube film 8 is exposed. Thus, an electron emission portion is formed.

  In the present invention, by forming a film using a liquid in which the carbon nanotubes are uniformly dispersed, the unevenness of the carbon nanotube film 8 can be reduced to ± 1 μm or less, further ± 0.5 μm. Therefore, even if the insulating layer formed on the carbon nanotube film 8 has a thickness of about 3 to 5 μm, there is no short circuit with the gate electrode 10. Therefore, an electron emission source having an electron emission start voltage of, for example, 8 to 10 V can be obtained. Further, the obtained electron emission source can uniformly emit electrons.

  On the other hand, when an electron emission portion is made of a carbon nanotube aggregated film using a conventional dispersion liquid of low dispersibility, the aggregated projection portion of the carbon nanotube and the gate electrode are short-circuited and do not function as an element. Frequently occur. Therefore, it was necessary to increase the thickness of the insulating layer. However, this requires a lot of time in the process of forming the insulating layer, and the distance between the carbon nanotube film and the gate electrode, which is the extraction electrode, increases. There was a problem of becoming.

  The light-emitting portion facing the electron-emitting portion obtained by the above-described method is provided on the upper substrate 5 at a position corresponding to the cathode electrode 7 formed on the lower substrate 6, in each of the red, blue, and green phosphor layers 11. Is formed by a printing method, a spin coating method, or the like, and an aluminum film layer 12 serving as an electrode is formed thereon as a solid film. The phosphor screen structure obtained by the present invention has the same structure as the phosphor screen used in the current television tube, and can obtain high luminance. Further, the trend surface structure obtained in the present invention may be a structure in which a transparent electrode such as ITO or SnO is formed on the upper substrate 5 and a phosphor is applied thereon by a printing method or the like.

  INDUSTRIAL APPLICABILITY The display light-emitting device of the present invention is excellent in performance such as low-voltage driving, low power consumption, high luminance, and high definition, and can be used for, for example, a large-screen television for home use and an information display.

Example 1
Carbon nanotubes produced by chemical vapor deposition (CVD) are fired in the air at 550 ° C., left for 5 minutes in a mixture of concentrated sulfuric acid and concentrated nitric acid at a ratio of 1: 1, and the liquid is removed by centrifugation. By performing the treatment, purification such as removal of impurities such as amorphous carbon was performed, and high-purity carbon nanotubes were obtained.

  0.15 g (5 parts by weight based on 100 parts by weight of carbon nanotubes) of Solsperse 24000GR as a base comb block copolymer was dissolved in 200 mL of α-terpineol, and 3 g of the obtained carbon nanotubes (5 nm in diameter) were mixed. The obtained liquid was stirred with a zirconia ball having a diameter of 1 mm using a bead mill for 5 hours to obtain a dispersion liquid having an average particle diameter of carbon nanotube particles of 0.1 μm.

  An excess organic solvent was removed from the obtained dispersion with a centrifuge (or a filter or a drying oven) to adjust the amount of the organic solvent. Ethyl cellulose was added so as to be 100 parts by weight based on 100 parts by weight of the carbon nanotubes. Thereafter, the mixture was kneaded in an automatic mortar for 2 hours to form a paste to form a film by a printing method. FIG. 5B shows the result of observing the print film at a magnification of 2500 times. It can be seen that there are no aggregated particles in the printed film and the carbon nanotubes are uniformly dispersed. Therefore, it can be seen that the base comb-shaped block copolymer is adsorbed on the carbon nanotube and functions as a dispersant.

Example 2
A high purity carbon nanotube was obtained in the same manner as in Example 1.

  In 200 mL of α-terpineol, 3 g (100 parts by weight per 100 parts by weight of carbon nanotubes) of KBM603 (manufactured by Shin-Etsu Chemical Co., Ltd.) as a silane coupling agent was dissolved, and 3 g of the obtained carbon nanotubes (5 nm in diameter) were dissolved. Was mixed. The obtained liquid was stirred with a zirconia ball having a diameter of 1 mm using a bead mill for 5 hours to obtain a dispersion liquid having an average particle diameter of carbon nanotube particles of 0.2 μm.

  An excess organic solvent was removed from the obtained dispersion with a centrifuge (or a filter or a drying oven) to adjust the amount of the organic solvent. Ethyl cellulose was added so as to be 100 parts by weight based on 100 parts by weight of the carbon nanotubes. Thereafter, the mixture was kneaded in an automatic mortar for 2 hours to form a paste to form a film by a printing method. FIG. 5C shows the result of observing the printed film at a magnification of 2500 times. It can be seen that there are no aggregated particles in the printed film and the carbon nanotubes are uniformly dispersed. Therefore, it can be seen that the silane coupling agent is adsorbed on the carbon nanotube and functions as a dispersant.

Comparative Example 1
A dispersion liquid of carbon nanotubes was prepared in the same manner as in Example 1 except that a homogenol L18 manufactured by Kao Corporation, which is a polycarboxylic acid-based polymer dispersant, was added instead of the base comb block copolymer as a dispersant. did.

  FIG. 5A shows the result of observing a printed film formed in the same manner as in Example 1 using the obtained dispersion. Large aggregated particles having a particle size of about 20 μm were observed in the printed film.

Example 3
An ITO film was formed over a glass substrate by a sputtering method to form a conductive film layer (cathode electrode). Using the carbon nanotube dispersion liquid obtained in Example 1, a carbon nanotube film serving as an electron emission source was formed on the obtained cathode electrode by a printing method. The thickness of the formed carbon nanotube film was 2.4 μm. Further, when the roughness of the carbon nanotube film was examined using a surface roughness meter (DEKTAK3030 manufactured by ULVAC, Inc.), it was found to be ± 0.5 μm or less, indicating that the roughness was small. Further, an insulating layer was formed on the carbon nanotube film by a printing method. The thickness of the insulating layer was 5 μm. Next, an extraction electrode (gate electrode) was formed by a vacuum evaporation method using a vacuum evaporation apparatus.

  Subsequently, a resist film (AZP4330 manufactured by Clariant) is applied by a photolithography technique, a pattern is formed by mask exposure, and a fine opening of 10 μm is formed in the gate electrode and the insulating layer by a dry etching method. Was exposed.

  In the obtained electron emitting portion, there was no short circuit with the electrode because the carbon nanotube film had few irregularities.

Example 4
An electron-emitting portion was obtained in the same manner as in Example 3, except that the carbon nanotube dispersion was changed to the carbon nanotube dispersion obtained in Example 2.

  In the obtained electron emitting portion, there was no short circuit with the electrode because the carbon nanotube film had few irregularities.

Example 5
A light-emitting display element was manufactured using the electron-emitting portion obtained in Example 3. Obtaining a light emitting portion by stacking red, blue, and green phosphors on the upper substrate by a printing method, and forming an aluminum film layer serving as an electrode on the phosphor layer by a vacuum deposition method. Was completed. The light-emitting portion obtained and the electron-emitting portion obtained in Example 2 were sandwiched with a spacer glass coated with low-melting glass, the upper and lower substrates were aligned, fired at 450 ° C. to form a container, and connected to the container. The light emitting display element was able to be obtained by evacuating the vacuum through the exhaust pipe.

  A voltage Va of 5 to 10 kV is supplied to the aluminum film of the upper substrate of the obtained light emitting display element, and a voltage Vg of about 10 to 100 V is supplied between the cathode electrode and the gate electrode of the electron-emitting portion, whereby the opening of the opening is formed. Electric field concentration occurs at the tip of the carbon nanotube in the carbon nanotube film inside, and electron emission starts at around 2 V / μm. The emitted electrons are led by the high voltage applied to the aluminum electrode, and collide with the opposing phosphor to emit light. Thus, high-luminance light emission of the display light-emitting element was observed.

Example 6
A light-emitting display element was obtained in the same manner as in Example 5, except that the electron-emitting portion obtained in Example 4 was used.

  A voltage Va of 5 to 10 kV is supplied to the aluminum film of the upper substrate of the obtained light emitting display element, and a voltage Vg of about 10 to 100 V is supplied between the cathode electrode and the gate electrode of the electron-emitting portion, whereby the opening of the opening is formed. Electric field concentration occurs at the tip of the carbon nanotube in the carbon nanotube film inside, and electron emission starts at around 2 V / μm. The emitted electrons are led by the high voltage applied to the aluminum electrode, and collide with the opposing phosphor to emit light. Thus, high-luminance light emission of the display light-emitting element was observed.

It is a figure for explaining the dispersing action of a base comb block copolymer. It is a figure for explaining the dispersing action of a silane coupling agent. It is a figure for demonstrating the state of a silane coupling agent ((a) monomer, (b) silanomer, (c) oligomer). FIG. 2 is a diagram illustrating a configuration of a display light emitting device using a carbon nanotube dispersion. It is an observation result of a carbon nanotube printing film when (a) a single polymer is used as a dispersant, (b) a base comb block copolymer is used, and (c) a silane coupling agent is used.

Explanation of reference numerals

  Reference Signs List 1 base comb block copolymer, 1a main chain, 1b side chain, 2 carbon nanotubes, 3 organic solvent, 4 silane coupling agent, 4a main chain, 4b side chain, 5 upper substrate, 6 lower substrate, 7 cathode electrode, 8 carbon Nanotube film, 9 insulating layer, 10 gate electrode, 11 phosphor layer, 12 aluminum film layer, 13 opening.

Claims (7)

A carbon nanotube dispersion liquid comprising a polymer compound having a plurality of amino groups, an organic solvent, and carbon nanotubes. The carbon nanotube dispersion according to claim 1, wherein the polymer compound having a plurality of amino groups is a base comb block copolymer. The carbon nanotube dispersion according to claim 1, wherein the polymer compound having a plurality of amino groups is a silane coupling agent. 4. The carbon nanotube dispersion according to claim 1, wherein the organic solvent contains a hydroxyl group and has 4 or more carbon atoms. A method for producing a carbon nanotube dispersion in which carbon nanotubes are dispersed in an organic solvent containing a polymer compound having a plurality of amino groups. An electron emission source obtained by using the dispersion according to claim 1. A display light emitting device having the electron emission source according to claim 6.

Images