JP2011210591A - Electron emission source, paste for electron emission source, and method of manufacturing the paste for electron emission source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide paste for an electron emission source which can lower a drive voltage required for electron emission, and to provide a method of manufacturing the electron emission source, and the electron emission source.SOLUTION: The problem is solved by: the paste for an electron emission source, wherein the paste contains a carbon nanotube bundle-like assembly having a bundle diameter 50 nm or more and a bundle length 3 μm or more; and the method of manufacturing the electron emission source and the electron emission source, using the paste.

Description

  The present invention relates to a field emission type electron emission source that emits electrons at a low voltage, a paste used for manufacturing the same, and a method for manufacturing the paste.

  Conventionally, as an electron emission source paste applied on an electrode substrate, for example, a paste containing carbon nanotubes, glass frit, a binder resin, and a solvent is known (Patent Document 1). For example, 3% carbon nanotubes, 25% ethyl cellulose as a binder, 5% glass powder as a vehicle, and 67% terpineol as a solvent are screen-printed on a substrate to a thickness of 20 microns and fired at 400 ° C. After that, peeling with an adhesive tape is performed. SEM images of the carbon nanotubes fixed on the electrode substrate obtained by this method are shown in FIGS.

JP 2005-56818 A

  Microscopic observation of the state of the film surface where the surface of the paste film is raised with an adhesive tape reveals that one or several bundles of carbon nanotubes are raised (the diameter of the bundle is about 10 nm to 50 nm). The height (distance from the base to the tip of the raised carbon nanotube) is 1 μm to 6 μm. In order to cause field emission of electrons from an electron emission source in which carbon nanotubes are raised in such a state, it is necessary to load a high electric field, resulting in an increase in size and cost of a power supply and a drive circuit. The carbon nanotube gradually deteriorated when a large current flowed, and the emission current decreased. Thus, when the raised carbon nanotubes are thin and short, the durability as an electron emission source is poor and the electric field concentration is low, so that a high driving voltage is required.

  The present invention has been made to solve the above-mentioned problems, in which carbon nanotubes are dispersed with an organic solvent for dispersion, and the organic solvent for dispersion, the glass frit, the binder resin, and the solvent for paste are dispersed in an organic solvent for dispersion. When the paste was produced by kneading while evaporating the solvent, it was found that many aggregates of carbon nanotubes gathered like bundles in the same direction were dispersed in the paste. When the film produced by printing and baking the paste produced in this way on a substrate is peeled off with an adhesive tape or the like, many bundles of brushed carbon nanotubes appear on the film surface, and many electrons are generated even in a low electric field. It was discovered that the electron emission efficiency of the electron emission source is increased.

  That is, the present invention disperses carbon nanotubes in an electron emission source paste and an organic solvent for dispersion characterized by containing a bundle of carbon nanotubes having a bundle diameter of 50 nm or more and a bundle length of 3 μm or more. A dispersion step, a carbon nanotube dispersion obtained in the dispersion step, a glass frit, a binder resin, and a paste solvent having a boiling point higher than that of the organic solvent for dispersion while kneading the organic solvent for dispersion A method for producing an electron emission source paste characterized by comprising a kneading step, and a bundle of carbon nanotubes having a bundle diameter of 50 nm or more and a bundle length of 3 μm or more. An electron emission source characterized by being fixed to the surface of a substrate is provided.

  In the present invention, a carbon nanotube bundle aggregate in which many carbon nanotubes are bundled appears on the paste film, so that the electric field concentration is increased and electrons can be emitted even at a low electric field strength. Therefore, the driving voltage required for electron emission can be lowered as compared with the conventional method, and the energy saving effect is enhanced. Moreover, since the carbon nanotube bundle aggregate is composed of a large number of carbon nanotubes, the current density or the current value per one carbon nanotube is lowered. As a result, the carbon nanotubes are hardly deteriorated, and the durability of the electron emission source is improved. If the electron emission source according to the present invention is used in, for example, a light emitting device that irradiates electrons to a fluorescent material, a long life can be realized with power saving.

FIG. 1 is a graph showing electron emission characteristics of an electron emission source manufactured using the paste of the present invention and a conventional paste. It is a SEM image which shows the state after raising of the printed film produced using the paste of this invention. It is a SEM image which shows the state after raising of the printed film produced using the conventional paste.

  The paste for an electron emission source of the present invention includes carbon nanotubes, glass frit, a binder resin and a paste solvent, and the glass frit is dispersed in a dispersion organic solvent during paste production. And a paste resin is produced by adding a binder resin and a paste solvent and kneading while evaporating the organic solvent for dispersion.

  Organic solvents for dispersion used for dispersion are ketones such as acetone and methyl ethyl ketone, alcohols such as methyl alcohol, ethyl alcohol and butyl alcohol, esters such as ethyl acetate, ethers such as ethyl ether, benzene, toluene, xylene A general organic solvent for dispersion that is inert to carbon nanotubes, such as aromatic hydrocarbons such as, can be widely used. In addition, since the organic solvent for dispersion needs to be evaporated (volatilized) when mixed with glass frit or the like, it is desirable that the boiling point is low. In particular, when water is used in paste production, it is desirable that the boiling point is less than 100 ° C., particularly 80 ° C. or less in order to evaporate at a temperature lower than that of water. The amount of the organic solvent for dispersion with respect to the carbon nanotubes is determined so that the dispersed state of the carbon nanotubes can be maintained, and is about 100 to 5000 times, particularly about 300 to 1000 times, with respect to the weight of the carbon nanotubes.

  When manufacturing a paste, first, carbon nanotubes are dispersed in an organic solvent for dispersion. As a dispersion method, a known dispersion method may be used. For example, ultrasonic waves can be used. Thereafter, glass frit, binder resin and paste solvent are added and kneaded while evaporating the organic solvent for dispersion.

  The kneading conditions may be about 0 to 50 ° C., usually about 10 to 30 ° C. until the organic solvent for dispersion evaporates and a predetermined paste viscosity is obtained. The paste may be kneaded until the viscosity becomes about 2 to 500 Pa · s, usually about 20 to 200 Pa · s.

  The glass frit is used as a vehicle, and glass powder or the like can be used.

  As the binder resin, for example, acrylic resins, epoxy resins, cellulose resins such as ethyl cellulose, and the like can be used.

  As the solvent for the paste, an organic solvent such as terpionol, butyl carbitol acetate, or texanol can be used. The boiling point of the paste solvent needs to be higher than the boiling point of the dispersing organic solvent.

  The mixing ratio is suitably about 1 to 5% by weight of carbon nanotubes, about 10 to 30% by weight of binder resin, about 1 to 10% by weight of glass frit (vehicle), and about 40 to 80% by weight of solvent. is there.

The paste is created, for example, according to the following procedure.
(1) Disperse carbon nanotubes with an organic solvent for dispersion.
(2) A glass frit, a binder resin, and a paste solvent are mixed in the carbon nanotube dispersion solvent.
(3) The organic solvent for dispersion is evaporated while mixing the carbon nanotube dispersion solvent through (1) and (2), the glass frit, the binder resin, and the paste solvent in a mortar.

  When a paste is manufactured based on the above-described process, at least a part of the carbon nanotubes gathers in a bundle shape during mixing with glass frit or the like. That is, a paste containing a bundle of carbon nanotubes in which carbon nanotubes are gathered in a bundle can be obtained. A bundle of carbon nanotubes is a bundle of about several to several thousand carbon nanotubes, most of which are about 10 to 500, and the diameter of the bundle is 50 nm or more, usually about 50 to 3000 nm, and most is 100 to 1000 nm. Degree. The length of the bundle is 3 μm or more, usually about 5 to 20 μm.

  This paste is applied to a glass substrate having an ITO (tin-doped indium oxide) film on its surface to form a paste film. The thickness of the paste film may be about 1 to 10 μm in dry thickness. For example, the film can be formed by screen printing or the like.

  Once the paste film is formed, it is then fired. Firing is performed to carbonize the organic component in the paste and strengthen the adhesion to the substrate. Firing may be performed in air at a temperature of about 400 to 500 ° C. for about 10 to 30 minutes. After firing, the adhesive tape is applied and peeled off as it is to raise the carbon nanotubes.

  In the electron emission source thus obtained, carbon nanotubes are gathered in a bundle and fixed to the surface of the substrate, and the diameter of the bundle is 50 nm or more, usually about 50 to 3000 nm, and many are about 100 to 1000 nm. The length of the bundle is 3 μm or more, usually about 5 to 20 μm.

(1) 0.1 g of carbon nanotubes were placed in a mixed solution of 50 cc of acetone and 1 cc of methanol as an organic solvent for dispersion, and ultrasonically dispersed for 10 minutes.
(2) On the other hand, 2 g of binder resin was added to 6 g of terpineol (paste solvent) and dissolved in a thermostatic bath at 80 ° C. for 10 minutes.
(3) (1), (2) and 0.6 g of glass frit were put in an automatic mortar, and the organic solvent for dispersion was evaporated while kneading for 1 hour.
The paste thus obtained was screen-printed to a thickness of about 20 μm on a glass substrate having an ITO film. This was placed on a hot plate at 100 ° C. for about 10 minutes, the paste solvent was evaporated to dry the paste, and then baked at 450 ° C. for 10 minutes in the atmosphere.

  After firing, the pressure-sensitive adhesive tape was lightly pressed and pasted, and then the pressure-sensitive adhesive tape was peeled off to obtain a carbon nanotube electron emission source.

SEM images of the obtained carbon nanotube electron emission source were taken, and images shown in FIGS. 2A and 2B were obtained. As shown in the figure, it can be seen that there are portions in which a large number of carbon nanotubes (CNT) are bundled. As shown in FIG. 1, the average electric field value at which an emission current with a current density of 1 mA / cm ² was obtained with this CNT electron emission source was 1.6 V / μm. In FIG. 1 and FIG. 3, the conventional method is obtained by the same treatment except that the organic solvent for dispersion is not used. Table 1 shows the results of a durability test of a printed film produced using the paste of the present invention and the conventional paste.

これは、放出電流密度１ｍＡ／ｃｍ^２一定とした時の印加電界強度の増加率を示している。本発明のペーストによる膜は従来ペーストに比べ、劣化の速度が１／１５である。つまり、従来法に比べ、１５倍の耐久性を有することが分かる。

This shows the increase rate of the applied electric field strength when the emission current density is fixed at 1 mA / cm ² . The film of the paste of the present invention has a degradation rate of 1/15 compared to the conventional paste. That is, it can be seen that the durability is 15 times that of the conventional method.

  The reason why a bundle of carbon nanotubes is obtained is that carbon nanotubes are more dispersible in organic solvents for dispersion having a low boiling point than in organic solvents for paste having a high boiling point. In the meantime, the carbon nanotube concentration in the organic solvent for dispersion becomes high. As the organic solvent for dispersion evaporates, the concentration of carbon nanotubes in the organic solvent for dispersion gradually increases and is stretched by the kneading step, so that the orientation of the carbon nanotubes is aligned. Therefore, many bundles of carbon nanotubes in which the carbon nanotubes are finally bundled in the same direction are formed in the paste.

  In the examples, a mixed solvent is used as a solvent for dispersing acetone and methanol, but the present invention is not limited to this. Further, a liquid such as water having affinity for these dispersing solvents may be added.

  Since the carbon nanotube electron emission source obtained by using the paste of the present invention has excellent electron emission characteristics and durability, it can be used as a field emission type electron emission element in various electric devices and electronic devices. .

Claims (4)

  A paste for an electron emission source, comprising a bundle of carbon nanotubes having a bundle diameter of 50 nm or more and a bundle length of 3 μm or more.   An electron emission source, wherein a bundle of carbon nanotubes having a bundle diameter of 50 nm or more and a bundle length of 3 μm or more is fixed to the surface of the substrate. A dispersion step of dispersing carbon nanotubes in an organic solvent for dispersion;
A kneading step of kneading the carbon nanotube dispersion obtained in the dispersing step, a glass frit, a binder resin, and a paste solvent having a boiling point higher than that of the dispersing organic solvent while evaporating the dispersing organic solvent; A method for producing a paste for an electron emission source, comprising:   4. The electron emission source paste according to claim 3, wherein the dispersing organic solvent is made of one or more liquids selected from ketones, alcohols, esters, ethers or aromatic hydrocarbons. Manufacturing method.

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