JP2007051410A - Carbonaceous fiber and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a carbonaceous fiber of which both ends are sharp, useful as an electron emission material. <P>SOLUTION: This carbonaceous fiber having fused ring-formed carbon surfaces piled as annual rings centering around its fiber axis and characterized with that the both ends of tip ends of the fiber have sharp angles, and preferably the fiber has a hollow structure at the fiber axis part of the carbonaceous fiber is obtained by heating the carbonaceous fiber having the fused ring-formed carbon surfaces piled as annual rings centering around fiber axis in the presence of oxygen at ≥400°C and ≤1,200°C temperature until ≥75% of its mass is burnt down. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a carbonaceous fiber and a method for producing the same. More specifically, the present invention relates to a carbonaceous fiber having sharp edges at both ends, which is useful mainly for a field electron emission source, and a method for producing the same.

  In recent years, it has been studied to use a carbonaceous fiber as an electron source for an electron-emitting device for a cold cathode used in an electronic display device, an image forming apparatus or the like. Regarding the production of the carbonaceous fiber, for example, in Japanese Patent Application Laid-Open No. 8-115652, it is generated as a result of thermally decomposing hydrocarbon gas as a raw material in a minute gap between two electrodes set on an insulating substrate. A manufacturing method for depositing carbonaceous fibers is shown. Japanese Patent Application Laid-Open No. 10-112257 describes a method of ion-implanting carbon ions or carbon cluster ions into the surface of a base cathode, and using a nucleus generation site formed therefrom as a nucleus to synthesize diamond-like carbon in a gas phase. Yes. All of these can be technically manufactured, but since the thermal influence on the cathode member becomes a problem, the heat treatment of the carbonaceous fiber is difficult, and thus the electron emission effect of the carbonaceous fiber is limited. In addition, all of them synthesize carbon directly on a cathode such as a substrate. Mass production requires know-how and equipment technology unique to the manufacturer, and the process is complicated, so that it is not a method generally used by cathode material manufacturers.

  On the other hand, minute carbon nanotubes with a diameter of several tens of nm or less have been in the spotlight for several years as electron emission materials. This is usually a graphite tube with a thickness of about 1 nm to 50 nm, and its production method is performed on the surrounding electrode by generating a carbon electrode on the electrode by arc discharge or applying a powerful laser beam to the carbon electrode. Generate. The shape of this nanotube is generally a shape with one pointed tip as seen in Hyundai Kagaku P57 (July 1998). Carbon nanotubes are chemically stable and mechanically strong, and are being studied as field emission electron sources. For example, Saito et al., Ceramics 33 (1998) No. 6 shows an example in which a large number of these are attached on a cathode plate and used as a fluorescent display tube, suggesting the possibility of use in an energy-saving flat display and a high-definition color CRT.

  However, for carbon nanotubes, an industrial production method has not been established, and stable quality products are not supplied at low cost. In recent years, vapor-grown carbon fibers have been mass-produced as having properties similar to carbon nanotubes. This is a method of spraying an organic compound into a reaction vessel to produce carbon fibers by thermal decomposition as shown in the production methods of Japanese Patent Publication Nos. 04-24320 and Japanese Patent No. 2778434. Carbon fibers having a diameter of several μm or less are mass-produced. Is obtained. Examining these shapes in detail, the condensed ring carbon surface shows the appearance of laminated annual rings around the fiber axis, and when these end surfaces are viewed, it is closed in a round sphere or is divided, and its cross section Indicates a state substantially perpendicular to the fiber axis direction. As described above, when used as a field electron emission source, a condensed ring-shaped carbon surface end face appears at an acute angle and an edge appears, so that field electron emission characteristics are improved. In particular, carbonaceous fibers with sharp end faces have not been discovered at present, and if they can be used as electron emission materials, it is expected that the efficiency of electron emission will be improved.

  The present inventors pay attention to vapor-grown carbon fibers for which industrial production methods are currently established, and consider that the carbonaceous fibers are sharply sharpened at both ends at the tips that can be used for electron emission materials. Is to be obtained on a mass production scale. That is, an object of the present invention is to obtain a carbonaceous fiber having pointed ends that could not be produced conventionally, and to provide a method for mass production.

  In order to make the shape of the tip of the carbonaceous fiber an acute angle, the present inventors have studied various methods including pulverization by mechanical impact and wear. The inventors have found that both ends have acute angles and have completed the present invention, and have obtained carbonaceous fibers with sharp ends that have not been seen in the past. That is, 1) A carbonaceous fiber in which condensed cyclic carbon surfaces are laminated in an annual ring shape with the fiber axis as the center, and the tip of the fiber is acute at both ends. 2) The carbonaceous fiber according to 1) above, wherein the carbonaceous fiber used as a raw material is fired or graphitized. 3) The above 1) or 2) is characterized in that the fiber axis portion of the carbonaceous fiber has a hollow structure. Further, 4) The above 1), 2) or 3) is preferably characterized in that both ends of the tip are mixed with an acute angle carbonaceous fiber and one or both of them are not acute angles. The carbonaceous fiber is 5) a carbonaceous fiber in which condensed cyclic carbon surfaces are laminated in an annual ring shape around the fiber axis at a temperature of 400 ° C. or higher and 1200 ° C. or lower in the presence of oxygen at least 75% of its mass. Obtained by heating until burned out.

According to the present invention, carbonaceous fibers having sharp ends desired as an electron emission material can be obtained at low cost from a gas phase process carbon fiber on a mass production scale by a simple manufacturing method.

  The present invention will be described in more detail. The carbonaceous fiber in which the condensed cyclic carbon surface of the present invention is laminated in an annual ring shape around the fiber axis is a carbon fiber typified by vapor grown carbon fiber or carbon nanotube. Yes, the fiber shaft portion may have a hollow structure. The vapor grown carbon fiber is disclosed in Japanese Patent Publication No. 4-24320, Japanese Patent No. 2778434, and the like. Carbon nanotubes have been discovered by Iijima et al. And various production methods have been proposed, but the present invention is not limited to the production methods for both vapor-grown carbon fibers and carbon nanotubes. However, according to the study by the present inventors, only the carbonaceous fibers in which condensed carbon surfaces peculiar to carbon fibers obtained by vapor phase growth are laminated in an annual ring shape around the fiber axis, the acute shape at both ends of the present invention. A carbonaceous fiber with a high yield was obtained.

  In addition, the definition of the acute angle state of the tip of the present invention is as shown in FIG. 1 where the fiber diameter of the carbonaceous fiber is d0 and the tip diameter is d1, and the distance between the point where the fiber diameter starts to become narrower and the tip becomes smaller. Assuming L, d1 / d0 <0.5 and 0.5 <L / d0. Further, most of the sharp carbon fiber tips are present on the fiber center axis, but may be displaced from the fiber center axis as shown in FIG. As shown in FIG. 2, the structure of the tip is such that a condensed annular carbon surface exists in an annual ring shape around the fiber axis, and the center axis of the tip may or may not take a hollow structure. The carbonaceous fiber having a sharp tip of the present invention may contain a carbonaceous fiber having a sharp angle at both ends of the tip and a carbonaceous fiber having one or both of which are not acute angles. As for the abundance ratio, carbon fibers having sharp edges at both ends account for 10% or more of the total. The fiber diameter and length of the carbonaceous fiber of the present invention are not particularly limited. Usually, the fiber diameter is 0.0005 μm to 50 μm, and the fiber length is 0.5 μm to several mm. Preferably, the fiber diameter is The fiber length is about 0.0005 μm to 1 μm, and the fiber length is about 0.5 μm to 500 μm. Further, a part of the carbonaceous fiber surface may be thinner than the other part by oxidation or the like. In the method for producing carbonaceous fibers having sharp edges at both ends according to the present invention, carbonaceous fibers in which condensed cyclic carbon surfaces are laminated in an annual ring shape around the fiber axis are heated at a temperature of 400 ° C. or higher and 1200 ° C. or lower in the presence of oxygen. To do. Below 400 ° C., oxidation does not occur and sharpening of the tip does not proceed. Moreover, when it exceeds 1200 degreeC, the speed | rate of oxidation is quick and control of appropriate time becomes difficult. Moreover, the heat-treated state of the carbonaceous fiber used as a material may be baked at 800 ° C. or higher, or graphitized at 2000 ° C. or higher. Unfired or non-graphitized products undergo oxidation at temperatures below 400 ° C. and are similarly difficult to control. In addition, process temperature and time are adjusted with the heat processing log | history of carbonaceous fiber. Moreover, after performing this oxidation process, you may perform a graphitization process.

  Hereinafter, the present invention will be described in more detail with reference to examples. In addition, this invention is not limited to a following example.

Example 1
As shown in Japanese Patent No. 2778434, a vertical heating furnace equipped with a reaction tube having an inner diameter of 170 × length of 1500 is used, a two-fluid spray nozzle is attached to the top of the reaction tube, and the reaction tube is heated and maintained at 1200 ° C. The raw material is sprayed and supplied to the inner wall of the reaction tube by a two-fluid spray nozzle using 20 g / min of raw material containing 4% by weight of ferrocene and 100 L / min of hydrogen. The reaction was carried out for 1 hour while the vapor grown carbon fiber produced in the reaction tube was scraped at an interval of 5 minutes, and the vapor grown carbon fiber was recovered. The obtained vapor grown carbon fiber was graphitized at 2800 ° C. It was packed in a crucible and placed in a muffle furnace heated to 750 ° C. and heated for 4 hours. At that time, the residual ratio of carbonaceous fibers was 21 wt%. The obtained oxidized carbonaceous fiber was observed with a transmission electron microscope (TEM). The photographs are shown in Figs. Table 1 shows the diameter and shape of carbonaceous fibers having sharp edges at both ends measured from FIG. 3. One of the carbonaceous fibers in FIG. 3 is d1 / d0 = 0.08, L / d0. = 3.4; d1 / d0 = 0.05, L / d0 = 5.4, the other is d1 / d0 = 0.13, L / d0 = 1.3; d1 / d0 = 0.06, L / d0 = 1.9.

It is explanatory drawing which defines the acute angle state of the front-end | tip of this invention. It is a figure which shows the structure of the carbon fiber with the acute angle | corner of a front-end | tip. It is a transmission electron micrograph which shows an example of the carbon fiber with the acute angle | corner by this invention. 6 is a transmission electron micrograph of another example of a carbon fiber having a sharp tip according to the present invention.

Claims (5)

  A carbonaceous fiber in which condensed cyclic carbon surfaces are laminated in an annual ring shape around a fiber axis, wherein both ends of the fiber are acute angles.   2. The carbonaceous fiber according to claim 1, wherein the carbonaceous fiber used as a raw material is fired or graphitized.   The carbonaceous fiber according to claim 1 or 2, wherein the carbonaceous fiber has a hollow structure in a fiber shaft portion.   The carbonaceous fiber according to any one of claims 1 to 3, wherein a carbonaceous fiber having acute angles at both ends of the tip and a carbonaceous fiber having one or both of which are not acute angles are mixed.   Heating the carbonaceous fiber in which condensed cyclic carbon surfaces are laminated in an annual ring shape around the fiber axis in the presence of oxygen at a temperature of 400 ° C. or higher and 1200 ° C. or lower until 75% or more of its mass is burnt down. The method for producing a carbonaceous fiber according to any one of claims 1 to 4.

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