JP2005074472A - Method of brazing carbon nanotube to base material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a brazing method of a carbon nanotube (CNT) to a base material, the method with which a sufficient CNT adhesive strength can be obtained while low gas releasability and electrical conductivity are secured. <P>SOLUTION: In the brazing method of a CNT to a base material, a metal or a metallic compound is stuck to a part of the CNT and then, the CNT is brazed to the base material using a brazing filler metal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates generally to a method for bonding carbon nanotubes, and more particularly to a method for bonding carbon nanotubes to a metal or glass substrate.

  Carbon nanotubes (CNT) are characterized by ultra-fine and high aspect ratios of approximately 0.4 to 100 nm in diameter and 1 to several hundred μm in length, and have a tensile strength and electrical conductivity several tens of times that of steel. Therefore, it is expected to be used as a field emission display (FED) and other field emitters (FE).

  However, in order to use the CNT as an electron emission source, it is necessary to apply or bond the CNT to a substrate such as a metal, semiconductor, glass, or the like as a base material. However, a bonding method that satisfies adhesive strength, low gas emission in vacuum, and conductivity has not been found, and this is a problem for commercialization of electron emission sources using CNTs.

  For example, as a method of manufacturing an electron source by bonding a minute carbon substance such as carbon nanotube to a base material, vapor-grown carbon fiber is used instead of carbon nanotube, and this is applied to an aqueous solution or dispersion of a conductive polymer. A method of dispersing and adhering to a conductive substrate by means such as immersion is known. (See Patent Document 1).

  Further, a method is known in which graphite powder is kneaded into a polymer resin, formed into a plate shape, and then calcined carbonized (see Patent Document 2). The carbon-based emitter thus obtained is bonded to the substrate using an adhesive.

  A conductive layer is formed on the electrode substrate, and this is immersed in a liquid in which carbon nanotubes are dispersed, and the carbon nanotubes are attached to the surface of the conductive layer by electrophoresis, and this is heated to a temperature higher than the melting point of the conductive material. Also known is a method of manufacturing an electron emission source that is heated at a high temperature (see Patent Document 3).

JP 2002-8517 A Japanese Patent Laid-Open No. 2002-1000027 JP 2003-59391 A

  As described above, in order to use this CNT as an electron emission source, it is necessary to apply or bond CNT to a substrate such as a metal, semiconductor, glass, etc. as a base material. A bonding method that satisfies adhesive strength, low outgassing in a vacuum, and conductivity without damaging properties has not been found.

For example, when a conductive adhesive using an organic material, the adhesion force of the substrate and the CNT can be sufficiently obtained, but remains untreated, high vacuum for use as an electron source (10 - about ^{5 Pa)} in a container When sealed, the degree of vacuum in the vacuum container deteriorates due to gas release from the adhesive, and the performance and life as an electron emission source are significantly impaired.

  To solve this problem, for example, as disclosed in Patent Document 2, a method is disclosed in which heat treatment is performed before vacuum sealing to carbonize the adhesive to suppress outgassing in vacuum. By carbonizing, the original adhesive strength of the adhesive is lost. In other words, the carbide is only adhered to the substrate, and sufficient adhesive strength cannot be obtained. In addition, carbonization requires heating the adhesive to a high temperature for several hours or more, which not only reduces productivity, but also gas components partially confined in the carbonization adhesive, even if carbonization is performed for a long time. Is gradually released, so that it is difficult to suppress the amount of gas released that can be used as an electron emission source.

  In order to solve this problem, Patent Document 1 discloses bonding of a CNT and a base material using tin-doped indium oxide (ITO) as an example of using an inorganic conductive adhesive. ITO is a material that is widely used as a conductive adhesive in vacuum because it has electrical conductivity, has a small amount of outgassing in a vacuum, and has good adhesion to a glass substrate. However, ITO is difficult to mix with CNT. For example, even if ITO and CNT are kneaded, it is difficult to uniformly disperse CNT in ITO. Moreover, even if it can be uniformly dispersed, when applied to a substrate and baked, most of the CNTs are buried in the ITO, and only a small part of the CNTs appear on the surface, impairing the uniformity of electron emission. , CNT yield is reduced. In addition, even if ITO is applied to the substrate in advance and then CNTs are dispersed and heat-treated, the CNTs and the ITO do not blend together, so that it is impossible to bond them.

  Moreover, in the method of brazing CNT and a base material using a metal having a low melting point as described in Patent Document 3, the CNT and the metal are not easily mixed with each other, and sufficient adhesion between the CNT and the brazing material can be obtained as described above. Absent.

  The present invention has been made in order to solve the above-described problems, and provides a method for brazing CNT to a base material, which can provide a sufficient CNT adhesive force while ensuring low outgassing properties and conductivity. It is intended to provide.

  The present invention has been made to solve the above-mentioned problems, and is characterized in that a metal or a metal compound is attached to a part of the carbon nanotube and then brazed to a base material using a brazing material. This object is achieved by the method of brazing to the base material.

  As described above, according to the present invention, the metal is adhered to the carbon nanotube and the wettability with the brazing material is improved, so that the brazing property between the carbon nanotube and the metal plate or glass as the base material can be improved. It is possible to obtain a sufficient adhesive strength. In addition, since an adhesive can be obtained while ensuring low gas emission and conductivity without impairing electron emission characteristics, a high quality electron emission source can be obtained.

As the carbon nanotube, those obtained by a known method can be used as they are, and any shape such as powder or sheet may be used. For example, the tape-like thing obtained using the carbon hollow electrode developed previously by the present inventor can be applied (Japanese Patent Application No. 2002-192749). The carbon nanotubes to be brazed to the substrate are usually planar (sheet-like), about 0.1 to 5 μg / mm ² , and usually about 1 to ² μg / mm ² .

  The carbon nanotubes to which the metal or metal compound is attached are preferably in an aggregated state. For example, they are attached to a substrate, aggregated, or formed into a tape shape or a sheet shape.

This CNT spraying substrate is used as a substrate when depositing metal on CNTs to obtain a CNT layer with a uniform thickness during coating or spraying. It does not contaminate CNTs and is used in a vacuum. Any material can be used as long as it is possible. Typical examples include glass, metal plates, ceramics and the like. Preferably, the CNT-coated surface is mirror finished. As for the method of applying and spreading CNTs, there can be used a method in which CNTs are dispersed in a solvent and sprayed, a method in which a tape or sheet-like CNT aggregate is placed and pressed with a wire mesh or the like. At this time, the bonding force between the substrate and the CNTs is sufficient as long as it has an adhesive force capable of vapor deposition, and the above method is sufficient.

  Metals or metal compounds improve the adhesion (wetting properties) between CNT and brazing material and improve the adhesion of CNT to the substrate. Both carbon and brazing material have better wettability than brazing material. It preferably satisfies the requirements such as a high melting point, does not adversely affect carbon and the substrate, and can perform vacuum deposition.

  Here, the wettability is good when the interfacial energy of the vapor-deposited metal or metal compound is γA, the interfacial energy of the brazing material is γB, and the interfacial energy at the contact portion between the vapor-deposited metal or metal compound and the brazing material is γAB. ΓA + γB ≧ γAB. In this state, the metal or metal compound is compatible with the brazing material, and brazing becomes possible.

  Further, the melting point of the metal or metal compound is preferably the melting point of the brazing material + 100 ° C. or more, preferably the melting point of the brazing material + 500 ° C. or more. The lower limit of the melting point is not less than the melting point of the brazing material.

Furthermore, the metal or metal compound attached to the CNT and the brazing material are combined to form an alloy, so that the metal or metal compound attached to the CNT and the brazing material are integrated to obtain a higher bonding force. In addition, it is possible to achieve both a low brazing temperature and a high use temperature by combining materials whose melting points are higher when alloyed than the melting points of metals or metal compounds and brazing filler metal alone.

  Or what a metal or a metal, and a brazing material form a eutectic is also preferable. For example, there are combinations such as In—Ni, In—Sn, and Pb—Sn.

  Specific examples of the metal include nickel, tin, lead, copper and the like. Examples of metal compounds include oxides such as ITO (tin doped indium oxide).

  As a method for attaching metal or metal compound particles to CNTs, the amount of adhesion can be controlled uniformly by using vapor deposition. Vapor deposition as used herein means physical vapor deposition performed in vacuum, for example, vacuum deposition method in which a metal is sublimated and evaporated with a heater, a method using an electron gun, ion plating, and sputtering.

  A metal or a metal compound is attached to a part of the CNT. The part in this case means that when observed with an electron microscope or the like, CNTs are observed between the metal or metal compound on the adhesion surface, that is, it is not necessary to adhere to the entire surface.

  The adhesion amount of the metal or metal compound to the CNT is usually about 0.1 to 10 μm, preferably about 1 to 4 μm in terms of film thickness. However, a sufficient effect can be obtained with a film thickness of 1 μm or less. In this case, for example, when aluminum (Al) is deposited to a thickness of 10 to 100 μm, the aluminum forms a thin film, and the CNT applied to the substrate can be taken out in a sheet form. It is also possible to do.

  The brazing material is a metal (including an alloy) or a metal compound having a melting point lower than that of the CNT and the base material, and has good wettability to the CNT and the base material. The melting point of the brazing material is the melting point of the base material −500 ° C. or less, preferably the melting point of the base material −800 ° C. or less. The lower limit of the melting point is about 100 ° C.

  As an example of the brazing material, in the case where the base material is stainless steel, indium, solder (Sn—In series, Sn—Pb series, etc.), other low melting point metals, alloys, and the like can be used.

  When glass is used as the base material, it is possible to obtain a considerably high adhesive force even if In is used, but it is desirable to use a conductive inorganic material having a high adhesive force with glass such as solder for glass and ITO. It is preferable to use it. In this case, it is desirable that the metal deposited on the CNT is a material that forms a compound with a brazing material such as tin or In.

The shape, material, and the like of the base material are determined according to the use of the CNT brazing material, but as a material, generally, a metal such as stainless steel, nickel, copper, and a copper alloy, glass, ceramics, or the like is used. The size is about 1 to 750,000 mm ³ , usually about ³ to 500 mm ³ , and the area of the CNT brazing surface is about ² to 400,000 mm ² . The brazing surface can be subjected to processing such as mirror surface processing, plating processing, or preprocessing such as degreasing and oxide film removal, such as ion bombardment.

  In the present invention, the brazing material is first adhered to the brazing surface of the substrate. However, conversely, the metal or metal compound attached to the CNT may be attached and brazed to the brazing surface of the substrate.

  Vapor deposition is preferable because the brazing material adheres uniformly to the base material surface, but other adhering means, for example, dispersion of powder brazing material, spraying of suspension or solution or application by other means, foil, etc. Any means such as pasting may be used. The adhesion amount of brazing may be about 5 to 200 μm, usually about 10 to 100 μm in thickness.

  The brazing of the CNTs to the substrate is performed by bringing the CNTs into close contact with the substrate surface in this state.

The adhesion of the CNTs to the substrate surface may be achieved by pressing the CNTs against the substrate surface if the CNTs are attached to the substrate or the like, or if the CNT is a molded product such as a film or sheet. The pressing pressure need not be particularly strong, and may be, for example, about 0.1 g / cm ² or more, particularly about 1 g / cm ² or more, and may be due to the weight of the substrate or the substrate.

  Heating may be performed in an atmosphere in which the brazing material and the metal or metal compound are not denatured. This may be in the atmosphere as long as the brazing material and the metal or metal compound are stable and the CNT does not denature. If necessary, a vacuum (reduced pressure) or an inert gas atmosphere such as He or Ar is used. The heating temperature is a temperature at which the brazing material is melted, and the melting point of the brazing material is 50 ° C. or higher, and preferably the melting point + 200 ° C. or higher. The upper limit of the heating temperature is a range in which the substrate or the like does not change or melt. For example, when indium is brazed to SUS, about 200 to 500 ° C. is appropriate. The heating time may be sufficiently brazed, and 10 minutes is sufficient.

  FIG. 1 is a diagram showing a schematic procedure of a method of brazing carbon nanotubes to a base material, which is a practical example of the present invention.

As shown in the figure, first, CNT was applied or dispersed on a CNT coating substrate. This CNT-coated substrate is a disk made of SUS304 and having a mirror-finished surface with a diameter of 30 mm and a thickness of 5 mm. CNT is dispersed in methyl alcohol at a concentration of 0.03 mg / ml, and this is circular in the approximate center of the substrate. An amount of 0.007 μg / mm ² of CNT was sprayed on. After evaporating the solvent, 4 μg / mm ² (4 μm thickness) of nickel was vacuum-deposited on the surface of the substrate on which the CNTs were adhered.

A stainless steel (SUS304) disk having a diameter of 10 mm and a thickness of 10 mm was used as a substrate to which CNTs were adhered, and indium was vacuum-deposited on the brazed surface of the substrate at 70 μg / mm ² .

The CNT adhering surface of the substrate was aligned with the indium deposition surface of the base material and heated to about 500 ° C. for 10 minutes in a vacuum of 5 × 10 −3 Pa to melt the indium of the brazing material. At that time, an adhesive force of about 8 g / cm ^{2 is} applied depending on the weight of the base material or the CNT coating substrate. As a result, the molten In forms a eutectic compound with Ni, and the In and Ni, that is, the CNT on which Ni is deposited, and the substrate are bonded. Note that In only wets the Ni-deposited portion of CNT, and Ni adheres to only one surface of the CNT coating film, so that only the Ni deposition surface of the CNT coating film is wet with In. Thus, the CNT is not buried in In.

  After cooling, when the substrate for CNT spraying and the base material were peeled off, the CNT coating film was peeled off from the substrate for CNT spraying and was uniformly bonded to the base material.

  As a result of blowing air at a flow rate of 5 m / min on the CNT bonding surface of the base material bonded in this manner, a small part of the CNT on the surface layer was scattered, but the CNT was peeled off at any location of the bonded area. I couldn't see it. From this, the scattered CNT is an impurity, in other words, a state in which there is almost no bonding with other CNTs and the substrate adhering to the surface of the CNT film.

  FIG. 2 shows a schematic procedure of a brazing method which is another embodiment of the present invention.

In this example, an aggregate of tape-like CNTs obtained in the example of Japanese Patent Application No. 2002-192749 was used. The tape-like CNT had a thickness of 100 μm and contained 2 μg / mm ² of CNT.

  After vacuum-depositing Ni on both sides of the tape-like CNT, it was punched into a circle having a diameter of 10 mm, although not essential. The thickness of Ni was 5 μm each.

On the other hand, two stainless steel (SUS304) disks having a diameter of 10 mm and a height of 10 mm were prepared as substrates, and In was vacuum-deposited to a thickness of 50 μm on each side. The In vapor-deposited surfaces of both substrates were faced to each other, and CNTs in which the Ni was vacuum-deposited on both surfaces were sandwiched therebetween. This 5 × ¹⁰ - heated 3 Pa 30 minutes at about 500 ° C. in a vacuum of.

  When both substrates were peeled off after cooling, CNTs were adhered to the peeled surfaces of the respective substrates, and neither brazing material nor vapor deposited metal was found on the CNT surfaces that appeared.

When the electron emission characteristics of the CNT brazing substrate thus obtained were measured, an average current density of 100 μA / mm ² could be obtained at an electric field strength of about 4 V / μm. This value is equivalent to that in a state where CNT is simply applied to a SUS substrate, and higher adhesive strength can be obtained without impairing the electron emission characteristics.

  A schematic procedure of a brazing method which is still another embodiment of the present invention is shown in FIG.

In this example, Ni was further vacuum-deposited on the CNT brazing surface of the CNT brazing substrate obtained in Example 1 to 4 μg / mm ² (thickness 4 μm).

On the other hand, 70 μg / mm ^{2 of In was} vacuum deposited on one surface of a stainless steel (SUS304) disk having a diameter of 10 mm and a height of 10 mm as another substrate.

The combined base Ni vapor deposited CNT brazing surface In the deposition surface of the disk, which 5 × ¹⁰ - heated 3 Pa 30 minutes at about 500 ° C. in a vacuum of.

  When both substrates were peeled off after cooling, CNTs were adhered to the peeled surfaces of the respective substrates, and neither brazing material nor vapor deposited metal was found on the CNT surfaces that appeared.

When the electron emission characteristics of the CNT brazing substrate thus obtained were measured, an average current density of 100 μA / mm ² could be obtained at an electric field strength of about 4 V / μm. This value is equivalent to that in a state where CNT is simply applied to a SUS substrate, and higher adhesive strength can be obtained without impairing the electron emission characteristics.

  In Examples 2 and 3, CNT is selectively bonded to the brazing material adhering portion of the base material by patterning the brazing material vapor deposition on one of the base materials with lithography or a mask at the time of vapor deposition. I was able to.

Comparative example

  For comparison, FIG. 4 shows an outline of a procedure in which CNT is brazed to a substrate without performing a pretreatment with a metal or a metal compound.

  Indium was deposited on one side of the same SUS substrate as in Example 1 in the same manner as in Example 1.

  The same CNT as in Example 1 was sprayed on the indium vapor deposition surface as an alcohol suspension.

  After evaporation of the solvent, the substrate was heated as in the example, and the CNTs were brazed to the substrate.

  After cooling the base material, an air flow rate of 5 m / min was blown onto the CNT-spreading surface. As a result, about 95% of the CNTs were scattered and only a small part of the CNT adhered to the base material.

  The thing brazed by the method of the present invention has high bonding strength, low gas emission characteristics, and high electron emission characteristics, and therefore can be used as an electron emission source. Applications include electron beam sources, fluorescent display tubes, FEDs, and the like.

It is process drawing which shows the schematic procedure of the brazing method to the base material of the carbon nanotube which is one Example of this invention. It is process drawing which shows the schematic procedure of the brazing method to the base material of the carbon nanotube which is another Example of this invention. It is process drawing which shows the schematic procedure of the brazing method to the base material of the carbon nanotube which is another Example of this invention. It is process drawing which shows the schematic procedure of the brazing method to the base material of the carbon nanotube which is a comparative example of this invention.

Claims (7)

  A method of brazing a carbon nanotube to a base material, comprising attaching a metal or a metal compound to a part of the carbon nanotube and then brazing the base material using a brazing material   2. The brazing method according to claim 1, wherein the carbon nanotube to which the metal or the metal compound is attached is attached on the substrate.   The brazing method according to claim 1, wherein the carbon nanotube is a sheet-like aggregate, and a metal or a metal compound is adhered to both surfaces thereof.   2. The brazing method according to claim 1, wherein the carbon nanotube to which the metal or metal compound is attached is a carbon nanotube aggregate in which the base material is brazed.   The brazing method according to claim 1, 2, 3, or 4, wherein the metal or metal compound is attached to the carbon nanotube by vapor deposition of the metal or metal compound.   The brazing method according to claim 1, 2, 3, 4 or 5, wherein the metal or the metal compound and the brazing material form an alloy.   Field emission electron source in which carbon nanotubes are bonded to a substrate via a metal or metal compound and a brazing material

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