KR20080045858A - A composition of carbon nanotube paste and process for preparing an electron emitter using the composition - Google Patents

Abstract

A carbon nanotube paste composition and a manufacturing process of field emission emitter using the composition are provided to obtain better development by employing alkaline aqueous solution or organic solvent as a developer, and to improve field emission by facilitating dispersion of carbon nanotube. A manufacturing method of carbon nanotube paste composition comprises steps of: sonication of a mixture comprising solvent and carbon nanotube; applying shear force on the mixture by flowing the mixture solution in a fine tube with high pressure in order to minimize aggregation of carbon nanotube for stable dispersion state; and preparing a paste. The sonicated mixture is optionally coated with coating material in the amount of 0.5-2 times as much as the carbon nanotube powder by weight and dried for stable dispersion state. The paste composition comprises 1-10% by weight of carbon nanotube, 5-25%by weight of copolymer resin of glycidyl (meth)acrylate and (meth)acrylic acid, 1-5% by weight of photopolymerization initiator, 5-10% by weight of photopolymerization monomer, 1-5% by weight of glass frit, 1-30% by weight of conductive metal powder and 15-80% by weight of organic solvent. A manufacturing process of field emission emitter comprises steps of: printing or spraying the carbon nanotube paste; drying the coated film; and exposing the resultant film to light, developing and calcining the resultant.

Description

A composition of carbon nanotube paste and process for preparing an electron emitter using the composition}

1 is a graph showing a change in current density according to the intensity of the electric field of Example 1,2 and Comparative Example 1,2.

2 and 3 are image photographs of Example 1 and Comparative Example 2 developed after printing, drying, and exposure.

FIG. 4 is an SEM image of a cross section after the carbon nanotube emitter is formed in Example 1. FIG.

The present invention relates to a paste composition including carbon nanotubes, which are field emission materials, and a method of forming a cathode electrode of a field emission device using the same.

In general, the field emission display device emits electrons from an emitter, which is a field emission material formed on the cathode electrode, by using a quantum mechanical tunneling effect, and the emitted electrons collide with the fluorescent film attached to the anode electrode to emit light. It is an element to implement. Spint type emits electrons at the tip of the emitter tip when positive electrode is applied at the external gate electrode to the cone-shaped emitter tip of molybdenum or silicon, and the emitted electron is discharged to the phosphor coated anode electrode. They collide with each other to play the role of a display device. However, the spin type emitter has a problem in that it is difficult to form the electrode in a fine pattern, the operation voltage is very high and there is a problem that the performance degradation due to deterioration of the tip.

In order to improve the problem of the field emission display device using the silicon tip, a field emission display device using carbon nanotubes having excellent chemical emission characteristics and field emission characteristics has been proposed. Field emission devices using carbon nanotubes have been tried in the form of growing carbon nanotubes directly on cathode electrodes and using them as emitters, and forming cathode electrodes using mass-produced carbon nanotubes in an appropriate manner. The growth temperature of the carbon nanotubes is too high, resulting in deformation of the substrate, it is difficult to form an emitter on a large area of the substrate. In the latter case, in order to form the carbon nanotubes in the form of particles in the form of a cathode of a fine pattern, a method of forming a photosensitive paste composition and developing the developer or using electrophoresis has been attempted. There is a problem such that the contact resistance is increased or the polymer material remaining after the emitter is formed to prevent the field emission of the carbon nanotubes is not completely made.

In the field emission device using carbon nanotubes, dipole and triode structures are commonly used. A field emission display device having a triode structure typically includes a pair of opposing cathode and anode substrates and a cathode electrode provided on one surface of the cathode substrate. An insulating layer has a gate electrode thereon and an anode electrode is included on one surface of the anode substrate. As described above, the cathode electrode has a structure having an insulating layer and a gate electrode in addition to the electrode and the emitter. To this end, carbon nanotubes must be subjected to processes such as deposition, photoresist coating, exposure, development, etching, and photoresist removal. The emitter electrode is formed on the substrate in the last step, and is produced by firing at a high temperature of more than 400 ℃. At this time, uneven dispersion of carbon nanotubes causes uneven field emission between the devices, and the amount of carbon nanotubes exposed to the surface of the devices is small so that sufficient current density cannot be obtained. There is a problem in that the number of emitters must be increased.

The present invention is to solve this problem is to uniformly disperse the carbon nanotubes, to adjust the composition of the composition is possible fine pattern while improving the contact between the electrode and the carbon nanotubes and exposed carbon nanotubes on the surface of the electrode structure The purpose of the present invention is to improve the ratio of the tube and to obtain excellent field emission characteristics while using a small amount of carbon nanotubes.

Hereinafter, a method of manufacturing a field emitter of a carbon nanotube paste composition and a field emission display device according to a preferred embodiment of the present invention will be described.

 Carbon nanotubes are materials with excellent physical and electrical properties, and are being applied to various fields due to their high applicability to nanocomposites as well as optoelectronic devices and electrical materials. Combination is required, and uniform dispersion of carbon nanotubes has emerged as an important issue. In the present invention, the carbon nanotubes are dispersed in the solvent using strong shearing force by flowing the mixture at high speed and high pressure together with the method of sonicating the carbon nanotubes mixed with the organic solvent for uniform dispersion. A uniform dispersion can be obtained with minimal damage to the tube.

The composition of the present invention is 1 to 10% by weight of carbon nanotubes, 5 to 25% by weight of a copolymer of glycidyl (meth) acrylate and (meth) acrylic acid, 1 to 5% by weight of a photopolymerization initiator, and 5 to 10% by weight of a photopolymerization monomer. %, 1 to 5% by weight of glass frit, 1 to 30% by weight of conductive metal powder, and 15 to 80% by weight of organic solvent.

The carbon nanotubes use single-walled or double-walled carbon nanotubes, which are known to have excellent field emission characteristics, and multi-walled carbon nanotubes having a thickness of 3 to 10 nm. If the content of carbon nanotubes in the paste is less than 1% by weight, the current density of the field emission device may be lowered. If it exceeds 10% by weight, the printability of the paste may be poor due to the high surface area of the carbon nanotubes. have. In addition, after obtaining a stable dispersion state by minimizing the aggregation of carbon nanotubes by applying a shearing force by applying a shear force to the microtube after ultrasonication of the mixture with the solvent in order to obtain a uniform dispersion state of the carbon nanotubes, carbon nanotube paste To prepare. Preferably, after dispersing the carbon nanotubes do not have a dissolving power in the organic solvent used in the paste, it is used by coating with a material that is pyrolyzed at a temperature of 400 ℃ or less.

The acrylic copolymer resin uses a copolymer resin of glycidyl (meth) acrylate and (meth) acrylic acid having an acid value of 100 mg KOH / g or more, but an epoxy acrylate may be used, and in addition to the acrylic resin dissolved in an aqueous alkali solution, Solvent hydroxy cellulose can be used in a mixture of 1/5 to 1/10 weight ratio of the acrylic resin. When the content of the acrylic copolymer resin exceeds 25% by weight, the carbon nanotubes are not sufficiently exposed to the surface or the contact resistance is high, and the field emission characteristics are deteriorated by the residual resin component after firing, 5% by weight. In the following cases, there is a problem that sufficient developability cannot be obtained.

 As the photopolymerization monomer, a compound having two or more double bonds such as trimethyl propane triacrylate, trimethyl propane ethoxylated triacrylate, pentaerythritol triacrylate, and dipentaerythritol hexaacrylate can be used. Preferably, two or more monomers are mixed and used.

As the photopolymerization initiator, a benzophenone-based, acetphenone-based or thioxanthone-based compound may be used. However, when the content is less than 1% by weight, sufficient polymerization does not occur during exposure, and when the content exceeds 5% by weight. There is a problem that the reaction occurs excessively during exposure, so that an appropriate development pattern cannot be obtained.

The glass frit enables carbon nanotubes to be stably attached and operated on a substrate, but when the content exceeds 5% by weight, there is a problem of deteriorating the field emission characteristics of the carbon nanotubes.

The conductive metal powder may use silver and copper powder having excellent conductivity to smoothly supply current to the carbon nanotube emitter, and particles having a particle size of 0.1 to 1 μm may be used. If the supply effect is not obtained and the content is more than 30%, there is a problem that the carbon nanotubes are prevented from being present on the surface to lower the current density.

The organic solvent is preferably a solvent having a high boiling point such as terpineol, texanol, carbitol acetate, butyl carbitol acetate, benzyl alcohol, phenoxyethanol, and the like.

Hereinafter, a method of manufacturing a carbon nanotube paste and a method of manufacturing an emitter will be described.

In the carbon nanotube paste of the present invention, in order to uniformly disperse carbon nanotubes in a solvent, carbon nanotubes are mixed with an organic solvent, and ultrasonic dispersion having an output of 1 Kw or more is predispersed to the carbon nanotubes, and the mixed solution is applied to a fine tube. It flows at high pressure and high speed to make dispersion by high shear force. In order to improve the field emission characteristics, the surface of the carbon nanotubes may be coated with a material that does not dissolve in the solvent used in the paste. For example, after dissolving sucrose insoluble in organic solvents in water, the carbon nanotubes are mixed, followed by performing the above dispersion process and drying.

Acrylic copolymer, photopolymerization monomer, photopolymerization initiator, glass frit, and conductive metal powder are added to the coated carbon nanotube or carbon nanotube dispersion and mixed, and then the roll-to-roll distance of the 3-roll-mill is adjusted and passed through five times. The carbon nanotube paste is prepared by uniformly dispersing it. The prepared paste is sprayed by printing or diluted to an appropriate viscosity to form a film, dried at 80 ° C. to evaporate the organic solvent, and then exposed using a mask having a designed pattern. In this case, the exposure energy is preferably 200 to 1000 mJ / cm 2, and can be adjusted according to a desired film thickness. The exposed film is developed by spraying 0.4 wt% to 2 wt% aqueous sodium carbonate solution and washed with pure water. Ultrasonic cleaners can be used to effectively remove residues during cleaning.

The developing film is baked in an air or nitrogen atmosphere at a temperature of 400 to 500 ° C. for 20 minutes to 40 minutes to prepare a carbon nanotube emitter. When the firing temperature is 400 ℃ or less, there is a problem that the field emission characteristics are not removed because the organic matter is not removed or the adhesion strength to the substrate is lowered because the glass frit is not melted. If the temperature is above 500 ℃, carbon nanotubes are oxidized or thermally decomposed to obtain the field emission characteristics. There is a problem of deterioration.

Hereinafter, examples of the present invention will be described. The following examples are merely for the purpose of more clearly expressing the present invention, and the contents of the present invention are not limited to the following examples.

(Example 1)

2% by weight of carbon nanotubes and 20% by weight of texanol were mixed and predispersed by applying an ultrasonic wave of 3 kW. Then, a pressure of 18000 psig was applied to a disperser (US microfluidics microfluidizer) using a 100 uM diameter tube. Pass twice to disperse the carbon nanotubes. 10% by weight of commercially available Elvasite was dissolved in 20% by weight of terpinol, and added to a mixed solution of carbon nanotubes dispersed therein, followed by stirring, with 2% by weight of trimethyllopropaneethoxylate triacrylate and trimethylropropane as a photopolymerization monomer. 2% by weight of triacrylate, 1% by weight of Irgacure 369 (manufactured by Ciba Chemicals), 1% by weight of Darocur ITX (manufactured by Ciba Chemicals), 2% by weight of glass frit, 20% by weight of silver powder 10 wt% of Sanol 10 wt% of Terpinol is added and stirred for 30 minutes. The mixture was passed through a three-roll-mill five times or more to prepare a paste to sufficiently disperse the composition, and a carbon nanotube emitter was manufactured by printing, drying, exposure, developing, and washing.

(Comparative Example 1)

The carbon nanotube mixture was dispersed with a 3-roll-mill in which an acrylic binder and other compositions were added while stirring, without pre-dispersing the carbon nanotube mixture, to prepare a paste, and to prepare a carbon nanotube emitter through the same process.

(Comparative Example 2)

In Example 1, a paste was prepared using an acrylic binder having no acid value instead of the acrylic binder, and a carbon nanotube emitter was manufactured through the same process.

Example 2

5 wt% of carbon nanotubes are mixed with 5 wt% of sucrose aqueous solution, sonicated, passed through a disperser using a 100 uM diameter tube, and dried to obtain sucrose coated carbon nanotubes. 10% by weight of commercially available 3% by weight of sucrose-coated carbon nanotubes (Elvasite) was added to a mixed solution of 20% by weight of terpinol and stirred while trimethylpropane ethoxylate triacrylate 2 as a photopolymerization monomer. % By weight, 2% by weight of trimethylpropane triacrylate, 1% by weight of Irgacure 369 (manufactured by Ciba Chemicals), 1% by weight of Darocur ITX (manufactured by Ciba Chemicals), 2% by weight of glass frit, 20% by silver photopolymerization initiator % Is mixed, 29% by weight of texanol and 10% by weight of terpinol are added and stirred for 30 minutes. The mixture was passed through a three-roll-mill five times or more to allow the composition to be sufficiently dispersed to prepare a paste, and a carbon nanotube emitter was manufactured by printing, drying, exposure, developing, and washing.

1 is a graph showing a change in current density according to the intensity of the electric field of Example 1,2 and Comparative Example 1,2. It can be seen that the current density of Examples 1 and 2 and Comparative Example 2, which is the case of linear dispersion in order to improve the dispersion of carbon nanotubes, is higher than that of Comparative Example 1.

2 and 3 show image photographs of Example 1 and Comparative Example 2 developed after printing, drying, and exposure. In the case of Comparative Example 2 it can be seen that the development is not at all.

FIG. 4 is an SEM image of a cross section after the carbon nanotube emitter is formed in Example 1. FIG. It can be seen that the carbon nanotubes are densely present on the surface in the same length.

Therefore, it can be seen that the carbon nanotube emitter can be effectively formed when forming the paste composition and the field emission device using the same, and the current density can be improved.

As described above, the carbon nanotube paste of the present invention has good developability by using an aqueous alkali solution or an organic solvent as a developer, and improves the field emission characteristic by improving the dispersibility of carbon nanotubes.

Claims (4)

A method of producing a carbon nanotube paste after obtaining a stable dispersion state by minimizing agglomeration of carbon nanotubes by applying a shearing force by flowing a solvent and a carbon nanotube mixed solution at a high pressure through a microtube after ultrasonication when preparing the carbon nanotube paste. The method of claim 1, wherein the carbon nanotube paste is coated with a coating material of 0.5 to 2 times the weight of the carbon nanotube powder and dried to impart dispersion stability. The method according to claim 1, wherein 1 to 10% by weight of carbon nanotubes, 5 to 25% by weight of a copolymer of glycidyl (meth) acrylate and (meth) acrylic acid, 1 to 5% by weight of a photopolymerization initiator, and 5 to 10% by weight of a photopolymerization monomer. A paste composition comprising 1% to 5% by weight of glass frit, 1 to 30% by weight of conductive metal powder, and 15 to 80% by weight of organic solvent. A method of manufacturing an emitter for a field emission display device comprising the steps of printing or spraying the carbon nanotube paste of claim 1, drying the coating film, exposing and developing the film, and baking the same.

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