KR20020005325A - Method for fabricating electromagnetic wave compatibility materials using carbon nanotube or carbon nanofiber, and materials thereby - Google Patents

Abstract

PURPOSE: A method for manufacturing an electromagnetic wave shielding and absorbing material using a carbon nano tube and a carbon nano fiber, and an electromagnetic wave shielding and absorbing material manufactured thereby are provided to achieve an easy manufacturing method, that is environmental-friendly. CONSTITUTION: A carbon nano tube or carbon nano fiber(5) is added to a matrix(20). A mixing ratio of the carbon nano tube or carbon nano fiber to the matrix is adjusted to make an electric conductivity of an electromagnetic wave shielding and absorbing material becoming about 100S/cm. The carbon nano tube or carbon nano fiber is used in a state that there is a catalyst used in growth of the tube or fiber. A ferrite is additionally added. A nano wire to inside of which a metal is added is used in the carbon nano tube. The carbon nano tube or carbon nano fiber is added in the minimum amount, thereby reducing a cost.

Description

Method for manufacturing electromagnetic shielding and absorbing material using carbon nanotubes or carbon nanofibers, and electromagnetic shielding and absorbing material produced by the above method.

The present invention relates to an electromagnetic shielding and absorbing material for shielding electromagnetic waves that cause malfunction of the electronic device, and more particularly to a method of manufacturing an electromagnetic shielding and absorbing material using carbon nanotubes or carbon nanofibers and the method It relates to a manufactured electromagnetic shielding and absorbing material.

Carbon nanotubes have recently been in the spotlight due to their small size. Synthesis methods of the carbon nanotubes include an electric discharge method, a laser deposition method, a thermal decomposition deposition method, a thermochemical vapor deposition method, a plasma chemical vapor deposition method and the like. In addition, the structure of the carbon nanotubes may vary depending on the presence and type of transition metal used as a catalyst. The carbon nanotubes are several nanometers in diameter, can be manipulated with a conductor or a semiconductor, and have a strength about 10 times that of steel. In addition, the tube is infinitely available due to its hollow and thin structural properties. Referring to FIGS. 1A and 1B, while the volume occupied by the spherical particles 1 for contact is about 74% by volume (FIG. 1A), the tube-shaped particles 5 have a length with respect to the particle diameter. Since the ratio of is large, the three-dimensional connection, that is, the network structure, is possible with one to several volume% of moisture.

Recently, due to the harmfulness to the human body has been tightening regulations on electromagnetic waves. Electromagnetic waves are energy waves combined with electric and magnetic fields. Electromagnetic waves at 200 MHz or higher can dominate electromagnetic waves through shielding of electric fields, but electromagnetic and magnetic fields should be shielded together at electromagnetic waves below 200 MHz.

The electromagnetic shielding and absorbing material for shielding the electromagnetic wave may be shielded by transmitting, reflecting, or absorbing the electromagnetic wave according to the conductivity of the constituent material, that is, the retention of the movable charge. When the electromagnetic shielding and absorbing material does not have a mobile charge, the electromagnetic wave is transmitted through the shielding material, and when the electric charge is small but the resistance is small and energy is not consumed by Joule heat, the electromagnetic wave is absorbed. .

Currently used electromagnetic shielding and absorbing material is a metal, electromagnetic shielding and absorbing material using a metal is manufactured by the following method to reflect or scatter shielding electromagnetic waves.

The first metal particles, that is, copper or silver, are applied to an object for shielding electromagnetic waves, for example, inside the mobile phone. Secondly, a metal fiber is dispersed and used in a matrix such as plastic or polymer, and the metal fibers form a mesh structure to shield electromagnetic waves. Third, there is a shielding method by a metal thin film or a metal thick film.

Electromagnetic shielding and absorbing material using the metal fiber has the following problems.

First, the shield simply reflects or scatters electromagnetic waves. Thus, the shielding material can protect the human body, but the reflected electromagnetic waves affect the device again, increasing the malfunction and noise of the device.

Second, although a metal particle having a small particle diameter and a long length is required to obtain a mesh structure of the metal fiber in the matrix, the metal fiber having a small particle diameter is expensive to manufacture and can be easily broken.

In addition, the conventional electromagnetic shielding and absorbing material has a disadvantage that it can not completely shield the magnetic field generated in the low frequency electromagnetic waves of 200MHz or less.

The present invention has been made to improve the above-mentioned conventional problems, an object of the present invention is to absorb and shield electromagnetic waves of all frequency ranges, and to easily manufacture a network structure in a small amount, it is natural and environmentally friendly and manufactured The present invention provides a method for producing an electromagnetic shielding and absorbing material using carbon nanotubes or carbon nanofibers, which is inexpensive, and an electromagnetic shielding and absorbing material prepared by the above method.

1A is a schematic view showing contact of spherical particles in a space;

Figure 1b is a schematic diagram showing the network structure of the fibrous particles in a certain space according to an embodiment of the present invention;

2A, 2B, and 2C are cross-sectional views showing catalytic metal particles remaining in various forms on carbon nanotubes in the electromagnetic shielding and absorbing material of the present invention;

3A is a schematic diagram showing a process of absorbing electromagnetic waves in a conductor of a film structure;

Figure 3b is a schematic diagram showing the electromagnetic wave absorption process in the conductor of the network structure of the present invention; And,

Figure 4a is a schematic diagram showing that an appropriate amount of ferrite is added to the composite of the carbon nanotubes or fibers and the matrix according to another embodiment of the present invention, Figure 4b is an empty space of the carbon nanotubes according to another embodiment of the present invention It is sectional drawing of the nanowire to which the metal was added.

Brief description of the main parts of the drawing

1: spherical particle

5: Carbon nanotubes or fibers filled with or filled with catalytic metal

7: ferrite

9: carbon nanotubes used as formwork

11: catalytic metal

13: carbon nanotube

15: electromagnetic waves

17: metal

20: matrix

30: conductor film of film structure

40: conductor film of the network structure

A: charge transfer path in the conductor film of the film structure

B, C: charge transfer path in the conductor film of the network structure

The present invention relates to a method for producing an electromagnetic shielding and absorbing material consisting of adding carbon nanotubes or carbon nanofibers to a matrix, and to an electromagnetic shielding and absorbing material prepared by the method.

The mixing ratio of the matrix and carbon nanotubes or carbon nanofibers is controlled so that the electrical conductivity of the electromagnetic shielding and absorbing material is about 100 S / cm.

In addition, the carbon nanotubes or carbon nanofibers may be used in a state where a catalyst used for growth of the tubes or fibers is present.

The method of manufacturing the electromagnetic shielding and absorbing material may preferably further include adding ferrite.

The carbon nanotubes may be used in the form of nanowires in which a metal is added therein by using a liquid phase method or a gas phase method.

In the electromagnetic shielding and absorbing material of the present invention, carbon nanotubes or carbon nanofibers form a mesh structure in a matrix. In this case, carbon nanotubes or carbon nanofibers have a large length ratio with respect to the particle diameter, and according to percolation theory, the network structure may be achieved with one to several volume% of moisture.

At this time, the point to look at the complete network structure is the contact resistance between the tube or fiber. In other words, if the contact resistance is high, it cannot be used as a conductor. However, not only the resistance of the carbon nanotubes themselves but also the resistance side at the contact surface between the tubes has no problem in using the mesh structure as a conductor.

The resistance is controllable by controlling or doping the structure of the fiber or tube. In general, the most favorable conductivity for electromagnetic wave absorption is known to be about 100 S / cm and can be obtained by controlling the material manufacturing process and controlling the mixing ratio of the matrix and carbon nanotubes or carbon nanofibers. In addition, the provision of appropriate conductivity allows for electrostatic discharge.

In addition, the electromagnetic shielding and absorbing material of the present invention can absorb not only high frequency electromagnetic waves but also low frequency electromagnetic waves. Catalytic metals such as Fe, Co, Ni, and the like used in the synthesis of carbon nanotubes or carbon nanofibers are end portions (1), body portions (2), and root portions (tubes) of the tubes or fibers as shown in FIGS. 2A, 2B, and 2C. 3) will be stuck. Until now, the catalytic metal is treated as an impurity and is recognized as a big problem in purification. However, the catalytic metal is a transition metal and a ferromagnetic material that plays a large role in shielding the magnetic field, thereby efficiently blocking electromagnetic waves in the low frequency region. Therefore, the present invention can absorb and shield electromagnetic waves of various frequencies by using the catalyst metals used to grow carbon nanotubes without purification.

Referring to FIG. 4B, the carbon nanotubes or carbon nanofibers may be dispersed in a matrix to form a three-dimensional network structure. The mesh structure may have a higher electromagnetic shielding absorption capability than the film structure of FIG. 4A. That is, the film structure 30 forms a path, for example, A, which is not varied with respect to the incident electromagnetic wave 15, but the network structure 40 has different paths with respect to the electromagnetic waves of various frequencies that are incident, such as B and C. Can be reacted to achieve efficient absorption. Looking at the absorption process of the electromagnetic wave, the incident electromagnetic wave is converted into thermal energy by the movement of the charge, and the thermal energy is conducted along the conductive film and disappears. At this time, the charge circulation path and the circulation frequency of the conductor are closely related to the frequency of the electromagnetic wave. For low frequency electromagnetic waves we will find the corresponding short circuit path B and for high frequency electromagnetic waves we will find the corresponding long circuit path C. As shown in FIG. 3B, the carbon nanotubes or carbon nanofibers 5 form a three-dimensional network structure, and various paths such as B and C are configured with respect to the incident electromagnetic wave 15. Therefore, the electromagnetic shielding and absorbing material of the present invention can efficiently absorb and shield electromagnetic waves of various frequencies.

In addition, an appropriate amount of ferrite 7 may be added to the composite of the carbon nanotubes or carbon nanofibers 5 and the matrix 20 as shown in FIG. 4A to effectively shield the low frequency electromagnetic waves according to the present invention. Likewise, nanowires generated by adding the metal 17 to the inside of the carbon nanotubes 9 used as the form using a liquid phase method or a gas phase method may be used.

In addition, the electromagnetic shielding and absorbing material of the present invention can be applied to communication devices, home appliances, and the like.

Electromagnetic shielding and absorbing material using the carbon nanotubes or carbon nanofibers of the present invention has the following advantages.

First, since a small amount of carbon nanotubes or carbon nanofibers can be added to obtain a conductive film having a mesh structure, the cost is low. Second, since the desired physical properties can be obtained even in the very small amount, the manufacturing process of the existing electromagnetic shielding and absorbing material can be used without significant change. Third, the desired physical properties of the conductive film can be obtained by controlling the mixing ratio of the nanomaterial to be added and the matrix. Fourth, the mechanical strength of the polymer itself is increased by adding the nanotubes or fibers. Fifth, in the case of metal fibers, the surface layer is easily oxidized to form oxides, so that mechanical strength and EMI (Electromagnetic radio frequency interference / Radio frequency interference) shielding ability are deteriorated, but the surface oxidation phenomenon is obtained by using the electromagnetic shielding and absorbing material of the present invention. Since it does not occur, the phenomenon of electromagnetic wave shielding ability is not lowered. Sixth, since the affinity between the matrix and carbon nanotubes or carbon nanofibers is excellent, separation or separation of the tubes or fibers does not occur. Seventh, in the case of metal fiber, the waste of metal resources is severe and the cost of recovery and recycling is high. However, carbon in carbon nanotubes or fibers is a material that circulates in nature and thus does not require special reprocessing, and is environmentally friendly and resource-saving. Eighth, the carbon nanotubes or fibers are added to the electromagnetic shielding and absorbing material in a very small amount to form a conductive film of the network structure, and thus does not change the appearance of the product.

Claims (6)

A method of manufacturing an electromagnetic shielding and absorbing material, comprising adding carbon nanotubes or carbon nanofibers to a matrix. The method of claim 1, The mixing ratio of the matrix and the carbon nanotubes or carbon nanofibers is controlled so that the electrical conductivity of the electromagnetic shielding and absorbing material is about 100S / ㎝. The method of claim 1, The carbon nanotube or carbon nanofiber is a method of manufacturing an electromagnetic shielding and absorbing material, characterized in that used in the presence of the catalyst used for the growth of the tube or fiber. The method of claim 1, The method further comprises the step of adding ferrite electromagnetic shielding and absorbing material manufacturing method. The method of claim 1, The carbon nanotube is a method of manufacturing an electromagnetic shielding and absorbing material, characterized in that the use of nanowires with metal added therein. Electromagnetic shielding and absorbing material produced by any one of claims 1 to 5.