KR20060075234A - Composition for electromagnetic interference shielding using carbon nanotube - Google Patents

Abstract

The present invention relates to a composition for shielding electromagnetic waves using carbon nanotubes, including carbon nanotubes, metal powders, water dispersion polyurethane dispersions, solvents, and rheology modifiers. When forming a thin film, it has excellent conductivity, adhesion and shielding efficiency even at low film thickness, and provides remarkable advantages that are stable to heat and salt water. Therefore, it is effective in preventing electromagnetic waves emitted from outside as well as interference caused by electromagnetic interference between circuits of various electronic devices. Can be blocked by

Electromagnetic Shielding, Carbon Nanotubes, Conductive, Anti-Static, Water Dispersed Polyurethane Dispersion, Solvents, Rheology Modifiers

Description

Electromagnetic shielding composition using carbon nanotubes {COMPOSITION FOR ELECTROMAGNETIC INTERFERENCE SHIELDING USING CARBON NANOTUBE}             

1 is a structural diagram of a specimen for evaluating the physical properties of the composition for electromagnetic shielding of the present invention used in the embodiment of the present invention.

The present invention relates to a composition for shielding electromagnetic waves using carbon nanotubes, and more particularly, to a composition for shielding electromagnetic waves by reducing the content of metal powder and improving the electrical conductivity properties by using carbon nanotubes.

There is a growing controversy over the harmful effects on the human body of electromagnetic waves generated from internal devices of various electronic devices such as mobile communication terminals, notebook computers, office equipment, and medical devices. In addition, as the integration of devices increases due to the light weight of electronic products, electromagnetic noise generated from each component may cause peripheral devices to malfunction, causing device failure. Therefore, in recent years, in addition to strengthening shielding standards for electromagnetic waves generated from home, office, and industrial electronic products such as computers, wireless telephones, automobiles, medical devices, and multimedia players, EMI (Electromagnetic Interference) and RFI (Radio Frequency Interference) emissions have been strengthened. As regulations on Korea have been tightened, electromagnetic wave shielding measures for various electronic devices and components have emerged as important issues.

Attempts have been made to change the arrangement and design of the chip in terms of circuitry in order to block such unwanted electromagnetic waves, but this is limited. A method of enveloping the entire chip, which is a direct source of electromagnetic radiation, with a metal cabinet has been developed, but this method is not widely used because of the problem of increasing the weight and thickness of portable electronic devices.

Other methods of shielding metal particles by vacuum evaporation or electroless plating have been attempted as an electromagnetic shielding method. However, since the equipment used in such a method is expensive, reliability under severe conditions cannot be satisfied, and harmful substances are emitted, it is environmentally friendly. This is not a disadvantage.

In order to overcome this problem, conductive coating liquids for shielding electromagnetic waves containing metal powder and water-soluble urethane dispersions have been developed. However, since the metal content is high, the raw material cost is increased and the adhesion to the plastic substrate is poor. It has a problem of deterioration.

In order to reduce the cost, improve adhesion, eco-friendliness, and excellent durability in the electromagnetic shielding material using a finite resource of metal, many researches using carbon nanotubes have been conducted. However, the development of a conductive material that can exceed the performance of metals has not been made yet.

As a method of shielding electromagnetic waves of an electronic device using a conductive paint, a method of coating a paint containing an electrically conductive material such as a metal such as gold and copper into an electronic device housing is widely used. However, the plastic injection parts of electronic devices have ribs or walls to prevent interference between driving chips, and since they have a three-dimensional structure, conductive paints made of only metal have high density of the metal itself. There is a problem that a decrease in the conductivity caused by the partition wall flows down by the weight of. Therefore, a problem arises in that the thickness of the coating film is increased and the cost is increased.

The present invention is to overcome the problems of the prior art as described above, the object of the present invention is low density, even in the three-dimensional injection molding structure there is no flow phenomenon due to its own weight, excellent conductivity even at low coating amount, adhesion and wear resistance, etc. It is to provide a coating liquid composition for shielding electromagnetic waves using carbon nanotubes that exhibits excellent electrical conductivity compared to the existing conductive paints.

One aspect of the present invention for achieving the above object relates to a composition for shielding electromagnetic waves using carbon nanotubes, including carbon nanotubes, metal powder, water dispersion polyurethane dispersion, solvent and rheology modifier.                         

Another aspect of the present invention relates to a conductive thin film produced using the coating liquid composition of the present invention.

Another aspect of the present invention relates to a substrate for electromagnetic shielding, comprising the conductive film of the present invention.

Hereinafter, with reference to the accompanying drawings will be described in more detail with respect to the present invention. The composition for shielding electromagnetic waves according to the present invention includes carbon nanotubes, metal powders, water dispersion polyurethane dispersions, solvents, and rheology modifiers.

Carbon nanotubes, which are characteristically used in the present invention, have large anisotropy in structure, tens to hundreds of nanometers in diameter, and tens to hundreds of micrometers in length. There are various structures such as single-walled or multi-walled, and it has the characteristics of conductor and semiconductor depending on the wound shape. In addition, carbon nanotubes are smaller in diameter compared to their length, so when the electric field is applied, the electric field is amplified at the end of the tube. Many methods for producing carbon nanotubes have been known so far, such as electric discharge, laser deposition, plasma imaging, vapor phase synthesis, and electrolysis. In 1998, Frank used scanning probing microscopy (SPM) to convert carbon nanofibers to mercury. The conductivity was measured by supporting the liquid phase, and as a result, the carbon nanotubes reported quantum behavior and had a ballistic conductance. The conductivity of MWNTs (MWNTs) increased by 1 G _o as each nanotube was added to the mercury liquid phase. At this time, the value of G _o is 1 / 12.9 ㏀ ⁻¹ . In 1999, Sanvito et al. Measured the conductivity of multi-walled nanotubes using scattering techniques, reaffirmed Frank's results, and observed that the quantum conductive channels in the MWNTs were reduced by the interwall reaction. It was observed that the electron flow of each carbon nanotube was rearranged by this reaction.Thess et al. Used a four-point technique to measure the resistance of rope-type metallic single wall nanotubes (SWNTs). It was observed that it was about 10 ⁻⁴ μm-cm at 300 K, which was found to have a higher value than the currently known high conductivity carbon nanofibers. Frank et al. Avouris et al observed that stable current densities of 107 A / cm 2 or more and 1013 A / cm 2 or more were observed.

The present invention is being developed a lot and using a single-walled or double-walled carbon nanotubes having excellent electrical properties by mixing the electromagnetic shielding material containing an existing metal to obtain a composition for electromagnetic shielding of excellent electromagnetic shielding properties and electrical conductivity Let's do it.

One of the components for imparting conductivity in the coating liquid composition of the present invention has a carbon nanotube having a length of 50 μm or less and a width of 20 nm or less, and the content of 0.3 to 20 wt% It includes.

The metal powder usable in the conductive composition of the present invention may be used alone or in combination of silver powder, copper powder or silver coated copper powder. The amount of the metal powder used in the present invention is 5% by weight to 60% by weight. If the metal powder is less than 5% by weight, the conductivity may be insufficient, and when the metal powder is more than 60% by weight, the manufacturing cost increases. In the present invention, the average particle size distribution of the metal powder is 1 to 60 µm, and the shape thereof is preferably flake, spherical or branched.

The water-dispersed polyurethane dispersion applied in the present invention is a water-dispersed polyurethane dispersion having an aromatic functional group, which enables spraying upon coating on a plastic substrate, and may have excellent body adhesion and wear resistance after drying. Urethane dispulsation used in the present invention is a disulsion synthesized by applying a polyol using an aliphatic and aromatic polyhydric acid, the content is 0.2 wt% to 60 wt%, preferably 5wt% to 40wt% (product Weight basis). If the content of the water-dispersed urethane dispersion is less than 0.2% by weight, the adhesion and abrasion resistance of the device may be poor, and if it exceeds 60% by weight, the resistance may increase.

Alcohol solvent is used as the solvent used in the composition of the present invention, and more specifically, methanol, ethanol, isopropanol, normal butanol, isobutanol and the like can be used alone or in combination of two or more thereof. 10 to 60% by weight.

In addition, in the composition of the present invention, a rheology modifier is added to adjust the viscosity of the coating liquid. Preferred rheology modifiers usable in the present invention include crosslinked polyacrylate polymers, celluloses, urethanes, acrylic emulsion types and bentonite. The crosslinked polyacrylate polymer type is particularly preferred because it is well soluble in alcoholic solvents and is effective in preventing sedimentation of the metal and improving spray workability without affecting conductivity. Specific examples of such rheology modifiers include Carbo-pol EZ-2 manufactured by Noven. In the present invention, the content of the rheology control agent is 0.01 to 5% by weight. If the amount of rheology modifier is less than 0.01% by weight, the thickening effect may be reduced and sedimentation of the metal may occur. If the amount of the rheology control agent is greater than 5% by weight, the strong interaction with the resin may result in poor storage properties, leading to an increase in the resistance value. Can be.

The conductive composition according to the present invention may further include various additives in addition to the essential components within a range not impairing the object of the present invention.

The conductive composition according to the present invention may be coated on a substrate by a coating method commonly used in the art to form a conductive thin film. Examples of preferred coating methods include, but are not limited to, spin coating, dip coating, spray coating, flow coating, and screen printing. . The most preferred application method in terms of convenience and uniformity is spin coating.

The conductive composition according to the present invention may be applied onto a plastic substrate made of a polymer such as polycarbonate or polycarbonate alloy, acrylobutadiene styrene / polycarbonate, polyphenylsulfite, or the like.

The conductive composition according to the present invention can reduce the content of metal powder by using carbon nanotubes, and when the carbon nanotubes are formed into a network structure to reduce contact resistance and thus have excellent electrical conductivity of the coating liquid composition, they are moved when the conductive thin film is manufactured. It can solve the electromagnetic interference problem by blocking the noise generated inside the electronic devices such as communication devices, laptops, portable electronic devices, medical devices, and can prevent harmful electromagnetic waves from being emitted to the outside.

Hereinafter, the present invention will be described in more detail with reference to Examples. These embodiments are merely for illustrative purposes and are not intended to limit the protection scope of the present invention.

Example 1

Carbon nanotubes were added little by little while stirring 30 g of water-dispersed polyurethane dispersion at 2000 rpm for 30 minutes using a stirrer. The carbon nanotubes used at this time were carbon nanotubes obtained by a conventional method, having a single wall of 20 μm in length and a width of 10 nm, and having a content of 0.5 g. 25g of commercially available silver powder (SF-70A, Ferro) was added, and it stirred at 2000 rpm for 20 minutes. 41g of ethanol was added thereto and stirred at 500 rpm for 15 minutes. 3 weight% of commercially available polyacrylate polymers were added here as a viscosity modifier, and it stirred at 1000 prm for 30 minutes. The conductive composition was prepared by maintaining the temperature of the stirrer at 10 ° C. or lower for uniform dispersion. The electromagnetic shielding composition thus prepared was diluted with 100% by volume of ethanol to prepare a spray coating solution, and then spray coated onto a polycarbonate sheet. At this time, the size of the specimen was 15cm in width, 6cm in length and used as three partitions having a thickness of 5mm, width 5mm in the middle as shown in FIG. After the ethanol solvent was dried, a specimen was prepared by adjusting the spray nozzle so that the coating thickness applied to the sheet was about 12 μm. The physical properties of the prepared specimens were evaluated by the following method, and the results are shown in Table 1 below.

[Property evaluation method]

* Resistance: The surface resistance per unit area was measured using a multimeter.

Adhesion: evaluated according to ASTM D3359.

* Shielding efficiency: Measured from 30 MHz to 10 GHz using a network analyzer and set as the average value in the range.

* Thermal stability: The resistance after standing at 50 ° C. for 10 days was measured.

Salt resistance: The resistance after immersion in 5 wt% NaCl solution for 3 days was measured.

Example 2

Except that the carbon nanotube content was increased to 5g and the silver powder content was changed to 12.5g, the specimens were prepared in the same manner as in Example 1, and the physical properties thereof were shown in Table 1 below.

Example 3

Except for increasing the size of the carbon nanotubes to 50㎛ length, 20nm in width was carried out in the same manner as in Example 1 to prepare a specimen and the physical properties thereof are shown in Table 1 below.

Example 4

The specimen was carried out in the same manner as in Example 1 except that the carbon nanotube content was 0.1 g, the silver powder (SF-70A, Ferro) was 30 g, and the ethanol content was changed to 35.4 g. To prepare and evaluate the physical properties are shown in Table 1 below.

Comparative Example 1

30 g of water-dispersed polyurethane dispersion, 5 g of carbon nanotubes having a length of 20 μm and a width of 10 nm, 10 g of commercially available silver powder (SF-70A, Ferro), 5 g of ethanol, 3.5 g of polyacrylate polymer After preparing a conductive composition including a conductive composition, a specimen was prepared in the same manner as in Example 1 and the physical properties thereof were evaluated and the results are shown in Table 1 together.

Comparative Example 2

A specimen was prepared in the same manner as in Example 1 except that the carbon nanotube content was 0.05 g, the silver powder (SF-70A, Ferro Co.) was added 30 g, and the ethanol content was 36.45 g. The evaluation is shown in Table 1 together.

Comparative Example 3

The carbon nanotubes were prepared in the same manner as in Example 1 except that the size of the carbon nanotubes was 60 μm in length and 30 nm in width, and the physical properties thereof were shown in Table 1 below.

Comparative Example 4

A specimen was prepared in the same manner as in Example 1 except that 20 g of water-dispersed polyurethane dispersion, 50 g of silver powder, 26.5 g of ethanol, and 3.5 g of polyacrylate polymer were added without including carbon nanotubes, and the physical properties thereof were prepared. To evaluate the results are shown in Table 1 together.

division Coating thickness (㎛) Initial resistance (ohm / □) Adhesion Shielding Efficiency (dB) Resistance after thermal stability test Resistance after saline resistance test  Example 1 12.3 0.15 5B 85 0.17 0.15  Example 2 12.2 0.07 5B 92 0.1 0.08  Example 3 12.4 0.2 5B 93 0.23 0.21  Example 4 12.1 0.17 5B 87 0.19 0.15  Comparative Example 1 12.0 0.7 5B 75 1.0 2.1  Comparative Example 2 12.6 1.3 5B 85 3.3 3.5  Comparative Example 3 12.2 1.75 4B 85 2.5 2.9  Comparative Example 4 12.0 2.15 5B 83 3.4 3.6

The composition for shielding electromagnetic waves using carbon nanotubes according to the present invention is cost competitive by reducing the content of metal powder, and has a low density and no drift due to its own weight even in a three-dimensional injection molded structure. Its electrical conductivity is significantly superior to that of conventional conductive paints, and its conductivity, adhesion and shielding efficiency are excellent, even at low film thicknesses, and it has the advantages of being stable against heat and brine. Therefore, it is possible to provide the effect of blocking the electromagnetic waves emitted to the outside as well as the interference caused by the electromagnetic interference between circuits of the miniaturized and thinned portable electronic devices and to improve the radiation characteristics of the communication device.

Claims (10)

A composition for shielding electromagnetic waves using carbon nanotubes, including carbon nanotubes, metal powders, water dispersion polyurethane dispersions, solvents, and rheology modifiers. The composition of claim 1, wherein said composition is 0.3-20 wt% of carbon nanotubes; Metal powder 5 to 40% by weight; Water dispersion polyurethane dispersion 5-40 wt%; 10 to 60% by weight solvent; And A composition for electromagnetic shielding comprising 0.01 to 5% by weight of a rheology modifier. The composition for shielding electromagnetic waves according to claim 1 or 2, wherein the carbon nanotubes have a length of 50 µm or less and a width of 20 nm or less. The composition for electromagnetic shielding according to claim 1 or 2, wherein the water-dispersed polyurethane dispersion is synthesized by applying a polyol using an aliphatic and aromatic polyhydric acid. The electromagnetic shielding composition of claim 1 or 2, wherein the water-dispersed polyurethane dispersion has a solid content of 1 to 10% of the polyurethane resin. 3. The electromagnetic shielding according to claim 1 or 2, wherein the metal powder is silver, copper, or silver coated copper powder having an average particle diameter of 1 to 60 µm, and the shape of which is flake, spherical or branched. Composition. The composition of claim 1, wherein the solvent is an alcohol solvent selected from the group consisting of methanol, ethanol, isopropanol, normal butanol, and isobutanol. The composition of claim 1, wherein the rheology control agent is selected from the group consisting of a crosslinked polyacrylate polymer, cellulose, urethane, acrylic emulsion type and bentonite. Electromagnetic shielding conductive film prepared by the conductive composition of claim 2. An electromagnetic shielding substrate comprising the conductive film of claim 9.

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