KR100500542B1 - Composition of Electromagnetic Interference/Radio-Frequency Interference shielding coatings - Google Patents

Abstract

The present invention relates to an EMI coating composition having excellent electromagnetic shielding performance using alcohol-based resin as a binder and alcohol as a solvent. The present EMI coating composition comprises 1 to 60% by weight of an acrylic acid-modified urethane resin, a binder resin, 2 to 60% by weight of metal powder of at least one of copper, nickel and silver, 0.5 to 30% by weight of thickener, and 10 to ethanol. 60 weight% and 1 to 2 weight% of a dispersing agent. Accordingly, since organic solvents are not used, there is no surface damage of the adherend, there is no fear of contamination, and workability is easy, and the electromagnetic wave shielding effect is excellent, and polycarbonate, ABS resin, polystyrene, and polyvinyl chloride used in various electronic parts are excellent. It has the advantage that it can be widely used for coating a plastic element such as a resin or various plastic cases in which electromagnetic waves are generated, in particular, a mobile phone case, a notebook case and an electronic component case coating.

Description

EMI Coating Composition {Composition of Electromagnetic Interference / Radio-Frequency Interference shielding coatings}

The present invention relates to an EMI coating composition, and more particularly, to an EMI coating composition having excellent electromagnetic shielding performance using alcohol-based resin as a binder and alcohol as a solvent. Electromagnetic waves are transmitted, absorbed, and reflected as they pass through the medium. These phenomena are influenced by the type and shape of the medium and can be classified into absorbers and reflectors according to the electromagnetic properties of the medium. An electromagnetic wave absorber means a material having a larger area of absorption than reflection, and electromagnetic wave absorption is known to be caused largely by conduction loss, dielectric loss, or magnetic loss. In general, the conduction loss is a conductive material such as metal, and the dielectric loss is barium titanate. It is known that in dielectric materials such as and magnetic losses mainly occur in magnetic materials such as ferrite and the like, and may be used to absorb electromagnetic waves using appropriate materials among them according to the purpose. Solvent EMI paints generally used have a solvent, which deteriorate the working environment, provide the main cause of environmental pollution, and because most of the applied elements are plastics that are weak to solvents, the impact resistance of the plastics after coating becomes weak. There are many disadvantages to this. U.S. Patent No. 4,305847 describes an EMI composition that can maintain conductivity even when exposed to heat, humidity, or salt. Specifically, a metal pigment selected from the group consisting of copper and a copper alloy having a particle size of 200 microns or less, and thermoplastic acrylic , Vinyl, urethane, alkyd, polyester, hydrocarbon, fluoroelastomer, and binders selected from celluloid resins and thermosetting acrylics, polyesters, epoxies, urethanes and alkyd resins in a ratio of 20: 1 and 2: 1 relative to metal pigments. In order to provide a thermal stability of the coated portion, the organic titanium material is provided with a composition comprising 0.5 to 18% by weight of the organic pigment and about 20 to 85% by weight of the organic solvent. Could not solve the problem. US Patent No. 4,556,506 provides a water-soluble EMI coating composition in order to solve the contamination problem caused by the use of organic solvents in conventional EMI paints, the specific configuration is 0.3 to 15% by weight of difunctional zwitterion, A dispersant comprising 5-20% by weight of polyacrylamide, 0.5-20% by weight of nonionic surfactant, 20-60% by weight of nickel, copper, aluminum or their combined flakes and powders and metal particles and water It is characterized by a method of producing a bifunctional zwitterion.

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The present invention has been made to solve the conventional problems as described above, to prevent contamination due to the use of organic solvents, to provide an alcohol-type EMI coating composition excellent in adhesion to the surface and excellent electromagnetic shielding efficacy.

According to the present invention, the object is 1 to 60% by weight of an acrylic acid-modified urethane resin, which is a binder resin, 2 to 60% by weight of at least one metal powder of copper, nickel and silver, 0.5 to 30% by weight of a thickener And 10 to 60% by weight of ethanol and 1 to 2% by weight of a dispersant. Preferably, the metal powder has a particle size of 2 to 300 µm. The acrylic acid-modified urethane resin may be prepared by adding a diisocyanate to a polyol to increase the temperature, and then proceeding with a reaction to obtain a polyurethane. It is preferable that the present invention is formed by a manufacturing method comprising the step of reacting acryl having a hydroxyl group to the isocyanate to add acrylic acid to the carbon double bond of the acrylic to bond the acrylic acid to the urethane. Explained as follows. The alcohol-type resin used in the present invention refers to a resin dissolved in alcohol. In general, the urethane resin is most widely used because it has excellent properties in thermal stability, solvent resistance, adhesion, water resistance, impact strength, and the like. EMI paints must have excellent workability, especially when spraying, and must have some viscosity to achieve this. The reason for giving the viscosity of the paint is to prevent the metal from sinking easily in the binder and the solvent or to make the coating easier. Generally, inorganic thickeners such as bentonite and silica or polyacrylic acid, polyvinyl alcohol, polyurethane, etc. Organic thickeners are used. However, organic thickeners have a disadvantage in that they are avoided by escaping on the metal surface, and inorganic thickeners have a disadvantage of low thickening ability with respect to alcohol. In the present invention, the resin used as a binder has a thickening property in itself, so that the resin can be easily dissolved in alcohol to exhibit the maximum thickening power, and can maximize the compatibility with inorganic or organic thickeners in the alcohol solvent. Easy to thicken to have optimum paint workability. Alcohol-type urethane resin having a thickening property used in the present invention is prepared by introducing acrylic acid into the urethane resin and is dissolved in water or alcohol by neutralizing the urethane resin and acrylic acid with amine. Specifically, the alcohol-type urethane resin according to the present invention is diisocyanate, for example, all isocyanates having reactive active hydrogen such as IPDI (Isophorone diisocyanate), MDI (methylene diisocyanate), H12MDI (H12MDI), HDI (Hydrogene diisocyanate) As the polyol, polyether polyol, carbonate polyol, polycaprolactam polyol, etc., which are formed by reaction of alcohol and acid, are used, and dimethyl propion acid (DMPA) is used as a water dispersion site. As a neutralizing agent to neutralize, a trivalent amine such as trimethyl amine (TEA) may be used. In the dispersion, a solvent of water, such as ions or ethanol or ethylene glycol, may be used as a dispersion solvent. As a chain extender for lengthening chains by reacting with unreacted isocyanates, diamines or triamines having two or three active hydrogen groups such as hydrazine hydride (HH) and ethylene diamine (ED) may be used. The urethane resin prepared as described above has the characteristics of a general urethane resin, but the urethane resin used in the present invention is characterized by combining an acrylic acid component in order to more easily dissolve in alcohol and to exhibit the thickening characteristic to the maximum. The method of combining the acrylic acid component with the urethane resin includes acrylics having a hydroxyl group in the unreacted isocyanate of the urethane, for example, hydroxyl ethyl methacrylate (HEMA) and hydroxyl ethyl acrylate (HEA: Hydroxyl ethyl acrylate). ) And hydroxyl propyl methacrylate (HPMA: Hydroxyl Propyl Metacrylate) and the like, and acryl acid is added to the carbon double bond of the acryl to allow the acrylic acid to bind to the urethane. More specifically, the above-mentioned diisocyanate reacts with the polyol mentioned above and the alcohol at the end of DMPA to form a urethane bond, and after the alcohol of HEMA reacts again with the remaining isocyanate, it is added to the carbon double bond of HEMA. The acrylic acid is reacted to add an acrylic bond to form an acrylic acid grafted to the final urethane chain. The urethane-acrylic polymer thus prepared may be prepared in various ways depending on physical properties and viscosity. Physical properties such as tensile strength, hardness, water resistance, pigment dispersibility, etc. depend greatly on the type of polyol, and tensile strength, hardness, etc. vary depending on the type of isocyanate, and the final particle size varies depending on the DMPA content. Dispersion stability. The content of HEMA depends on the content of acrylic acid, which can be standardized by the acid value (mgKOH / g). The acid value control can vary the content according to the required conductivity or dispersion stability of the final paint. To disperse the urethane-acrylic prepolymer thus prepared, neutralize the carboxyl group of the prepolymer with amine with trivalent amine, mainly TEA. . After neutralization, high-speed stirring while adding water forms stable particles. After the water dispersion, the isocyanate of the prepolymer is designed to remain. The remaining isocyanate is reacted with diamine or triamine to increase the molecular weight through a chain extend process. As the acrylic acid component, all acrylic components having a carboxyl group in acrylic may be used. For example, acrylic (Acrylic acid), methacrylic acid (MAA), or the like may be used. The acrylic modified urethane resin prepared as provided in the present invention is easily dissolved in alcohol, in particular ethanol, has excellent viscosity characteristics, and has excellent conduction characteristics since it has ionization sites compared to solvent-type resins. The amount of the acrylic acid-modified urethane resin according to the present invention is preferably used in an amount of 1 to 60% by weight in the total composition. In this case, when the content of the resin is less than 1% by weight, it is difficult to form a coating film during coating, even if a coating film is formed. There is a disadvantage in that the physical properties such as properties and durability, etc., in the case of exceeding 60% by weight, the metal powder content is relatively low, the resistance is high and the shielding performance is inferior. The metal powder according to the present invention may be selected from silver, silver coated copper or nickel powder, and the particle size is preferably 2 to 300 μm, and is not particularly limited for the present invention. As the thickener used in the present invention, an inorganic thickener such as bentonite or silica, or an organic thickener such as polyacrylic acid, polyvinyl alcohol or polyurethane may be used, and a metal powder having a high specific gravity may be separated from the binder resin at less than 0.5 wt%. When coating the coated object, the film flows down or the metal is separated, so that the shielding property is partially lost.If the coating property exceeds 30% by weight, the viscosity of the coating liquid increases, so that the coating film of the thin film cannot be formed when the coating agent is applied. It is coated on the metal, which lowers the electrical conductivity, thereby reducing the shielding performance. In the present invention, unlike conventional organic solvents, alcohol is used as a solvent, 10 to 60% by weight, but less than 10% by weight is difficult to paint due to the increase in viscosity and difficult to dissolve binders and other additives difficult to secure proper physical properties When it exceeds 60% by weight, the composition may not be provided with an appropriate viscosity, resulting in a decrease in coating properties due to metal separation and lack of binder resin. Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by the following Examples, and those skilled in the art do not depart from the scope of the claims. It is obvious that the modifications can be made within the scope.

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Examples 1-4

Preparation of Acrylic Acid Modified Urethane Resin

Put a polyol, trimethyol propane (TMP, Trimethyol propane), N-methyl pyrrolidone (NMP) and dimethyl propionic acid (DMPA) in a 2000 ml four-necked flask The reaction was carried out with the addition of isophorone diisocyanate (IPDI) and dibutyltin dilaurate (DBTDL, Dibutyltin dilaulate), followed by maintaining for at least 30 minutes, followed by hydroxy ethyl methacrylate (HEMA, Hydroxyl ethyl metacrylate) and acrylic acid (AA) are added and maintained for more than 30 minutes. At this time, the isocyanate reacts with the alcohol of HEMA, and AA undergoes the addition reaction with the carbon double bond of HEMA. After lowering the temperature to 28 ~ 38 ℃, triethylamine (TEA, Triethyl amine) is added and maintained for about 30 minutes, and stirred while adding the water (Deionized Water). After all of the water is added, hydrazine hydrate is added to react with unreacted isocyanate and maintained for at least 30 minutes. TEA is neutralized by reacting with the acid groups of DMPA and AA and acts as a site for dispersing water. The resin thus prepared has a solid content of 33 to 38%, an acid value of about 119 mgKOH / g, a viscosity of 410 to 470 cps, and a resin that is easily dissolved in ethanol.

Specific composition ratios of the acrylic acid-modified urethane resin production are shown in Table 1 below.

ingredient content(%) Isophorone diisocyanate 12.39 Polyol 13.04 Trimethyol propane  0.43 N-Methyl pyrrolidone  9.26 Dimethyl propionic acid  1.74 Dibutyltin dilaulate  0.02 Hydroxyethyl methacrylate  2.17 Acrylic acid  4.35 Triethyl amine  2.17 Deionized Water 53.98 Hydrazine Hydrate 0.43 Total 1,000.0

Subsequently, the resin and ethanol were added to a 200 ml plastic can, mixed with a high speed dissolver, and then metal was added and stirred at 800 to 1500 rpm for 10 minutes. Then add the thickener SCT-275 and stir for 8 minutes, add Byk 345 dispersant and stir for 20 minutes. Components and contents of the prepared coating composition are shown in Table 2 below.

Example 1 Example 2 Example 3 Example 4 ingredient Content (% by weight) Suzy 20 20 20 20 ethanol 34 44 52 60 Silver powder 40 30 - - Silver Coated Copper Powder - - 20 10 Thickener 5 5 7 10 Dispersant One One One One Sum 100 100 100 100

Comparison of the physical properties of the EMI coating composition prepared in Examples 1 to 4 with the conventional solvent-type EMI stone and water-based EMI paint as shown in Table 3 below.

           Classification Property Solvent EMI Aqueous EMI Example 1 Example 2 Example 3 Example 4 Initial resistance (Ω) 0.3 0.5 0.1 0.2 0.2 0.4 Adhesiveness (1mm interval, cross cut tape test) 100/100 80/100 100/100 100/100 100/100 100/100 Long-term high temperature test (85 ℃ × 10days) 0.5 0.7 0.3 0.4 0.3 0.5 High Humidity Test (35 ℃ × 90% RH × 10days 0.5 0.6 0.3 0.4 0.3 0.5 Cold and cold cycle test 0.6 0.7 0.4 0.5 0.4 0.5 Plastic impact resistance 5 > 20 > 20 > 20 > 20 > 20

It can be seen from the Table 3 that the initial resistance is similar to the solvent type, aqueous and alcohol type EMI coating compositions but slightly different depending on the physical properties. In terms of adhesion, aqueous EMI is somewhat poor, and it can be seen that the properties of alcohol type are excellent in long-term high temperature test, high humidity test, and cold / heat test. This is because it has a high compatibility with the metal lying on the surface when forming a coating film. Solvent EMI has a very low impact resistance of the plastic compared to the composition of the present invention because the solvent melts the plastic surface.

As described above, the alcohol-type EMI composition according to the present invention does not use an organic solvent, there is no surface damage of the adherend, and there is no fear of contamination, so it is easy to work and has excellent electromagnetic shielding effectiveness, which is used in various electronic components. It can be widely used for coating a plastic element such as polycarbonate, ABS resin, polystyrene, polyvinyl chloride resin or various plastic cases in which electromagnetic waves are generated, in particular, cell phone case, notebook case and electronic component case coating.

Claims (4)

1 to 60% by weight of an acrylic acid-modified urethane resin which is a binder resin, 2 to 60% by weight of a metal powder of at least one of copper, nickel and silver, 0.5 to 30% by weight of a thickener, 10 to 60% by weight of ethanol, EMI coating composition comprising 1 to 2% by weight of dispersant. The method of claim 1; EMI coating composition, characterized in that the metal powder has a particle size of 2 to 300㎛. The method of claim 1, The acrylic acid modified urethane resin, Adding a diisocyanate to the polyol to raise the temperature, and then performing a reaction to obtain a polyurethane; EMI reaction composition comprising the step of reacting acryl having a hydroxy group to the unreacted isocyanate by the addition of acrylic acid to the carbon double bond of the acrylic to bond the acrylic acid to the urethane. delete