FIG. 1(A) depicts a transmission electron microscope ("TEM") micrograph of silver nanoparticles used in a metallic nanoparticle radio frequency (RF) shielding structure. The metallic nanoparticle shielding structure has a sheet resistance of less than 1.5 ohms/square/mil.
In some instances, metallic nanoparticles can be used in applications where metal flakes are typically used. The metal flake typically used can be irregularly shaped metal flake that often is combined with a solvent to form a metal flake formulation. Metal flake can be used in shielding applications to provide electromagnetic interference ("EMI") and radio frequency interference ("RFI") shielding. The metal flake can be formulated with adhesion promoters and other additives in a solvent. The metal flake formulation can then be sprayed or otherwise applied to the plastic housing of devices such as mobile phones to create a shield. Now novel nanoparticles have been developed that provide superior EMI and RFI shielding.
The substrate comprises any one of a polyester substrate, a polycarbonate substrate, a liquid crystal display substrate, glass, silica-based substrate, metal substrate and metal oxide substrate. Embodiments may include a protective film that can comprise any of the following materials: polyethylene; polypropylene or any other material able to be applied over the deposited metallic nanoparticles and able to provide a level of protection to the cured metallic nanoparticle structure
FIG. 1(B) illustrates an embodiment of a scanning electron microscope ("SEM") micrograph of a trace comprised of a composition of the metallic nanoparticles cured for 1 minute at 100 degrees Celsius.
FIG. 1(C) depicts a SEM micrograph of a trace comprised metallic nanoparticles cured for 3 minutes at 85 degrees Celsius.
To test the described structure's effectiveness for shielding, a formulation prepared according to the disclosed methods was sprayed onto the surface of polyester film and cured at 130 degrees Celsius for 1 minute. The silver coating was estimated to be 1.5 micrometers thick, and the sheet resistivity was measured to be 0.080 ohms/square at the coating thickness of 1.5 micrometers. A bag, 10 cm by 15 cm, was fashioned by folding over silver coated polyester film having metal on the inside. Opposing surfaces adjacent to the fold were heat sealed together. A cell phone was then placed inside bag, and the bag was completely sealed.
Before placing the cell phone in the bag, the cell phone signal strength was 4 bars, according to the cell phone's signal strength meter. The silver coating thickness was thin enough to allow the cell phone display to be seen through the metal/substrate matrix.
After placing the cell phone in the bag, the bag was completely sealed. Upon sealing the bag, the cell phone signal strength showed zero bars. An attempt was then made to call the cell phone, but no connection was made. When one end of the bag was reopened, the cell phone signal strength returned to 4 bars, and calling the cell phone resulted in a connection.
Before placing the cell phone in the bag, the cell phone signal strength was 4 bars, according to the cell phone's signal strength meter. The silver coating thickness was thin enough to allow the cell phone display to be seen through the metal/substrate matrix.
After placing the cell phone in the bag, the bag was completely sealed. Upon sealing the bag, the cell phone signal strength showed zero bars. An attempt was then made to call the cell phone, but no connection was made. When one end of the bag was reopened, the cell phone signal strength returned to 4 bars, and calling the cell phone resulted in a connection.
The metallic nanoparticles can be comprised of silver nanoparticles. The metallic nanoparticles can also comprise any combination of the following compositions or elements: copper; gold, zinc; cadmium; palladium; iridium; ruthenium; osmium; rhodium; platinum; aluminum; iron; nickel; cobalt; indium; silver oxide; copper oxide; gold oxide; zinc oxide; cadmium oxide; palladium oxide; iridium oxide; ruthenium oxide; osmium oxide; rhodium oxide; platinum oxide; iron oxide; nickel oxide; cobalt oxide; indium oxide; or any other conductive metal or metal oxide suitable for shielding method.
Depositing the metallic nanoparticles onto the substrate, in some embodiments, can comprise coating the substrate with a formulation comprising the metallic nanoparticles and any aqueous medium described herein. The substrate can be coated using any of the following methods: spray coating; curtain coating; dip coating; spread coating; roller coating; spin coating; blade coating; wire rod coating; or any other type of physical coating. The coating can cover substantially the entire surface of the substrate.
The metallic nanoparticles can be deposited in any of the following patterns: a continuous film; a wire mesh pattern; a series of dots or marks; a series of lines; randomly placed markings; a series of dots and lines; a series of dots, lines and other markings; or any other pattern of deposition able to achieve the methods and structures described herein. The markings can be of any shape, size and can be placed along the substrate in any ordered or random pattern.
