Stock material or miscellaneous articles – All metal or with adjacent metals – Having metal particles
Reexamination Certificate
2000-06-09
2002-05-28
Acquah, Samuel A. (Department: 1711)
Stock material or miscellaneous articles
All metal or with adjacent metals
Having metal particles
C427S304000, C427S305000, C427S306000, C427S404000, C427S443100, C106S001250, C106S001260, C106S001280, C428S613000, C428S672000, C428S675000, C428S680000, C428S929000, C428S936000
Reexamination Certificate
active
06395402
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of preparing an electrically conductive polymeric foam. The invention also relates to an electrically conductive polymeric foam which can be formed by such method. The invention has particular applicability to the manufacture of EMI (electromagnetic interference) shielding and grounding devices and filters.
2. Description of the Related Art
EMI shielding devices are employed in the electronics industry with application in, for example, telecommunication and computer related technologies.
There are a number of EMI gaskets commercially available in which a metallized yarn is knitted over a soft foam core or a metallized fabric is wrapped around a soft foam core. Such gaskets include, for example, Instrument Specialties Soft Knit, UltraSoft Knit and ElectroFab, Chomerics Soft-Shield and Schlegels fabric-over-foam product. Another type of gasket is available from Seiren Co., Ltd., which offers an open cell polyurethane foam that is attached to a thick, woven backing layer. This composite is then metallized, starting with a deposited aluminum (Al) layer. There are, however, various potential problems associated with such conductive foam materials. For example, these multistructured materials are typically somewhat complicated in structure, which can lead to high manufacturing costs as well as to inconsistencies in the product formed. For some of these products, adhesion of the metallic coating to the polymer substrate has been a problem. For example, flaking and loss of the coating typically occurs which can ultimately reduce the conductivity and shielding effectiveness of the foam.
Another known conductive foam structure is described in U.S. Pat. No. 5,151,222, to Ruffoni, the entire contents of which document are incorporated herein by reference. That document discloses a foam absorber having electromagnetic energy attenuation characteristics comprising an open cell reticulated polyurethane foam impregnated with a conductive ink applied by spraying to a surface of the foam. In such spray coating processes, it can be difficult to obtain a uniform coating on the foam surface.
An additional known process for forming conductive foam involves impregnation of a foam with a conductive material. Such structures typically suffer from poor mechanical properties, such as compressive force and compressive set.
To overcome or conspicuously ameliorate the problems associated with the related art, the present inventors have provided a method of preparing a low compression force foam and a low compression force foam prepared thereby. The foam is made conductive by metallizing the surface thereof, preferably the entire surface thereof. Such conductive foam provides significant advantages when employed in a component such as a gasket. For example, the conductive foam in accordance with the invention is of a simpler and more consistent design than known materials. The conductive foam preferably has a one-piece design. As a result of the simple design, the conductive foam components such as gaskets are considerably easier to manufacture than conventional foam-based components. The simple design typically makes just-in-time delivery easier to achieve since there are fewer manufacturing steps involved. In addition, the cost for manufacturing the conductive foam in accordance with the invention typically is less than that for the knitted and fabric covered gaskets. The plating technology used in the present invention can also enhance the adhesion of the plating to the polymer substrate. This improved coating adhesion can greatly reduce flaking of the coating(s) and help maintain good EMI performance during use.
Other objects and aspects of the present invention will become apparent to one of ordinary skill in the art upon review of the specification and claims appended hereto.
SUMMARY OF THE INVENTION
The foregoing objectives are met by the methods and polymeric foams of the present invention. According to a first aspect of the present invention, a method is provided of preparing an electrically conductive polymeric foam. The method comprises the steps of:
(a) contacting a polymeric foam with a surfactant solution;
(b) contacting the polymeric foam with a sensitizing solution;
(c) contacting the polymeric foam with an activation solution; and
(d) forming at least one metallic layer on the polymeric foam with an electroless plating process.
According to another aspect of the present invention, a method is provided of preparing an electrically conductive polymeric foam. The method comprises the steps of:
(a) contacting a polymeric foam with a surfactant solution, wherein the surfactant solution comprises a material selected from the group consisting of an anionic surfactant, a cationic surfactant, a non-ionic surfactant and combinations thereof;
(b) contacting the polymeric foam with a sensitizing solution, wherein the sensitizing solution comprises a salt, a solvent and water;
(c) contacting the polymeric foam with an activation solution, wherein the activation solution comprises a metal compound, a solvent and water; and
(d) forming at least one metallic layer on the polymeric foam with an electroless plating process, wherein the at least one metallic layer comprises a metal selected from the group consisting of palladium, platinum, silver, copper, nickel, tin and combinations thereof.
According to a further aspect of the present invention, a method is provided of preparing an electrically conductive polymeric foam. The method comprises the steps of:
(a) contacting a polymeric foam with a surfactant solution;
(b) contacting the polymeric foam with a sensitizing and activation solution; and
(c) forming at least one metallic layer on the polymeric foam with an electroless plating process.
According to further aspects of the present invention, electrically conductive polymeric foams formed by the above methods are provided.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
In accordance with a first aspect of the invention, a method of forming an electrically conductive, low compression force polymeric foam is provided. Such a foam has numerous EMI shielding applications including, but not limited to, gasketing, die cut sections, vent panels, air filtration panels and laminates. The invention allows for both the electrical conductivity necessary for EMI shielding as well as very low closure forces in a single component product. The methods of the present invention can also be used in non-EMI applications such as, for example, water and chemical filters, and medical applications.
The conductive foams produced by the methods of the present invention typically provide a high degree of shielding effectiveness. For example, the foam exhibited a shielding effectiveness of greater than 70 decibels (dB), from 100 kHz to 100 MHz. The shielding effectiveness of the foam, which demonstrates the attenuation of a signal transmitted therethrough, was measured in accordance with the SAE-ARP-1705 transfer impedance test. In addition, the foam typically demonstrates a pressure probe resistance of less than 25 milliohms per square inch.
The polymeric foam can be any one or combination of a large variety of foams which are commercially available. For example, the polymeric foam can be a thermoplastic elastomer (TPE) such as Santoprene®, Neoprene® or a polyurethane-containing material such as polyester polyurethane, or combinations thereof. Of these, polyurethane-containing materials are particularly preferred.
The cell structure of the polymeric foam employed in the invention can be fully open, partially open or fully closed. Various techniques can be used to provide an open or partially open cell structure. For example, the foam can be quenched, i.e., contacted with a caustic solution. Additionally or alternatively, the foam can be treated with a flame, i.e., subjected to a zapping process. Preferably, the polymeric foam which is used as the starting material in the present methods is a quenched foam.
The inven
Chandra Satish
Lambert Michael
Sosnowski Tony
Acquah Samuel A.
Laird Technologies Inc.
Pitney Hardin Kipp & Szuch LLP
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