Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
1999-03-05
2001-07-24
Kopec, Mark (Department: 1751)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C428S304400, C428S308800, C428S309900, C428S311110, C428S317100, C428S317300, C428S319300, C428S320200, C428S327000, C361S271000, C361S306300, C361S311000, C361S312000, C361S313000, C361S314000, C361S315000
Reexamination Certificate
active
06265058
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention (Technical Field)
The present invention relates to dielectric films, particularly dielectric films for use in wound capacitors, and specifically to a polymer-substrate film and method for making same.
2. Background Art
The development of high energy electrical storage systems with reduced size and weight are important for tactical and strategic pulsed power applications such as: electric armor, electric guns, particle beam accelerators, high power microwave sources and ballistic missile applications. In addition, commercially produced defibrillator systems have a significant need for higher energy density capacitors to achieve size and weight reductions. The dielectric energy storage density of pulsed power materials must be increased to provide feasibility or improve performance of these systems. The dielectric characteristics that represent a material's energy density are dielectric constant and operational electric field. Energy density is proportional to the dielectric constant and varies as the square of the electric field.
It is known to provide dielectric films incorporating polymers for use in capacitor production. However, with polymers having low physical strength, the full energy density potential cannot be realized because, at polymer thicknesses required for optimum performance (e.g. ≦8.0 &mgr;m), the physical strength of a polymer film is insufficient for incorporation into a wound capacitor. At greater thicknesses, the polymer film's energy density reaches only a fraction of the polymer's potential due to the logarithmic decrease in dielectric strength associated with increasing polymer thickness. A need remains for a dielectric film featuring both optimal energy density as well as sufficient strength for incorporation, using conventional winding fabrication techniques, into capacitor devices. Against this background, the present invention was developed.
SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION
The invention is dielectric film apparatus and fabrication method. The dielectric film is usable in capacitors, and at least in part is characterized by a substrate having a thickness and porous surface, a siloxane polymer deposited upon the surface to define a polymer layer, and infiltrated into the pores of the surface to define an interfacial composite layer comprising substrate and polymer. The substrate preferably comprises paper, and most preferably is metallized Kraft paper. The interfacial layer comprises a thickness of up to or equaling approximately one-half the thickness of the substrate. The polymer layer preferably, but not critically, has a thickness from about 4.0 &mgr;m to about 6.0 &mgr;m, and the substrate having a thickness of about 6.5 &mgr;m, and the interfacial composite layer having a thickness of less than about 3.25 &mgr;m. The preferred polymer is a siloxane polymer. Triflouro- and cyano- polar pendant groups are attached to the siloxane polymer to provide the increased dielectric constant. Networking siloxane molecules (d-hydroxy functionalized short chain phenyl-methyl siloxanes) are combined to the base polymer to increase molecular weight and establish material integrity in film form.
The invention also includes a process for fabricating a dielectric film characterized by the steps of preparing a polymer solution comprising a siloxane polymer, depositing the polymer solution onto a substrate, permitting the polymer solution to infiltrate into the substrate, drying the polymer solution upon the substrate and curing the polymer solution upon the substrate. The step of depositing a polymer solution preferably comprises extruding the polymer solution through a die head and onto porous paper, and optionally may further comprise adjusting the die head gap to approximately 25 &mgr;m; placing an extrusion die head at a distance of about 51 &mgr;m from a casting surface; and providing a back pressure of about 6.9 kPa in the die head. The step of drying the polymer solution upon the substrate preferably comprises the step of placing the polymer solution and substrate in an evaporation oven at a temperature of between approximately 20° C. and approximately 100° C., and the step of placing the polymer solution and substrate in an evaporation oven may comprise allowing the polymer solution and substrate to dwell in the evaporation oven for from about 1 minute to about 10 minutes. Similarly, the step of curing the polymer solution upon the substrate comprises the step of placing the polymer solution and substrate in a curing oven at a temperature of between approximately 100° C. and approximately 200° C., while the step of placing the polymer solution and substrate in a curing oven may comprise allowing the polymer solution and substrate to dwell in the cure oven for from about 1 minute to about 10 minutes. The fabrication process preferably involves a extrusion of the polymer onto a moving substrate, and thus may comprise the further step of the moving the substrate beneath the die head at a rate between about 0.02 m per minute and about 0.9 m per minute.
Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
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Hartman William F.
Law Kristen J.
Slenes Kirk M.
Baker Rod D.
Boyer Charles
Kopec Mark
TPL, Inc.
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