Highly conductive elastomeric sheet

Details Highly conductive elastomeric sheet Highly conductive elastomeric sheet

2000-01-27

2002-11-05

Cole, Elizabeth M. (Department: 1771)

Fabric (woven, knitted, or nonwoven textile or cloth, etc.)

Scrim

Woven scrim

C442S001000, C442S002000, C442S006000, C442S015000, C442S019000, C442S029000, C442S037000, C442S043000, C442S110000, C442S111000, C442S228000, C442S229000, C442S237000, C428S295100, C428S297400, C428S372000, C428S402000

Reexamination Certificate

active

06475933

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
(Not Applicable)
STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT
(Not Applicable)
BACKGROUND OF THE INVENTION
Among the most elusive goals in materials science has been the development of sheeting material that is both highly conductive and elastic. As is well recognized in the art, such properties are highly desirable in a number of applications, and in particular the construction, maintenance and repair of aircraft. In this regard, the property of high conductivity is important to provide absorption and shielding of electromagnetic radiation. The property of elasticity in contrast is necessary to resist the harsh environment such materials are subjected to, particularly with respect to aerospace applications, which necessarily requires that such materials possess sufficient material durability and reliability.
As is well-recognized by those skilled in the art, however, the materials that must be utilized to impart such properties, namely conductivity and elasticity, poorly complement one another. Specifically, highly conductive materials generally lack elasticity, and the incorporation of such conductive materials with materials that are elastic, such as rubbers and silicones causes the result in compound to become less elastic. In this regard, the actual strain on the matrix increases proportionally as the matrix material becomes increasingly displaced by loading material, which particularly comprises conductive particulates. Furthermore, it is recognized that the matrix experiences a substantially reduced tear strength, and hence reducing the ultimate yield strength, as conductive particulates become increasingly loaded therein.
In order to produce a greater amount of elasticity, attempts have been made to incorporate conductive wire meshes or metalized organic meshes into an elastomer base or matrix to thus produce a result in conductive elastomer. Generally, the elasticity of such meshes is depended upon the strain direction, and it is known in the art that a variety of weaves and nets can be used to create a desired mesh for a desired application.
Notwithstanding the slightly enhanced performance of such conductive elastomers incorporating conductive wire meshes, cyclic fatigue testing of such materials has identified that the resistivity thereof increases over time. In this regard, most conductive wire mesh elastomers have been shown to produce unacceptable resistivity after as few as five thousand (5,000) cycles. Further disadvantages are the fact that such conductive wire mesh elastomers experience greater wear and fatigue than non-conductive elastomer materials. For example, a typical conductive elastomer, such as Ni/Ag coated bi-directional scrim loaded in a silicone matrix at twenty-five percent (25%) strain and fifteen-percent (15%) strain, respectively, after five-thousand (5,000) cycles experiences the following increases in resistivity.
TABLE 1
Initial
Final
Initial (at
Final (at
Resistance
(relaxed)
strain)
strain)
Sample
(Ohms/sq)
Resistance
Resistance
Resistance
(1) (25%
0.55
3.00
1.05
11.0
strain)
(2) (15%
0.55
1.75
0.80
3.15
strain)
As will be noted, the resistance of the Ni/Ag scrim elastomeric sheet increases nearly six-fold in the relaxed state, and nearly eleven-fold whole in the strained state when tested at twenty-five percent (25%) strain. Significant increases are also noted in samples having undergone testing at fifteen percent (15%) strain, as illustrated.
Accordingly, there is a substantial need in the art for a highly conductive elastomeric sheet that possesses sufficient durability and retains high conductivity after having undergone repeated cyclical exposure to strain cycles of up to twenty-five (25%). There is a further need for such highly conductive elastomeric sheet that can be readily utilized for a variety of commercial applications, and in particular the manufacturer, maintenance and repair of aircraft. Still further, there is a need in the art for a highly conductive elastomeric sheet that, in addition to possessing and retaining high conductivity and elasticity, can be readily formulated and fabricated from commercially-available materials.
BRIEF SUMMARY OF THE INVENTION
The present invention specifically addresses and alleviates the above-identified deficiencies in the art. In this regard, the present invention comprises a highly conductive elastomeric sheet that is substantially more durable and has a significantly more durable and has a significantly longer life than prior art conductive elastomers. According to a preferred embodiment, the conductive elastomeric materials of the present invention comprise the combination of a highly conductive mesh and a sub-micron sized particulate loaded into an elastomeric matrix. The conductive mesh may take any of a variety known in the art, including those formed from NI/Ag and may be further woven to assume any of a variety known in the art. The sub-micron sized particulate preferably comprises carbon particles present in an amount of approximately 10 to 20% by volume and in a more highly preferred embodiment, ten percent (10%) by volume. Advantageously, the conductive elastomers of the present invention retain superior conductivity in both relaxed and strained states (e.g., fifteen percent (15%) and twenty-five percent (25%) elongation) well-over ten thousand (10,000) cycles. The conductive elastomeric materials of the present invention have further retained superior conductivity in both relaxed and strained states over as many as seventy-five thousand (75,000) cycles.
It is therefore an object of the present invention to provide a highly conductive elastomeric material that is highly durable and retains a high degree of conductivity over repeated cyclical exposures to strain.
Another object of the present invention is to provide a highly conductive elastomeric material that is substantially more durable than prior art conductive of elastomeric materials.
Another object of the present invention is to provide a highly conductive elastomeric material that may be readily formulated and fabricated from conventional, commercially-available materials.
Another object of the present invention is to provide a highly conductive elastomeric material that can be ideally used in aerospace applications, and in particular the construction, maintenance and repair of aircraft.
Still further, another object of the present invention is to provide a highly conductive elastomeric material that is of low cost to manufacture, does not utilize costly materials and may be readily utilized.


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