Seal for a joint or juncture – Seal between fixed parts or static contact against... – Contact seal for other than internal combustion engine – or...
Reexamination Certificate
1998-07-17
2001-07-03
Knight, Anthony (Department: 3626)
Seal for a joint or juncture
Seal between fixed parts or static contact against...
Contact seal for other than internal combustion engine, or...
C277S652000, C277S654000, C174S0170CT
Reexamination Certificate
active
06254107
ABSTRACT:
The invention concerns an electrically conductive seal, consisting of a freshly-extruded sealant that is still in a plastic condition and which is mixed with electrically conductive components, is applied onto a sealing surface for the sealing gap of a conductive housing which accommodates electronic modules for the purpose of electromagnetic shielding and for the prevention of a material transfer through the sealing gap, as well as a process for the manufacture of a seal of this type.
It is known that electronic modules create electromagnetic interference signals which escape to the outside through the gaps of the housing in which the electronic modules are located and are transmitted to other electronic modules by means of signal conductors, specifically once again through the gaps of the housings which accommodate them, and which may lead to damage and malfunctions of the other electronic modules.
In order to prevent electromagnetic waves which have the effect of interference signals from escaping from one housing and penetrating into another housing, which may thus impair the function of the influenced electronic module, the surfaces which form the gap of the housing are sealed from one another by means of an electrically conductive seal. The housing, which is also constructed to be conductive, works together with the conductive seal as a Faraday cage, in order to thus prevent the radiation of electromagnetic waves or to shield against interfering radiation effects.
Together with the shielding from electromagnetic interference radiation because of the conductivity of the utilized material, another significant function of this type of seal exists in the protection of the electronic device from the effects of contaminant particles, moisture and toxic gases. The electronic seal must therefore satisfy at the same time the demands usually placed on a seal used in structural technology and in machine construction for the prevention of material transfer between two spaces.
In an electromagnetic sealing medium which is described in DE 39 34 845 A1 in the criticized state of the art, conductive metallic solid particles are incorporated into a material with rubber-like elasticity in order to effect an electromagnetic sealing between the two housing sections simultaneously with the mechanical seal. Silver is utilized as an excellent conductive component which, however, is expensive on the one hand and, on the other, leads to a reduction in elasticity which negatively influences the sealing properties in the quantity needed to achieve the required conductivity and also to a significant increase in the specific weight of the seal. As a solution to the aforementioned problems, DE 39 34 845 A1 recommends a conductive seal which is formed from a non-conductive elastic seal element and a conductive layer which is applied to the non-conductive layer on the concerned sealing surface, and whose edge areas are in direct contact with the housing surface. The conductive layer consists of an elastic material mixed with a conductive supplement.
In this manner, a conductive seal with a low proportion of metal and high elasticity is made available. However, the costly production process in which a paste in the form of a strand is first applied to the sealing surface of a housing and the paste is then hardened to a rubbery-elastic sealing profile, on which and on the adjacent areas of the seal gap surface the conductive layer is sprayed in an additional process step in the form of a liquefied mass, is disadvantageous. Together with the costly formation of the sealant strand, this process is also disadvantageous for the reason that increased space is required for the conductive layer which is sprayed on.
In DE 43 19 965 C2 which is more recent in priority compared to the afore-mentioned state of the art, a paste-like initial material is also applied to the housing surface to be sealed, which also hardens elastically to a sealing element of a specific form. However, according to this solution, the elastic initial material is mixed in a known manner with the conductive particles. The disadvantages previously stated in the criticism of the state of the art in recommendation based on DE 39 34 845 A1, which consist of the high costs for the large proportion of silver, the high weight, the decrease in elasticity with the growing metallic proportion and the worsened sealing effect because of the unsatisfactory contact with the sealing gap surface are the result of this.
For an improvement in the elasticity properties of the shielding profile formed from the conductive materials mixed with the elastic material, the solution revealed in DE 43 19 965 C2 recommends a seal which is formed from several individual strands in order to create profile cross-sections in a form which effects a certain elasticity. From the processing and equipment aspect, the application of multiple sealant strands is costly and has the additional requirement for more space, wider housing surfaces and higher material costs as a result.
In the sealing of the gap which remains between the two sections of the housing, the compensation for dimensional deviations between the housing and the cover often presents problems, so that cost-intensive seals with a larger diameter and, in addition to this, significant clamping forces which lead to distortion of the housing are required with larger tolerances.
The object which forms the basis of the invention is therefore to develop an electrically conductive seal for the prevention of a material transfer and for the electromagnetic shielding of electronic modules which are accommodated in a conductive housing, which have high elasticity and sealing effect with low space requirements and costs, and which can be produced with low costs.
In accordance with the invention, this object is achieved by an electrically conductive seal according to the preamble of patent claim
1
in such a manner that it is made by means of co-extrusion double- or multilayered and is constructed from at least one internally-positioned elastic sealant strand which is free of conductive components and from one ring-shaped external conductive strand which encompasses the latter with low inherent elasticity and is made of a sealant which is mixed with electrically conductive components.
In other words, the basic idea of the invention lies in the construction of a conductive seal which is made of a non-conductive, large-volume and thus highly-elastic core and a comparably thin-walled and flexible conductive sheathing which consists of an elastic sealing material that is mixed with conductive particles, whereby the two differing materials are simultaneously extruded and applied to the sealing surface in a condition which is still plastic and not yet hardened.
As a result, a seal is made available which, because of the large-volume core which is free of conductive components, is highly elastic in its entirety and therefore makes possible a reliable seal of the junction point between the housing cover and lower section with low clamping forces, specifically without distorting the housing, even with larger tolerances. The high elasticity of the seal in accordance with the invention ensures adequately-high restoring forces even after lengthy stressing and thus reliable radiation shielding and sealing protection against material transfer, even after multiple opening and closing procedures. Because of the fact that the conductive strand is constructed as the sheath which encompasses the sealant strand on all sides, a reliable electrical connection between the sealing surfaces may be produced with low space requirements because of the high elasticity, so that the effect of the housing as a Faraday cage is not interrupted. In addition, the comparatively-low proportion of electrically conductive particles, which are nevertheless tightly packed in the sheathing and which guarantee high conductivity, has a weight and cost reducing effect.
An essential benefit is the simple manufacturing of the proposed conductive seal, which is accomplished b
Knight Anthony
Neuhaus Elektronik GmbH
Patel Vishal
Wood Phillips VanSanten Clark & Mortimer
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