Coating processes – Electrical product produced
Reexamination Certificate
1999-03-10
2001-12-11
Talbot, Brian K. (Department: 1762)
Coating processes
Electrical product produced
C427S123000, C427S265000, C427S284000, C427S385500
Reexamination Certificate
active
06329014
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for producing a casing providing a screen against electromagnetic radiation according to the preamble of claim
1
, and a casing according to the preamble of claim
6
.
2. Description of the Prior Art
Electronic components and also measuring, detection and similar devices sensitive to interference by electromagnetic radiation require a screen against the electromagnetic fields present at the operational site in order to ensure a problem free operation.
They are therefore accommodated in screening cases which comprise conductive material in the walls and act as a Faraday cage.
Such casings are also used for equipment or components which, themselves, emit electromagnetic rays that must be excluded from the environment, in order for example, to prevent the emission of secret information or the malfunction of external appliances.
Today such a screening against the emission or irradiation of EMI must be more effective the more electronic apparatuses are operated and the greater the proximity at which these apparatuses must operate next to each other. Finally, the continuous increase in performance and sensitivity of such equipment also necessitates an improvement of the screening measures for which increasingly less space is available, since the relevant appliances must, moreover, be miniaturised. Thus, apart from the actual operational properties of electronic appliances, the “electromagnetic compatibility” is today a significant factor determining quality.
If, as is mostly the case in practice, the casings are multi-part constructions which must be capable of being opened occasionally (e.g. in order to renew the energy source or for maintenance purposes), it is necessary to provide the parts of the casing to be separated from each other during opening and to be reconnected again during closing, with elastic conductive seals in order to achieve an effective screening.
Whilst, on the one hand, spring-like metal seals are known for this purpose, they are, however, comparatively expensive to construct and their operability may be greatly affected by oxidation and soiling.
Furthermore, resilient sealing profiles made of elastomer which is conductive or has been made conductive, which has been mixed with carbon or metal particles in order to make it conductive, are known from e.g. U.S. Pat. No. 4,659,869 or DE-OS 28 27 676.
Such sealing profiles are normally manufactured as separate seals. They may be moulded or extruded as a continuous section and then placed into the casing to be screened.
This is a labour-intensive operation and especially in small casings it causes difficulties as seals with correspondingly small dimensions are difficult to handle. The provision of suitable guides (grooves) which facilitate the mounting on the casing requires an unreasonable amount of space and is thus a hindrance to the further miniaturisation of the appliances.
Intricately moulded seals likely to be needed for special casings require specific positioning equipment which makes the manufacture of the casing altogether more expensive. The exact positioning is, moreover, time-consuming and necessitates additional inspection.
The hot-moulding, in moulds, of such screening profiles onto the relevant casing portions or parts and the setting at a relatively high temperature and/or high pressure is also known.
This process cannot be used with parts sensitive to pressure and/or temperature such as printed circuit boards or metallised plastics casings and, as a result of the low tear resistance of the related materials, problems arise during the removal from the mould resulting in a relatively high number of rejects and, more particularly in intricately shaped casings and seals, also frequently necessitating time-consuming and labour-intensive machining on the pressed-out edges.
SUMMARY OF THE INVENTION
The invention has the object of providing a process of the above kind for producing protective screens, more particularly within the region of casing joints, which may be adapted, in a simple manner, to the most varied requirements, even in a miniaturised construction. It must also be possible to use the process according to the invention for casings to be produced in larger quantities, in a simple manner and at low cost. The casing produced according to this process must be provided with a screening profile which meets the electromagnetic and mechanical requirements and remains in good condition even after a repeated opening of the casing.
This object is achieved by a casing with the features of claim
6
or a process with the features of claim
1
.
The invention is based on the concept of not producing the screening profile separately but directly and without using a mould on the casing, by means of a hardening pasty or liquid compound with the required properties which issues from an opening guided over the geometrical extent to be sealed, thereby avoiding any problems in handling, on the one hand, and the process-related disadvantages of compression moulding, on the other hand. Here, the material consists of a plastics compound which contains conductive inclusions, more particularly in the form of metal or carbon particles.
If, for forming the profile, the guidance of the needle or nozzle over the portion of the casing part, on which the screening profile is intended to be mounted, is done by machine, more particularly controlled by computer, a high precision and great flexibility is ensured in shaping the profile so that moreover intricately moulded casings or openings of casings in small series may easily be provided with the necessary screening seal in an economic manner.
Special profiles, for example comprising undercuts, recesses etc., on the casing, are advantageously produced by guiding the needle or nozzle several times at least over predetermined regions of the portion on which the screening profile is intended to be mounted, in order to produce a multi-layer screening profile, thereby forming an exactly predetermined profile section. In so doing, a profile with a given cross-section, as desired, may advantageously be produced in several successive stages, either one nozzle coating the respective area several times, or several nozzles successively applying different strands which combine to form the desired sealing shape.
In this way cross-sectional profiles may preferably be produced which have given elasticity properties and do not acquire said elasticity because of their compressibility but because of a bending deformation, as is the case in bent lip sections or hollow sections.
It is, particular, not necessary to provide each strand of the material with conductive inclusions since linear conductors already provide a great screening effect due to the laws of the electromagnetic field.
The inventive measures also make it possible to produce complicated seal constructions with dimensions which vary along their extent, without special difficulties. Here, according to the relevant requirements, the cross-section may vary along the edge to be sealed, within wide limits. It is also possible to produce such constructions of screening profiles which are interconnected in a way that an individual production and mounting thereof, separate from the casing, would not have been possible. Any joints in the extent of the screening seal are thus obviated by the measures according to the invention so that the sealing effect is not interrupted.
Smaller casing zones or additions which are not made of metal or metallised, which would produce a break in the closed screen, may, in an operation carried out at the same time as the other seal is produced, be coated grid-like with the profile strands according to the invention, so that homogenous screening conditions also exist in such regions.
In this way elements of a Faraday cage may even be formed from tracks of conductive plastics material and thus of the sealing compound itself, if they are mounted in the shape of a grid in a plane and conductively connected at the intersec
Kahl Helmut
Tiburtius Bernd
EMI-TEC Elektronische Materilien GmbH
Gottlieb Rackman & Reisman P.C.
Talbot Brian K.
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