WO2003101630A1

WO2003101630A1 - Manufacturing method for form-in-place gaskets having complex cross sections

Info

Publication number: WO2003101630A1
Application number: PCT/US2003/017546
Authority: WO
Inventors: Rachid Ait El Cadi
Original assignee: Laird Technologies, Inc.
Priority date: 2002-06-04
Filing date: 2003-06-03
Publication date: 2003-12-11
Also published as: AU2003245392A1; TW200403019A; TWI230034B

Abstract

A method of manufacturing a form-in-place gasket includes the step of providing a substrate (30) having a surface adapted for receipt of a gasket having a noncircular cross section. A form-stable fluent material having a cross-section substantially matching the non-circular cross section is extruded via a nozzle (32) onto the surface, and the fluent material is cured to form the gasket.

Description

MANUFACTURING METHOD FOR FORM-IN-PLACE GASKETS HAVING COMPLEX CROSS SECTIONS

FIELD OF THE INVENTION The present invention relates to methods of making form-in-place gaskets, and more particularly to form-in-place gaskets having non-circular cross sections.

BACKGROUND OF THE INVENTION The operation of electronic devices such as televisions, radios, computers, medical instruments, business machines, communications equipment, cellular telephones among others is often accompanied by the generation of electromagnetic radiation within the electronic circuitry of the equipment. The radiation often develops as a field within the radio frequency band of the electromagnetic spectrum, i.e., between about 10 kHz and 10 GHz, and is referred to as "electromagnetic interference" or "EMI". EMI interferes with the operation of other electronic devices within the proximity of the EMI emitting device. Thus, it has been a long-standing concern in the electronic field to ameliorate EMI.

A common approach for ameliorating the effects of EMI is to provide shielding having the capability of absorbing and/or reflecting EMI energy within the source device to confine the EMI energy, and to insulate other devices from EMI source device. Shielding is typically provided as a barrier between the source device and the other devices and is in the form of a electrically conductive material. However, most devices generally must remain accessible for servicing and as a result the housings are provided with removable accesses such as doors, hatches, panels, or covers. Openings for access often present gaps that reduce the efficiency of the shielding by allowing openings through which radiant energy may leak or otherwise pass into or out of the device.

Gaskets and other seals are used to fill the gaps within mating surfaces of housings to prevent EMI leaks and to exclude contamination from moisture and dust. Such seals are bonded or mechanically attached to, or press-fit into, one of the mating surfaces, and function to close any interface gaps. Seals for these applications need to exhibit electrical surface conductivity even while under compression, resiliency thereby allowing the seals to conform to the size of the gap, in addition to being wear resistant, economical to manufacture, and capable of withstanding repeated compression and relaxation cycles. Conventional manufacturing processes for EMI shielding gaskets include extrusion, molding, or die-cutting, with molding or die-cutting being commonly used for particularly small or complex shielding configurations. Die-cutting involves forming the gasket from a cured sheet of an electrically conductive elastomer which is cut or stamped using a die into the desired configuration. Molding, in turn, involves the compression or injection molding of a thermoplastic elastomer into the desired configuration.

Another technique for manufacturing EMI gaskets is the form-in-place process. These processes involves the application of a bead of a viscous, curable, electrically conductive composition in a fluent state to a surface of a substrate such as a housing or other enclosure. The composition, typically a silver-filled silicone elastomer, then is cured in place via the application of heat or with atmospheric moisture or ultraviolet (UV) radiation to form an electrically conductive, elastomeric EMI shielding gasket in situ on the substrate surface. By forming and curing the gasket in place directly on the substrate surface, the need for separate forming and installation steps is eliminated. Moreover, the gasket may be adhered directly to the surface of the substrate to further eliminate the need for a separate adhesive component or other means of attachment of the gasket to the substrate. In contrast to more conventional die cutting or molding processes, the form-in-place process reduces waste generation, and additionally is less labor intensive in that the need for hand assembly of complex gasket shapes or the mounting of the gasket into place is obviated. The process further is adaptable to an automated or robotically controlled operation, and may be employed to fabricate complex gasket geometries under atmospheric pressure and without the use of a mold.

However, the preparation of complex gasket geometries (i.e., gaskets having other than circular or semi-circular cross sections) often require multiple passes due to the circular bead of gasket material being dispensed. Multiple passes with the dispensing or extruding apparatus adds time and therefore costs to production. In addition, a circular bead often will not provide an optimal fit for non-circular cross sections.

Therefore, there is a need in the art for methods of manufacturing shielding gaskets with complex cross sections with reduced dispensing times and improved fits. Accordingly, it is an object of the present invention to provide methods of manufacturing gaskets for environmental sealing and/or EMI/RFI shielding with complex cross-sections with reduced dispensing times and improved fits.

SUMMARY OF THE INVENTION The present invention is a method of manufacturing a form-in-place gasket.

The method comprises the step of providing a substrate having a surface adapted for receipt of a gasket having a non-circular cross section. A form-stable fluent material having a cross-section substantially matching the non-circular cross section is extruded onto the surface, and the fluent material is cured to form the gasket. The present invention will now be described in greater detail with reference being made to the drawing figures identified below.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial cross-sectional view of a two-piece housing having opposing channels which when mated define a non-circular cross section for receipt of an EMI shielding gasket.

FIG. 2 is a front view of a dispensing nozzle having an orifice for dispensing gasket material substantially matching the non-circular cross section defined by the two-piece housing of FIG. 1. FIG. 3 is a partial cross-sectional view of one of the housing pieces of FIG. 1 having disposed in its channel a gasket with a non-circular cross section dispensed with the nozzle of FIG. 2.

FIG. 4 is a 3D view of a gasket material being extruded with a triangular cross section from a vertically positioned nozzle having triangular matching cross section as it turns along an axis perpendicular to the substrate. FIG. 5 is a 3D view of a triangular shaped gasket material extruded from an horizontally positioned nozzle as it turns along an axis perpendicular to the substrate.

FIG. 6 are cross-sectional views of commonly used gasket shapes that can be made using the process of the present invention. FIG. 7 are cross-sectional views of gaskets extruded with a perpendicular nozzle that has been misaligned (i.e., skewed) relative to the surface of the substrate illustrating the effect on the gasket shape.

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method of manufacturing form-in-place EMI gaskets having complex cross sections with reduced dispensing times. As previously described, form-in-place gaskets have heretofore been prepared using a circular bead of gasket material. Surfaces that require gaskets with complex cross sections such as non- circular cross sections typically require multiple passes or fills with the circular bead to form the complex cross section gasket. Advantageously, the present invention provides methods in which production times are reduced by extruding the gasket material with a cross-section matching the cross-section of the desired gasket. This entails providing a substrate having a surface adapted for receipt of a gasket with a complex cross section. A form-stable fluent material having a cross section matching the complex cross section is then extruded onto the surface. The fluent material once extruded is cured thereby forming the gasket.

Referring to FIG. 1 , a non-limiting example of a substrate to be provided with a gasket is shown in the form of a two-piece housing 10 arranged in an opposing orientation. The lower housing 12 includes channel 14 which defines a rectangular cross section (i.e., a complex cross section). A corresponding upper housing 16 having corresponding channel 18 is shown in an opposing orientation. When housings 12 and 16 are brought together in an opposing orientation channels 14 and 18 define a square cross section for receipt of a gasket in accordance with the invention. Any substrate having a surface adapted for receipt of a gasket having a complex cross section can be provided with a form-in-place gasket using the present invention. Reference to "complex cross sections" means any cross section defined by a substrate or substrates that is not circular or semi-circular. Examples of complex cross sections to be prepared in accordance with the invention are squares, rectangles, triangles or any other type of polygonal cross section.

FIG. 2 shows a front view of dispensing nozzle 100 having a square orifice 102, which substantially matches the dimensions of the square cross section defined by channels 14 and 18 shown in FIG. 1. As shown in FIG. 3, nozzle 100 when used with an extruder (not shown) provides channel 14 with an extruded gasket material 104 having the requisite cross section. The matching of the extruded material to the desired gasket cross section facilitates single pass production of the gasket on the substrate while at the same time providing an improved fit. Once cured, a resilient gasket is formed in place.

The production of nozzles with orifices matching a cross section for a desired gasket is accomplished using any technique known in the art. For convenience, the nozzle is preferably made (e.g., molded) from a polymeric material such as a thermoplastic or thermoset polymer. For example, once the dimensions of the gasket cross section have been ascertained, a requisite nozzle can be produced by injection molding of a thermoplastic polymer. Likewise, the nozzle can be produced by conforming a heat-shrinkable polymer onto a mandrel with the required dimensions for the complex cross section. These parameters can be easily ascertained by one skilled in the art.

Gasket materials to be used in accordance with the invention are any fluent material having sufficient thixotropic properties to be extruded as a form-stable material. "Fluent" means that the material exhibits fluid-like behavior allowing the material to extruded through a dispensing nozzle. "Form-stable" means that the extruded material substantially retains its extruded shape and does not exhibit any appreciable slumping, sagging or loss of form. The fluent material is preferably a curable polymeric material with elastomeric materials being more preferred. The fluent material is rendered electrically conductive preferably through the use of a conductive filler such as metal particles or a metal-coated particulate. Fluent materials for form-in- place EMI gasket applications are well known in the art. The materials can be provided as a single or dual component system which cure preferably upon exposure to ambient conditions (e.g., atmospheric moisture). Examples of these materials are found in U.S. Patents Nos. 5,910,524 and 6,096,413, which are herein incorporated by reference.

Applicators 33 for extruding (i.e., dispensing) the fluent material to the substrate are well known in the art. The fluent material can be manually applied to the substrate with a caulking gun or equivalent device adapted with the requisite nozzle. However, commercial applications preferably utilize automated injection equipment such as robotic applicators with two or more degrees of movement (x-y-z) alone or in combination with a movable table. The position of the nozzle 32 to the substrate 20,30 is variable and can range from a position perpendicular to a position parallel to the substrate as shown in FIGS. 4 and 5, respectively. Positioning the nozzle 32 perpendicular to the substrate 30 provides the advantage of leaving the nozzle 32 out of the dispensing path. This is particularly useful when the fluent material is dispensed in a groove or connected to itself at the end (e.g., to produce O-ring gaskets).

Moreover, due to the non-circular cross sections being dispensed, it is preferred that the orifice of the nozzle 32 be maintained at a fixed angle relative to the dispensing path on the substrate 20,30 to ensure the requisite cross section of fluent material is maintained. This is achieved by allowing the nozzle 32 to turn (i.e., rotate) to follow the dispensing path on the surface of the substrate 20,30. This is more easily understood with reference to FIG. 5. As shown in FIG. 5, the position of the nozzle orifice remains in line with the dispensing path. This can be done manually in turning the nozzle by hand, but also automatically by adding a further degree of movement to the injection robot. In the latter situation, a small motor, in which rotation is controlled by a microprocessor, drives the nozzle or the dispensing head so its angle remains constant relative to the dispensing path (or to the tangent of semi-circular dispensing path). The same relative movement could be achieved with the substrate being on a movable table (i.e., turntable) using a stationary nozzle. If the angle of the orifice relative to the dispensing path on the surface is not maintained (i.e., skewed or misaligned) the resulting cross section may also be skewed as shown in FIG. 7. Thus, the movement and angle of the nozzle relative to the dispensing path is an important consideration for extruding fluent materials with non-circular cross sections. The matching of the nozzle orifice to the gasket cross section facilitates one pass production of the gasket on the substrate. As previously described, the production of complex cross sections with conventional circular beads of fluent material often requires multiple passes to build up the gasket cross section. Likewise, the extrusion of the fluent material in a non-circular form as shown in FIGS. 3 and 6 is not possible. Moreover, as will be apparent to one skilled in the art, a bead having a shape substantially matching the requisite cross section provides a significantly better fit than is achieved with conventional circular bead. Thus, the methods of the present invention facilitate quicker production times and improved fits for form-in-place gaskets.

Claims

WHAT IS CLAIMED IS:

1. A method of manufacturing a form-in-place gasket which comprises: providing a substrate having a surface adapted for receipt of a gasket having a non-circular cross section; extruding onto said surface a form-stable fluent material having a cross section substantially matching said non-circular cross section; and curing said fluent material to form said gasket.

2. The method of claim 1, wherein said fluent material is extruded through a dispensing nozzle rotatable along an axis perpendicular to said surface of said substrate, the rotation of said nozzle being controlled to maintain a fixed angle between said fluent material being extruded relative to said surface.

3. The method of claim 1, wherein said fluent material is extruded through a rotatable dispensing nozzle, said dispensing nozzle being rotated to modify said cross section of said fluent material being extruded onto said surface.

4. The method of claim 1, wherein said non-circular cross section is a rectangular cross section.

5. The method of claim 1, wherein said non-circular cross section is square cross section.

6. The method of claim 1, wherein said non-circular cross section is a triangular cross section.

7. The method of claim 1, wherein said fluent material is an elastomeric material.

8. The method of claim 1, wherein said fluent material is formulated to produce after curing a high frequency shielding gasket.

9. The method of claim 1, wherein said fluent material is formulated to produce an electrically conductive elastic gasket.