Plastic-clad metals as electromagnetic interference protection for electrical boxes

Abstract

An electromagnetic interference (EMI) protection enclosure for protection of electrical boxes includes a resin layer. A plastic-clad metal layer is bonded to the resin layer. The metal layer can provide EMI protection. The plastic-clad metal layer bonded to the resin layer is thermo-formed into a shape. The shape can receive an article to be protected from EMI.

Description

PLASTIC-CLAD METALS AS ELECTROMAGNETIC INTERFERENCE PROTECTION FOR ELECTRICAL BOXESTECHNICAL FIELD

[0001] This disclosure relates to protecting electrical boxes from electromagnetic interference (EMI).BACKGROUND

[0002] Metal enclosures are used in electrical boxes to shield any external signal lines from electromagnetic impulses. The electrical conductivity of such enclosures allows grounding. Grounding dissipates electrical fields. In addition, enclosures made of ferromagnetic materials absorb magnetic fields. However, electrical conductivity is undesirable when trying to limit short circuits or human exposure to electricity.

[0003] U.S. 6,090,728 describes EMI shielding enclosures. Such an enclosure, for an electronic assembly, includes a ground plane of a printed circuit connected to a shaped EMI shielding cover. The cover results from thermoforming a composite sheet of several layers, including a carrier for a fibrous metal mat that has fibers substantially surrounded by a fiber-coat. Connection of the cover to the ground plane, to form the EMI shielding enclosure, requires the fiber-coat to adhere to the printed circuit in the vicinity of the ground plane.

[0004] U.S. 2004 / 0048077 describes electromagnetic interference shield for electronic devices. The EMI shield for personal computers, cellular phones, and other electronic devices is constructed from thermoformable polymeric material which is then metallized on all surfaces by vacuum metallization techniques to provide an inexpensive, lightweight, effective EMI shield.

[0005] U.S. 7,005,573 describes a composite EMI shield having at least one compartment for enclosing circuitry of an electronic device. The shield includes a first member formed of a first material such as a thin metal sheet or screen, or a metal-plated fabric or other electrical ly-conductive mesh, and a second member formed of a second material different than the first material. The second material is an admixture of a plastic or other polymeric component and an electrically-conductive particulate filler component.The second member is integrally joined to the first member, and has at least one wall which extends from the first member and which together with the first member defines at least a portion of the compartment.

[0006] U.S. 6,202,276 describes a process for manufacturing an electromagnetic interference shielding superplastic alloy foil cladded outer shell product. To do so, a first side of a superplastic alloy foil is coated with an adhesive and then the foil is placed in a first half mold to allow the foil to be initially superplastically formed. A second half mold attached to a nozzle of an injection machine is covered onto the first half mold, and the two half molds are closed to further deform superplastic alloy foil. Softened plastic is introduced from the injection machine to a mold cavity between the foil and the second half mold, such that the superplastic alloy foil covered on the first half mold is completely formed and the softened plastic adheres on the adhesive-coated side of the superplastic alloy foil to form an electromagnetic interference shielding metallic foil cladded plastic outer shell product. Two types of products can be obtained, that is, the superplastic alloy foil can be either the outer wall or inner wall. Moreover, the final metallic plastic product can not only have as intricate a shape as an ordinary plastic product, but also a shielding effectiveness as high as an ordinary metallic shield.SUMMARY

[0007] This disclosure describes plastic-clad metals as EMI protection for electrical boxes. The plastic-clad metal described here includes a plastic cladding that is laminated on a metal layer to form a plastic-clad metal laminate. Such a construction offers greater adhesion and formability compared to metal meshes with over-molded plastic. The construction described here consumes fewer resources and is consequently less expensive compared to vacuum deposition of paints, coatings or metal. The consumption of resources is especially reduced for nonpolar plastics which require an additional activation step to achieve good bonding. The construction described here is superior to meshes constructed using non wovens, which offer low magnetic absorption and limited grounding due to the limited metallic cross section.

[0008] The details of one or more implementations of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, andadvantages of the disclosure will be apparent from the description and drawings, and from the claims.DESCRIPTION OF DRAWINGS

[0009] FIG. 1 is a schematic diagram of an example of a first implementation of an EMI protection enclosure.

[0010] FIG. 2 is a schematic diagram of an example of a second implementation of an EMI protection enclosure.

[0011] FIG. 3 is a schematic diagram of an example of a first tooling arrangement to manufacture the EMI protection enclosure of FIG. 1.

[0012] FIG. 4 is a schematic diagram of an example of a second tooling arrangement to manufacture the EMI protection enclosure.Like reference symbols in the various drawings indicate like elements.DETAILED DESCRIPTION

[0013] This disclosure describes an EMI shield for electrical boxes that includes a plastic enclosure with a metal layer to allow grounding and shielding. The EMI shield includes a plastic - clad metal tape or foil. During construction, the plastic surface melts, thereby achieving high bonding strength to the over-molded plastic. In turn, such bonding allows the multilayer to be draped on shaped molds. The techniques described here can be implemented in both compression and injection molding. The techniques can also be implemented with a variety of metal substrates. The techniques can be used to produce sheets by cast film extrusion of a plastic onto a plastic - clad metal tape. The techniques can be used in lamination of a plastic sheet to a plastic - clad metal. The plastic - clad metal can then be thermoformed to form the enclosure. By adding flame retardant additives to the resin, the flame retardancy of the multilayer can exceed that of plastic.

[0014] FIG. 1 is a schematic diagram of an example of a first implementation of an EMI protection enclosure 100. In particular, FIG. 1 shows the material with which the enclosure 100 is made, laid flat. As described below, the material can be shaped to adapt to the form of the electrical box to be covered using the enclosure 100. The enclosure 100can be used to cover not only the electrical box but any other structure that needs EMI shielding. The enclosure 100 includes a resin layer 102. The resin in the resin layer 102 can be a thermoset resin. Alternatively, the resin in the resin layer 102 can be a thermoplastic resin. Unfilled and glass fiber reinforced thermoplastic resins including polycarbonate (PC), polycarbonate and acrylonitrile butadiene styrene (ABS) blend, and polypropylene (PP) can be used. Unfilled and glass fiber filled thermoset resins including epoxy, polyester, polyurethane can also be used.

[0015] In some implementations, the resin in the resin layer 102 can include a flame retardant additive. Intumescent flame retardant additives are added to the thermoplastic resins during their compounding. In addition to EMI protection, the flame retardant additives can provide thermal protection to the electrical box or other article enclosed by the enclosure. In some implementations, the resin in the resin layer 102 can include fiber. The fiber can include glass fiber, carbon fiber, aramid fiber, natural fiber, other types of fiber or any combination of any two or more types of fiber.

[0016] The enclosure 100 includes a plastic-clad metal layer 104. The metal layer 104 includes a metal substrate 106 with a plastic layer 108 laminated onto the metal substrate 106. For example, the plastic-clad metal layer 104 can be formed as a metal tape clad with plastic. Metal coated tapes including aluminum, steel and copper coated tapes can be used. The metal is coated with thin film of plastic on either one side or two sides of the metal. The coating can be based on ethylene acrylic acid co-polymer and ethylene vinyl acrylic acid co-polymer. The thickness of the metal varies from 0.10 to 0.15 mm whereas the thickness of the thin plastic film in the range of 0.050 to 0.10 mm..

[0017] In some implementations, the metal in the metal substrate 106 is a thin sheet of metal that can be ferromagnetic, paramagnetic or diamagnetic. The addition of such materials can improve the capability of the enclosure 100 to absorb magnetic and electric fields.

[0018] The resin layer 102 can be over-molded onto the plastic-clad metal layer 104. The metal layer 106 of the plastic-clad metal layer 104 can provide EMI protection. The enclosure 100 can be thermoformed into any desired shape based on the shape of the article (e.g., an electrical box or other article) to be protected from EMI. The thermoformed enclosure 100 can be wrapped around the article. When wrapped, themetal layer 106 is in direct contact with an outer surface of the article. The plastic layer 108 is in direct contact with the metal layer 106 such that the metal layer 106 is in between the plastic layer 108 and the article. The resin layer 102 is in direct contact with the plastic layer 108 such that the plastic layer 108 is in between the resin layer 102 and the metal layer 106.

[0019] FIG. 2 is a schematic diagram of an example of a second implementation of an EMI protection enclosure 200. Like FIG. 1 , FIG. 2 shows the material with which the enclosure 200 is made, laid flat. Similar to the enclosure 100 (FIG. 1), the material can be shaped to adapt to the form of the electrical box or other article to be covered using the enclosure 200. The enclosure 200 includes a resin layer 202, which is identical to the resin layer 102 (FIG. 1). The enclosure 200 includes two plastic-clad metal layers on either side of the resin layer 202.

[0020] The first plastic -clad metal layer 204a includes a metal substrate 206a with a plastic layer 208a laminated onto the metal substrate 206a. The first metal layer 204a is bonded to one side (e.g., a bottom surface) of the resin layer 202. The second plastic-clad metal layer 204b includes a metal substrate 206b with a plastic layer 208b laminated onto the metal substrate 206b. The second plastic-clad metal layer 204b is bonded to another side (e.g., a top surface) of the resin layer 202. The metal substrates 206a, 206b are identical to the metal substrate 106 (FIG. 1). The plastic layers 208a, 208b are identical to the plastic layer 108 (FIG. 1).

[0021] The resin layer 202 can be over-molded onto the plastic-clad metal layers 204a, 204b. The resin layer 202 resides between the first plastic-clad metal layer 204a and the second plastic-clad metal layer 204b. The metal layers 206a and 206b of the plastic-clad metal layers 204a, 204b can provide EMI protection. Similar to the enclosure 100 (FIG. 1), the enclosure 200 can be thermoformed into any desired shape based on the shape of the article (e.g., an electrical box or other article) to be protected from EMI. The thermoformed enclosure 200 can be wrapped around the article. Similar to the resin layer 102, in some implementations, the resin layer 202 can also include a flame retardant additive. In such implementations, the thermoformed enclosure 200 can provide thermal protection in addition to EMI shielding.

[0022] FIG. 3 is a schematic diagram of an example of a first tooling arrangement to manufacture the EMI protection enclosure 100 (FIG. 1). Overall, there are four main steps to manufacture the EMI shielding protection enclosure 100 [FIG.1]. Firstly, a high strength, two part metallic mold is fabricated that exactly matches the dimensions required to fabricate the desired enclosure. This two part metallic mold, which includes the mold cavity and the mold core, is installed in a compression molding press. The mold cavity is connected to the stationary platen 302 and the mold core is connected to the moving platen 304 of the compression molding press. Both the mold cavity and the mold core are heated to the desired mold temperature to promote good adhesion between the plastic layer 108 of the plastic-clad metal layer 104 and the over-molding resin layer 102.

[0023] Secondly, the desired plastic-clad metal layer is placed into the mold cavity. For a complex geometry mold for example, a pre-forming step of the plastic-clad metal layer into the shape of the mold is desired. Pre-forming helps to improve the performance of the finished product by mitigating defects. Thirdly, the mold with the desired plastic-clad metal layer (blank / flat or pre-formed) is compressed under very high force typically ranging from 8000 to 20000 kN depending on the geometry, the size and the thickness of the enclosure and the type of the over-molding resin 102 used. Lastly, the enclosure is removed from the mold after the force is released.

[0024] In some implementations, in a first step, the plastic-clad metal layer 104 is formed. For example, the plastic-clad metal layer 104 is formed as a foil clad with plastic. In a second step, the plastic-clad metal layer 104 is positioned within a tooling arrangement 300. The tooling arrangement 300 includes a stationary platen (or flat platform) 302. The plastic-clad metal layer 104 can be positioned on the stationary platen 302. Specifically, the plastic-clad metal layer 104 can be positioned such that the metal substrate of the plastic-clad metal layer 104 contacts the stationary platen 302 and resides in between the plastic layer and the stationary platen 302. The tooling arrangement 300 includes a moving platen 304. The resin is formed as a plasticized charge 306. In some implementations, the plasticized charge 306 includes fibers while in others, the plasticized charge 306 does not. In some implementations, the plasticized charge 306 is a thermoset resin. In some implementations, the plasticized charge 306 is a thermoplastic resin. The plasticized charge 306 is positioned between the mold cavity connected to the stationary platen 302 and the mold core connected to the moving platen 304. When positioned, theplasticized charge 306 contacts the plastic layer of the plastic-clad metal layer 104. The moving platen 304 is then moved towards the stationary platen 302 to press and overmold the plasticized charge 306 to the plastic layer of the plastic - clad metal layer 104. The heat capacity of the plasticized charge 306, which under desired compression force of the compression molding machine, is enough to melt the plasticized charge 306 allowing formation of the multilayer.

[0025] FIG. 4 is a schematic diagram of an example of a second tooling arrangement to manufacture the EMI protection enclosure. In the first step, two plasticclad metal layers 104 are formed. In the second step, a first plastic-clad metal layer 401 is positioned in the mold cavity and a second plastic-clad metal layer 403 is positioned onto the mold core using a gripping mechanism. The mold cavity and the mold core are connected to the stationary platen 402 and the moving platen 404, respectively. . In the third step, the over-molding resin is formed as a plasticized charge 406 and is placed onto the plastic layer of the first plastic-clad metal layer 401 positioned into the mold cavity connected to the stationary platen. In some implementations, the plasticized charge 406 includes fibers while in others, the plasticized charge 406 does not. In some implementations, the plasticized charge 406 is a thermoset resin. In some implementations, the plasticized charge 406 is a thermoplastic resin. The mold core comprising the second plastic-clad metal layer 403, connected to the moving platen 404 is then moved towards the mold cavity connected to the stationary platen 402 to press and over-mold the plasticized charge 406 between the plastic layer of the first plastic - clad metal layer 401 and the plastic layer of the second plastic-clad metal layer 403. The heat capacity of the plasticized charge 406, which under desired compression force of the compression molding press, is enough to melt the plasticized charge 406 allowing formation of the multilayer.

[0026] The platens are schematically shown in FIGS. 3 and 4 as being flat platforms. In other constructions, the platens can be constructed based on a desired shape of an enclosure. The shape of the enclosure, in turn, is driven by the shape of the electrical box or article that the enclosure is meant to cover. As described above with reference to FIGS. 3 and 4, the plastic of the plastic-clad metal layer can be compression molded onto the resin layer. In some implementations, the plastic of the plastic-clad metal layer can be injection molded onto the resin layer. In some implementations, the plastic -clad metal layer can be of the type that is used in barrier food packaging or in wire and cable moisture barriers. The plastic cladding can have a thickness ranging from 0.050 to 0.10 mm whereas the thickness of the metal layer can range from 0.10 to 0.15 mm.

[0027] A number of implementations of the disclosure have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure.

Claims

CLAIMS1. An electromagnetic interference (EMI) protection enclosure comprising: a resin layer; and a plastic-clad metal layer bonded to the resin layer, the plastic-clad metal layer comprising a metal layer providing EMI protection, the plastic-clad metal layer being bonded to the resin layer thermo-formed into a shape configured to receive an article to be protected from EMI, wherein the metal layer is in between the resin layer and the article.

2. The enclosure of claim 1, wherein the plastic-clad metal layer is a first plastic-clad metal layer bonded to the resin layer, the enclosure further comprising a second plastic-clad metal layer bonded to the resin layer.

3. The enclosure of claim 2, wherein the resin layer is in between the first plastic-clad metal layer and the second plastic-clad metal layer, wherein the second plastic-clad metal layer is formed as a metal tape clad with plastic.

4. The enclosure of any one of claims 1-3, wherein the resin comprises flame retardant additive, wherein the resin is compression molded onto the plastic layer of the plastic-clad metal layer.

5. The enclosure of any one of claims 1-4, wherein the resin is injection molded onto the plastic layer of the plastic-clad metal layer, wherein the plastic-clad metal layer bonded to the resin is formed as a laminate.

6. The enclosure of any one of claims 1-5, wherein the plastic-clad metal layer is formed as a foil clad with plastic, wherein the metal in the metal layer comprises ferromagnetic, paramagnetic or diamagnetic materials.

7. The enclosure of any one of claims 1-6, wherein the resin comprises a thermoplastic resin or a thermoset resin.

8. The enclosure of any one of claims 1-7, wherein the resin comprises fiber, wherein the fiber comprises a glass fiber, a carbon fiber, an aramid fiber, or a natural fiber or any combination thereof.

9. A method of making an electromagnetic interference (EMI)-shielding enclosure, the method comprising: positioning a plastic-clad metal layer within a tool; positioning a plasticized charge of a resin on the plastic-clad metal layer within the tool; and bonding the plastic-clad metal layer to the resin, the metal layer configured to provide protection against EMI.

10. The method of claim 9, wherein the plastic-clad metal layer is a first plastic-clad metal layer, wherein bonding the plastic-clad metal layer to the resin comprises bonding the first plastic-clad metal layer to the resin.

11. The method of any one of claims 9 or 10, further comprising bonding a second plasticclad metal layer to the plasticized charge of the thermoplastic resin layer.

12. The method of any one of claims 11, wherein the resin layer is in between the first plastic-clad metal layer and the second plastic-clad metal layer.

13. The method of claim 9-12, wherein bonding the plastic-clad metal layer to the resin comprises forming the plastic-clad metal layer as a metal tape clad with plastic, wherein the method further comprises adding flame retardant material to the resin.

14. The method of any one of claims 9-13, wherein bonding the plastic-clad metal layer to the resin comprises compression molding or injection molding the plastic-clad metal layer onto the resin or cast film extruding the resin onto the plastic-clad metal layer.

15. The method of any one of claims 9-14, wherein bonding the plastic-clad metal layer to the resin comprises: laying the plastic-clad metal layer in a mold; and casting the resin onto the plastic-clad metal layer in the mold.

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