Conductive plastic compositions and method of manufacture thereof

Abstract

An improved, conductive, polymeric composition comprises a polymeric resin; an electrically conductive filler system comprising small carbon fibers and either carbon powder or fibrous non-conductive filler or a combination of both. The amount of the conductive filler system utilized is dependent upon the desired electrical conductivity (surface and volume conductivity or resistivity) while preferably preserving intrinsic properties of the polymeric resin such as impact, flex modulus, class A finish, and the like. The conductive articles made from these compositions can therefore be used for electromagnetic shielding, electrostatic dissipation or antistatic purposes in packaging, electronic components, housings for electronic components and automotive housings.

Description

[0001] This application is a Continuation of U.S. Ser. No. 09 / 683,069, filed Nov. 15, 2001, and claims priority to U.S. Provisional Application Serial No. 60 / 287,127 filed Apr. 27, 2001, the entire contents of which are incorporated herein by reference.[0002] Plastic (polymeric resin) is often the material of choice for components in electronic products such as computers, photocopiers, and the like because it offers design flexibility, cost-effective manufacturing, and light weight products. In order to function efficiently in such applications, normally insulating polymeric resin must be made electrically conductive to provide electromagnetic shielding, electrostatic dissipation or antistatic properties to such components.[0003] Polymeric resins are typically made conductive by incorporating electrically conductive fillers such as carbon fibers, metal powders or flakes, vapor grown carbon fibers, carbon nanotubes, carbon black, and the like. However, the incorporation of carbon fib...

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Benefits of technology

[0010] It has been unexpectedly found by the inventors hereof that an electrically conductive filler system comprising small carbon fibers and carbon powders, fibrous non-conductive fillers, or both, can be used to impart increased electrical conductivity to polymeric resins while maintaining properties such as impact strength, flexural modulus, shrinkage, class A finish, and the like in injection molded products. Small carbon fibers as defined herein may be either vapor grown carbon fibers or carbon nanotubes or a combination of both. In particular, it has been found that by adding either carbon powder or glass fibers or a combination of both with small carbon fibers to a polymeric resin, the electrical conductivity of the composition and its advantageous physical properties are maintained, while the weight percent (wt %) of small carbon fibers in the composition is substantially reduced. For example, the small carbon fiber concentration can be reduced up to about 85 wt % by the addition of up to about 25 wt % carbon powder without significant loss of electrical conductivity.

[0038] Conductive compositions made in this manner can be used for a variety of useful applications where electromagnetic shielding, electrostatic dissipation and antistatic properties are necessary such as in IC chip trays, electronic packaging, automotive exterior body panel applications, computer housings etc. The addition of glass helps maintain dimensional stability and prevent warping in such applications.

Problems solved by technology

However, the incorporation of carbon fibers having diameters greater than about 3 micrometers is detrimental to other properties such as the impact and surface finish of the composite.

Metal powders and flakes greatly increase the specific gravity of polymeric compositions, making them less cost effective, while the use of carbon black can lead to components that exhibit sloughing.

However the high cost of VGCF / carbon nanotubes makes the development of improved, cheaper, conductive polymeric composites important.

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