Long fiber thermoplastic process for conductive composites and composites formed thereby

Abstract

The present invention relates to a polymer article that includes electrically conductive fibers to provide electrical electromagnetic interference (EMI) shielding and their method of manufacture. The invention includes a method for forming shielding materials by impregnating conductive fibers in a polymer material via direct injection of the conductive fibers into the extrusion process. The invention also includes EMI shielding polymers and products that are radio-frequency and electromagnetically shielded by parts formed of the shielding polymer.

Description

[0001] This Application claims the benefit of U.S. Provisional Application 60 / 729,695, filed Oct. 24, 2005.TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION [0002] The present invention relates to a polymer article that includes electrically conductive fibers to provide electrical electromagnetic interference (EMI) shielding and their method of manufacture. More particularly, the invention relates to a method for forming shielding materials by impregnating conductive fibers in a polymer material via direct injection of the conductive fibers into the extrusion process. EMI shielded polymers of the present invention may be formed into a wide variety of products such as radio-frequency and electromagnetic shielded plastic articles. BACKGROUND OF THE INVENTION [0003] With the increased usage of electronic equipment such as computers and other digital devices there is a heightened concern for the hazards associated with electromagnetic radiation, in particular radar waves, mi...

AI Technical Summary

Benefits of technology

[0016] The invention answers the problems connected with previous methods of forming EMI shielded polymer. Long fiber thermoplastic technology allows the conductive fibers, to maintain a length sufficient to provide EMI shielding at lower fiber loading. The long fiber thermoplastic process for forming EMI shielding composite articles also provides increased impact resistance, enhanced surface aesthetics and improved extrusion and injection molding processing at a lower material cost and with decreased waste and scrap.

[0017] The long fiber thermoplastic process for conductive composites and composites formed thereby of the present invention is simpler, more efficient and provides improved properties than the prior art methods.

Problems solved by technology

The shortened fibers impart reduced electromagnetic shielding properties to the composite due to their reduced ability to form a conductive fiber network and conduct electricity through the composite article.

Such large amounts of powder can result in a poor dispersion of the powder or reduced mechanical strength of the final product.

Accordingly, composite articles formed with broken fibers and powders require higher loadings or filler concentrations which leads to decreased mechanical strength of the composite article formed and higher material costs.

Each step of the pelletized fiber approach allows for material loss and inefficiency, slows cycle times and provides an opportunity for defects.

Heating of the thermoplastic polymer during the wire coating process and again during the injection molding process degrades the performance of the polymer.

Severe degradation can break down the polymer and form gasses that result in voids and a subsequent loss of shielding and mechanical properties.

High shear from the screw provides for sufficiently high melt flow but breaks the conductive fibers into smaller and smaller lengths and diminishes the ability of the fibers to form a continuous network of fibers.

This typically results in very poor fiber dispersion and inconsistent electrical performance from part to part.

Previous methods of forming EMI shielding composite articles have not been entirely satisfactory for due to short fiber length in the finished part which reduces the shielding and necessitates additional loading of fibers.

This high level of fiber loading increases the cost of the composite article due to the high cost of the fibers and inhibits the flow of the polymer in the mold.

The high fiber loading also significantly increases the modulus of the article but lowers impact resistance.

% fibers becomes brittle and susceptible to breakage.

Another drawback to the previous methods of forming EMI shielding composite articles is poor fiber dispersion.

The pelletized material is difficult to process such that the fibers are fully dispersed and do not form an efficient network of conducting fibers in the composite material.

When good fiber distribution is sometime achieved; however, the pellets and fibers will have been comminuted to such an extend that the average fiber length is approximately 0.5 mm and, as a result, the short fibers do not form an efficient network of conducting fibers in the composite material.

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