Elsevier

European Polymer Journal

Volume 34, Issue 2, 1 February 1998, Pages 261-267
European Polymer Journal

Optimum conditions of electroless nickel plating on carbon fibres for EMI shielding effectiveness of ENCF/ABS composites

https://doi.org/10.1016/S0014-3057(96)00248-0Get rights and content

Abstract

Nickel coated carbon fibres, the best conductive fillers for electromagnetic interference (EMI) shielding, were produced by electroless nickel plating. The carbon fibres, T300C and T700SC, were plated at different workloads, pH values and temperatures of plating bath, and were used for preparing composites of acrylonitrile–butadiene–styrene by polymer blending to test the EMI shielding effectiveness (SE) by the coaxial transmission line test method. The best SE (44 dB) was reached by the deposition conditions of workload=2 g/L, pH 9 and temperature 70°C.

Introduction

The tremendous growth and universal application of plastic housings in the computer, electronic devices and scientific instrumentation has brought about a demand for electromagnetic interference (EMI) shielding. There is an urgent need for conductive plastic to resist EMI1, 2.

The electrical conductivity of plastic is usually enhanced by coating3, 4or synthesizing inherently conductive plastic5, 6, and by compounding with conductive filler7, 8, 9in order to exhibit the required shielding effectiveness. The most economical process is the incorporation of conductive filler into the polymer matrix to produce conductive composites[10]. Nickel coated carbon fibres, which combine high strength, low weight, high aspect ratio and processability of a fibre core with the conductivity and corrosion resistance of a plated nickel skin, are the best conductive filler for EMI shielding11, 12.

Electroless plating is a chemical reduction process which depends upon the catalytic reduction of a metallic ion in an aqueous solution containing a reducing agent, and the subsequent deposition of the metal without the use of electrical energy13, 14, 15, 16. Due to the advantages of excellent uniformity, good resistance to corrosion, oxidation and wear, low labour costs, and ready plating on nonconductors, electroless nickel (EN) plating has become a popular technique for surface finishing14, 15, 16. Thus, electroless nickel is a convenient approach to produce Ni coated carbon fibres.

Because to our knowledge, no work has been reported on the effects of EN operating parameters on the EMI shielding effectiveness (SE) of conductive composites, this study investigates the composition, morphology, adhesion and structure of EN deposits on carbon fibres. Ni coated carbon fibres were produced by the EN method with different workloads, pH values and temperatures of plating bath, and were blended with acrylonitrile–butadiene–styrene (ABS) by polymer blending to produce conductive composites for EMI shielding. The surface morphology of fibre, which was reported to greatly influence the properties of EN deposits, were also studied.

Section snippets

Electroless nickel plating on the carbon fibres

PU-coated carbon fibres (CF) used in this study were T300C CF & T700SC CF made by Japan Toray Co. Ltd. The electroless Ni-P alloy films were deposited on carbon fibres which had been catalyzed. A two-step pretreatment was used for catalyzing the carbon fibres: the sensitizer and activator were stannous chloride/hydrochloric acid and palladium chloride/hydrochloric acid solution. After rinsing, electroless nickel films were then deposited from solutions at various workloads, pH and temperatures

Type of fibres (morphology of substrate)

For ENCF/ABS composites, the most important factors which affect the SE of composites are length of fibres and adhesion between EN coating and fibre. Longer fibres had a higher aspect ratio and readily formed a conductive network. Good adhesion between EN coating and fibre can reduce delamination of EN deposits by shear stress during compounding and can maintain the conductive network. Fig. 1 shows the influence of fibre type in SE. It is found that SE of T700SC (uncoated)/ABS composite is

Conclusions

When the compounding conditions were maintained at constant levels, the best EMI SE of ENCF/ABS composites could be reached by good adhesion between fibre and EN coating, thicker EN coating and higher crystallinity of EN coating. Good adhesion was given by selecting the carbon fibre of optimum surface roughness and plating carbon fibres at lower plating temperature. Thicker EN coating was obtained by plating carbon fibres at lower workload. Higher crystallinity of EN coating was controlled by

Acknowledgements

The authors express their sincere appreciation to Dr T. S. Lin, President of Tatung Institute of Technology, for his encouragement and support. Thanks are due to the National Science Council for financial support under contract number NSC-83-0405-E-036-022.

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