Filled resin systems electrical properties

Electrical properties of filled resin systems can also be improved by filler treatment. A filler particle is naturally hydrophilic via its metal hydroxide... 

Electrical properties of filled resin systems are also improved by filler treatment. Filler particles are naturally hydrophilic via their metal hydroxide surfaces, and the particles naturally seek to agglomerate with each other, and so transport electrical charges through resin composite. Treatment with silane-coupling agent alters the chemistry of the filler surface, allow better dispersion of the filler throughout the resin matrix, and imparts improved electrical properties to the composite. Table 15.13 indicates the improved electrical properties of a quartz-fiUed epoxy resin system with 0.3% silane admixed into the formulation. Improved insulation values, including reduced dielectric constant and reduced dissipation factor, are also denoted. 

Small nitrile-rubber inclusions in epoxy resin electrical en-capsulants have been examined in both amine (29-31) and acid (32) epoxy cures, in filled and unfilled systems. The value of rubber inclusion in a boron trlfluorlde/amine complex epoxy cure has also been demonstrated (33), where elevated-temperature, high-humldlty testing showed electrical properties retention to be better than a comparable system cured with dodecenylsucclnic anhydride. Rubber benefits low-temperature properties specifically and thermocycling in general. It affects high temperature insulation properties negatively therefore, the amount of rubber incorporated must be judiciously chosen. 

Cured epoxy-anhydride systems exhibit excellent thermal, mechanical, and electrical properties, and are used in filament-wound epoxy pipe, PCB laminates, mineral-filled composites, and electrical casting and encapsidation applications. Anhydride-cin-ed epoxies also have better aqueous acid resistance than similar amine-cured systems. Anhydrides are the principal curing agents for cycloaliphatic and epoxidized olefin resins in electrical casting and potting. Some... 

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