October 24, 2013
The True Meaning of “High Dielectric Strength”
Many industrial coatings are described as having high dielectric strength. Here’s what that actually means, in numbers:
Kynar® PVDF by Arkema and Dykor® by Whitford are thick film dispersions with outstanding dielectric strength – up to 6000 volts/mil, when applied correctly.
Halar® ECTFE by Solvay Solexis and Tefzel® ETFE by DuPont are not only known for their chemical resistance, but also offer dielectric strength of 2000 – 2500 volts/mil.
Certain functional epoxies can provide dielectric strength of 1200 volts/mil.
Rilsan® Polyamides and other nylons can provide up to 800 volts/mil, while providing many other desirable properties.
Of the above, it’s interesting to note that the Dykor® and the Rilsan® Nylon can be autoclaved – a rare property of coatings with high dielectric strength.
Understand Real-World Thickness Requirements for Performance
These coatings provide insulation from a certain number of volts per mil of thickness – so the thicker the coating, the greater the dielectric strength it will provide. But in order to provide any dielectric strength at all,the coating must have a pinhole-free surface, because pinholes can cause failure due to electrical leakage. And in order to achieve a pinhole-free surface, you’ll need both a minimum thickness and a high-quality application.
If you’re looking for a thin film coating that provides good dielectric strength, such as Rilsan® Nylon, you’ll need at least 1 mil of coating for a consistent, pinhole-free surface.
For a thick-film dispersion such as Kynar®, you’ll need to build up a surface of at least 3 – 4 mils for a pinhole-free surface.
Get a Coater who will do Hipot Testing
Want to avoid reworks and part failures? Make sure you find a coater willing and able to do complete electrical safety testing for your parts. Some of the most common tests your coater should be able to provide include:
The Dielectric Breakdown Test, which determines the breakdown voltage for the part, is most important in the design and sample part coating phase.
The Dielectric Withstanding Voltage Test is a non-destructive test that will measure the leakage current over a prescribed period of time.
The Insulation Resistance Test is a DC test that verifies the insulation capacity of the coating as applied.
Be Aware of Static Charge Buildup
We once used Halar® ECTFE for a part that needed a strength of 15000 volts. The coating provided the required insulation, but a static charge built up on the surface of the coating. We resolved this with aconductive coating attached to a grounded clip that ran off the static charge. The buildup of static charge depends on the dielectric constant or relative permittivity of the coating, and obviously can be a serious issue that must be dealt with during the coating solution design phase.
Have a technical question or need more specific advice about what coating to use for your needs? Contact AIC’s COO Dave Arney at (866) 858-9881, or submit your question through our contact form.