Not all coatings with “high dielectric strength” are created equal. We talked to Dave Arney, our COO, about the different coatings and different issues that can arise when coating for dielectric strength. Here’s what you need to know:
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 a conductive 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 the form on the AIC website.
Industrial Coating for Dielectric Strength: 4 Crucial Things to Consider
AIC Staff Writers, October 2013
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