Cancarb Thermax N990 in Butyl Capacitor Seals
January 20, 2026
Cancarb Limited has published a Technical Bulletin about how Thermax® N990 affects the properties of butyl seals for capacitors. Thermax® N990 is a non-reinforcing medium thermal carbon black that can replace parts of Thermax® N550, a medium-reinforcing product, in this application. Both products have excellent dispersion, but N990 requires less mixing power for a potential savings in electricity costs.
Butyl Seals for Electrolytic Capacitors
Electrolytic capacitors are commonly used in electrical systems. Butyl is used for sealing the capacitor’s electrically-conductive electrolytic solution because of its gas permeability and good aging, heat, and chemical resistance. Butyl also offers good compression set resistance and high electrical resistivity.
Thermax® N990 vs. Thermax® N550
As the Technical Bulletin explains, Thermax® N990 replaced a portion of Thermax® N550 at a ratio of 2.4:1.0 to maintain a compound hardness of approximately 70 Shore A. N990 exhibited smaller changes in hardness and tensile strength after heat aging and had a higher surface resistivity. N990 also required less mixing power and exhibited increased scorch time and elongation.
Test Results
Compounding and testing were completed at Smithers in Akron, Ohio. The test results show:
- Dispersion was excellent for all butyl compounds
- Mooney Viscosity did not have significant differences
- Scorch time increased
- Cure time increased
- Shore A Hardness was consistent at 70 ±3.
- Stress at 100% and 300% strain did not cause significant differences in butyl’s modulus
- Tensile Strength decreased
- Elongation increased
- Compression set was not significantly different
- Heat aging improved slightly with N990
- Surface resistivity increased
Additional information
To receive the full Technical Bulletin in PDF format, visit this page on Cancarb’s website, choose the Request button, and complete the online form.
RDAbbott represents Cancarb products in the United States and Canada and is the exclusive distributor for Thermax® brand medium thermal carbon black in Mexico. For more information about these functional fillers, contact RDAbbott today.
