Kapton® CRC Polyimide Disk

Kapton® CRC is DuPont's corona-resistant polyimide film, formulated to withstand partial discharge — the localised dielectric breakdown that occurs in high-voltage AC insulation systems operating above the corona inception voltage. When alternating voltage exceeds a threshold, small voids and imperfections in the insulation allow localised ionisation (corona) that produces ozone, UV radiation, and heat, progressively degrading the insulation until it fails. Kapton® CRC resists this degradation mechanism far more effectively than standard HN, with significantly higher voltage endurance under sustained partial discharge conditions.

Variable-frequency drives (VFDs) and pulse-width modulated inverters generate fast-switching voltage waveforms with high dV/dt and voltage spikes that exceed the corona inception voltage of standard polyimide insulation, even at moderate DC bus voltages. Under these conditions, partial discharge activity is sustained throughout continuous motor operation. Standard HN degrades progressively under this exposure, with dielectric failure occurring well before its rated thermal service life would be exhausted. Kapton® CRC is formulated specifically to maintain dielectric integrity under these inverter-driven conditions — it is the correct insulation specification for inverter-duty motors rather than an upgrade from HN.

Kapton® CRC also provides greater thermal conductivity than standard Kapton® HN, allowing heat generated within motor windings and coil assemblies to dissipate more effectively through the insulation system. In high-power-density traction and industrial drive motors, this reduces operating temperatures in the winding, extending insulation service life and improving the thermal efficiency of the motor assembly — a compounding benefit on top of the corona resistance itself.

Kapton® CRC is specified for the turn-to-turn and ground wall insulation in AC inverter-duty motors driven by variable-frequency drives; rail and automotive traction motors in locomotives, metro systems, and high-performance electric vehicles; wind turbine generators and hydroelectric alternators where PWM converters create partial discharge conditions in the stator winding insulation; industrial high-voltage dry-type and resin-cast transformers for industrial power distribution; electric submersible pump motors in oil and gas production; and aerospace starter-generators and actuator motors where the more-electric aircraft architecture demands high power density at elevated bus voltages.

Kapton® CRC retains the full Kapton® family thermal range — −269 °C to +400 °C continuous service — and has a UL Electrical Relative Thermal Index (RTI) of 240 °C. This thermal rating is relevant to motor and transformer insulation qualification, where the RTI defines the maximum continuous temperature at which the insulation maintains its electrical performance for the rated design life of the equipment.

Kapton® CRC achieves high dielectric strength, with the 25 µm grade rated at approximately 236 kV/mm, a dielectric constant of 3.4 at 1 kHz, a dissipation factor of 0.002, and volume resistivity exceeding 10¹⁶ Ω·cm. Combined with its corona resistance, these properties qualify it as both primary insulation and turn-to-turn insulation in high-voltage motor and generator windings.

Yes. Kapton® CRC resists most solvents, hydrocarbons, and the impregnating varnishes and resins used in motor manufacturing, making it compatible with vacuum pressure impregnation (VPI) processes and dip-and-bake varnish treatments. It can also be laminated with DuPont™ Nomex® paper and mica-based insulation systems for composite insulation structures optimised for specific voltage class and thermal rating requirements.

Yes. The combination of high dielectric strength and mechanical toughness in Kapton® CRC allows thinner insulation wall thicknesses compared with conventional film-based or mica-based insulation systems at the same voltage class. Thinner insulation frees slot space for additional conductor material, increasing the copper fill factor and enabling more power output without increasing the motor frame size — a significant advantage in traction motors, aerospace drives, and high-power-density industrial machines.

Kapton® CRC carries a UL 94 V-0 flame rating and resists greases, fuels, aromatic hydrocarbons, lubricants, and the cooling fluids and cleaning solvents used in motor manufacturing. Poor resistance to concentrated acids, alkalis, and alcohols — the same limitation as other Kapton® grades.