In the field of dielectric insulators, thermal management is a major challenge. Polymer matrix composites with fillers make it possible to combine electrical insulation and efficient heat dissipation. An overview of the fundamental principles.
Definition: composite material. A composite material is a heterogeneous material made up of at least two immiscible constituents, whose combination gives the whole properties that none of the components would have separately. Two main phases are defined: the reinforcements and the matrix.
Key figures
| Value | Description |
|---|---|
| ~0.2 W/m·K | Typical conductivity of a pure polymer |
| > 4 W/m·K | Achievable with ceramic fillers |
| 300 W/m·K | Intrinsic conductivity of boron nitride |
Structure of a composite material
A composite consists of two main phases whose roles are complementary:
Phase 1 — Matrix: Ensures material cohesion, gives it its shape and chemical resistance. Can be:
- Mineral (CMC, MMC)
- Thermosetting organic (epoxy, silicone)
- Thermoplastic organic
Phase 2 — Reinforcement (fillers): Thermally conductive particles incorporated to improve heat transfer while preserving electrical insulation:
- Ceramic fillers (BN, AlN, Al₂O₃)
- Metallic fillers (Ag, Cu, Al)
- Carbon fillers (graphite, graphene, CNT)
Why add thermal fillers?
Polymer matrices inherently have very low thermal conductivities, generally below 0.5 W/m·K. For dielectric insulation applications subjected to intense thermal cycles (transformers, electric motors, power modules), this level is increasingly insufficient.
Adding thermally conductive fillers significantly increases this value without compromising the electrical insulating properties. Filler selection depends on several criteria such as their chemical nature, morphology, particle size, incorporation rate and the quality of their interface with the matrix.
Thermoset matrices: the reference material
In the field of flexible dielectric insulators, thermosetting matrices, and in particular epoxy resins, occupy a predominant position. Their cross-linking provides dimensional stability and excellent mechanical resistance, while offering an ideal medium for the incorporation of thermally conductive fillers.
Fillers of different natures can be combined to obtain synergistic effects, making it possible to achieve effective thermal conductivities greater than 4 W/m·K with ceramic fillers at high volume fractions (60-80%).
Market outlook 2025. The global electrical insulation materials market is valued at $11.9 billion in 2024, with a projected annual growth rate of +6.6% through 2034. Electric vehicle and renewable energy applications are the main growth drivers.
Do you want to identify the right thermally conductive composite for your application? Contact our technical team at sales@segdielectriques.com for tailored support.
