DMD laminate is a three-layer composite consisting of two outer layers of polyester nonwoven and a central layer of polyester film. The outer layers, often referred to as Dacron, provide mechanical robustness, flexibility and good impregnation capability. The central layer, often referred to as Mylar, takes on the electrical barrier function and ensures high dielectric strength. Together, the layers form a material that is mechanically robust, easy to process and electrically reliable.
Structure and Material Properties
Classic 3-layer structure:
- Outer layers: polyester nonwoven (Dacron), ensures good impregnation, mechanical strength and soft handling during insertion.
- Central layer: polyester film (Mylar, Hostaphan), ensures electrical dielectric strength.
Properties of DMD laminate:
- Electrical: high dielectric strength (typically 6 to 12 kV/mm, depending on thickness).
- Thermal: thermal class B (130 °C) or F (155 °C), depending on film quality and resin system.
- Mechanical: high tear strength, good dimensional stability, abrasion resistant.
- Chemical: resistant to many resins, varnishes and solvents.
- Processable: easily stamped, roll-slittable, laminatable, suitable for automated processes.
Typical thicknesses: 0.15 mm to 0.40 mm, depending on application.
Manufacturing and Processing
DMD laminates are created by laminating the polyester film with nonwoven layers under pressure and temperature. Adhesive systems are usually heat-curing and selected so that the composite properties remain stable.
- Roll goods: for slot insulation and coil interlayers.
- Stamped parts: for custom-fit slot formats or spacer discs.
- Laminated components: combination with other insulating materials, for example Nomex laminates (NMN).
- Impregnation: DMD allows resins to penetrate well, which improves partial discharge resistance.
Key manufacturing processes: stamping, roll slitting, kiss-cut, forming.
Applications of DMD Laminate
Electric Motors
- Slot insulation for low-voltage motors.
- Layer and phase separations.
- Slot closure wedges in combination with resin systems.
Generators
- Layer insulation in field coils.
- Spacer layers between winding packages.
Transformers
- Interlayer insulation in windings.
- Spacers and distance insulation.
General Electrical Equipment Engineering
- Insulating parts for switchgear, chokes and relays.
Advantages and Challenges
Advantages
- Combination of electrical strength and mechanical robustness.
- Flexible and easy to process.
- More cost-effective than high-performance papers or polyimide laminates.
- Good impregnation capability for resin systems.
Challenges
- Limited temperature class (B/F), unsuitable for high-temperature motors.
- Faster ageing under high thermal and electrical loads compared with Nomex or Kapton.
- Adhesive systems must be resin-compatible and ageing-stable.
Standards and Quality Requirements
- IEC 60085: classification of thermal classes of insulation.
- DIN EN 60641: requirements for pressboard and film composite materials.
- DIN EN 60216: thermal ageing of insulating materials.
- DIN ISO 2768: dimensional and form tolerances for manufactured parts.
In addition, manufacturer-specific inspection plans apply for dielectric strength, thermal ageing, dimensional accuracy and mechanical tests.
GOBA Takeaway
DMD laminate is a universally applicable insulating material for motor and generator construction. It offers a good compromise between electrical safety, mechanical robustness and cost-effectiveness. For applications up to class F, DMD is a proven solution. Anyone planning higher temperatures or extreme electrical loads can turn to alternatives such as Nomex or Kapton laminate.