Technology Spotlight 15: Selecting Polyimide Varnishes

Get to know these elite coating materials for advanced industrial and electronic applications.

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Polyimide varnishes are advanced, high-performance coatings prized for their exceptional thermal stability, robust mechanical properties, and outstanding electrical insulation. They are widely used in demanding industry segments including aerospace, automotive, and electronics. Selecting the right polyimide varnish requires careful consideration of several critical factors, including processing and property requirements[1].

• Thermal Stability: Polyimide varnishes are distinguished by their outstanding thermal endurance. Most commercial grades maintain performance at continuous use temperatures between 240°C and 350°C, with some advanced formulations, such as UBE’s UPIA® and Mitsubishi Gas Chemical’s Neopulim™, capable of short-term exposure up to 500°C. Temperature index (ASTM D2307 [2]) is a reliable benchmark for insulation in motor windings, semiconductor packaging, and aerospace components[3, 4, 5].

• Electrical Insulation: Superior dielectric strength and volume resistivity are essential for applications requiring reliable electrical insulation. Polyimide varnishes typically exhibit volume resistivity values exceeding 10E16 Ω·cm and dielectric strengths of 7–10 kV for 20–50 µm coatings, as demonstrated by UBE’s UPIA® and Evonik’s P84®. These properties make polyimide varnishes ideal for high-voltage environments and miniaturized electronic components[3, 4, 6].

• Mechanical Properties: Tensile strength and elongation at break are important for ensuring the durability and flexibility of coatings in service. For instance, UPIA® varnish forms films with tensile strengths of 229 to 526 MPa and 35% to 99% elongation, depending on the grade. This combination of strength and flexibility helps prevent cracking and delamination under thermal or mechanical stress[3, 4, 6].

• Chemical Resistance: Polyimide varnishes offer excellent resistance to a wide range of chemicals, including solvents, acids, alkalis, and oils. This makes them suitable for harsh industrial environments and applications where long-term reliability is required[3, 6, 7].

• Processing and Application: Most polyimide varnishes are polyamic acids that require heat for imidization, but pre-imidized polyimide varnishes are exceptions and do not require thermal imidization.

  Solvent-borne polyimide varnishes utilize organic solvents such as Dimethylacetamide (DMAc), Dimethylformamide (DMF), Dimethylsulfoxide (DMSO), N-methylpyrrolidone (NMP), or Trimethylbenzene (TMB), with application by dipping, spraying, or spin-coating. They are chosen for their ability to dissolve polyimides at high solids content, resulting in robust, defect-free films with excellent adhesion and electrical properties. Application methods are flexible and can be tailored to the substrate and desired film thickness[1, 4, 8].

Waterborne polyimide varnishes are gaining interest for their reduced environmental impact and improved workplace safety. While these systems emit fewer VOCs, they may require additional drying steps or process modifications to achieve comparable film quality[1, 8].

Photosensitive polyimide (PSPI) varnishes are processed via UV light and thermal imidization.

Polyimide varnish suppliers and products include the following:

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Application-Specific Guidance

• Aerospace, Automotive: Opt for varnishes with superior chemical resistance and long-term stability. For electric vehicle motors and battery insulation, select varnishes with high temperature indices and thin film capabilities, including Arkema’s PI varnish and Evonik’s P84®[3, 4, 6, 7].

• Semiconductors & Electronics: Choose varnishes with high thermal stability and excellent adhesion, such as UBE’s UPIA®, Toray’s SEMICOFINE™, or Mitsubishi Gas Chemical’s Neopulim™[3, 4, 6].

Selecting the right polyimide varnish requires careful consideration of thermal, mechanical, electrical, and chemical properties, as well as processing requirements. The table above lists all major suppliers and their main polyimide varnish products. For detailed specifications and custom solutions, consult manufacturer datasheets and technical support[1, 3, 4].

Want to learn more about sourcing polyimide varnishes for your next project? Reach out today for an initial consultation.