Anisotropic Thermal Conductivity of Kapton Films, Composites, and Laminates

We report the anisotropic thermal conductivity of five varieties of polyimide (PI) films sold under the Kapton brand name: Kapton EN, HN, FN, MT, and MT+. Kapton EN and HN are single-component PI layers; FN is a laminate of PI and fluorinated ethylene propylene (FEP), and MT and MT+ are composites of PI and inorganic fillers. We determine the in-plane thermal conductivity and cross-plane coefficient of thermal expansion by displacement thermo-optic phase spectroscopy (a variation on photothermal displacement methods) and determine the thermal conductivity in the cross-plane direction by time-domain thermoreflectance. We characterized the materials using IR and Raman vibrational spectroscopy and X-ray diffraction. All PI layers show pronounced anisotropy with the in-plane thermal conductivity a factor of 2–4 larger than the cross-plane thermal conductivity. The FEP layer of the Kapton FN laminate has anisotropy within the plane of the film with a machine-direction thermal conductivity of 0.24 W/(m K) and a transverse thermal conductivity of 0.11 W/(m K). Kapton MT+ has a high in-plane thermal conductivity of 2.3 W/(m K) due to the combined alignment of the molecular structure of PI and the preferred orientation of the filler particles.