Films, comprising anisotropic particles in a matrix resin, that are made by typical methods, such as by solvent casting or extrusion and biaxial orientation, result in the anisotropic particles being preferentially oriented parallel to the plane of the film. For this reason, properties such as modulus and electrical conductivity are typically higher in the plane of the film than in a direction perpendicular to the plane of the film. Composites Based on Micron-Sized Exfoliated Graphite Particles: Electrical Conduction, Critical Exponents and Anisotropy, A. Celzard, E. McRae, J. F. Mareche, G. Furdin, M. Dufort, and C. Deleuze, J. Phys. Chem. Solids Vol 57, pp. 715-718 (1996), Crystal Structure of Nylon 6/Inorganic Layered Silicate Composite Film, K. Fujimoto, M. Yoshikawa, S. Katahira, K. Yasue, Kobunshi Robunshu, 57(7), 433-439 (2000). Fiber Orientation and Rheology in Short Fiber Reinforced Thermoplastics, A. Vaxman, M. Narkis, A. Siegmann, S. Kenig, J. Materials Sci. Letters 7, 25-30 (1988), The Role of the Polymeric Matrix in the Processing and Structural Properties of Composite Materials, L. A. Goettler, (J. C. Seferis and L. Nicolais, eds.), New York, Plenum, 1983, pp. 289-318.
It is very difficult to prepare a film or article comprising anisotropic particles in a matrix resin in which the anisotropic particles are oriented perpendicular to the plane of the film. Typically, in order to do this, the film is fabricated under the influence of an externally applied magnetic or electric field while it is heated and cured. Such processes for producing anisotropic particle orientation perpendicular to the film plane are slow and cumbersome, are not easily done in continuous fashion, and do not lead to ease and efficiency of manufacturing, as described in Directionally-Conductive, Optically-Transparent Composites by Magnetic Alignment, S. Jin, T. H. Tiefel, R. Wolfe, IEEE Trans. Magn., 28(5, Pt. 2), 2211-13 (1992), Kokai Tokyo Koho JP 2002056719 A2 20020222, Japan, Kokai Tokkyo Koho JP 2001322139 A2 20011120, Japan, Kokai Tokkyo Koho JP 2001294676 A2 20011023, and Kokai Tokkyo Koho JP 2001335602 A2 20011204.
Polymeric films containing anisotropic particles that are oriented perpendicular to the plane of the film have among their desirable properties the fact that their thermal and electrical conductivities are higher in the direction perpendicular to the plane of the film than they are in the plane of the film. Such films have been reported to be useful as transparent visual sensors for visual communication devices, anisotropically pressure-dependent conductive sheets for electrical contacts, and thermally conductive adhesive films for bonding electronic components to the surfaces of heat sinks and thermal management devices, described in PCT Int. Appl. WO 9840431, Sep. 17, 1998.
This invention provides a desirable method for preparing oriented anisotropic particles, oriented anisotropic materials, and articles made therefrom.