Microscale Property Control on Polymer films by Utilizing Interfering Laser Heating

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In this research project, we focused attention to the microscale property control by using an interfering IR radiation. As the first step, birefringence in skin-layers of an injection-molded polymer strip was controlled as a "pattern" by irradiation of interfered IR laser. Controllability of the birefringence pattern was experimentally examined, and the results showed that (1) an evident birefringence pattern, spacing of which is less than 70 μm, can be "recorded" on the skin-layer by the interfered IR irradiation, and that (2) the minimum spacing of the recordable birefringence pattern is influenced by the molding conditions, such as melt temperature and velocity, mold wall temperature, and radiation intensity. In order to investigate the relation between the pattern recordability and temperature distributions in the polymer melt, heat transfer within the melt was numerically estimated under the interfered IR laser irradiation condition. The results showed that (3) the temperature distributions within the skin-layer correspond well with the birefringence pattern recorded on the polymer strip, and that (4) thermal diffusion within the polymer obstructs the recording of birefringence pattern especially when the pattern spacing becomes narrower. Applying the basic findings obtained, molecular orientation in a polymer film was controlled by using the interfered IR irradiation as the second step. The birefringence pattern was recorded also on the film as same manner as the injection-moldings by using the interfered IR irradiation, but it was shown that the irradiation condition for the film where the evident birefringence pattern can be recorded is more rigid than for the injection-molding. This is explained by the fact that cooling of the film by the surroundings is weaker than that of the injection-molding, and that the thickness of film is too thin to absorb irradiated IR energy in general; both of them result in "flat" temperature distribution within the film.