Studies on the mechanism of printing film-coated tablets containing titanium dioxide in the film by using UV laser irradiation

Abstract

Aim: The purpose of this article is to study a detailed mechanism of printing when film-coated tablets were irradiated by UV laser at a wavelength of 355 nm. Methods: Hydroxypropylmethylcellulose (HPMC) film containing titanium dioxide (TiO2) and the film not containing TiO2 and TiO2 powder were lirradiated by the UV laser and estimated by the morphological observation by zoom stereo microscope, thermogravimetric analysis (TGA), total color difference (dE), X-ray powder diffraction (XRD), and dispersive Raman microscopy. Results: In the case of the film containing TiO2, the film showed a visible change in its color from white to gray by the UV laser irradiation. By zoom stereo microscope, it was found that the entire UV laser-irradiated area was not grayed uniformly, but many black particles, whose diameter was about 2 μm, were observed on the film. When TiO2 powder was irradiated by the UV laser, a visible change in its color from white to gray was observed similar to the case of the film containing TiO2. There were many black particles locally in the UV laser-treated TiO2 powder by the morphological observation, and these black particles, agglomerates of the grayed oxygen-defected TiO2, were associated with the visible change of the TiO2. Conclusion: It was found that the film-coated tablets were printed utilizing the formation of the black particles by the agglomeration of the grayed oxygen-defected TiO2 by the UV laser irradiation.