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

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 (TiO<SU2</SU) and the film not containing TiO<SU2</SU and TiO<SU2</SU 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 TiO<SU2</SU, 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 mu m, were observed on the film. When TiO<SU2</SU 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 TiO<SU2</SU. There were many black particles locally in the UV laser-treated TiO<SU2</SU powder by the morphological observation, and these black particles, agglomerates of the grayed oxygen-defected TiO<SU2</SU, were associated with the visible change of the TiO<SU2</SU. 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 TiO<SU2</SU by the UV laser irradiation.</.