Factors affecting color strength of printing on film-coated tablets by UV laser irradiation: TiO₂ particle size, crystal structure, or concentration in the film, and the irradiated UV laser power

Abstract

Aim: The purpose of this article is to study factors affecting color strength of printing on film-coated tablets by ultraviolet (UV) laser irradiation: particle size, crystal structure, or concentration of titanium dioxide (TiO₂) in film, and irradiated UV laser power.

Methods: Hydroxypropylmethylcellulose films containing 4.0% of TiO₂, of which BET particle sizes were ranging from 126.1 to 219.8 nm, were irradiated 3.14 W of UV laser at a wavelength 355 nm to study effects of TiO₂ particle size and crystal structure on the printing. The films containing TiO₂ concentration ranging from 1.0 to 7.7% were irradiated 3.14 or 5.39 W of the UV laser to study effect of TiO₂ concentration on the printing. The film containing 4.0% of TiO₂, was irradiated the UV laser up to 6.42 W to study effect of the UV laser power on the printing. The color strength of the printed films was estimated by a spectrophotometer as total color difference (dE).

Results: Particle size, crystal structure, and concentration of TiO₂ in the films did not affect the printing. In the relationship between the irradiated UV laser power and dE, there found an inflection point (1.6 W). When the UV laser power was below 1.6 W, the films were not printed. When it was beyond the point, total color difference increased linearly in proportion with the irradiated laser power.

Conclusions: The color strength of the printing on film was not changed by TiO₂ particle size, crystal structure, and concentration, but could be controlled by regulating the irradiated UV laser power beyond the inflection point.

Keywords::

• Printing
• film-coated tablets
• color strength
• UV laser
• laser energy
• titanium dioxide
• total color difference (dE)
• particle size
• anatase
• rutile

Acknowledgements

The authors thank Mr. Yasuhiko Nakashima for his technical assistance of printing films by the UV laser and Miss Kazumi Nambu of Eisi Co. Ltd., for her assistance of determination of the BET surface area of TiO₂.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this paper.