| 摘要 |
<p>A method of marking or forming a transparent window in an article 6, such as a security document, is provided in which areas of opacifying layers of printed ink 8, 10 on opposite surfaces of a polymeric film or substrate 12 are irradiated by laser radiation 4 of a selected wavelength. The opacifying layers 8, 10 have greater absorption characteristics for the laser radiation than the film or substrate 12 which is substantially transparent to the selected wavelength of the laser radiation so that after ablation of the area of printed matter 8 on one surface, the radiation passes through the substrate 12 substantially unaffected to ablate the area of printed matter 10 on the opposite surface. In the resultant article, the markings or windows formed by the areas of printing removed from each surface of the substrate 12 are in register, and provide a deterrent against counterfeiting.</p> |
