| 摘要 |
<p>A security element having a variable optical effect, including at least one quasi-spherical particle having at least one external part and at least one internal part, said external part including at least one cholesteric liquid crystal and said internal part including at least one thermochromic compound and/or at least one photochromic compound undergoing a reversible transition from a colourless state to a dark colour or from a dark colour to a colourless state when said compound is subjected to an activation temperature or to activation radiation respectively, the dark colour making it possible to see the interference effect of said liquid crystal, and the colourless state making this interference effect no longer visible.</p> |
