| 摘要 |
<p>An optically-readable value card for use in a vending system for vending goods or services includes a plurality of heat-sensitive optically-readable value elements (3,4,5) each of which, upon heating to a first temperature above ambient, changes its color in a reversible manner, but upon heating to a second temperature above ambient and higher than the first temperature, changes to a second color in an irreversible manner. Each of the value elements (3,4,5) is in a form of a light window having a layer of a thermochromic material (4) which changes its color in a reversible manner when heated to the first temperature, and a layer of a thermographic material (3,5) which changes its color in an irreversible manner when heated to the second temperature.</p> |
