| 摘要 |
A method of printing security documents is disclosed wherein images on the security document are comprised of patterns of dots of different colours, the dots being of a diameter of less than 15 mu m. This reduced dot size allows for a number of security features to be incorporated into an image printed on a security document. For example, dots of this diameter printed on a document at a certain tint weight cannot be reproduced by currently available photocopying equipment, and therefore what appears in the original document to be a complete image is incomplete after photocopying, particular portions of the image "dropping out". Alternatively, the reduced dot size allows for the offset lithographic and gravure printing of complex images with multiple colours depending on the concentrations, interspersion and/or overlap of dots of different colours. This facilitates the creation of images whose colour varies imperceptibly in two dimensions across a substrate, an effect never before achieved in security document printing. Also, micro-fine text can be printed which is substantially indecipherable to the human eye and to a photocopier but which can be easily read on magnification of the original document. A further security feature available is the printing of an image constituted entirely of miniaturised replicas of itself, the miniaturised replicas being indecipherable both to the human eye and to a photocopier. One or more of these security features can be incorporated in a security document to prevent compromise thereof.
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