Verification latent image
US5468581A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Nov 4, 1993 |
| Grant date | Nov 21, 1995 |
| Priority date | — |
| Expiry date | Nov 4, 2013 |
Classification
- Technology area (CPC Y)Emerging Cross-Sectional Technologies
- CPC primaryY10S430/153
- WIPO fieldTextile and paper machines
- WIPO sectorMechanical engineering
Abstract
A security document with a design (e.g. a generally oval seal) is constructed in such a way that the design is full value halftone, such as produced from juxtaposed line screens having a frequency between 100-133 lines per inch. Negative and positive masks having an image (e.g. arabic numeral, letter, or other symbol), are used with the screens to produce a printing plate. A document is printed with the printing plate in a conventional lithographic process, and there is an overprinting on the design (at least that portion having the image) with a white opaque ink or overprint varnish to produce an image. The image is not readily visible to the naked human eye when viewed generally perpendicular to the plane of the document, but is readily visible by the naked human eye when the document is tilted so that it is viewed distinctly non-perpendicular to the plane of the document. A fluorescent material or brightener may be added to the white ink, and the image will then also be visible by shining long wave length black light on the design.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.