SECURITY PRINTED DOCUMENTS

摘要

The invention provides a document designed to prevent reproduction by xerographic copying comprising a sub- strate (12) printed with a background printing (20) over a substantial portion of its surface, the background printing comprising a first printed pattern, first warning printed matter (21) located within the first pattern and second warning printed matter (22) located within the first warning printed matter. The first pattern is formed from a plurality of parallel lines extending in a first direction spaced from one another with a first spacing and having a first size, the first warning printed matter having a second size different from the first size, one of the first and second sizes being such that is readily copyable by a copier and the other being such that it will not copy with the same clarity as the one, such that on a copy the warning printed matter will be clearly distin- guishable. The second warning printed matter is formed from parallel lines extending at an angle of at least 20.degree. to the direction of the lines of the background, and preferably having substantially the same spacing as the lines of the background. All of the printing has a density less than 50% and preferably less than 20% and arranged in a pattern such that it appears to the eye that there are areas of printing (14) interspersed with blank areas (15) in a distinct pattern, the arrangement being such that the areas containing the first and second warning printed matter are substantially indistinguishable from the overall pattern when viewed by the human eye.