1. Field of the Invention
This invention relates to a method of, and apparatus for, producing piles of serially-indexed security papers from a plurality of imprints on printing paper, which paper may be a continuous web or may be a plurality of discrete strips, each strip carrying a plurality of the said imprints.
2. Discussion of the Prior Art
Security papers such as bank notes, each with an individual identification index, are conventionally produced from printed sheets. Each sheet carries a matrix of unindexed security paper imprints. Successive sheets are advanced through an indexing station in which each of the imprints is given its unique index. As they emerge from the indexing station, the sheets are stacked in a pile and the pile is then cut along the rows and columns between the imprints to yield individual piles of security papers.
Each sheet may have up to, say, 8 columns and 12 rows, that is, 96 imprints. Normally each imprint carries its unique index in two positions. To index one such sheet 192 indexing operations are required.
Each index may consist of a 6-figure number and a 4-digit prefix or suffix. These indexes are applied by a letterpress printing step with the figures and digits arranged around the periphery of 10 print wheels stacked together on a common rotatory axis as a single indexing unit. In the above example, there would be 192 such units. Conventionally, the prefix or suffix is set manually, whereas the 6-figure index is given an initial setting, but thereafter advances automatically by one unit with each sheet which passes the indexing unit.
If each imprint has a unique prefix or suffix then, for a sheet with x notes on it, manual resetting is not necessary until x million notes have been indexed. If x is a large number such as 96, then the number of notes which could be printed may well be more than are required. If the requirement is for only a fraction of x million notes, then groups of indexing units can be set with the same prefix/suffix. For example, in a case where there are 8 columns of 10 imprints, a print run of 8 million notes could be conveniently achieved by assigning a different prefix/suffix to each of the 8 columns, and setting a step of 100,000 between the indexing numbers for each of the 10 imprints in each column. Problems can arise, however, when a less distinctive numbering step is indicated. Errors can easily be made during manual re-setting, resulting in the production of wrongly-indexed notes and additional security risks.
It is not unusual for the size of individual notes, and hence the number of notes on each sheet, to vary with such factors as bank note denomination. These size changes present difficulties in changing between one denomination and another, leading again to lower production rates and increased production costs.
There is always the possibility of printing blemishes on the sheets, leading to piles containing defective security papers. Various solutions to the problem of eliminating defective papers from the bundles have been proposed.
EPO No. 167196 is a proposal to detect blemished imprints on a continuous multi-column web prior to indexing, and produce at the indexing station the required unbroken sequence of indexes from the unblemished imprints. Blemished imprints are removed immediately downstream of the indexing station, after the sheets have been cut up into individual security papers, but before stacking into piles.
One problem with the proposal of EPO No. 167196 is that there is invariably a difference in the number of blemished notes in each of the columns of the web, so that the last index of the chosen index series is reached in one column of the web before it is in the remaining columns. To run off all the required index series from all the columns, a number of unindexed or cancellation-indexed imprints have to be run off in all the columns except the one which completes its print run last. These unindexed or cancelled imprints have to be removed downstream of the indexing station.
A second problem is that any malfunction of the indexing apparatus within the indexing station will produce defectively-indexed papers. For example, the ink supply to the index printer could fail, or the index-advance device could fail to operate. EPO No. 167196 lacks any proposal how to solve this problem.
A third problem is with security. Experience in the field of security printing teaches that access to the flow of security notes must be kept to a minimum to prevent unauthorised removal of imprints from the equipment. With the proposal of EPO No. 167196, a relatively large number of mechanical operations are performed downstream of the indexing station, with consequently increased likelihood that the finishing line will be accessible to unauthorised human interference, at least intermittently when the equipment needs attention. Furthermore, there are present, within the sequence of correctly-indexed notes, a relatively large number of notes not part of the unique indexing sequences destined to be checked off as part of an individual and unique packet of notes at the end of the finishing line. The need to ensure that none of these surplus notes is lost or stolen increases the costs of the process.